Sexual violence by young men against women is common, but efficacious primary prevention interventions tailored to men are limited in low- and middle-income settings like Vietnam. GlobalConsent, a web-based sexual violence prevention intervention tailored to university men in Hanoi, is efficacious. Implementation research is needed to understand facilitators and barriers to scaling GlobalConsent and prevention programs generally. We conducted qualitative research with key informants from three youth-focused organizational settings to understand the context of implementation in Vietnam.n = 15), high-school (n = 15) and non-governmental (n = 15) key informants focused on perceptions about sexual violence among young people and prevention programming. Four focus group discussions with 22 interviewed informants, following the Consolidated Framework for Implementation Research, asked about facilitators and barriers to implementing GlobalConsent. Narratives were transcribed, translated, and coded inductively and deductively to identify salient themes.Interviews with university (Outer-setting influences included greater expectations for sex among young people alongside norms favoring men’s sexual privilege, ostensibly ambiguous and lax laws on sexual violence, government ministries as bureaucratic but potential allies, external subject-matter experts, and the media. Inner-setting influences included variable cultures regarding openness to discuss sexual violence and equitable gender norms, variable departmental coordination, limited funding and ‘red tape’ especially in public institutions, inconsistent student access to technologies, and limited time and competing priorities among students and teachers. Several actors were considered influential, including institutional leaders, human-resource staff, the Youth Union, and student-facing staff. Important characteristics of individuals for implementation included subject-matter expertise, science or social science training, younger age, engagement in social justice related activities, and more open attitudes about sex. Regarding characteristics of sexual violence prevention programming, some participants preferred online formats for busy students while others suggested hybrid or in-person formats, peer education, and incentives. Participants generally accepted the content of GlobalConsent and suggested adding more content for women, ancillary support services, and adapted content for high-school students.Implementation of sexual violence prevention programs in youth-focused organizations in Vietnam requires multilevel strategies that connect outer-setting subject-matter experts with supportive inner-setting leaders and student-facing staff to overcome normative and organizational constraints, and thereby, to deliver institution-wide programming.The online version contains supplementary material available at 10.1186/s12889-023-15973-5. Sexual violence by young men against women is common, but tailored prevention is lacking in LMICs.GlobalConsent, a web-based sexual violence prevention program, is efficacious among university men in Hanoi. Understanding facilitators and barriers to scale-up is neededKey informants from youth-focused organizations across Vietnam suggest that institution-wide implementation of prevention programs requires multilevel strategies connecting outer-setting experts/allies with inner-setting leaders and student-facing staff to overcome normative and organizational constraints.Implementation champions may be younger, urban, subject-matter experts with open attitudes about sex among young people.This framework offers novel guidance for implementing sexual violence prevention programs in LMIC settings.Sexual violence includes any sexual act committed against a person without active consent , 2. SexuIn Vietnam, sexual violence against women persists despite legal and policy reform to define it and to support survivors . In 2019Efficacious interventions to prevent SVB among men remain rare in lower- and middle-income countries (LMICs) , 15. EviTo address the high prevalence of SVB against young women amidst unfavorable sexual and gender norms in Vietnam, our team adapted , 19 an eSystematic implementation is essential to maintain the fidelity and effectiveness of evidence-based interventions (EBIs). Yet, challenges during implementation are common and often attributable to contextual factors , 23, resMoreover, numerous theories and frameworks exist within implementation science, but publication on global implementation science is limited  and requThe study aims were twofold. First, we explored perceptions among key informants from youth-focused organizations about the nature, scope, and reasons for sexual violence among young people in Vietnam. Second, we explored views among key informants about the facilitators of and barriers to implementing sexual violence prevention programs in these organizational settings. The CFIR guided our investigation to ensure that implementation factors were explored comprehensively. Findings offer insights about the implementation strategies needed to scale-up GlobalConsent and other sexual violence prevention programs in these organizational settings in Vietnam.Vietnam, a lower middle-income country occupying the eastern portion of mainland Southeast Asia, has a population of over 98.5 million . About 8The government of Vietnam has undertaken several legal reforms to prevent sexual violence. Revisions of the Penal Code  have widened the definition of rape to include “other sexual activities” and have added an article on employment of persons under 16 for pornographic purposes. The Supreme Court issued Resolution 06/2019/NQ-HDTP (2019) to guide interpretation of new terms in the Penal Code, including intercourse with children, by age, within same-sex and opposite-sex relationships, and with a “defenseless” victim. The Ministry of Health issued Decision 3133/2020/QD-BYT (July 2020) to guide health professionals in caring for victims of sexual violence and in examining, documenting, and reporting on cases for investigation processes.Despite legal reforms, sexual violence victimization persists, and sexual violence prevention programming remains uncommon. Given the availability of efficacious sexual violence prevention programming tailored to young men in Vietnam , 21, a uThe study design involved semi-structured interviews and focus group discussions with a purposive sample of key informants from universities, high schools, and youth-focused civil society organizations (CSOs) throughout Vietnam. Semi-structured interviews focused on key informants’ perceptions about the context of sexual violence among young people and the prospects for prevention intervention. A subset of interviewed key informants participated in focus group discussions to understand more systematically the facilitators and barriers to implementing GlobalConsent and other sexual violence prevention programming, using the CFIR as a guide .The team developed three study forms—a key informant interview guide, a GlobalConsent viewing guide, and a focus group discussion guide—to facilitate the collection of comparative data from participants across all three institutional settings. Study forms in English are available in the The key informant interview guide asked open-ended questions to elicit perceptions about: gender and sexual norms among youth; the nature and scope of sexual violence among youth; causes and effects of SVB; strategies to prevent SVB; and barriers to and facilitators of efforts to prevent SVB. Questions about programmatic approaches were general, to elicit unframed responses about strategies that were and were not recommended in their regional, organizational setting.A viewing guide was developed to elicit feedback on GlobalConsent from key informants who agreed to participate in focus groups. The guide provided space to record positive and/or negative impressions of each module, to rate on a scale from 1 to 5 the feasibility of implementing the program at their organization, and the acceptability of the program for different stakeholder groups. Participants were invited to share their personal impressions in more detail in the group discussions.The focus group discussion guide included questions focused on each of the five CFIR domains of influence in the implementation of EBIs. Focal domains included 1) the outer setting, or the environment external to the implementing organization, including broader policies, norms, and influential organizations; 2) the inner setting, or the organizational environment in which the intervention is implemented, including norms, resources, and priorities; 3) intervention characteristics, including the content, administration, and source; 4) characteristics of individuals, including those of individuals administering and receiving the intervention; and 5) process, including planning and evaluating implementation . For exath Asian-Pacific Conference on Reproductive and Sexual Health and Rights in Vietnam using the search phrase “youth, students and violence” (APCRSHR 2017). This list then was supplemented using snowball sampling [n = 15), universities (n = 15), and youth-engaged CSOs (n = 15). Women and others from diverse backgrounds were included to ensure representation of those voices. From the 45 interviewed key informants, 32 were invited to participate in focus group discussions (FGDs), of whom 22 agreed to participate. Those who were invited to take part in FGDs had expressed some support for sexual violence prevention programming for young people. Four discussion groups were formed . Participants were compensated $20 for the key informant interview, $30 for reviewing the GlobalConsent program, and $20 for taking part in a group discussion.Participants were leaders or other key personnel at universities , high schools , or youth-centered CSOs who were engaged in sexual and reproductive health and rights in Vietnam. Individuals in senior positions, with potential influence on programming at their institution, were prioritized for recruitment. An initial list of potential participants was developed from 1) professional networks of the team’s local research collaborators, 2) a Google Scholar search using terms “youth and violence in Vietnam,” and a search of abstracts from the 9sampling  while enInvitations to participate in interviews and discussions were sent via email, with the consent form attached and a request to confirm via return email of having read the information and of agreement (with a check box in the consent form) to participate. Interviews and group discussions were held using Zoom audio conferencing software, which ensured a diverse sample across organizations and regions of Vietnam, enabled participants to select a private location from which to participate, and aligned with COVID-19 social distancing guidelines that were in place during the period of data collection. Only facilitators and participants were present at focus groups and interviews. At the time of each interview and group discussion, research staff explained the aims of the study and clarified that private, sensitive information would not be asked. Research staff obtained verbal consent to participate and to be recorded from all participants before all interviews and focus group discussions. Personally identifiable information, including participants’ names and employers, was retained. Several methods were used to protect the privacy and confidentiality of participants, including the use of audio-only