The increase in female participation in athletics over the past decade has been accompanied by an increase in injury rates as a result of higher demands placed on athletes. Although previous studies have shown that anatomic, biomechanical, hormonal, and psychological factors may play a role in differences between men and women that can influence injury risk in athletes, there is still a lack of understanding of sex-related mechanisms of injury, guidelines, and prevention strategies. This article provides an overview of common injuries affecting female athletes. We present guidelines for upper- and lower-extremity injury rehabilitation, focusing on considerations specific to the female athlete with the goal to facilitate a safe return to sports.Level V, expert opinion. Female participation in athletics has increased over the past decade, with a rapid rise in participation in sports previously deemed “male dominated.”,Increased sports participation has led to an increased rate of injury in female athletes, and previous studies have shown an increased risk of certain injuries in women when compared with men.,ACL tears are 2 to 8 times more common in female athletes than in their male counterparts.,Previous studies have shown sex differences in the epidemiology of ankle injuries, particularly ligament sprains and instability.,Although traumatic shoulder instability is more prevalent in male athletes, female athletes often present with multidirectional instability and studies have shown that female athletes have poorer outcomes after surgical management of shoulder instability.,Several innovative therapeutic modalities have been developed and used to reduce rates of injury and minimize the amount of rehabilitation required for athletes to return to play (RTP) after an injury. One such modality is cryotherapy—a well-established and widespread therapy used in athletes in an attempt to treat soft-tissue injuries and reduce post-training inflammation and pain.,,Another often-performed therapeutic technique is iontophoresis, whereby a direct current of low amperage is applied to the skin by means of bipolar electrodes to increase the permeability of skin and enhance the delivery of transdermal drugs or prodrugs into the deeper tissues such as the muscles or tendons or the synovial fluid.Blood-flow restriction (BFR) therapy is a more recently developed technique often used in the athletic population. BFR involves localized restriction of venous blood outflow from a specific portion of the body using an occlusive pressure device such as a tourniquet or inflatable cuff placed at the proximal end of an extremity. The restriction of venous outflow results in an anaerobic environment, which promotes muscle hypertrophy through cellular signaling and hormonal changes similar to those seen during higher-intensity training with more resistance.Finally, there are several injectable therapies used in the athletic population including platelet-rich plasma therapy, autologous conditioned plasma therapy, mesenchymal stem cell exosome therapy, mesenchymal stem cell–Wharton jelly therapy, gold-induced cytokine therapy, and prolotherapy. These and several other recently developed therapeutic techniques have been seen more prevalently in the recent sports medicine literature and have been gaining popularity with athletes, coaches, physiotherapists, and physicians alike.Injury rehabilitation typically involves several sequential phases . The iniOnce pain-free ROM and mobility have returned to or are near baseline, the athlete can advance to the strength redevelopment phase of rehabilitation. An athlete’s baseline strength level and sport are integral factors to consider when developing a strength training program. A strength training program should maximize the use of compound movements if the athlete’s injuries allow for it. Compound movements facilitate functional strength development by having the athlete perform complex movements that involve multiple joints and muscle groups . These movements are more neurally demanding and allow for larger loads to be lifted, leading to greater neuromuscular development. Compound training has also been proved more effective for increasing overall muscular strength, promoting hypertrophy, and reducing rates of injury and reinjury in athletes when compared with isolation movements.,Once these initial phases have been completed, sport-specific exercise selection then allows for adaptations tailored to the athlete’s sport. Given that the risk factors for sustaining an injury vary based on sport, tailoring the rehabilitation program to the athlete’s sport can result in better outcomes.,For the upper extremity (UE), there are several devices that can allow for self-myofascial release. The Graston technique, massage balls, and massage guns are the primary methods by which UE self-myofascial release is performed because foam rollers are generally larger and more suited for the lower extremity (LE) and posterior chain.Once ROM is re-established, the strength training phase of rehabilitation should start with low-intensity exercises. Single arm–throwing athletes typically have significant asymmetry in shoulder strength and flexibility, which can frequently cause injury.Although there are some compound exercises that allow for shoulder development , these can be challenging to perform, especially by female athletes with pre-existing shoulder injuries. Instead, shoulder strength can be developed by performing isolation exercises with lighter loads such as light dumbbells, resistance bands, or cable machines. Such exercises include lateral raises, internal and external shoulder rotation, and the Y-T-W-L exercise (a popular shoulder exercise performed while prone with the UE taking the shape of each letter).Elbow and wrist training plays an important role, particularly in participants in throwing sports, in reducing the risk of medial and lateral epicondylitis. Resistance training has proved to be an effective method in strengthening the muscles of the forearm and reducing the incidence of epicondylitis.30Finally, grip training is widely recognized as a crucial part of UE development and rehabilitation. Many recently developed creative techniques target this specifically, including the use of handgrip tools, kettle bells, farmer’s walks, and TheraBand Flexbars. Grip training can also be incorporated into general strength training by using handles that are more difficult to grasp, forcing the development of strength and dexterity in the muscles responsible for grip. This can be further extended into the specific development of the intrinsic muscles of the hand by using finger exercise methods, such as finger extension resistance bands and finger exercisers.31,UE orthotics and taping can be a very useful tool during the RTP phase because they can provide an extrinsic support that reduces the risk of reinjury. Splints and braces are particularly useful in the treatment of elbow, wrist, and finger injuries because they can effectively limit ROM and protect against hyperextension and valgus-varus stresses. Kinesio Taping has been shown to be effective in improving shoulder proprioception and reducing the risk of shoulder injury.LE rehabilitation follows many of the same principles as UE rehabilitation. The added difficulty, however, is that effective strength training in the LE, unlike in the UE, is heavily dependent on compound movements , which often involve the UE and the core. This can be challenging because injuries involving other joints in the UE or core might limit an athlete’s ability to adequately perform LE strength rehabilitation.,,To some degree, this can be overcome by performing isolation resistance training that focuses on monoarticular movements, but unfortunately, this is not a very effective method of building LE strength or functional rehabilitation when used as a monotherapy. In addition, addressing lower-limb coordination and proprioception can be challenging during rehabilitation. However, it is of utmost importance to avoid reinjury, particularly in female athletes with knee and ankle injuries , which cannot be addressed with isolation training.,,,Dynamic stabilization of the knee is primarily achieved via the hamstrings and quadriceps. The functional hamstring-to-quadriceps (H/Q) ratio—the functional ratio of eccentric hamstring to concentric quadriceps moments (extension) and concentric hamstring to eccentric quadriceps moments (flexion)—has been described as one of the integral principles that determine the degree of strain on the ACL.,At high knee flexion angles, a low H/Q ratio may represent a compromised ability of the hamstrings to stabilize the knee joint throughout the full ROM. Near full knee extension, shifts in favor of the knee flexors may represent an attempt to stabilize the knee at the angle of greatest ACL strain.,Given the crucial protective value of the hamstrings and quadriceps in reducing the risk of ACL injuries, developing functional strength is at the core of LE rehabilitation. A highly cited study by Renström et al.Similarly, rehabilitation after an acute ankle sprain or chronic ankle instability includes early functional rehabilitation, which focuses on increasing ROM, resistance strength training, proprioception exercises, and sport-specific training.,,Anatomic differences, hormonal differences, biomechanical factors, neuromuscular factors, genetic predisposition, and even psychological assessment of competitive ability have all been suggested to play roles in the differences between male and female athletes.,Although there is a paucity of literature evaluating outcomes of various gender- and sex-specific rehabilitation strategies, many protocols address the 4 following deficits typically seen in the injured female athlete: (1) ligament dominance, (2) quadriceps dominance, (3) leg dominance, and (4) trunk dominance.Psychological factors including self-efficacy, identity, and fear of reinjury may all play a role in an athlete’s ability to return to sport.Increased female sports participation has been accompanied by an increase in injury rates. Understanding how female athletes differ from their male counterparts regarding the mechanism of injury and recovery is important to tailor rehabilitation strategies to the individual female athlete. This article shows the importance of rehabilitation considerations specific to female athletes to more effectively return them to their sports efficiently and safely.


Across species, animals organize into social dominance hierarchies that serve to decrease aggression and facilitate survival of the group. Neuroscientists have adopted several model organisms to study dominance hierarchies in the laboratory setting, including fish, reptiles, rodents and primates. We review recent literature across species that sheds light onto how the brain represents social rank to guide socially appropriate behaviour within a dominance hierarchy. First, we discuss how the brain responds to social status signals. Then, we discuss social approach and avoidance learning mechanisms that we propose could drive rank-appropriate behaviour. Lastly, we discuss how the brain represents memories of individuals  and how this may support the maintenance of unique individual relationships within a social group.This article is part of the theme issue ‘The centennial of the pecking order: current state and future prospects for the study of dominance hierarchies’. While the neural mechanisms of aggression—an important feature of dominance—have been explored and reviewed elsewhere ,2, less attention hierarchies, or the monitoring of more dominant individuals by subordinates, have been observed in species ranging from humans to fish to facilitate avoidance of aggression, recognition of opportunities to rise in rank, and observational learning from successful individuals [There is extensive behavioural evidence that animals are aware of their rank and the ranks of other group members. For example, ividuals –9. Imporividuals –13. An a. 2et al. [The expression of dominant or subordinate behaviour does not always require physical competition, but rather can be based on conspecific cues about individuals' competitive ability known, as status signals . It haset al. ,15–17. Tet al. . Importaet al. . Althoug (a) (i)Mus musculus), specific receptors in the VNO have been identified as necessary for sex cue discrimination and expression of sexual and aggressive behaviour [cfos immunoreactive cells, a proxy of neuronal excitation [Chemical signals, such as pheromones and urinary proteins, are perhaps the most common mode of communication used by social species to convey identifying information including sex, species, status and individual identity –23. The ehaviour ,27. In bcitation ,29. Thiscitation . Furthercitation ,32.2+ dynamics of neuronal ensembles and individual neurons differentiate between conspecific cues in a sex-specific manner, suggesting that biological relevance shapes social odour representations in the MeA [cfos immunoreactivity (cfos-ir) after subjects are exposed to urine from an alpha  compared to a subordinate conspecific, and this does not depend on the subject's own social rank or their familiarity with the cue source, although these factors may influence the biological relevance of the cue [Tscheskia triton) following agonistic encounters and is not correlated to expression of aggression or defensive behaviour [One of these downstream regions is the medial amygdala (MeA), which receives input from both vomeronasal and main olfactory systems and is an early node in the odour processing stream across vertebrates –35. The  the MeA . Further the MeA –41. How  the cue . Activitehaviour . These fcfos-ir within the ventromedial hypothalamic nucleus (VMH) is greater when they are exposed to alpha versus subordinate urine regardless of whether the urine is from a familiar mouse. However, in the most dominant  mice from a hierarchy, cfos-ir in the VMH is only greater when they are exposed to unfamiliar alpha urine compared to either familiar or unfamiliar subordinate urine [cfos-ir in the VMH upon exposure to urinary cues is modulated by familiarity with the cue, the social rank of the animal who provided the cue, and the animal processing the cue. How the social rank of an animal modulates how it processes social cues is expanded upon in §2a(iii). Also, in both dominant and subordinate animals, the ventral premammillary nucleus (PMv) exhibits greater cfos-ir when animals are exposed to familiar alpha urine compared to familiar subordinate urine. Interestingly, this differential cfos-ir in the PMv is not observed when animals are exposed to unfamiliar alpha versus unfamiliar subordinate urine. This suggests that the PMv is not detecting features of urine cues that would necessarily qualify as status signals and that are related objectively to social rank regardless of familiarity. Rather, the PMv appears to detect features that are associated with memory of social rank.While the MeA plays a critical role in identifying social rank based on olfactory cues from mouse urine, it is not clear whether this process is further modified by social memory. Interestingly, several MeA hypothalamic projection targets are activated upon exposure to urine and are modulated by social rank and familiarity with the urine source . For exate urine . Thus, ccfos-ir in response to dominant versus subordinate cues regardless of familiarity with a cue. Others, such as the VMH and PMv, are modulated by additional factors, including an animal's own social rank and familiarity with the individual providing the cue, suggesting that features of learned social rank relationships or social memory are also represented in these regions.This evidence from chemical processing of social odours in rodents suggests that various brain regions represent social rank at different scales. Some regions, such as the MeA, appear to detect status signals, as they exhibit differential  (ii)Astatotilapia burtoni and Oreochromis spp.) use urine to signal dominant status and have increased urine storage compared to subordinates [The neural circuits for processing social chemosensory cues are less well characterized outside of rodents, although social chemicals appear to be especially important in other taxa living in environments where vision is obscured, such as nocturnal primates and aquatic animals living in turbid environments ,44. Likerdinates ,46. Whenrdinates . Interesrdinates ,49. Domirdinates . Furtherrdinates . Thus, tUnlike fish and rodents, primates are generally assumed to rely on visual information rather than chemical or olfactory information when assessing social cues . However (b) (i)Macaca spp.) in a dominance hierarchy resulted in drastic but variable effects on dominant and subordinate behaviour and social rank changes. This included a complete reduction in aggression and loss of high status in one individual, as well as increase in aggression and a transition from typical dominant behaviour to despotic dominance in another individual [Some of the earliest investigations into the neural correlates of dominance hierarchies identified the amygdala as a crucial brain region for appropriate expression of dominant and subordinate behaviour. For example, bilateral amygdala lesions given to the highest-ranking macaques The degree to which animals innately recognize status signals or must learn to appropriately interpret them is not known. Typically, the process of signal detection and response is presented as innate; however, this may not be true for all types of signals. For instance, amygdala lesions in neonatal monkeys increase social fear in social interactions despite a lack of warning facial expressions , but lesThe role of the amygdala in fear and threat learning associations has been thoroughly studied in rodents in the context of Pavlovian conditioning. While conditioning experiments have traditionally demonstrated the learning of associations between an electric shock and an object or environmental context, it is likely that physical injury incurred through competition is associated with status signals in a similar manner. Briefly, the circuitry underlying the fear conditioning process involves the BLA, which integrates sensory information about the external environment and an animal's internal state with contextual information and memories from the hippocampus (HPC) and prefrontal cortex (PFC) ,73. This (iii)c-fos immunoreactivity in the central region of the ventral telencephalon (Vc), a homologue of the mammalian striatum [Anolis carolinensis), DA signalling in specific brain regions is elevated in various brain regions in response to changes in status signals. Males that viewed an opponent with a covered dominance-signalling eyespot had increased DA in the ventral tegmental area (VTA), substantia nigra (SNR), nucleus accumbens (NAcc) and hypothalamus, and became dominant. By contrast, males that viewed opponents with artificial eye-spots had increased DA in the dorsal raphe nucleus (DRN) and amygdala, and became subordinate [Across species, the dopaminergic system is involved in processing social status signals. In cichlid fish, presentation of a dominant male is associated with increased number of dopamine (DA) neurons with striatum . In greeordinate .Homo sapiens) also impairs the ability to recognize angry unfamiliar facial expressions [Lesioning regions that are strongly innervated by dopaminergic neurons also appears to impair status signal detection. Lizards with unilateral lesions to the ventral striatum are unable to detect dominance signals from intruder conspecifics presented to the part of the visual field corresponding to the lesioned hemisphere, but no impairment is seen when they are presented to the intact hemisphere . Interesressions .Beyond signal detection, the release of DA serves as a prediction-error signal alerting discrepancies in the experienced value of a cue and its expected value. This phenomenon builds on the Pavlovian learning system, such that DA signalling can assign strength and valence to CS–US associations and facilitate reinforcement learning of action patterns such as social approach and avoidance ,80. Simi (iv)Considering the prominent role of the PFC in social cognition and in decision making –86, it iPrefrontal representations of status could also reflect attentional processes and the salience of viewing a dominant individual. This could explain why similar BOLD signal responses are observed when subjects are presented with dominant facial expressions and neutral faces of familiar dominant individuals. The PFC's role in sustaining attention has been extensively studied . The eleBeyond the PFC, parietal cortical regions are also involved processing visual status signals. For example, the superior temporal cortex (STC) exhibits greater BOLD signal when human subjects are presented with dominant facial features and postures and when they use these features to make judgements regarding the relative dominance of two other individuals ,94,95. T. 3observational or vicarious learning), or the determination of social status based on cognitive processes such as transitive inference [Status signalling is not the only mode by which animals perceive social rank. Even species that rely on status signals appear to prioritize behavioural demonstrations of dominance in competitive interactions and memories of those interactions over status signals to guide their behavioural decisions. For example, in lizards, manipulating the dominance-signalling dark eyespot does not alter previously established dominant–subordinate relationships , but it nference .et al. [Notably, these learning processes and status signalling are not mutually exclusive and coexist. As mentioned in §2b(iv), elaborate status signals may serve to direct attention towards dominant conspecifics, which is crucial for learning about them. This could manifest as an attention hierarchy, which then facilitates learning about and from highly ranked group members . Furtheret al. ). In the (a)cfos immunoreactive cells increases over subsequent days of SDS [We propose that the amygdala facilitates learning about social rank relationships through competitive