interviewing and group discussion, password-protected computer data files, and locked cabinets to store digital recorders (if used). All team members were trained in research ethics.Two experienced researchers at the Center for Creative Initiatives in Health and Population (CCIHP) conducted the key informant interviews. Each interview was digitally recorded and lasted 45–90 min. After each interview, the interviewer summarized their observations. All digital recordings were transcribed, and random segments of the transcriptions were verified against the recordings. All transcriptions were translated into English, and random segments of the translations were verified against the transcriptions. Once the transcriptions, translations, and quality checks were complete, the digital recordings were destroyed.Consenting participants in the group discussions were asked to view the Global-Consent program and to note their personal perspectives on the viewing guide before attending the group discussion. Before starting each discussion, trained facilitators from CCIHP clarified the guidelines to maintain respect and confidentiality during the discussion. During each discussion, facilitators elicited individual responses to the viewing guide while administering questions from the focus group discussion guide. Discussions lasted 120–150 min. The same process as that used for the key informant interviews was used to transcribe and to translate the digital recordings, with verification of random text segments at each stage to ensure data quality.Qualitative data analysis entailed deductive and inductive techniques and a two-step coding process to discern general themes and emergent sub-themes . First, Table Figure Key informants from all organizational settings characterized gender and sexual norms in Vietnam as in a state of transition. While premarital sex among young people was becoming more common and accepted, other entrenched gender norms persisted  was considered common knowledge, and potential prosecution based on violation of the age of consent was cited frequently   and requirements for successful implementation . Teachers and lecturers, who are potential facilitators, have varying levels of subject-matter expertise on sexual violence .The present study faced some challenges that required strategic solutions. Stakeholder recruitment was more difficult in Central and South Vietnam, so the team diversified its networks for snowball sampling and recruitment. CCIHP, for example, approached staff in youth-engaged CSOs who were not sexual violence experts and asked their help to expand the network for recruitment. The key informant interview guide did not follow the CFIR framework; whereas, the discussion guide did. This lack of comparability in the guides actually allowed the team to use inductive and deductive strategies to understand the implementation context and to triangulate data from different approaches to ensure the validity of both sources. The CFIR domains were employed to contextualize findings to intervention implementation, but not all constructs in each CFIR domain were employed; this flexibility enabled the team to identify salient emergent constructs among participants. The lack of some CFIR sub-domain constructs may impact comparability of this work to other implementation efforts. Finally, the data on intervention characteristics and implementation process were thinner, in part as a result of the organization of the key informant interview guide. Therefore, interpretations of the salience of these domains should be made with caution. Otherwise, rich data were available on other major domains of the CFIR.Findings from this study offer several insights about promising strategies to test in implementation/ effectiveness research on sexual violence prevention programming in Vietnam. First, implementation researchers should be sensitive to prevailing gender norms that privilege men as an important element of the outer setting, which may influence organizational decisions about program uptake and about implementation strategies to increase program acceptability. Second, engaging external subject-matter experts could address low legal knowledge about sexual violence, misperceptions of low prevalence, and reputational concerns among institutional leaders. Third, subject-matter experts may be useful to train internal champions in program implementation as well as to provide on-going technical support. Protecting the time of trained staff could help to allocate human resources needed for implementation fidelity, to promote open discussion of sexual violence among student-facing staff, and to engage students in program activities. Fourth, strategies to address the competing demands on students’ time may be needed for program uptake, retention, and completion. Possible strategies may include a school-based orientation to the program, regular participation reminders, and incentives to complete the program. Testing these implementation strategies as a ‘bundle’ may help to address the multilevel barriers to implementation that key informants identified in the present study, and reduce the efficacy-effectiveness gap of promising programs, like GlobalConsent. Finally, the incorporation of cost-effectiveness research when evaluating gender-based violence interventions is overlooked and greatly needed to assess the practical feasibility of various intervention approaches in real-world environments. Based on the findings from the present study, testing the incremental cost effectiveness of more intensive, ‘bundled’ implementation strategies versus less intensive, ‘standard’ implementation strategies also would provide practical guidance about the resources needed for sustained implementation.Implementation of sexual violence prevention programs in youth-focused organizations in Vietnam requires multilevel strategies that connect outer-setting organizational allies and subject-matter experts with supportive inner-setting leaders and student-facing champions to overcome normative and organizational constraints, and thereby, to deliver institution-wide prevention program with sustainment. Understanding the costs of implementing at scale efficacious sexual violence prevention interventions also is needed for uptake and sustained implementation in LMIC settings.Additional file 1.


Acute kidney injury and chronic kidney disease are among the most common non-communicable diseases in the developed world, with increasing prevalence. Patients with acute kidney injury are at an increased risk of developing chronic kidney disease. One of kidney injury’s most common clinical sequelae is increased cardiovascular morbidity and mortality. In recent years, new insights into the pathophysiology of renal damage have been made. Oxidative stress is the imbalance favoring the increased generation of ROS and/or reduced body’s innate antioxidant defense mechanisms and is of pivotal importance, not only in the development and progression of kidney disease but also in understanding the enhanced cardiovascular risk in these patients. This article summarizes and emphasizes the role of oxidative stress in acute kidney injury, various forms of chronic kidney disease, and also in patients on renal replacement therapy . Additionally, the role of oxidative stress in the development of drug-related nephrotoxicity and also in the development after exposure to various environmental and occupational pollutants is presented. Kidney disease is an important worldwide health problem, leading to increased morbidity and mortality. Additionally, it is also associated with high economic burden. For patients with chronic kidney disease (CKD), the leading cause of mortality is cardiovascular disease . TraditiThe Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) 2020  was usedAcute kidney injury (AKI) is a syndrome defined by a rapid increase in serum creatinine, reduced urine output (oliguria or anuria), or both. It is an essential complication in hospitalized patients, occurring in 10–15% of all hospitalizations . It is eIt should be remembered that AKI is a clinical term and can be due to glomerular or tubulointerstitial involvement or both. In AKI, tubular involvement is more common and is the focus of this article. Pathologists use descriptive pathological findings, often called acute tubular injury (ATI). Prerenal, intrarenal, and postrenal causes of AKI can all cause different degrees of ATI. Dissociation between clinical and pathological findings is not rare, especially in prerenal causes of AKI, for example, hypovolemia and hemorrhagic shock. In such cases, ATI is mild or even absent . At the ATI is characterized by focal or diffuse tubular luminal dilatation, simplification of the lining epithelium, loss of the brush border in proximal tubules, loss of nuclei, and the presence of nucleoli. At times, signs of epithelial cell regeneration are present . In severe cases, especially in prolonged AKI, focal or diffuse tubular cell necrosis is present. In these instances, the term acute tubular necrosis (ATN) is used . Oxidative stress is crucial in developing kidney injury, ranging from AKI to irreversible CKD  Figure . In thisOxidative stress is the imbalance favoring the increased generation of ROS and/or reduced body’s innate antioxidant defense mechanisms . The proDirect analysis of free radicals in an in vivo system is demanding due to their short lifespan. Additionally, measuring antioxidants is challenging, primarily because many antioxidants with different properties exist. A significant limitation is that oxidative stress is usually a focal response to tissue injury, making detecting it even more taxing. Due to this, these measurements are complex, expensive, and time-consuming . StudiesOxidative stress is commonly found in CKD and is associated with increased all-cause mortality in these patients. It is already present in the early stages of CKD and is even more apparent in patients on hemodialysis (HD) and peritoneal dialysis (PD) ,24. MoreDuring the last two decades, oxidative stress has been at the center of attention as a novel, non-traditional risk factor for inflammation, atherosclerosis, diabetes mellitus (DM), and CKD progression. The heavy cardiovascular burden in patients with CKD is at least partly due to the oxidative stress observed in these patients . ROS in the kidneys is mainly produced by the mitochondrial respiratory chain and enzymes, such as Nicotinamide Adenine Dinucleotide Phosphate (NADPH) oxidase (NOX). The different NOX isoforms, including NOX1, NOX2, and NOX4, are associated with oxidative stress, worsening vascular function, and promoting interstitial fibrosis . Recentl2- leads to decreased production of nitric oxide (NO), an essential antioxidant protecting kidney function by increasing renal blood flow, enhancing pressure natriuresis, regulating tubuloglomerular function, and preserving fluid and electrolyte homeostasis [Additional oxidative markers in CKD are malondialdehyde (MDA), oxidized low-density lipoprotein (LDL), AGEs, and 8-hydroxyde-oxyguanosine . A deciseostasis . Studieseostasis . 2-, H2O2, and OH. A defective antioxidant system is also important. It appears that ROS production is present not only in the podocytes and the glomerulus but also in the tubulointerstitium and is associated with pronounced and enhanced inflammation and fibrosis [Diabetic kidney disease (DKD) is one of the most common causes of end-stage renal disease and is also associated with severely increased morbidity and mortality. The pathogenesis and clinical manifestations of DKD usually follow a predetermined course, beginning with albuminuria, advancing to overt proteinuria, and ultimately leading to a progressive reduction in the estimated glomerular filtration rate (eGFR). Accumulating evidence has demonstrated the overproduction of ROS as the common denominator linking the altered metabolic pathways in the kidney with disrupted renal hemodynamics known to be associated with DKD . Renal Rfibrosis .Autosomal dominant polycystic kidney disease (ADPKD) is the most common hereditary kidney disease. Renal manifestations of ADPKD are gradual cyst development and kidney enlargement, ultimately progressing to end-stage renal disease. Patients with ADPKD have increased serum levels of asymmetric dimethyl arginine (ADMA), MDA, and oxidized LDL cholesterol, compared to the healthy cohort. Additionally, their antioxidant capacity is reduced, which is evident from reduced plasma SOD concentrations. It appears oxidative stress plays an important role in the development and progression of kidney disease in these patients, as well . A major characteristic of focal segmental glomerulosclerosis (FSGS) is podocyte injury. Studies have shown podocyte injury can be at least partly attributed to oxidative stress. It appears that an increase in transforming growth factor beta (TGF-β) induces endothelin synthesis and oxidative stress in glomerular endothelium. Mitochondrial oxidative DNA damage was found even before podocyte injury ,35.In patients with HD, increased concentrations of oxidative stress biomarkers have been found. Some of them are due to comorbidities and conditions accompanying these patients, such as dyslipidemia, arterial hypertension, old age, metabolic syndrome, DM, and atherosclerosis . SecondlMoreover, the HD procedure is interlinked with activating prooxidative mechanisms  and the loss of antioxidative mechanisms . HD-relaPD is more biocompatible than HD, resulting in less oxidative stress. However, PD patients still manifest oxidative stress compared to the general population and predialysis CKD patients, mainly due to the composition of the PD solution . In addition to apparent detrimental cardiovascular effects, oxidative stress in PD patients is linked to the loss of residual renal function, peritoneal fibrosis, and ultimately, the development of encapsulating peritoneal sclerosis ,42. Kidney transplantation leads to lower levels of ROS and a better preservation of anti-oxidant capacity compared to HD or PD, which is most likely one of the reasons why these patients have improved survival compared to patients with HD or PD . HoweverConventionally, acute kidney injury (AKI) has been viewed in an anatomical context , whereas, at the same time, it has been considered a risk factor for the development of subsequent CKD . SeveralThe most important causes of AKI, especially ATN, are linked to ischemia and hypoxia. The kidneys have a sensitive system of blood flow autoregulation, which causes the GFR to be stable throughout different blood pressures. Two main mechanisms involved in maintaining renal autoregulation are tubuloglomerular feedback and myogenic response . In addition to nitrogen waste products, AKI is associated with elevated levels of indole and carbonyl compounds, which can upregulate systemic oxidative stress . NO is a2 and disjointed mitochondria, concluding that mitochondrial dysfunction is an essential step in the early phase of ischemic renal injury [Hall et al. studied mitochondrial structure, function, and oxidative stress in rat kidneys in response to ischemia . Their rl injury . During l injury . In a stl injury . Mitochol injury . An addil injury . 2-) is generated by oxidases or inside mitochondria through the electron transport chain. Local ischemia and cytokines induced by AKI  activate the endothelium of renal vasculature and recruit cells from the immune system that can generate O2- via NOX [The superoxide anion  generated by dismutation or by oxidases from molecular oxygen, causing diverse cell injury and also reacting with iron-containing molecules, releasing more ROS [Additional ROS found to be involved in AKI are hydrogen peroxide  can be measured in serum and urine and is a marker of acute tubular injury. It has bacteriostatic and anti-oxidative properties. An induction of urine NGAL under harmful conditions (such as oxidative stress) is a compensatory response to ameliorate oxidative stress-mediated toxicity. It is, therefore, a good indirect predictor of oxidative stress and also a marker of AKI, especially when compared to serum creatinine, which has several drawbacks in detecting AKI . According to Tanase et al., urinary kidney injury molecule-1 (KIM-1) indicates acute kidney injury due to tubulointerstitial injury and can also be used in certain cases of xenobiotic nephrotoxicity, such as cisplatin-induced nephrotoxicity. It is important to emphasize that it is a non-specific marker of tubular injury and can be elevated due to a plethora of causes, including oxidative stress . A meta-Thioredoxin (Trx) protects proteins and cell membranes from oxidative injury. In addition to its antioxidant effects, it also regulates cytokine transcription and apoptosis. In ROS-induced cardiomyocyte injury, Trx clears ROS and enhances mitochondrial function, preventing cardiomyocyte hypertrophy and apoptosis. There are also some data on the antioxidant and protective effects of Trx in preventing acute kidney injury . In Sodium–glucose cotransporter-2 (SGLT-2) inhibitors are a new class of glucose-lowering agents. Extensive clinical trials have revealed several cardiac and renal protective effects of these drugs, even in non-diabetic patients, expanding their uses in clinical practice . Several mechanisms underlying the renal benefits of SGLT-2 inhibitors have been proposed. They reduce high glucose-induced oxidative stress in the proximal tubule, decrease intraglomerular pressure via afferent arteriole modulation, decrease proteinuria and inflammation, ameliorate interstitial fibrosis, improve mitochondrial function, and lead to reduced sympathetic nervous system activation . Cardiop2- levels due to an upregulation in SOD activity. This finding was associated with increased renal SOD activity and reduced albuminuria [A new drug used for treating diabetic CKD patients—a non-steroid, selective mineralocorticoid antagonist, finerenone—also has several antioxidative properties. Preclinical studies on rats (treated with finerenone) have shown improved endothelial function due to enhanced NO bioavailability and decreased Ouminuria . Additiouminuria .The kidney is exposed to a higher concentration of drugs and their metabolites due to the secretion of ionic drugs through tubular organic ion transporters across the luminal membranes of renal epithelial tubular cells, and through the reabsorption of filtered toxic substances back into the lumen of the tubule. Drug-induced kidney injury is a serious and common cause of AKI in hospitalized patients, accounting for roughly 20% of cases. Usually, two common pathological entities are seen in these patients, acute interstitial nephritis (AIN) and ATN. While AIN is caused by allergic reactions, ATN is often caused by drug-induced oxidative stress . An important pathway involved in these cases is the vanin-1 pathway. An inciting drug causes the generation of ROS. In the presence of oxidative stress, antioxidant response-like elements within the vinin-1 promoter region enhance vinin-1 expression. Consequently, more cysteamine is formed from the hydrolysis of pantheteine, and cysteamine is then converted to cystamine. Cystamine inhibits glutathione synthesis. Glutathione stores decrease, leading to an intensification of oxidative stress and enhanced production of inflammatory cytokines and chemokines . It appeMoreover, several biomarkers of drug-induced oxidative stress have been found, including advanced oxidation protein products, protein reactive carbonyl derivatives, and methylglyoxal. A reduction in plasma catalase level have also been observed ,87. In 2+-metallothionein complexes in the proximal and also distal tubule, release of free Cd2+, perturbation of cellular calcium homeostasis, and interference with mitochondrial electron transport chain. Clinical consequences are partial or complete Fanconi syndrome and progressive kidney disease [Cadmium (Cd) is a nonessential metal that has heavily polluted the environment due to human activities. It has a tendency to accumulate within the proximal tubule and can induce dysfunction of the mitochondrial electron transport chain, leading to enhanced production of ROS and impaired function of NOX. Most important steps in Cd-induced nephrotoxicity are reabsorption and lysosomal degradation of Cd disease .2). Similar to Cd, they also induce oxidative stress predominantly in the proximal tubule [2 is weakly acidic and can cause renal injury through mesoporous SiO2 (MSNs) particles and oxidative stress [Additional constituents of electronic waste include lead (Pb), mercury (Hg), arsenic (As), and silica (SiOl tubule . Interesl tubule . Exposurl tubule . Patientl tubule . SiO2 ise stress . Trichloroethylene (TCE) is an important organic solvent widely used as a metal part cleaner, dry cleaning agent, and chemical extractant. Experimental studies have demonstrated an increase in oxidative stress biomarkers in mice sensitized with TCE  .Hexachloro-1:3-butadiene (HCBD) is a halogenated solvent that is known to cause damage specific to pars recta of the renal proximal tubule in rats. Experimental studies have shown a proportional increase in urinary excretion of α-glutathione S-transferase (α-GST) and KIM-1, emphasizing the role of oxidative stress in HCBD-induced kidney injury .One of the central factors for developing progressive kidney injury (either acute or chronic) is oxidative stress and ROS formation. It appears oxidative stress is also critical in increased cardiovascular risk observed in these patients. Additionally, nephrotoxicity of several medications and occupational and environmental pollutants are mediated through oxidative stress. Despite several new drugs in recent years , new treatment strategies explicitly targeting oxidative stress are required. Further studies are needed to conceptualize and expand our understanding of oxidative stress in developing kidney injury.