social interactions. With the establishment of dominance relationships, subordinate animals yield to higher-ranking group members and avoid pain and injury incurred by fighting , a phenos of SDS , suggestWhile amygdala circuits involved in fear and social avoidance may underlie how the most low-ranking animals in a group may learn their subordinate status, it does not explain how intermediately ranked animals learn to flexibly avoid and submit to some group members and exhibit aggression towards others. Generalized social avoidance induced by fear learning of conspecifics or conditioned social defeat would prevent intermediate animals from expressing both submissive and dominant behaviour when appropriate and prevent socially enriching affiliative behaviours. Another possibility to explain flexible behaviour in intermediates is that social defeat in naturalistic settings induces an anxiety-like social state, such as social vigilance, rather than complete avoidance. Social vigilance, or monitoring of conspecifics, could enhance observational learning and selective avoidance of aggressive conspecifics. While hypervigilance is considered a maladaptive response to uncertainty and associated with higher risk for anxiety disorders , an apprSocial vigilance also appears to be modulated by one's own social rank. In primates, rodents and fish, social vigilance is skewed, giving rise to attention hierarchies where subordinates have elevated levels of social vigilance –9. In maIn addition to stress hormones, OT signalling varies based on an individual's social rank and mediates social vigilance. In female macaques exposed to stress, dominant social status is associated with elevated OT in cerebrospinal fluid . In maleWhile the function of the BNST in relation to social behaviour has not been thoroughly studied in non-mammalian species, recent evidence from fish indicates that activity in the supracommissural subdivision of the ventral telencephalon (Vs), considered homologous to a combined MeA/BNST complex, is increased during cue learning in social (i.e. group-living) compared to non-social conditions . Thus, t (b)The dopaminergic system is another associative learning system that may be involved in social rank learning. As described in §2b(ii), elevated DA signalling is observed when animals are presented with dominant signals. Further, dopamine neurons in the DRN modulate social behaviour in a social rank-dependent manner, with the impact of activating DRN DA neurons greater in more dominant mice ,126. AltStudies in rodents have shown that reward learning via dopaminergic signalling mediates aggressive behaviour. In dominant animals, aggression serves as a naturally rewarding US and can reinforce behaviours that lead to attacking a submissive animal . In bothWhile not directly tested in a dominance hierarchy context, a highly conserved dopaminergic circuit has been identified in rodents and primates , in whicIt is not known whether differences in DA receptor expression pre-determine an animal's social rank or whether they are the result of acquired social rank differences. It is possible that DA signalling differences are inherent as well as mediated by experience, such that animals with initially greater motivation experience greater reinforcement of this behaviour through the rewarding aspects of winning. Elevated DA signalling has been associated with the winner effect, a phenomenon where winning fights perpetuates further winning against new individuals in the future, leading to increased social status ,141. FurInterestingly, DA signalling is also involved in mediating subordinate behaviour. As discussed in §3a, SDS is similar to the repeated defeat experienced by subordinate animals in a hierarchy. DA transmission in the VTA–NAcc circuit has been implicated in social defeat learning in mice and hamsters by modulating plasticity ,144. FurIn summary, dopamine circuits across species facilitate social reward learning and mediate an animal's decision to engage with or avoid certain individuals. This learning mechanism could be used as animals develop social hierarchies and learn their social ranks within that hierarchy.. 4Animals living in social dominance hierarchies have to behave dynamically, such that they express dominant behaviour towards some individuals and subordinate behaviour towards others. Therefore, social memory of individual group members is required in conjunction with the associative learning processes that facilitate approach and avoidant social behaviours. In highly linear dominance hierarchies, where each individual attains a unique social rank, animals behave based on subtle rank differences. For example, dominant male mice tend to exhibit the majority of aggression towards closely ranked competitors , and mal (a)Studies from a wide range of species support the hypothesis that the HPC is essential for both episodic and semantic memory . More recfos immunoreactivity under social compared to non-social contexts [Furthermore, recent studies in mice have identified intra-hippocampal circuits involved in social memory encoding and recall. The HPC consists of CA1, CA2, CA3 and dentate gyrus subregions  and extecontexts . Whethercontexts , potentiIn mammals, the frontal cortex and its connections to the HPC also facilitate encoding and storage of memories regarding specific group members. Studies in rodents have shown that the vHPC projections to the mPFC are necessary for recalling social memory . NeuroimIn conclusion, there is strong evidence that the role of the HPC in encoding individual social memories is conserved across social species. However, the intricacies of intra-hippocampal circuits and how they facilitate memory formation have predominantly been determined in rodents. In mammals, social memory circuitry extends to the PFC, a region that is critical for long-term memory ,159. Alt (b)The neuropeptides OT and arginine vasopressin (AVP) are widely known to regulate social cognition and behaviour across species, with a particular role in supporting social memory. The majority of AVP and OT synthesizing neurons originate in the suprachiasmatic nucleus (SCN) and PVN of the hypothalamus and project widely throughout the brain . One of OT and AVP transmission also affect social memory by acting on components of the amygdala and extended amygdala. Studies in mice and rats indicate that the MeA, known for processing social odours, also encodes memories of individual conspecifics. Blocking OTRs in the MeA impairs social recognition in rodents and activating these receptors during an initial encounter enhances their ability to encode social memory ,167,168.While evidence from rodents and primates strongly supports the function of neuropeptides in social memory, the function of the homologous neuropeptides in fish and lizards remains to be determined. Arginine vasotocin (AVT), the AVP homologue found in fish and reptiles, has a role in non-social spatial and cue learning , but its. 5The evidence reviewed supports that social rank recognition involves the coordinated activity of highly conserved neural circuits across multiple levels of cognition, ranging from the seemingly innate perception of social status signals to more fine-tuned learning of social rank of specific individuals. Notably, the amygdala and dopaminergic neurons are involved in responding to status signals and driving learning about social rank through social interactions. While it appears that status signals serve to bypass the need for experience-based learning and prior social interactions that could incur physical injury, the extent to which status signal responses are innate or learned needs to be more thoroughly investigated. This theory, along with several other critical questions about how the brain processes social status signals, needs to be further investigated. In particular, the impact of an animal's familiarity with a social stimulus on their perception of status signals needs to be systematically studied across species. In addition, the role of an animal's own social rank in modulating how they process external status signals is largely unknown. An individual's social rank appears to influence behaviours related to acquiring social information, such as attentional postures and visual gaze direction –9, but hThe technical difficulty of studying proximal mechanisms of brain function in naturalistic contexts has been a major hurdle in studying such questions and has led to our limited knowledge of the neural dynamics underlying social group behaviours. Although the species discussed in this review form dominance hierarchies, evidence for the neural systems involved in the representation of social rank typically does not come directly from animals living and behaving freely in groups. Laboratory-based neurobiological and behavioural studies have an overrepresentation of simple dyadic social interaction assays that do not directly examine the representation of social rank in groups, and traditionally measure behaviours that are exclusively expressed by males. Moreover, traditional neural recording methods, such as electrophysiology, have been hard to implement in multiple freely moving animals because of physical constraints. Several recent technological advancements have increased our ability to study the neural basis of social rank learning and memory in larger and more natural group settings. In the past few years, open-source tools have been developed to automatically track and assist in the quantification of behaviour of multiple group-living animals –185. Mor


Background: Non-compliance and non-persistence with endocrine therapy for breast cancer is common and usually related to treatment-induced side effects. There are anecdotal reports that simply changing the time of day when taking endocrine therapy  can reduce side effects. Literature review: We conducted a literature review to evaluate whether changing the timing of tamoxifen and/or aromatase inhibitor administration impacted patient outcomes. No randomized control trials or prospective cohort studies that looked at time of day of endocrine therapy were identified through our review of literature from 1947 until August 2020. Conclusions: Given the rates of endocrine therapy non-compliance and non-persistence reported in the literature, ranging from 41–72% and 31–73%, respectively, simply changing the time of day when medications are taken could be an important strategy. We could identify no trials evaluating the effect of changes in timing of administration of endocrine therapy on breast cancer patient outcomes. Randomized control trials are clearly indicated for this simple and cost-effective intervention. Endocrine therapy is a standard of treatment for hormone receptor-positive breast cancer ,2. The sCircadian rhythms, the internal processes that regulate cell metabolism and energy consumption over a 24 h schedule, are believed to play a direct role in drug effectiveness and toxicity . Indeed,Breast cancer patients often seek insights on online forums to determine the optimal time of day to take their endocrine therapy. While some patients have made recommendations that night administration improves side effects , we are A protocol was prepared a priori to guide the performance of this work and was registered with PROSPERO (Registration number CRD42020204822). The research question was phrased in the Population-Intervention-Comparator-Outcomes-study design framework as “Does the time of day at which endocrine therapy is taken affect outcomes in patients with breast cancer?” This review was prepared in consideration of guidance from the PRISMA statement ,20. ®, Embase and Embase Classic, and Cochrane Register of Controlled Trials published from 1947 to August 2020. The search