Despite the progress made in risk stratification, sudden cardiac death and heart failure remain dreaded complications for hypertrophic cardiomyopathy (HCM) patients. Myocardial ischaemia is widely acknowledged as a contributor to cardiovascular events, but the assessment of ischaemia is not yet included in HCM clinical guidelines. This review aims to evaluate the HCM-specific pro-ischaemic mechanisms and the potential prognostic value of imaging for myocardial ischaemia in HCM. A literature review was performed using PubMed to identify studies with non-invasive imaging of ischaemia  in HCM, prioritising studies published after the last major review in 2009. Other studies, including invasive ischaemia assessment and post-mortem histology, were also considered for mechanistic or prognostic relevance. Pro-ischaemic mechanisms in HCM reviewed included the effects of sarcomeric mutations, microvascular remodelling, hypertrophy, extravascular compressive forces and left ventricular outflow tract obstruction. The relationship between ischaemia and fibrosis was re-appraised by considering segment-wise analyses in multimodal imaging studies. The prognostic significance of myocardial ischaemia in HCM was evaluated using longitudinal studies with composite endpoints, and reports of ischaemia-arrhythmia associations were further considered. The high prevalence of ischaemia in HCM is explained by several micro- and macrostructural pathological features, alongside mutation-associated energetic impairment. Ischaemia on imaging identifies a subgroup of HCM patients at higher risk of adverse cardiovascular outcomes. Ischaemic HCM phenotypes are a high-risk subgroup associated with more advanced left ventricular remodelling, but further studies are required to evaluate the independent prognostic value of non-invasive imaging for ischaemia. Hypertrophic cardiomyopathy (HCM) is the most common inherited heart disease  reflect on the prevalence of ischaemia in HCM and its multifactorial causes, to establish potential therapeutic targets for the treatment of ischaemia without epicardial coronary stenoses; and (2) assess the prognostic impact of imaging for ischaemia in HCM in relation to other markers of disease severity (hypertrophy and fibrosis), to evaluate the role of ischaemia on imaging as a potentially novel SCD risk factor.To address these aims, the present study first reviews the frequency of myocardial ischaemia in HCM on non-invasive assessment, with a focus on modern advancements made in cardiovascular magnetic resonance (CMR) imaging. The pathophysiological mechanisms underlying the development of ischaemia in HCM are then explored, and how these may contribute to adverse LV remodelling and symptomatic status. The role of imaging for myocardial ischaemia in HCM as a risk marker for adverse outcomes including arrhythmias and heart failure is further considered, through review of follow-up studies. Finally, the role of myocardial ischaemia is discussed as a therapeutic target, through reviewing the latest clinical trials targeting metabolic and vascular dysfunction in HCM. We expect these findings to contribute to the scientific understanding and clinical management of myocardial ischaemia in this high-risk group of patients.Perfusion measurements are commonly used as a surrogate of ischaemia, as integrated measures of flow through both the epicardial coronary arteries and the microcirculation. Regional perfusion defects are characteristic of the HCM phenotype and present as regions of impaired myocardial blood flow (MBF) at rest or during exercise/pharmacologically induced hyperaemia Fig. . PerfusiTable Since the last review of imaging techniques for myocardial ischaemia in HCM in 2009 , ischaemAcross the perfusion imaging studies in Table With perfusion defects often remote from coronary territories , and in Structural abnormalities in the small blood vessels that supply the myocardium are a common finding in the histology of HCM hearts , 48. As Numerous studies have measured the density of small vessels in hypertrophied HCM septal/LV tissue samples and have found this to be 21–44% lower than in control patients , 60–63. LVOT obstruction is a hallmark feature of HCM and is defined as a peak LVOT pressure gradient ≥ 30 mmHg. LVOT obstruction may be present at rest  LVOT obstruction is associated with reduced perfusion reserve , 41, 68 Despite these reported associations, other studies have found no relationship between LVOT obstruction and ischaemia, and infarction has been reported in non-obstructive HCM , confirmDiastolic dysfunction, partially related to sarcomeric mutations, is an early feature of HCM in many patients , 75. WitDuring systole, hypertrophy causes excessive compression of intramyocardial blood vessels, leading to abnormal coronary haemodynamic forces , which cAnother potential mechanism of perfusion impairment among HCM patients is myocardial bridging, which is when a segment of a coronary artery tunnels through the myocardium rather than over it. This is seen in 23–41% of HCM patients compared to 5–7% of the general population , 82. MulIn multiple studies of genotyped HCM patients, vasodilator stress BOLD CMR has detected impaired myocardial oxygenation even in pre-hypertrophic carriers of sarcomeric mutations, despite preserved perfusion , 89, 90.The greater the degree of hypertrophy , the greater the degree of perfusion impairment . This has been reported both at a segmental level , 97–101 A further macroscopic explanation is that the increase in muscle mass characteristic of HCM is inadequately supplied by the major coronary arteries, which have reduced luminal volume per unit myocardial mass –105. HetAlthough perfusion defects are overall more prevalent in cohorts with hypertrophy Table , 20% of Two studies reported perfusion defects  and exerThere are also conflicting reports on the segmental distribution of perfusion defects in SPECT imaging studies , 80, 107Perfusion impairment in HCM is predominantly subendocardial , 108, alRepeated episodes of ischaemia have been implicated in fibrosis accumulation and extensive scarring in HCM , 53. A lHowever, whereas ischaemia is predominantly subendocardial in HCM , 108, fiImaging studies that did not perform epi-endocardial segmentation, but controlled for wall thickness, found independent associations between perfusion impairment and either LGE or extracellular volume , 99, 101Collectively, these findings suggest colocalization of pathology (microvascular dysfunction and fibrosis) and the potential for ischaemia to promote the fibrosis phenotype. However, it is possible that imaging difficulties in discerning regions of fibrosis and hypoperfusion could overestimate the fibrosis-ischaemia association . FurtherExtracellular matrix expansion in myocardial regions remote from microvascular dysfunction has been suggested to be triggered by pro-hypertrophic transforming growth factor beta (TGF-β) signalling secondary to the sarcomeric mutation . This noThe main clinical manifestations of myocardial ischaemia in HCM patients are angina and dyspnoea , 123, alPerfusion abnormalities may also be present in the absence of symptoms , 41, 102Figure As cells become hypertrophied, either to compensate for cells lost through ischaemia-induced fibrosis or other pathological processes, ischaemia is further promoted by local reductions in small vessel density , greaterWith disease progression, the ischaemic threshold is incrementally lowered, such that acute episodes of ischaemia are inducible despite non-stenotic epicardial coronary arteries. In some HCM patients, transient increases in energetic demands, such as during AF-induced increases in ventricular pacing  or durinIn patients with the most severe small vessel disease and insufficient capillary density, ischaemia leads to gross macroscopic transmural scarring , 62, 111The studies in Table Overall, the studies in Table The prognostic value of other pathophysiological mechanisms, such as myocardial bridging, is debatable. Although bridging has been shown to predict poorer prognosis in one paediatric cohort , this asAcute myocardial ischaemia  may be an important cause of fatal arrhythmias and SCD in HCM –7, 143, Numerous studies Table  have anaSome studies report an association between ischaemia and heart failure. Hamada et al. used Th-201 scintigraphy to study 48 HCM patients and found that development of heart failure was associated with perfusion impairment . SimilarIn evaluating the independent prognostic contributions of perfusion defects and presence of LGE, not only are perfusion defects confounded by presence of LGE due to the possibly causal link between ischaemia and fibrosis in HCM , but somAs a possible cause of ischaemia, LVOT obstruction is already recognised as a risk factor for SCD in adults  and chilMyocardial ischaemia in HCM is relevant in the context of evolving clinical guidelines on exercise restrictions. If SCD is related to exercise , then is2 (VE/ CO2) slope and anaerobic threshold during exercise, all of which could indicate prospensity for underlying myocardial ischaemia on cardiopulmonary exercise testing.Of note, two meta-analyses have shown that SCDs in young HCM patients are 75% more common in athletes than non-athletes , 154. AgThe potential for ischaemia as an early therapeutic target in HCM  is reinfMultiple promising studies of pharmacologic treatments with the potential to minimise ischaemic burden in HCM are ongoing or have been completed Fig. . These iAngiotensin receptor blockers (‘-sartans’), which target both vascular function and the TGF-β signalling pathway , have sPerhexiline, a vasodilator and metabolic modulator, recently showed lack of efficacy to improve exercise capacity in HCM patients with moderate to severe heart failure . However, the findings of this interventional study may have been significantly influenced by the advanced disease progression into heart failure of the recruited patients and the choice of primary endpoint. RESOLVE-HCM  is another study which is assessing the impact of perhexiline on LV hypertrophy . This trLate sodium blockers, which target the pathologically increased late sodium current in HCM cardiomyocytes , were hyPerhaps most promising is the novel allosteric myosin inhibitor mavacamten, which (in contrast to the drugs previously introduced) specifically targets the underlying pathogenic drivers of contractile dysfunction in HCM at the sarcomeric level . Both thAll the above routes towards a refined diagnosis and targeted treatment of myocardial ischaemia in HCM constitute important and promising prospects for future research into the amelioration of symptoms and risk of SCD in HCM. If successful, their integration into HCM risk stratification models and clinical guidelines is expected to yield significant advances for the management of this high-risk group of patients, as well as further insights on the overall contribution of ischaemia in cardiovascular disease. However, further research is needed to elucidate the clinical significance of ischaemia on imaging, and the relative contributions of the various pro-ischaemic mechanisms in HCM.Although ischaemic HCM phenotypes are consistently identified as a high-risk subgroup on long term follow-up Table , the rolAnother consideration is that despite the strong age-dependence of SCD risk in HCM, most analyses relating ischaemia and arrhythmic risk were performed in midlife cohorts Table , which mImportantly, multi-centre studies to evaluate ischaemic burden are needed to elucidate the incremental value of perfusion imaging for ischaemic myocardial substrates over potentially irreversible substrates like LGE, particularly in subgroups where guidelines are less certain (ESC SCD risk < 6%).In this review, we have presented a comprehensive discussion of the latest evidence corroborating profound links between myocardial ischaemia, disease severity and prognosis. This notably broadens former studies by covering HCM-specific ischaemic factors, the impairment of perfusion by myocardial hypertrophy, the characteristic distributions of ischaemic burden in HCM ventricles, the relationship between (hypo)perfusion and fibrosis, mechanisms of ischaemia progression in HCM, its clinical manifestations and prognostic value. Altogether, our analysis substantiates myocardial ischaemia as a strong and multifactorial contributor to adverse LV remodelling, arrhythmia, and SCD events in HCM. Despite the strong associations reported, further studies are needed to understand which non-invasive methods of ischaemia assessment have independent prognostic value in HCM, over and above co-existing myocardial fibrosis and LVOT obstruction.


Transport-related physical activity (TRPA) is recognised as a potential means of increasing total physical activity participation that may yield substantial health benefits. Public health campaigns focusing on promoting TRPA from a young age aim to develop life-long healthy habits. However, few studies have examined how TRPA changes across the lifecourse and whether childhood TRPA levels influence those observed later in life.Using the Australian Childhood Determinants of Adult Health study , latent class growth mixture modelling with adjustment for time-varying covariates was performed using four timepoints (ranging from 7 to 49 years) to assess behavioural patterns and retention of TRPA across the lifecourse. As child and adult adjusted TRPA measures could not be harmonised, trajectories of adult TRPA (n = 702) were instead identified, and log-binomial regression analysis was performed to determine whether childhood levels of TRPA (high/medium/low) influenced these trajectories.Two stable groups of adult TRPA trajectories were identified: persistently low , and increasingly high TRPA . There was no significant relationship between childhood TRPA levels and patterns in adulthood .This study found childhood TRPA levels were not associated with TRPA patterns in adulthood. These findings suggest that while TRPA in childhood may have health, social, and environmental benefits, it does not appear to impact adult TRPA directly. Therefore, further intervention is required beyond childhood to promote the implementation of healthy TRPA behaviours into adulthood.The online version contains supplementary material available at 10.1186/s12966-023-01462-w. Physical activity (PA) is a key behaviour for the prevention and management of chronic disease , 2. DespTRPA has been identified as a potential mechanism for increasing total PA participation and yielding considerable health benefits. Prior systematic review and meta-analyses have found greater TRPA was associated with decreased cardiovascular risk  and all-Compared to the study of total and leisure-time PA little examination of TRPA has occurred, particularly longitudinally . The traLiterature examining the factors that shape TRPA behaviour are primarily cross-sectional in nature. A systematic review of the cross-sectional correlates and longitudinal determinants of adult TRPA found 36 factors have been commonly examined, seven of which demonstrate consistent associations  .Despite this lack of longitudinal research, public health campaigns focus on the promotion of TRPA from a young age aim to develop healthy habits for retention across the lifecourse. Examples include initiatives such as the United States “Let’s Move” and “SafIt is important to understand whether TRPA behaviours formed in childhood are retained, or whether behaviours fluctuate over time. While the retention of childhood behaviours may suggest childhood intervention is warranted, a lack of lifecourse relationship would demonstrate that the immediate needs and circumstances of the individual may exert predominant influence over their TRPA behaviours. Absence of association between childhood and adulthood TRPA would highlight the need for period specific intervention in order to promote TRPA amongst adults whose TRPA and total PA levels are insufficient. Therefore, this analysis aimed to identify TRPA patterns across the lifecourse into mid-adulthood and whether childhood TRPA predicts lifecourse TRPA patterns.Participants for this analysis were drawn from the ongoing longitudinal Childhood Determinants of Adult Health (CDAH) study. A prospective cohort of Australian adults spanning over 30 years, the CDAH study is a continuation of the 1985 Australian Schools Health and Fitness Survey (ASHFS). Procedures describing the selection of participants at baseline have been outlined in detail elsewhere . ASHFS wAt baseline, participants aged 9–15 years completed questionnaires in small groups supervised by trained study data collectors. Participants were asked separate questions regarding the duration (“how many hours and minutes were spent each session?”), the frequency (“how many times last week?”), of travel to and from school via bicycle and walking. For each mode of transport, minutes per week performing these activities was calculated .TRPA was assessed at CDAH-1 , CDAH-2 , and CDAH-3  via completion of the International Physical Activity Questionnaire (IPAQ) . ParticiDetailed methods regarding the measurement of covariates are provided within Supplementary Material. At baseline, covariates of age, sex, self-reported health, smoking status, body mass index, area-level socio-economic status derived from residential postcode, and teacher-rated scholastic ability were recorded. During adult CDAH follow-ups the aforementioned covariates were assessed with the addition of highest education level, employment status, occupation type, number of children, and marital status.Latent Class Growth Mixture Modelling (LCGMM), a form of trajectory analysis, was performed with the initial intention of assessing the behavioural patterns and retention of TRPA from childhood across the life-course to mid-adulthood. This technique allows the examination of patterns of changes in TRPA across the lifecourse. However, as will be demonstrated in this paper, the use of trajectory analysis has its own unique challenges. Here, we detail the process that led to the modelling of adult TRPA trajectories and the analysis of their association with childhood TRPA.a priori , and High ). Similarly, stratification of the latent classes by tertiary childhood TRPA illustrated that TRPA tracked across adulthood via the two trajectories of high/increasing and persistently low with minimal difference in both magnitude and shape, irrespective of childhood values Fig. . FindingIn a sample of Australian children followed into mid-adulthood over three decades, we found two distinct classes of adult TRPA: persistently low and high/increasing. Our findings of two distinct groups show that independent of key individual-level covariates , TRPA remains an underlying behaviour that tracks across adulthood. No significant association was observed between child and adult TRPA behaviours. This lack of association was reflected in the visualisation of adult TRPA patterns stratified by childhood TRPA level. Stratified sub-classes showed minimal deviation from the adult TRPA patterns (persistently low and high/increasing) derived from LCGMM. These findings suggest that adult TRPA is not reflective of childhood behaviours and is instead reflective of more immediate individual circumstances.While studies have shown the prevalence of TRPA among individuals to decline with age , to our This study’s findings of no significant association between child and adult TRPA behaviours are perhaps unsurprising. With extensive evidence showing relationships between the built environment and TRPA , it is pWhile a lack of longitudinal relationship does not diminish the need to encourage childhood TRPA , it doesTRPA differs to many of the outcomes that trajectory analysis is typically applied to  as therA number of potential limitations are noted within this study. The childhood measure of TRPA presented in this study was comprised only of PA undertaken whilst walking or cycling to school. As such, childhood TRPA may not be completely representative of total TRPA as children during this period may have also used public transport (PT)  in their commute. Literature describing the relationship between childhood and adult PT use is sparce, therefore it is unknown whether adult PT behaviours are reflective of those in childhood. As a large component of adult TRPA is likely formed from PT use, the comparison of child and adult TRPA behaviours may be limited.Differential loss-to-follow-up was observed among participants across study follow-ups. Comparison of baseline characteristics found that those excluded from the LCGMM analysis (N = 7480) were an average of one year younger and of a lower scholastic ability than those included  As those lost to follow-up often exhibit poorer health behaviours, it is possible that the findings of this study may underestimate the proportion of people that may fall within the ‘persistently low’ class. Missing data among participants reduced the sample size. This study does not have observations of the social and built environment in which the participants reside. As prior studies have found there to be a number of factors associated with adult TRPA at the individual, social, and environmental level , the unaa posteriori determination of distinct trajectories without the risk of misclassification and information loss that often occurs when classes are defined a priori [This study was strengthened through its use of LCGMM. This approach allows a priori . AdditioThis study found that childhood TRPA levels were not associated with TRPA patterns experienced in adulthood when adjusted for individual-level covariates. Furthermore, TRPA behaviours tracked across adulthood with two stable TRPA trajectory groups, participants with persistently low, and those with high/increasing TRPA, independently of individual-level time-varying covariates. Identification of these two trajectories highlights an opportunity to better understand the characteristics of those whose TRPA is persistently low in adulthood, providing insights for intervention development. These findings suggests that while TRPA interventions targeting children may be beneficial to the development of TRPA behaviours during that age-period, further intervention is required to promote the implementation of healthy TRPA behaviours in adulthood.Below is the link to the electronic supplementary material.Supplementary Material 1


Statin-induced necrotizing myopathy (SINM) is an uncommon but severe complication associated with statin medication. SINM can develop at any point after a person starts taking steroids. It is now being acknowledged as a component of the broader category of "statin-induced myopathy." Like other immune-mediated necrotizing muscle diseases, statin-induced myositis is identified by weakness in proximal muscles, increased serum creatine kinase (CK) levels, and, in some cases, dysphagia and respiratory distress. In addition, there is evidence of muscle cell damage when examined under a microscope, occurring with minimal or no infiltration of inflammatory cells. Diagnosing SINM promptly is frequently challenging due to its unpredictable development over time, with symptoms sometimes emerging many years after the initial exposure to statins. One distinctive characteristic of SINM is the continued presence of muscle inflammation and elevated CK levels even after discontinuing statin treatment. Currently, no clinical trials are available to guide how to manage statin-induced immune-mediated necrotizing myopathy (IMNM). Here, we present a case of a 42-year-old woman diagnosed with SINM and was found to have persistently elevated CPK despite discontinuation of statins. Our case also suggests that intravenous (IV) immunoglobins and steroids are an effective and well-tolerated alternative to immunosuppressants. Immune-mediated necrotizing myopathy (IMNM) has been seen in adults and children, and the incidence of this myopathy has been increasing in recent years . FemalesA 42-year-old female with a medical history of hypertension, obesity, and recently diagnosed hyperlipidemia (seven months ago) presented due to complaints of muscle aches, purpura on her left arm, progressive odynophagia, and tongue swelling for the past three weeks. Past surgical history was unremarkable, and family history was significant for type II diabetes mellitus in the mother. On presentation, the patient was hemodynamically stable with a heart rate of 92 beats per minute, temperature of 98 F, and blood pressure of 119/69 mmHg. The patient showed symptoms of proximal muscle weakness, including the ability to stand up from a chair using hands. Her home medications include semaglutide and newly started atorvastatin. She was started on atorvastatin 40 mg seven months ago. On examination, the rash was purpuric, and the patient was noted to have weakness in the proximal and distal muscles in the arms and legs and mild tongue swelling; the rest of the examination was unremarkable. Her laboratory investigations were significant for transaminitis with elevated aspartate aminotransferase (AST) of 1088 unit/L and alanine aminotransferase (ALT) of 721 unit/L with normal bilirubin and elevated creatinine kinase (CK) of 22,000 U/L indicative of rhabdomyolysis, for which she was started on intravenous (IV) crystalloid fluid. Her initial laboratory results are shown in Table Moreover, atorvastatin was held due to transaminitis and rhabdomyolysis. The rest of the findings, including autoimmune workup, are shown in Table SINM is a part of a heterogeneous family of inflammatory diseases, which presents a diagnostic challenge because of its broad clinical presentation . SINM isThe clinical manifestations of SINM are consistent with inflammatory myopathies, which includes muscle weakness, elevated CK levels, diagnostic antibodies, and increased serum level of muscle enzymes . The patStatins have been known to cause liver toxicity with a frequency of one in 100,000 patient years and have been identified to trigger elevated amino transaminases in 3% of the patients’ prescribed statins . AlthougDiagnosis of SINM requires the detection of anti-HMGCR antibodies. One of the proposed mechanisms of SINM suggests an increased expression of HMGCR post-initiation of statins, leading to an autoimmune pathology . This peThe treatment and management for SINM patients involves the abrupt discontinuation of statins and immunosuppressive therapy . HoweverStatins are divided into lipophilic and hydrophilic agents depending on their ability to pass deeply into the cell membrane, interacting with the surrounding acyl chains . LipophiStatin-induced IMNM is an infrequent yet severe condition linked to the usage of statin drugs. Although it is an uncommon adverse outcome of using statins, healthcare providers should remain vigilant and consider the possibility of this rare condition in patients experiencing muscle-related symptoms associated with statin use, especially if the symptoms persist despite discontinuing the medication. To diagnose necrotizing autoimmune myopathy (NAM), it is crucial to rule out more prevalent autoimmune myopathic disorders, metabolic issues, and neurological causes that can lead to weakness in the muscles around the hips and thighs or nerve-related problems. This condition should be considered as a potential diagnosis when dealing with ongoing muscle weakness and elevated CK levels in individuals who have been exposed to statins, especially if the symptoms persist even after stopping statin treatment. Additional research is necessary to determine who is susceptible to developing statin-induced NAM and to establish whether there are specific individuals who should altogether avoid statin therapy.