included terms related to breast cancer and timing of endocrine therapy. The full search strategy is outlined in a We searched English language journal publications from Ovid MEDLINEWe looked for randomized control trials and prospective cohort studies that examined the difference in the time of day  at which women received their endocrine therapy (tamoxifen or aromatase inhibitors) for estrogen/progesterone receptor-positive (ER/PR+) invasive breast cancer. After screening 361 unique citations, we did not find any that had previously looked at this question. We conducted a second screen adding another broad term, “circadian” . This prWhile many strategies exist to reduce side effects and improve compliance and persistence with endocrine therapy for breast cancer, it appears that health care providers and patients themselves will often simply change the time of day that they take their medications, with some anecdotal evidence of success . This fiThere have been examples of chronobiology trials in medicine. The Hygia Chronotherapy trial found that bedtime administration of anti-hypertensive therapy led to better ambulatory blood pressure control and a decrease in primary cardiovascular outcomes . This waDeveloping new ways to mitigate side effects is important as we are increasingly prescribing longer durations of treatment ,22 and bIt is possible that there were case reports and retrospective series evaluating the effects of time of drug administration; however, our methodology for this literature review was to only access prospective trials. We also checked clinicaltrials.gov to see if any studies were cited, as well as reviewing the reference sections of the previously published chronobiology studies ,14,15,16In conclusion, while anecdotal evidence suggests that a trial-and-error approach for some patients of changing the time of day of taking their endocrine therapy may reduce side effects and improve quality of life in some patients, we were unable to identify any supporting studies. Given that many studies have been conducted investigating the use of more toxic and expensive interventions for reducing side effects, further studies evaluating this low cost, practical, and simple intervention are clearly warranted. A prospective pragmatic, multicentre, randomized clinical trial, REaCT-CHRONO, will soon start to establish the optimal timing (morning vs. evening) of administering endocrine therapy based on side effects and benefits in early-stage breast cancer patients  . While t


Neuronal networks can be viewed as learning and memory storage devices. They are highly “plastic,” changing the way they process information in response to external stimuli. Yet, they are also highly “tenacious,” with many neuronal networks retaining their functional identity over many years. Hebbian forms of synaptic plasticity, such as long-term potentiation (LTP) and long-term depression (LTD), use positive feedback mechanisms to either reinforce the more active synapses or weaken those that are less active, thus contributing to neuronal networks tuning their outputs to ever-changing external stimuli. By contrast, homeostatic forms of plasticity use negative feedback mechanisms to maintain the overall neuronal output as close as possible to an “internal” prefixed set point, thus restraining neuronal networks from becoming either silent or hyper-excitable. Recent findings have clearly shown that there is not one but multiple forms of homeostatic plasticity occurring at different levels of organization of the brain, from single synapses to dendritic branches to individual neurons to full neuronal networks Davis, .This ebook presents a collection of articles covering molecular and cellular mechanisms that drive forms of homeostatic plasticity whose dysfunction has been proposed to underlie the pathophysiology of many neurological disorders, such as autism spectrum disorder (ASD), schizophrenia, Alzheimer's disease, addiction, intellectual disability, depression and epilepsy  could transform the contribution of REST and HCN1 from homeostatic to pro-epileptogenic. Accordingly, external genetic interventions  may push back neural networks within their physiological boundaries and allow them to take back control of their own homeostasis. Maladaptive homeostatic response is also reported by Yeates and Frank at the Drosophila neuromuscular junction (NMJ), where impairment of intracellular calcium gates leads to excessive homeostatic presynaptic depression in response to chronic upregulation of the vesicular glutamate transporter (VGLUT).Homeostatic compensations are often presented as relatively slow processes developing in response to prolonged perturbations of neuronal activity and relying on the synthesis of new proteins that regulate key physiological parameters, such as synaptic efficacy, synapse number and membrane excitability. At the transcriptional level, the RE-1 Silencing Transcription factor (REST1) is ideally suited to achieve homeostatic plasticity as it has been shown to repress the expression of various channels and synaptic proteins and has been linked to both homeostatic plasticity and epilepsy. However, the actual role of REST in epilepsy, whether protective or pro-epileptogenic is debated. To clarify the role of REST in epileptogenesis, Thalhammer et al. discuss the emerging role of activity-dependent alternative splicing as a versatile mechanism to optimize homeostasis. This process not only expands the diversity of isoforms encoded by a single gene but also affects the spatiotemporal dynamics of the corresponding transcripts. The authors provide examples of genes which undergo activity-dependent alternative splicing and whose splice variants exhibit divergent -sometimes opposite- functions in compensating for activity perturbations. Those genes include REST1, the scaffolding protein Homer1 and the P/Q type calcium channels, which regulate intrinsic plasticity, synaptic scaling and presynaptic homeostasis, respectively. More recently, also alternative splicing of BK channels has been shown to participate to homeostatic adaptations by contributing to action potential widening in response to network inactivity , thus providing autonomy to subcellular functional units such as synapses and dendritic branches.Downstream of transcription, Goel et al. use the Drosophila NMJ to investigate how synapses from an individual neuron homeostatically adapt their strength according to the muscle targets they innervate. The authors identify target-specific homeostatic mechanisms that simultaneously balance for hypo- and hyper-innervation through a differential contribution of pre- and post-synaptic signaling pathways. This study thus highlights the diversity of the homeostatic mechanisms simultaneously implemented by a single neuron to accommodate the requirements of multiple types of outputs. In line with these findings, Lee and Kirkwood review recent evidence showing that neurons embedded in complex sensory networks of the mammalian CNS implement homeostatic synaptic plasticity in an input-specific manner following sensory deprivation. They discuss the role of the “sliding threshold” as a major in vivo mechanism to homeostatically adjust the propensity for future LTP and LTD at individual connections depending on prior experience. In contrast, synaptic scaling, in which the efficacy of all synapses is uniformly modified, may occur to stabilize neuronal activity under more extreme activity perturbations, for instance following pharmacological manipulations or widespread seizures.Whether cell-wide or local, homeostatic plasticity ideally should not compromise information processing occurring at various types of synaptic inputs and outputs. Indeed, most neurons receive synaptic inputs from multiple sources while projecting their axon onto distinct targets, where they form synapses displaying specific functional features. In their study, Galanis and Vlachos propose that Hebbian and homeostatic plasticities coexist at the same synapses, thereby limiting each other. In their model, Hebbian plasticity corresponds to the readjustment of the homeostatic set-point allowing for long-term changes to occur at recruited synapses. In turn, the failure of Hebbian plasticity observed in some physiological or pathological situations may represent enhanced homeostasis. The authors further propose a role for the proteolytic processing of the amyloid precursor protein to set the balance between homeostatic and Hebbian synaptic plasticity. Kruijssen and Wierenga discuss an alternative hypothesis, namely that homeostatic plasticity, rather than affecting directly synaptic strength, modifies the ability of synapses to undergo future LTP, depending not only on their own prior experience (the “sliding threshold” hypothesis discussed by Lee and Kirkwood) but also on that of the nearby synapses. In turn, eliciting LTP at individual synapses triggers compensatory changes at nearby synapses through heterosynaptic signaling. The idea that distinct inputs converging onto the same neuron can balance each other is also proposed by Bannon et al. as a mechanism to prevent the runaway dynamics inherent to Hebbian plasticity. In their review, the authors highlight the possible role of weight-dependent heterosynaptic plasticity in normalizing the excitatory drive to hippocampal inhibitory neurons.Whether homeostatic adaptations also take place in more physiological situations  is an enduring question in the field. While Hebbian plasticity is rapidly implemented, homeostatic plasticity is often viewed as a slow process. Yet, both types of plasticity share common signaling pathways and it remains unclear how homeostatic plasticity can operate without erasing Hebbian plasticity. Cingolani et al. discuss how ECM remodeling controls localization and function of various types of metabotropic receptors . In turn, metabotropic signaling modulates the extracellular environment, for example, by stimulating extracellular proteases. This synergistic crosstalk stabilizes network activity by regulating both synaptic and intrinsic forms of homeostatic plasticity. In a similar vein, Heir and Stellwagen review how the pro-inflammatory cytokine Tumor necrosis factor alpha (TNFα), which is mainly secreted by glial cells, controls various forms of homeostatic plasticity both in vitro and in vivo by modulating receptor trafficking. Importantly, both ECM and glial factors are amenable to therapeutic interventions, for example for the control of epileptogenesis  and glial cells in homeostatic plasticity. Moulin et al. reports some of the strengths and pitfalls of the research carried out in the field of homeostatic plasticity, focusing on the synaptic scaling literature. In addition to the lack of transparency and details regarding experimental and analysis procedures in some research articles, the authors highlight the underrepresentation of studies using in vivo models as well as of those investigating functional interactions with Hebbian plasticity. Like the authors, we believe that such studies should be encouraged in the future.Finally, the systematic review by In summary, this Research Topic provides an overview of recent advances in the field of homeostatic plasticity highlighting the complexity and dynamics of the molecular and cellular mechanisms involved. Perhaps more importantly, most articles presented here not only link homeostatic plasticity to neurological diseases such as epilepsy, neurodegenerative and neuropsychiatric disorders but also provide insights into new avenues for therapeutic intervention.All authors listed have made a substantial, direct and intellectual contribution to the work, and approved it for publication.The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.