Editorial on the Research TopicOptimization of spine surgery outcomes in the pre-, peri-, and postoperative settingsPatient optimization is one of the strongest predictive indicators to improve outcomes and mitigate complications after spinal surgery. While we have collectively known that optimizing a patient's cardiopulmonary and metabolic status are essential prior to any surgical procedure, it has been challenging to develop a set of clinical decision rules to help guide spine patients. Hence, the development of enhanced recovery after surgery (ERAS) protocols to standardize optimization across surgeons and healthcare systems .The importance of pre-operative optimization was recently highlighted by Maitra et al. who demonstrated patients who medically optimized prior to spine surgery demonstrate improvements in satisfaction scores, decreased complications, and decreased length of stay . The resInterventions aimed at enhancing intra- and post-operative optimization are essential, as well. For example, the use of intravenous tranexamic acid to mitigate blood loss, patient positioning to reduce intra-orbital pressure while prone, the use of intraoperative cell salvage, and blood pressure control when operating on or near the spinal cord have been shown to improve outcomes after spinal surgery –8. WhileClinicians should make every effort to “optimize” our patients before, during, and after spinal surgery. While more prospective and larger population studies are required, there is a strong consensus that optimization is as important as patient selection, decision-making, and surgical technique in guiding post-operative outcomes .


This paper provides an overview of flexible and wearable respiration sensors with emphasis on their significance in healthcare applications. The paper classifies these sensors based on their operating frequency distinguishing between high-frequency sensors, which operate above 10 MHz, and low-frequency sensors, which operate below this level. The operating principles of breathing sensors as well as the materials and fabrication techniques employed in their design are addressed. The existing research highlights the need for robust and flexible materials to enable the development of reliable and comfortable sensors. Finally, the paper presents potential research directions and proposes research challenges in the field of flexible and wearable respiration sensors. By identifying emerging trends and gaps in knowledge, this review can encourage further advancements and innovation in the rapidly evolving domain of flexible and wearable sensors. Wearable sensing is an emergent technology for the monitoring of human vital signs in various fields such as health, sports, and the military ,2,3. NowAmong the vital signs, the breathing rate holds particular significance in human physiology, as it contains a wealth of information about a person’s health condition. The normal respiratory rate for a healthy adult typically falls within the range of 12–20 breaths per minute (bpm). However, in specific situations such as high-intensity exercise, the respiratory rate may even increase to as much as 60 bpm . TherefoFurthermore, breathing rate is an important predictor for cardiac arrest, as reported in clinical studies ,14. Like2 monitoring, pulse oximetry (SpO2), and electrocardiogram-derived methods, while non-contact methods mainly included radar-based detection, optical techniques, ultrasound sensors, and thermal imaging.Several approaches that employ sensors to measure breathing rate for respiratory monitoring exist in the literature. These approaches vary on the basis of sensing techniques, sensor types, and sensor placements, among other factors. The literature presents a prevalent categorization into two main types, namely, contact and contactless sensors. As the name implies, contact-based sensors require physical contact with the subject, while contactless sensors measure breath parameters without physical contact using optical or electromagnetic principles, detecting variations in light or electromagnetic waves caused by breathing. A comprehensive overview of various sensing techniques for both contact and non-contact methods has been presented by ,19. ContMassaroni et al.  has condFurthermore, these breath monitoring techniques utilize a wide range of frequencies, allowing for their classification based on operational frequencies. Thus, flexible wearable sensors for breathing can be broadly categorized into high-frequency systems that operate in the microwave range and relying on changes in electromagnetic properties of surroundings and low-frequency systems that use passive sensing mechanisms to detect breathing motion. This classification is especially useful in the context of Specific Absorption Rate (SAR), which denotes the energy absorbed by human tissue when exposed to electromagnetic radiation. Current international standards mandate SAR testing for frequencies above 4 MHz ; howeverFor this review, conference proceedings and full-text articles were selected from a broad search containing diverse foundations and catalogs such as Science Direct, Web of Science, MDPI, and IEEE Xplore. Keywords were selected in each source as follows: (Flexible OR textile) AND (wearable AND sensor) AND (respiration OR breathing). The initial search returned 476 results, indicating that a significant number of studies have been conducted in recent years. Consequently, we refined our search for biophysical sensors by placing emphasis on the previously mentioned top three respiration sensing techniques identified in . Then, tHigh-frequency sensors offer unique advantages such as smaller size and wireless communication capabilities, making them suitable for various applications in healthcare and wearable technology. Among these sensors, antenna sensors, RFID/NFC-based sensors, metamaterial sensors, and Fiber Bragg Grating (FBG) sensors have emerged as the most promising candidates for high-frequency respiration monitoring. In the following subsections, a brief overview of each technique is presented, including its operating principle and associated challenges.Antenna sensors have become increasingly prominent in the last few years for the monitoring of vital signs, especially for respiration. The sensing mechanism is primarily based on two factors: chest wall movement, and displacement of air volume in the lungs. The movement of the chest wall leads to changes in the physical dimensions of the antenna, while the displacement of air volume alters the dielectric properties in the vicinity of the antenna. Both of these effects result in the variation of electrical characteristics of the antenna, such as its reflection coefficient, resonance frequency, and radiation pattern . The varVarious types of flexible and wearable antenna-based respiration sensors have been developed for respiration monitoring. For instance, an embroidered meandering dipole antenna-based sensor was integrated into a commercially available t-shirt that detects resonance frequency shifts induced by chest movements during breathing , as showCommercial RF platforms such as RFID and Bluetooth have been employed for wireless sensing by utilizing the variations in the received signal strength indicator (RSSI). For instance, Patron et al. presented a sensor that employed knitted antennas and inductively coupled RFID tags for comfortable and battery-free monitoring of respiration patterns . Figure Nevertheless, the development of flexible and wearable antenna sensors is accompanied by several significant challenges. First, achieving conformity to complex surfaces such as the human body poses a key hurdle. These antennas must be able to adapt and conform to irregular and curved surfaces while maintaining reliable signal reception and transmission. Second, balancing performance and efficiency in a compact and flexible form factor is crucial, as the human body acts as a very lossy medium that absorbs and attenuates electromagnetic signals. This results in decreased antenna efficiency, reduced signal transmission range, and altered radiation patterns. Therefore, wearable antennas need to exhibit high radiation efficiency, wide bandwidth, and reliable communication capabilities by carefully tackling these challenges.In addition, the safety of subjects is a crucial aspect to consider in the application of antenna sensors. Compliance with specific absorption rate (SAR) limits is essential to ensure the well-being of users. It can be observed from Wireless transmission of sensor data can be achieved through various technologies, including radio-frequency identification (RFID), near-field communication (NFC), and Bluetooth. However, when comparing RFID/NFC technology to Bluetooth one notable advantage is the potential for battery-free communication. The principle of operation for RFID is backscattering, where the tag receives energy from the reader’s transmission and uses it to send back a reply. In this case, the sensors can derive power from the electromagnetic (EM) field generated by a remote reader.With the advent of the Internet of Things (IoT) era, radio-frequency identification devices (RFID) sensors have gained popularity for wearable sensing. In particularly, passive UHF RFID sensors have become used widely due to their small size and lack of power requirements. These sensors have the advantage of being lightweight and comfortable due to their flexible nature. Typically, RFID systems are utilized for sensing applications in two manners. The first involves the measurement of back-scattered power intensity, while the second entails the transmission of sensor data towards the reader.For respiration measurements, RFID sensors have been mostly used as strain sensors utilizing the principle of backscattering. In this case, the main sensing element is an antenna which is specially designed according to the impedance of RFID chip and fabricated on a flexible or textile material. When a strain force is applied to an RFID tag, the physical deformation of the embedded antenna causes a shift in its resonant frequency. This results in a variation in the backscattered power (RSSI) transmitted from the passive RFID tag, which can be used as a metric for detecting mechanical deformations. Thus, RFID-based respiration sensors are designed by correlating the RSSI variation to the mechanical deformation of the RFID antenna. This approach has been demonstrated in various studies for monitoring respiration rate and detecting breathing patterns ,28,32,33Apart from RSSI, RFID technology is utilized to transmit data from other sensors towards the reader. In a study on graphene-based respiration sensing, the AMS SL900A microchip was employed for this purpose . The SL9NFC is a specific subset of RFID technology that is designed for short-range wireless systems. One significant advantage of NFC over conventional RFID is its ability to facilitate peer-to-peer communication between an NFC-based system and any NFC-enabled smartphone acting as a remote reader. This feature makes NFC technology accessible to individual users and thus expands its potential applications. Similar to RFID, the backscattering technique can be applied to NFC for sensing purposes as well.An embroidered inductive strain sensor was introduced in  for respDespite the inherent flexibility and lack of power requirements of passive RFID tags, a limitation of these tags is the inclusion of an electronic chip. This limits their large-scale production for wearable applications and renders them susceptible to harsh environmental conditions. Therefore, the future of RFID wearable sensing lies in chipless technology, which is more robust and feasible for production due to the absence of any electronic component .Electromagnetic metamaterials are man-made materials comprised of structures with electromagnetic properties that are deliberately engineered to offer a range of responses that are difficult or impossible to achieve in naturally occurring materials or composites. The growing popularity of metamaterials in sensing applications is evident from the increasing number of published works utilizing these engineered structures . In thesFrequency Selective Surfaces (FSS) are two-dimensional planar structures consisting of periodic arrays of sub-wavelength elements. They are designed to selectively transmit or reflect electromagnetic waves based on their frequency. FSSs are widely utilized in microwave frequency filters, radar absorbing materials (RAMs), and antenna reflectors . For resTraditional frequency selective surfaces used for sensing present certain limitations in terms of flexibility, as the materials and