Future military conflicts will require new solutions to manage combat casualties. The use of automated medical systems can potentially address this need by streamlining and augmenting the delivery of medical care in both emergency and combat trauma environments. However, in many situations, these systems may need to operate in conjunction with other autonomous and semi-autonomous devices. Management of complex patients may require multiple automated systems operating simultaneously and potentially competing with each other. Supervisory controllers capable of harmonizing multiple closed-loop systems are thus essential before multiple automated medical systems can be deployed in managing complex medical situations. The objective for this study was to develop a Supervisory Algorithm for Casualty Management (SACM) that manages decisions and interplay between two automated systems designed for management of hemorrhage control and resuscitation: an automatic extremity tourniquet system and an adaptive resuscitation controller. SACM monitors the required physiological inputs for both systems and synchronizes each respective system as needed. We present a series of trauma experiments carried out in a physiologically relevant benchtop circulatory system in which SACM must recognize extremity or internal hemorrhage, activate the corresponding algorithm to apply a tourniquet, and then resuscitate back to the target pressure setpoint. SACM continues monitoring after the initial stabilization so that additional medical changes can be quickly identified and addressed, essential to extending automation algorithms past initial trauma resuscitation into extended monitoring. Overall, SACM is an important step in transitioning automated medical systems into emergency and combat trauma situations. Future work will address further interplay between these systems and integrate additional medical systems. RapDespite the sophistication of these autonomous and semi-autonomous systems, each algorithm normally addressed a single patient condition or intervention while remaining blind to the overall patient status. Indeed, as is often the case in the perioperative setting  and the We argue that the next logical step in the field of autonomous medical systems is the development of supervisory algorithms that are specifically intended to integrate the performance of multiple closed-loop controllers towards a specific medical goal. To the best of our knowledge, supervisory algorithms for automating medical sub-systems have currently not been developed. As an initial proof of concept for a simple supervisory algorithm, we integrated the performance of our closed-loop tourniquet controller  and our The supervisory algorithm we describe here can recognize a simulated hemorrhage by sensing the loss of system pressure, activate a closed-loop tourniquet controller, and activate a closed-loop resuscitation algorithm to return the system to an arterial pressure setpoint. Importantly, the supervisory algorithm continues to monitor the patient for signs of tourniquet failure or ongoing hemorrhage and reacts accordingly. The supervisory algorithm is robust to many different patient presentations, as we detail here in five hemorrhage scenarios with increasing complexities.We previously developed a self-tightening, automated tourniquet ; but, inIn general terms, for every cycle, ARC calculated an intermediate MAP setpoint between the currently measured MAP and the actual overall target MAP. Using a formula that varied with the infusate, the algorithm then calculated an infusion rate to achieve that intermediate MAP. ARC then activated an infusion pump at this flow rate, sampling MAP once per second, until the system reached the intermediate setpoint. At that point, a new intermediate MAP setpoint was calculated for the next cycle of the controller. This process of infusing to an intermediate setpoint and calculating a new one continued to loop until the measured MAP was within 99.5% of the overall target setpoint.The ARC algorithm featured smarter flow rate decisions and adaptive capabilities for automated resuscitation by applying formulas derived from pressure-volume data sets of whole blood- and crystalloid-based resuscitation scenarios that we previously developed . Using tactualt) against the time predicted by the aforementioned experimental pressure-volume datasets. ARC used this discrepancy to calculate a correction factor for the infusion rate as: In addition to calculating deviations from the MAP setpoint, ARC also featured an adaptive component that compared the time required to achieve a MAP increase for a given infusion rate  and sampled at 50 Hz through a USB-connected data acquisition unit . After calculating an infusion flow rate, the algorithm sent flow rate instructions to an infusion pump  through a serial port using open-source Python libraries .The Supervisory Algorithm for Casualty Management (SACM), in its current implementation, was designed to control and manage two independent algorithms: the self-tightening tourniquet (aTKT) and the adaptive resuscitation controller (ARC). It integrated the functions of both algorithms in such a manner as to allow them to semi-independently operate within their own areas of concern concurrently and without interfering with each other. Generally speaking, the aTKT sub-component could perform its function of arresting uncontrolled hemorrhage in an extremity , while AThe system, as designed, assumed that the subject had a bleeding extremity and was entering hemorrhagic shock B. Upon mDuring the monitoring stage, SACM monitored certain conditions and concurrently activated the aTKT and ARC in separate processes, as needed. To achieve this, the system monitored two logical conditions every 15 s: whether the tourniquet had become loose, thus allowing a re-bleed in the injured extremity, and whether the MAP had dropped to a clinically relevant low level (below 85 mmHg).For detecting loosening of the tourniquet, SACM relied on input from aTKT, which was modified for this study to check for detection of air pressure oscillations in the cuff after tourniquet engagement (indicating a likely rebleed) as well as large drops in air pressure from the previous engagement . If SACM detected that the tourniquet was loose, it intervened by initiating aTKT as a separate and independent process, so it ran concurrently with the supervisory algorithm. The aTKT was able to operate normally to retighten the tourniquet and stop the extremity bleed.For assessing unexpected drops in MAP, SACM directly measured those values every 15 s using the same sensors as ARC. Just as with aTKT, should SACM detect a low MAP, it activated ARC as a separate and concurrent process, allowing it to continue its monitoring operation.As all three algorithms  were designed to run concurrently during this monitoring phase, at any given time the system was capable of re-tightening a loose tourniquet while simultaneously performing a hemorrhagic shock fluid resuscitation. The SACM algorithm, just as aTKT and ARC, was also implemented in Python.WB) and (2) a crystalloid PhysioVessel (PVC). Each PV mimicked the normalized pressure-volume relationships of a porcine model for infusions of the corresponding fluids [A diagram of the flow loop system used for testing SACM is shown in g fluids .WB, scaling factors of 0.5, 1 (baseline), and 2 were assessed with no hemorrhage occurring in the flow loop. A second set of testing scenarios observed how ARC responded while there was an ongoing hemorrhage occurring during resuscitation. The baseline scaling factor was used with the PVWB and hemorrhage rates of 120, 240, and 360 mL/min were evaluated. Lastly, resuscitation with ARC using PVC to alter the pressure-volume resuscitation curve was tested at a baseline scaling with no hemorrhage and a 240 mL/min hemorrhage rate.Several experiments were run to evaluate the responsiveness of ARC under various conditions , and thrWB was used. Five testing scenarios were conducted in triplicate . Two complications were evaluated. The first complication was loosening of the tourniquet, causing a re-introduction of an extremity hemorrhage for which SACM would need to re-engage aTKT to re-stabilize. The second complication was the introduction of a secondary internal hemorrhage site, which reduced central MAP but could not be stopped by tourniquet application, therefore requiring the ARC to restabilize central MAP. Each remaining scenario experienced two complications in all possible combinations . For SceA data acquisition system  recorded pressure waveform data using pressure transducers  connected to a patient monitor  at two locations: in the central loop (PT1) and distal to the TKT application site (PT2). In addition, the data acquisition system recorded pneumatic tourniquet cuff pressure using an air pressure transducer . Infusion rates set by ARC during resuscitation were sampled at a rate of 1 Hz. Extremity bleed volume was collected in real time by accumulation in a vessel weighed using a force sensor  and corresponding acquisition software . Internal hemorrhage volume was manually tracked by notes recorded during experiments as the flow rate was a constant when in use (240 mL/min).x-axis represents time, and the shade of gray represents the flowrate recorded. All heatmaps were scaled according to the longest infusion duration for their respective PV  and the maximum infusion rate (1200 mL/min) observed.For initial ARC evaluation studies, infusion flow rate heatmaps were generated in MATLAB  to compare the algorithm’s response to the test scenarios outlined in For the various SACM scenarios tested, three replicates were performed for each with data recorded continuously. As data were collected through different means, time stamps were aligned for pressure and flow rate results, and each scenario time interval  was divided and the time range for each replicate bin was set from n − 1 to n to confine the data into three or five bins . Next, fluid balance was calculated as the total infused volume minus the total hemorrhage to evaluate how close the system returned to its initial value. Replicates were plotted using MatPlotLib : initial hemorrhage, extremity bleed, aTKT activation and tourniquet tightening, and ARC-driven resuscitation to bring the central MAP back up to a baseline of 95 mmHg  whether SACM could detect a loosened tourniquet while an active internal bleed was underway. The initial hemorrhage, extremity bleed, aTKT engagement, and initial resuscitation all proceeded normally  ,23,24. TIn addition to integration of advanced physiological metrics and non-invasive sensing, next steps for this work will further develop the decision matrix required for SACM in two ways. First, a more robust supervisory algorithm can be developed using other architectures, such as an inference engine. This will allow for designing a supervisory algorithm capable of managing a larger number of sub-components along with more complex and possibly conflicting logical decisions for clinical interventions than the very limited set of systems that the current implementation of SACM can handle. Such a design will likely be essential as SACM encompasses additional closed-loop systems and handles more complex trauma scenarios. Second, next steps will translate SACM and closed-loop system testing into large animal model testing. The PV flow-loop platform is optimal for initial troubleshooting but incorporating additional systems and biological complexities will only be possible with animal testing and will inform subsequent SACM improvements.In conclusion, automating various medical systems can and will simplify emergency and military medicine, but overarching algorithms such as SACM demonstrated in this study will be essential to processing physiological inputs for when and how multiple automated systems should act.