structures used are rigid. Therefore, liquid metal-based technologies  and textPlanar spiral structures (SRs) are commonly used as lumped inductors in microwave circuits and serve as a fundamental element for metamaterials . The indSpoof localized surface plasmons (LSPs) are electromagnetic modes that are highly confined and can be realized using various techniques such as textured metal surfaces, thin metal layers, and conductive textiles ,46,47. TA wearable textile sensor based on LSP resonance was proposed in  for vitaResonators relying on surface plasmons generally have a very high quality factor, as the electrical field is confined in a very limited space. However, these sensors face challenges in terms of the complexity of their fabrication and sensitivity to the environment. Therefore, further research is needed to ensure their reliable performance in the context of wearable sensing.Fiber Bragg Grating (FBG) sensors are well suited for measuring biophysical parameters, including the respiratory behavior of the chest and abdominal regions. These sensors are comprised of a fiber optic grating that reflects a specific wavelength of light , as showFBG sensors are especially advantageous during MRI testing thanks to their immunity to strong magnetic fields. A study focusing on the design and assessment of an MR-compatible smart textile utilized six FBGs . The objFurthermore, elastic belts integrated with optical fibers for monitoring breathing activities were studied in . The aimThe biggest challenge associated with FBG sensors is that the optical fibers are typically rigid and fragile. Therefore, they need to be encapsulated in a material that can provide protection, flexibility, and biocompatibility in order to make them suitable for flexible and wearable applications. Such encapsulation additionally shields the FBG sensor from external influences such as moisture, mechanical stress, or bending which could compromise its performance or usability.Various low-frequency sensors have been developed to enable non-invasive and continuous breath monitoring. These sensors are often characterized as simple and passive devices that typically operate at sub-megahertz frequencies and do not require an external power source for their operation. They are relatively straightforward in terms of their design and implementation, often consisting of basic lumped component designs such as capacitors, resistors, coils, or electrodes. The following section discusses the most commonly used low-frequency techniques for flexible and wearable respiration sensors.Capacitive sensors are a type of flexible wearable sensor that has shown promising scope for monitoring breathing and respiration. The working principle of capacitive sensors relies on variations in capacitance due to changes in electrode dimensions, the separation distance between electrodes, or dielectric properties. These changes allow the capacitive sensor to detect physical quantities such as strain, pressure, or humidity. Capacitive sensors on the human body have been utilized in various ways to detect breathing. They can measure chest expansion and contraction during respiration by detecting changes in capacitance; additionally, these sensors can be employed to detect air humidity from exhaled breaths as a means of monitoring respiration. Another approach is to measure the pressure on the abdomen and chest during exhalation, which can be used to monitor respiratory movements.The simplicity of the working principle of capacitive sensors has led researchers to explore various fabrication techniques and materials to improve their flexibility and sensitivity for wearable applications. In , a flexiFurthermore, a facemask with an inter-digital embroidered capacitor was proposed for respiration monitoring in , as showSimilarly, a sensor for wearable electronics was fabricated in  using hiKang et al. developed a respiration sensor utilizing a variable parallel-plate capacitive design and incorporating nonwoven fabrics . This seConversely, capacitive sensors have a number of limitations on their use in respiration sensing. One such limitation is their sensitivity to environmental factors such as humidity and temperature, which can affect the accuracy of the measurements. Additionally, the placement of electrodes on the textile substrate may introduce variability in the signal due to movement or displacement during breathing. Therefore, calibration and compensation techniques are necessary to account for these variations.Resistive sensors for respiration monitoring employ different sensing mechanisms, including strain sensing, temperature sensing, and humidity sensing. Strain sensing involves flexible materials that changes their resistance in response to respiratory movements, thereby enabling measurement of the respiratory volume or rate. Most strain sensors employ resistive techniques due to the direct proportionality between the resistance of conductive materials and the strain. For instance, a respiration sensor based on stretchable conducting fabric was developed in  to detecVarious flexible humidity sensors based on different materials have been explored for vital sign monitoring by measuring impedance. Highly sensitive textile-based humidity sensors employing graphene oxide/Polypyrrole composites have been developed for real-time respiration monitoring ,82. In pDespite the potential advantages, resistive sensors are susceptible to drift and hysteresis, leading to potential inaccuracies in measurements. Moreover, unintended fluctuations in electrical resistance may arise as a consequence of variations in the ambient temperature and humidity conditions. Therefore, signal processing techniques are necessary in order to ensure accurate respiratory monitoring, address noise, and extract relevant respiratory information.Magnetic Induction (MI) is a non-contact technique used to measure changes in the impedance distribution of an object. It relies on the electromagnetic coupling between a coil and an object in close proximity. Human tissue is characterized as an electrical medium that is both inhomogeneous and anisotropic in nature. The impedance distribution within the thorax is influenced by physiological activities such as breathing, which can be attributed to various factors, including volume changes and displacement of organ boundaries. Currently, three primary categories of flexible inductive sensors are extensively employed: eddy current sensors, mutual-inductive sensors, and self-inductive sensors.In the eddy current method, the coil is driven by an alternating current, generating a primary alternating magnetic field that penetrates the conductive medium surrounding it, thereby inducing eddy currents within the medium. These eddy currents in turn generate a secondary alternating magnetic field that interacts with the primary field, resulting in changes in the coil’s impedance. These changes are directly related to the impedance distribution of the object. When the coil is positioned in front of the thorax, the thorax acts as the object under test and the coil’s impedance varies in response to the variation in thoracic impedance distribution caused by the movement of the lungs. In , a systeIn addition, inductive sensors can measure physical quantities such as displacement and pressure with high sensitivity utilizing the principles of mutual inductance. Inductive-based displacement sensors utilize electromagnetic induction to measure and monitor object displacement or position. These sensors generate an alternating magnetic field using a coil; the movement of the object induces a change in the magnetic field, allowing for displacement measurement. An embroidered inductive strain sensor was proposed in  fabricatMagnetic induction sensors used in respiration monitoring can be susceptible to measurement errors caused by external electromagnetic interference. It is essential to employ calibration and compensation techniques to mitigate variations in the magnetic field arising from different body positions or environmental factors. Furthermore, careful consideration of the sensor’s design and placement relative to the body is crucial to optimize measurement accuracy.Piezoelectric sensors are fabricated using piezoelectric materials, which exhibit an internal polarization phenomenon when subjected to an external force. This phenomenon leads to the appearance of positive and negative charges on the surfaces of the piezoelectric material, resulting in the generation of a piezoelectric potential. Upon removal of the external force, the polarization phenomenon disappears. Thus, sensors can be designed by using piezoelectric sensors during respiration monitoring to detect variations in the electrical signal.Several studies have proposed the use of piezoelectric sensors as part of multi-functional sensing technologies. These studies aim to integrate multiple smart functions into wearable sensors by employing hybrid mechanisms ,98,99. ISimilarly, Zhu et al. designed a self-powered hybrid electronic skin that combines triboelectric and piezoelectric effects to enable wearable multi-sensing , as showPiezoelectric-on-substrate (TPoS) refers to a specific type of piezoelectrically actuated resonators designed with a piezoelectric layer on top of a substrate layer. The incorporation of the substrate layer enhances power handling capabilities and improves the quality factor of the resonator. For respiratory monitoring applications, it is crucial to have a TPoS resonator that exhibits high sensitivity to changes in respiration flow as well as a high electromechanical coupling and quality factor.A wireless sensor utilizing a thin-film piezoelectric-on-substrate (TPoS) resonator was employed in  for respThe successful integration of piezoelectric materials into wearable sensors requires meticulous design considerations in order to ensure mechanical stability and durability. The accuracy of measurements can be compromised by sensor drift and noise, necessitating the implementation of suitable signal-processing techniques. Calibration and compensation methods are imperative to address individual variations and ensure consistent and reliable measurements.Bioimpedance sensors for respiration monitoring operate based on the principle of measuring changes in electrical impedance caused by respiratory movements. These sensors typically consist of electrodes that are placed on the skin surface, creating a closed electrical circuit , as showImpedance sensors play a crucial role in breath monitoring, offering a non-invasive and continuous approach that can track respiratory patterns and gather valuable health information. Several articles have explored the use of such flexible sensors to monitor physiological activities. For instance, a wearable smart clothing system was proposed in  integratIn addition, a wearable scheme incorporating an electrical impedance tomography (EIT) belt has been designed with a novel active electrode architecture, high image frame rate, and wide operating bandwidth, enhancing the neonatal thorax monitoring for vital signs . MoreoveBioimpedance measurements are sensitive to electrode placement and contact quality, and require careful attention to ensure consistent and reliable measurements. Calibration procedures and algorithms are necessary in order to accurately interpret impedance changes related to respiration and distinguish them from other physiological signals.The primary characteristic of respiration involves the movement of air in and out of the lungs, which results from the expansion and contraction of the lungs. The associated ribcage movement can be detected through inertial sensors ,114, as However, inertial measurement units (IMUs) are mostly incorporated to capture motion data and facilitate activity monitoring in conjunction with other sensors. For instance, the NeoWear system was developed to monitor neonatal vital signs using a sensor belt which comprises a pressure sensor and an Inertial Measurement Unit (IMU) . This syMany materials and techniques have been explored to date for the fabrication of flexible wearable sensors. The fundamental requirement for these sensors is to exhibit improved performance when applied to the human body while simultaneously possessing material flexibility, biocompatibility, and user comfort. Sensors are primarily comprised of two components, namely, the substrate and the sensing elements, which are connected by metallic interconnectors. This section provides a brief overview of substrate and sensing materials utilized in the context of respiration sensors, as depicted in Selection of the substrate plays a crucial role in designing