Heart disease remains one of the greatest killers. In addition to genetics and traditional lifestyle risk factors, we now understand that adverse conditions during pregnancy can also increase susceptibility to cardiovascular disease in the offspring. Therefore, the mechanisms by which this occurs and possible preventative therapies are of significant contemporary interest to the cardiovascular community. A common suboptimal pregnancy condition is a sustained reduction in fetal oxygenation. Chronic fetal hypoxia results from any pregnancy with increased placental vascular resistance, such as in preeclampsia, placental infection, or maternal obesity. Chronic fetal hypoxia may also arise during pregnancy at high altitude or because of maternal respiratory disease. This article reviews the short- and long-term effects of hypoxia on the fetal cardiovascular system, and the importance of chronic fetal hypoxia in triggering a developmental origin of future heart disease in the adult progeny. The work summarizes evidence derived from human studies as well as from rodent, avian, and ovine models. There is a focus on the discovery of the molecular link between prenatal hypoxia, oxidative stress, and increased cardiovascular risk in adult offspring. Discussion of mitochondria-targeted antioxidant therapy offers potential targets for clinical intervention in human pregnancy complicated by chronic fetal hypoxia. We accept that our genetic make-up interacts with traditional lifestyle risk factors, such as smoking, obesity, or a sedentary life, in triggering a risk of cardiovascular disease. In addition, it has become established that the gene–environment interaction before birth may be as—if not more—important in setting a future risk of heart disease through a process known as developmental programming.2 This concept supports that the environment experienced around conception or during the fetal and neonatal periods permanently alters the anatomy and physiology of key organs and systems in offspring, thereby leading to an increased risk of cardiovascular disease later in life.2 Developmental programming is an extension of the Barker hypothesis, proposed in the late 1980s by British epidemiologist David Barker, who stated that intrauterine growth retardation, low birth weight, and premature birth, acting as surrogate markers of adverse intrauterine conditions, have a causal relationship with the origins of hypertension, coronary heart disease, and non–insulin-dependent diabetes, in middle age.3 The concept of developmental programming makes good sense because our physiology  is much more malleable and plastic during early life. Therefore, periods during development relative to those in adulthood can be exquisitely sensitive to environmental conditions, yielding later-life traits shaped by early-life conditions through what has been described as developmental plasticity.4 One excellent example is that in some reptilian species, ambient temperature during a critical period of embryonic development can determine whether an egg develops as male or female.5 Thus, the magnitude of the effect of the environment on us across the life-course clearly varies, and it can be represented by a reverse exponential relationship having its maximal expression during embryonic or fetal life and diminishing progressively as we grow older , compared with those born after surgery.6 Therefore, such studies in humans highlight that a different environment in the same womb can program a differential risk of cardiovascular disease in offspring of the same family. This provides compelling evidence in humans that the environment experienced during critical, sensitive periods of early development directly influences long-term cardiovascular health. Therefore, in this field of science, there is interest in how adverse conditions during pregnancy may program an increased cardiovascular risk in the adult offspring and, if so, through which mechanisms, so that we can design interventional strategies.In humans, the best available evidence to support the concept of developmental programming comes from studies in women who were obese during a first pregnancy, lost weight through bariatric surgery, and were leaner during a second pregnancy.10 By contrast, the contribution of pregnancy complicated by chronic hypoxia has been comparatively ignored. This is surprising, given that chronic fetal hypoxia is one of the most common outcomes of complicated pregnancy in humans.11 In essence, any condition that increases placental vascular resistance will decrease oxygen delivery to the growing baby .12 It is important to note that inflammatory conditions during pregnancy are quite topical today; gestational diabetes and maternal obesity are just as concerning, since they also promote an increase in placental vascular resistance, thereby leading to chronic reductions in fetal oxygenation.13 Therefore, chronic fetal hypoxia provides a common path for several complications in pregnancy, and there is accumulating evidence derived from human studies as well as animal models to support that it can trigger an early origin of cardiovascular dysfunction and program susceptibility to cardiovascular disease in later life. To understand how fetal hypoxia may program an increased cardiovascular risk, we must first consider the short- and long-term effects of hypoxia on the fetal cardiovascular system.In recent years, many excellent reviews have discussed the effect of pregnancy complicated by changes in maternal nutrition, exposure to stress hormones, environmental pollution, or maternal substance abuse on programmed cardiovascular disease in the offspring at adulthood.16 The fetal cardiovascular defense responses to hypoxia exemplify all of these strategies , or better still carotid vascular conductance, which is the inverse of resistance . This calculation reveals a significant increase in carotid vascular conductance in the fetus during acute hypoxia .16 Consequently, during an acute episode of oxygen deprivation, the fetal cardiac output follows the path of least resistance, and blood flow is prioritized away from less essential vascular beds to maintain oxygen delivery to more hypoxia-sensitive regions, such as the developing brain, heart, and adrenal glands.11 In obstetric practice, this hemodynamic redistribution in the fetus is indicated by changes in Doppler blood flow velocimetry, whereby an increase in regional vascular resistance is picked up by an increase in the pulsatility index of the waveform of the vascular bed in question. Hence, clinically, a fall in the Doppler pulsatility index of the fetal middle cerebral artery relative to the umbilical artery flow velocity waveform is a sign of fetal hypoxia and fetal brain sparing.20Hypoxia also affects the fetal circulation. During acute fetal hypoxia, there is a redistribution of the fetal cardiac output, shunting blood flow away from the peripheral circulations toward the fetal brain, heart and adrenal glands.w Figure .16 Apply21 Decreased oxygen delivery to the fetal hind-limb musculature leads to anaerobic metabolism, increasing lactate output and acidifying the fetal blood.21 This not only facilitates the unloading of oxygen from hemoglobin to the fetal tissues through a Bohr effect; the fall in fetal pH also sensitizes the fetal cardiovascular defense to acute hypoxia, enhancing the magnitude of the fetal brain-sparing circulatory responses.23Oxygen delivery is coupled to oxygen consumption. Therefore, limiting blood flow to less essential vascular beds, such as the fetal gut and fetal hind limbs, during the fetal brain-sparing response also contributes to an overall fall in fetal oxygen consumption during acute hypoxia.11 We know that the cardiovascular responses are triggered exclusively by a carotid chemoreflex.16 Bilateral section of the carotid sinus nerves abolishes the fetal bradycardia and delays the increase in femoral vascular resistance without affecting the increase in carotid vascular conductance in response to acute hypoxia  relative to nitric oxide (NO), both of which are increased in the fetus during periods of oxygen deprivation.34 This vascular redox tone is operational in the late gestation fetus and it can be manipulated in favor of constriction or dilatation by altering the numerator or denominator of the O2•-:NO fraction.37 The magnitude of the peripheral vasoconstrictor response to acute hypoxia, an important contributor to the fetal brain-sparing response in the late gestation fetus, therefore depends on the aggregate contributions of chemoreflex, endocrine, and local vascular redox responses  is suppressed in virtually all models of fetal growth restriction.7 Further, fetal glycemia will reduce the maternal-to-fetal glucose concentration gradient, worsening substrate transfer for fetal growth.43 Recent evidence suggests that the growth-restricted human fetus in pregnancy is complicated by chronic hypoxia triggers compensatory mechanisms to reduce its metabolic rate, matching the proportion of substrate consumption relative to oxygen delivery as a survival strategy.44 Despite beneficial adaptations by the placenta, designed to lessen the negative effect of chronic hypoxia on fetal growth,45 these metabolic adaptations in the chronically hypoxic fetus coupled with the sustained redistribution of blood flow from the periphery results in asymmetrical fetal growth restriction. This yields offspring whom are thin for their length and/or have an appropriate head size relative to their comparatively shorter body length. In neonatology, this is indicated by a fall in birth weight with a reduced ponderal index or with an increase in the bi-parietal diameter relative to the body length ratio or with an increase in the head circumference relative to abdominal girth ratio of the new-born baby, all of which are clinical signs that the pregnancy has been complicated by chronic fetal hypoxia.11It has now become clear that the fetal hemodynamic response to oxygen deprivation, redistributing cardiac output toward the fetal brain, heart, and adrenals, can persist during pregnancy complicated by chronic fetal hypoxia.47 Studies of obstetric records in Bolivia from healthy term human pregnancies showed that babies born in the high-altitude city of La Paz (≈3600 meters above sea level) were significantly lighter compared with those born in the Bolivian sea-level city of Santa Cruz, independent of effects imposed by socioeconomic status.47 It is interesting that babies born in La Paz from mothers of Andean ancestry, compared with those of European ancestry, were less growth restricted, despite the former showing greater indices of poverty, including maternal malnutrition.47 These discoveries reveal a protective trait against the effects of high-altitude hypoxia on fetal growth has developed through generations of residence at high altitude and it is strong enough to overwhelm any potential detrimental effects of even maternal undernutrition on fetal growth.48Evidence in humans suggesting that oxygen tension is an important dictator of fetal growth is provided by the well-known effects of the hypobaric hypoxia of pregnancy at high altitude, which yields babies of low birth weight compared with those born at sea level, with clinical signs of asymmetry Figure .46,47 St49 Endothelial dysfunction and cardiac and aortic wall hypertrophy are the harbinger of cardiovascular disease, ideally placed to increase the risk of future cardiovascular susceptibility to dysfunction, even before birth.49Compared with asymmetrical fetal growth restriction, the lesser well-described adverse consequence of sustained fetal peripheral vasoconstriction is that it may lead to maintained increases in fetal cardiac afterload, ie, the force against which the fetal heart pumps. Persistent increases in fetal arterial blood pressure can remodel the cardiovascular system during sensitive periods of development and cause damage to blood vessels, leading to endothelial dysfunction and increased clotting, both of which are associated with an early origin of atherosclerosis.Given the significant effects of chronic fetal hypoxia in altering the physiology and anatomy of the developing cardiovascular system, attention has shifted to determine long-term consequences across the life course. Research has focused on the effects of hypoxic pregnancy on the cardiovascular health of the offspring at adulthood, aiming to isolate underlying mechanisms and thereby identify plausible interventions. The following sections summarized some of this research effort, focusing on human studies, and investigations in rodent, avian, and ovine species.51 Other reported abnormalities in the growth-restricted human fetus include a decrease in cardiomyocyte volume52 and impaired cardiac ejection force and diastolic filling.53 By early childhood, offspring born growth-restricted show atheromatous alterations in the abdominal aorta,54 with persistent thickening of the aortic wall even when adjusted for their smaller body size55 and increased risk of systemic hypertension.55 Other studies have revealed a significant inverse relationship between low birth weight and endothelial dysfunction in 9- to 11-year-old children.56 Longer follow-up studies of men and women who were born growth-restricted similarly show that low birth weight is associated with endothelial dysfunction and systemic hypertension by young adulthood.58Evidence from human pregnancy is consistent with chronic fetal hypoxia affecting progeny through the life course. In humans, chronic fetal hypoxia triggers not only fetal growth restriction, but also a fetal origin of cardiovascular dysfunction, and programs an increased risk of heart disease in adult offspring. In the late-gestation human fetus, persistent increases in fetal cardiac afterload can remodel the fetal cardiovascular system, promoting thickening of the walls of the heart and major blood vessels.In the setting of human pregnancy affected by fetal growth restriction, there have been some translational interventional studies, aiming to ameliorate deleterious effects on the mother and the offspring. Interventional clinical studies conducted during pregnancy have focused on the effects of maternal oxygen therapy and maternal exercise. Some studies conducted after birth have investigated early-life intervention strategies in children from fetal growth–restricted pregnancies, aiming to curtail possible adverse long-term cardiometabolic outcomes.60 Despite some evidence supporting that maternal oxygen therapy can improve fetal oxygen levels and fetal aortic blood flow in severe early onset fetal growth restriction,61 to date, all studies have concluded that the value of maternal hyperoxygenation for the treatment of hypoxic fetal growth restriction remains to be established.61 In fact, some studies have highlighted potential adverse effects of maternal oxygen therapy by increasing levels of oxygen free radicals in the maternal and fetal circulation.62 Higher levels of oxygen free radicals will sequester nitric oxide and offset any potential benefit of maternal hyperoxygenation on fetal oxygen levels by increasing vascular resistance.37 Accordingly, it has been reported that maternal oxygen therapy can impair the increase in maternal cardiac output and diminish the fall in maternal peripheral vascular resistance, which are part of the normal maternal adaptive responses to pregnancy.62 Certainly, there have been no human clinical studies testing maternal oxygen therapy intervention in hypoxic pregnancy to protect against an increased risk of cardiovascular disease in the adult offspring.Studies of maternal oxygen therapy in pregnancy with suspected chronic fetal hypoxia have been reported for more than 30 years, but clear evidence of any benefit for mother or child remains to be determined. Reviews on this topic, including a Cochrane analysis, report on clinical studies that primarily focus on fetal blood gases and fetal growth in complicated (human) pregnancy.63 Prenatal exercise lowers pregnancy complications, including gestational diabetes, gestational hypertension, and maternal depression.64 A systematic review and meta-analysis on the subject concluded that prenatal exercise is safe and beneficial for the fetus, as it reduced the odds of macrosomia and was not associated with adverse neonatal or childhood outcomes.65 A second systematic review and meta-analysis on the effects of vigorous exercise in the third trimester of pregnancy reported that pregnant women who engaged in vigorous physical activity had a small but significant increase in the length of gestation and a small but significant decrease in the risk of giving birth preterm.66 However, whether maternal prenatal exercise protects fetal growth in hypoxic pregnancy or has any benefit against cardiovascular disease in adulthood programmed developmentally by prenatal hypoxia has again not been investigated.Similarly, there has been interest in the potential beneficial effects of maternal exercise during pregnancy on the physiology of the mother and offspring for close to 2 decades.68 Children born from fetal growth–restricted pregnancies who are breastfed for at least 6 months have lower weight gain during childhood and improved cardiovascular remodeling.67 Consumption of diets rich in omega-3 fatty acids also conferred cardiovascular benefits, such as lower arterial blood pressure and protection against aortic wall thickening, in children who were born small for gestational age, but not to those born with normal birth weight.68Recognized postnatal interventions in early life that may protect the cardiovascular health of the child born from a pregnancy complicated by fetal growth restriction include the promotion of breastfeeding and intervention with diets rich in healthy fats.71 There is strong evidence to support that the peripheral endothelial dysfunction in the adult offspring of hypoxic pregnancy is attributable to impaired nitric oxide bioavailability and signaling.71 It has been suggested that the programmed cardiac phenotype of hypertrophy and cardiac sympathetic dominance may represent an attempt to maintain cardiac output in the face of increased afterload.71 However, there is evidence that cardiac hypertrophy may be triggered independently of changes in fetal arterial blood pressure in some rodent models of adverse intrauterine conditions, as is the case in maternal obesity during pregnancy.72 Cardiac function that is sympathetically dominant, although adaptive, cannot be sustained in the longer-term and this cardiac phenotype has been linked with eventual heart failure and cardiovascular collapse.71 Consistent with this idea, investigations in rodents have also reported that hypoxic pregnancy increases susceptibility of the heart to ischemia–reperfusion injury at adulthood.73Investigations in rodent species, including work using rats, mice, and guinea pigs, also support a link between pregnancy complicated by chronic hypoxia and an increased risk of cardiovascular dysfunction in the offspring. Several groups have reported that hypoxic pregnancy in rats programs endothelial dysfunction, hypertension, cardiac wall remodeling, and cardiac sympathetic dominance in adult offspring.32 and activation of inflammatory cascades,75 the weight of the evidence derived from many independent studies in rodents supports oxidative stress having a major role.78 Chronic hypoxia increases markers of oxidative stress in the placenta and fetal organs, including the heart and vasculature,78 and maternal treatment in hypoxic pregnancy with antioxidants, such as vitamin C,79 allopurinol,80 or resveratrol,12 all protect against programmed cardiovascular dysfunction in adult offspring. While such interventional studies provide a robust proof-of-principle supporting that maternal treatment with antioxidants in pregnancy complicated by chronic fetal hypoxia can be protective, translation of these discoveries to the human clinical situation is riddled with complications and questions that require further clarification. First, several of these experimental studies, including ours, have induced a reduction in oxygenation by placing the pregnant rodent dam in a hypoxic chamber.80 This experimental approach is one of the few that permits exposure to chronic hypoxia of the embryo or fetus without physical obstruction of the uterine and/or umbilical circulation. While such an experimental design is important to best isolate the effects of developmental hypoxia in programming without significant perturbation in other nutrient transfer across the placenta, exposure of the pregnant dam to hypoxia leads to oxygen deficits in the maternal, placental as well as the fetal compartments. Therefore, the differential effects of hypoxia on the mother, placenta, or fetus and their partial contribution to programming cardiovascular dysfunction in the adult offspring remains uncertain. Second, in contrast with humans, mice and rats are born highly immature, where many maturational processes carry on into the postnatal period.81 Therefore, antioxidant treatment in these species during pregnancy may not equate to a similar timeline in human development. Third, rats and mice are polytocous species, giving birth to litters where the maternal metabolic adaptations to pregnancy are