wearable sensors, as the substrate is essential for ensuring that the sensor can conform to the body’s contours and withstand its movements while maintaining optimal performance and providing a satisfactory user experience .Polymer-based materials have been extensively used as substrates for flexible sensors. These are heavy-weight molecules composed of repeating units that exhibit distinct characteristics based on their internal bonds. Polymers offer tunable chemical, structural, and electrical properties, making them attractive candidates for sensing applications. Several types of polymer-based materials have been used as substrates for flexible wearable respiration sensors. Polydimethylsiloxane (PDMS) is a silicone-based elastomer known for its excellent flexibility, biocompatibility, and optical transparency, and is the most commonly used substrate material for wearable sensors ,64. It hWearable sensor technologies have witnessed significant advancements in utilizing fabric and textile materials as substrates. These materials offer flexibility, durability, and comfort, making them highly suitable for a wide range of applications. Flexible sensors integrated into textile materials offer comfort, wearability, and ease of use. Several articles have focused on the integration of sensors into fabric and textiles to enable real-time monitoring of vital signs and respiration. For instance, wearable antennas and sensor tags are embroidered or printed on fabric substrates, ensuring unobtrusive and comfortable monitoring experiences ,41. ThesIn terms of specific sensing techniques, strain sensors have been fabricated on stretchable fabrics woven with fine yarns , while p2 multilayer composite can serve as the substrate for piezoelectric respiration sensors [A variety of composite materials employing different types of materials have been investigated for their applicability in respiration sensors. Thin films of Si/SiO sensors ,97. In a sensors . Further sensors ,75,120.  sensors . In addi sensors .The mechanical and biocompatibility characteristics of commonly used substrate materials are summarized in Paper-based (PB) sensors have been widely reported for respiratory detection owing to their excellent biocompatibility, cost-effectiveness, and eco-friendly nature. The primary material used in paper-based sensors is cellulose, which is a naturally occurring biopolymer. For this reason, PB sensors generally exhibit good biocompatibility. Furthermore, their lightweight and flexibility ensure ease of use for continuous monitoring without causing significant inconvenience to the wearer. PB sensors are very cost-effective, as the primary raw material is abundant and inexpensive and the manufacturing processes are not highly specialized. This cost-effectiveness makes them easily accessible for a wide range of healthcare applications. Another important feature is that paper sensors are biodegradable, meaning that they can naturally break down over time without leaving behind harmful residues. Therefore, environmentally friendly and disposable sensors can be fabricated with paper-based materials at a very fractional cost.2 printing paper was used as the dielectric material and polyester conductive tape as flexible electrodes. Likewise, a paper-based self-inductive folding displacement sensor (PSIFS) that used common paper material and copper tape was proposed for monitoring human respiration in [In addition, the PB sensors can be easily customized and adapted to various respiratory parameters, including humidity and pressure. For instance, a noninvasive wearable screen-printed sensor was proposed in  for humaation in .Wearable sensors rely on various materials to enable their sensing capabilities and enhance their overall performance. These materials are carefully chosen based on their specific properties and the requirements of the sensor design. The conductivity of surfaces plays a critical role in the operation of various respiration sensors, such as resistive, capacitive, inductive, and antenna-based sensors, as these sensors depend on the surface’s conductivity to facilitate precise detection and measurements.Metallic materials are used in sensors due to their excellent electrical conductivity, which enables efficient signal transmission and sensing capabilities. For instance, a high-frequency litz wire was integrated into a textile shirt to make a coil for magnetic induction sensor in . FurtherIn addition, conductive inks and paints have emerged as effective materials for the printing of sensors in the field of wearable technology. These offer numerous advantages, including flexibility, low-cost fabrication, and compatibility with various substrates. Silver conductive ink has been used to create sensing areas on nonwoven fabrics, enabling seamless integration into everyday clothing for textile-based respiration sensors ,71. MoreVarious types of carbon materials, including carbon nanotubes, graphene, and MXene, have been used to fabricate wearable sensors for respiration sensors. Carbon nanotubes are cylindrical structures made of carbon atoms arranged in a hexagonal lattice with diameters on the scale of a nanometer, and are classified into two main types: single-walled carbon nanotubes (SWCNTs), and multi-walled carbon nanotubes (MWCNTs). To address the need for cost-effective and non-invasive respiratory monitoring, researchers have explored the use of multi-walled carbon nanotubes (MWCNTs) and polydimethylsiloxane (PDMS) composites ,100,101.Another popular carbon-based material is graphene, which is a single layer of carbon atoms arranged in a two-dimensional honeycomb lattice. It is employed in breathing analysis due to remarkable properties such as biocompatibility, low cost, and ease of functionalization . In addiThe electrical and mechanical characteristics of commonly used sensing materials are summarized in Conductive polymers have emerged as promising materials for sensor applications due to their unique combination of electrical conductivity, mechanical flexibility, and tunable properties. For instance, a combination of polyethylene-co-vinyl acetate (PEVA) polymer and multi-walled carbon nanotubes (MWCNTs) has been utilized for antenna fabrication  for respVarious piezoelectric materials have been employed in sensing due to their ability to generate electrical signals in response to mechanical pressure or strain. Materials such as polyvinylidene fluoride (PVDF) film and lead zirconate titanate (PZT) film have been used as sensing materials in respiration sensors. PVDF films can be utilized in nasal sensors for non-invasive respiratory monitoring , and havOptical fibers are thin, flexible, and transparent strands made from high-quality glass or plastic materials that can transmit light signals over long distances with minimal loss. They have been extensively utilized in Fiber Bragg Grating (FBG) sensors used for strain sensing. These sensors are based on the principle of periodic variation in refractive index along an optical fiber, and offer unique advantages such as compatibility with magnetic resonance imaging (MRI) and immunity to electromagnetic interference . Small aSeveral existing fabrication techniques have been utilized to design functional and reliable sensors for a range of wearable applications. This subsection summarizes common fabrication techniques employed for wearable sensors, focusing on their application in breath monitoring.Various printing techniques, including screen printing, inkjet printing, and 3D printing, are employed in the fabrication of wearable sensors, as shown in Other printing techniques, such as inkjet printing and 3D printing, are employed in wearable sensor fabrication. Inkjet printing allows for the precise deposition of functional materials such as conductive inks or graphene oxide solutions onto substrates to create sensors with high resolution and customization capabilities. The droplet-based nature of inkjet printing enables the creation of intricate sensor designs and the integration of multiple sensing elements on a single substrate. This technique has been utilized in articles where conductive inkjet printing is employed to fabricate wearable sensors ,41. On tKnitting and weaving techniques are employed in the fabrication of wearable sensors using conductive fibers or yarns. These techniques allow for the integration of conductive elements directly into the textile substrate, enabling seamless and flexible sensors. Conductive fibers or yarns such as metal-coated fibers or carbon nanotube yarns are incorporated during the knitting or weaving process to create conductive paths within the textile structure, as depicted in Additionally, CNC knitting machines are employed to seamlessly produce and integrate various components in a single knitting process, including sensors, antennas, conductive fabrics, nonconductive fabrics, and in one case a PCB pockets for a batteryless wearable compression sensor . MoreoveEmbroidery has been utilized in the fabrication of wearable sensors for various applications, including real-time breath monitoring. In this technique, conductive threads or yarns are embroidered onto the textile substrate to create sensor electrodes and connectors. The electrical conductivity of the threads can be optimized for desired sensor performance by carefully controlling the stitching pattern and density. For instance, an embroidered antenna-based sensor is proposed for real-time breathing monitoring using a commercial two-ply conductive yarn . The laySimilarly, a textile-based embroidered passive strain and displacement sensor was developed using standard embroidery processes and commercially available conductive yarns in . Lastly,This review has shown that low-frequency and high-frequency sensors can both be effectively utilized in respiration sensing, each offering unique advantages while facing specific challenges. Low-frequency sensors provide direct measurements of respiratory movements with simple designs and wide frequency response. However, challenges exist in terms of hysteresis, electrode-to-skin contact, motion artifacts, and environmental interference. On the other hand, high-frequency sensors offer wireless and contactless operation with good communication capabilities, while challenges arise in terms of power consumption, data transmission, and complexity of design. Furthermore, it is apparent that a highly diverse range of materials can be employed in the design of respiration sensors, ranging from polymers and textiles to metals and carbon-based substances. Obviously, these materials all possess their respective advantages and limitations in the context of specific applications. Therefore, key considerations should include materials with key properties such as flexibility and biocompatibility that can ensure long-term operation without causing discomfort to the user. Moreover, commonly used fabrication techniques such as printing, knitting, and embroidery have been discussed and assessed based on factors such as the design resolution of the sensor, manufacturing cost, and suitability for large-scale production.In the context of future research, promising potential exists for self-powered wearable respiration sensors specifically designed for low-frequency applications. These sensors utilize piezoelectric and triboelectric components to create self-sustaining systems. However, challenges persist in miniaturization and efficiently when converting mechanical breathing energy into electrical power while ensuring user comfort. High-frequency sensors have emerged as a promising trend in the field of respiration sensors due to their ability to simultaneously sense and communicate breathing information in a compact form factor. In this context, antenna sensors and RFID sensors have shown promise as viable candidates for this purpose. Additional research could focus on enhancing the design of wearable antenna sensors to minimize radiation exposure to users. Furthermore, exploring chipless RFID sensors as an alternative to chip-based RFID could facilitate larger-scale production and ensure long-term operation. The integration of metamaterials into existing sensors holds great promise, offering advantages such as tunability and enhanced sensing capabilities. Additionally, as flexible metamaterials are very versatile on their own, they could be used for sensing, shielding, and energy harvesting in smart textiles. Opportunities for further research can be found in the optimization of metamaterial design and fabrication techniques that can enable their seamless integration into wearable devices for diverse sensing applications, including respiration monitoring.