very different. Fourth, although studies in rodent hypoxic pregnancy with maternal antioxidant treatment with vitamin C proved to be protective, only very high doses incompatible with human clinical translation were effective.79 This is problematic, as randomized placebo-controlled human clinical trials have reported that concomitant supplementation with vitamins C and E does not prevent preeclampsia in women at risk but does increase the rate of babies born with a low birth weight.82 Therefore, in this field of science, there is an important need to isolate the partial effects of hypoxic pregnancy on the maternal, placental, and fetal compartments, as well as to design interventional studies using candidate antioxidants of improved clinical translation in animal models of comparable cardiovascular developmental milestones to humans.Although several molecular pathways could link developmental hypoxia with programmed cardiovascular dysfunction in the adult offspring, including excess glucocorticoid exposure83 Since the embryo develops in isolation, studies in birds are ideal for disentangling the direct effects of adverse conditions on embryonic or fetal cardiovascular development from additional influences on the maternal or placental physiology. Additional advantages in chickens include their short incubation period, meaning that studies can be conducted more quickly; all available nutrition is fixed within the egg from the start of incubation; and there is no need for consideration of within litter variation or cross-fostering studies, as there are no effects of developmental conditions on lactation. Therefore, the model reduces the number of animals needed, abiding strongly to the 3R principle , enshrined by the Home Office EU Directive. In addition, the timing for many cardiovascular developmental milestones aligns more closely between chickens and humans compared with rodents.84 Further added value of research in the chicken embryo model is that candidate therapeutic agents can be administered topically via a small hole in the eggshell air cell onto the richly vascularized chorioallantoic membrane. Therefore, the chicken embryo model not only helps to isolate the direct effects of adverse developmental conditions, but also those of potential treatments, on the cardiovascular structure and function of the bird either during the incubation period or at adulthood.84Avian species offer several interesting characteristics as an animal model for developmental programming studies.85 Conversely, incubation of fertilized eggs laid by sea-level hens at high altitude with oxygen supplementation prevented the high altitude–induced reduction in embryo weight. Further, incubation at high altitude in La Paz of fertilized eggs laid by highland hens which had lived in La Paz for generations produced embryos that were larger compared with those of fertilized eggs laid by sea-level hens and incubated in La Paz. This finding in chickens confirms the protection against the effects of high-altitude hypoxia on fetal growth by prolonged highland residence ancestry first discovered in humans.48 Last, incubation of fertilized eggs laid by high-altitude hens at sea level in Santa Cruz prevented the expected reduction in embryo weight. In fact, this group of embryos not only recovered their growth potential, but they grew comparatively heavier than embryos from eggs laid by hens at sea level, despite high-altitude eggs being substantially smaller than sea-level eggs  or agents that increase nitric oxide bioavailability  rescues cardiovascular dysfunction during hypoxic development.98 Collectively, therefore, these studies in birds not only help to isolate the direct effects of chronic hypoxia on fetal cardiovascular development previously reported in mammals, including humans, but they also support that oxidative stress acting directly on the fetal cardiovascular system independent of the presence of a placenta is an important mechanistic driver of programming induced by developmental hypoxia, and that antioxidant therapy during the period of suboptimal development can be protective.Studies using the chicken embryo have also reported that incubation of fertilized eggs under hypoxic conditions recapitulates many components of the adverse cardiovascular phenotype described in rodent studies of chronic hypoxic pregnancy or in clinical studies of human pregnancy complicated by intrauterine growth restriction. Independent research groups have reported that chicken embryos incubated under hypoxic conditions show aortic wall thickening and nitric oxide–dependent endothelial dysfunction with enhanced sympathetic innervation in the peripheral vasculature, promoting a peripheral vasoconstrictor phenotype.99 Pioneering studies of sheep undergoing pregnancy at high altitude, exposure to high ambient temperature, after carunclectomy, or during restriction of uteroplacental blood flow have reported striking similar effects on fetal growth and cardiovascular adaptations in fetal life.105 It has been harder to attribute many of these effects to those induced by isolated chronic fetal hypoxia during pregnancy or to investigate the longer-term consequences of hypoxic pregnancy for the cardiovascular health of adult offspring. Progress in this field of science using sheep has been held back by several technical barriers. First, there has been an inability to induce significant long-term reductions in fetal oxygenation to values similar to those measured in human pregnancy complicated by fetal growth restriction, without incurring concomitant reduction in other nutritional substrates for fetal growth and development. Second, there has been an inability to record continuous in vivo cardiovascular function from the mother and the fetus as the hypoxic pregnancy is actually occurring. Third, few studies have maintained cohorts of lambs born from hypoxic pregnancies and raised them under normoxic conditions to study the cardiovascular system of the offspring at adulthood. To address these gaps of knowledge, we have now created isobaric chambers able to maintain pregnant sheep for long periods of gestation under tightly controlled reductions in ambient oxygenation. This has been coupled with the design of a wireless data acquisition system which permits recording of several maternal and fetal blood pressure and blood flow signals via surgically-implanted catheters and flow probes in free-moving animals. Using this novel technology, we now know that hypoxic pregnancy in sheep of the type that mimics the reduced fetal oxygen levels in human complicated pregnancy recapitulates many of the effects on fetal growth, fetal cardiovascular function, and increased programmed cardiovascular risk in the offspring.108 Pregnant ewes, in contrast with pregnant rodents, are a much more resilient to adverse hypoxic environments. Therefore, this level of chronic hypoxia in sheep occurs without any significant reduction in maternal food intake and in the absence of sustained elevations in maternal or fetal stress hormones.107 The latter point is important as it highlights that hypoxic pregnancy can program cardiovascular dysfunction in the adult offspring independent of activation of the hypothalamic–pituitary–adrenal axis. Elegant studies of sheep undergoing pregnancy at high altitude by the group at Loma Linda are also consistent with the idea that hypoxic pregnancy can trigger a fetal origin of cardiovascular dysfunction, independent of excess fetal glucocorticoid exposure.100To further translate these concepts into the human clinical situation, work described in small rodents and birds should ideally be replicated in a larger mammalian experimental model that boasts cardiovascular developmental milestones comparable to those in humans, such as those in sheep.40 reported that simultaneous measurement of fetal Pa2o in the carotid and femoral arteries and carotid and femoral arterial blood flow within the hypoxic chambers permitted calculation of regional oxygen delivery in the chronically hypoxic sheep fetus. That study reported that the ratio of oxygen delivery to the fetal carotid circulation relative to the femoral arterial circulation increased significantly and progressively in the chronically hypoxic fetus. This confirms a maintained fetal brain-sparing hemodynamic response in the chronically hypoxic fetus. Shaw et al106 reported that fetal heart rate variability in sheep is reduced by chronic hypoxia because of dysregulation of the sympathetic control of the fetal heart rate. That study suggested a potential mechanism by which a reduction in indices of fetal heart rate variability predicts infants at increased risk of neonatal morbidity and mortality in humans. In this ovine model of hypoxic pregnancy, oxidative stress remains an important culprit mechanism and there is successful intervention with antioxidants.108 Brain et al107 reported that maternal treatment with vitamin C in ovine hypoxic pregnancy protected against oxidative stress by enhancing fetal antioxidant capacity and improving transplacental oxygenation.107 These effects of maternal treatment with vitamin C in hypoxic pregnancy protected against fetal growth restriction and normalized nitric oxide bioavailability, peripheral vascular function, and arterial blood pressure in adult offspring. Botting et al108 more recently reported that the beneficial effects of maternal vitamin C treatment during hypoxic pregnancy in sheep on fetal growth and programmed hypertension in adult offspring could be replicated and improved by maternal treatment with MitoQ in hypoxic pregnancy. These findings are important because MitoQ is a mitochondria-targeted antioxidant with enhanced human translational capacity. Specifically, compared with conventional antioxidants, MitoQ protects against cardiovascular dysfunction in adult offspring programmed by hypoxic pregnancy, without opposing the fetal vascular oxidant tone that contributes to the fetal redistribution of blood flow during hypoxic conditions . Babies born from pregnancies complicated by chronic fetal hypoxia have an elevated risk of fetal growth restriction, endothelial dysfunction, sympathetic hyperinnervation, and alterations in the structure and function of the heart and vessels that increases susceptibility to cardiovascular dysfunction in later life. Descriptive studies in this field have now been extended with highly mechanistic investigations, aiming to isolate underlying signaling pathways to identify potential therapy. Studies from many independent laboratories now proposes oxidative stress in the placenta and developing fetal organs as a major mechanism linking suboptimal pregnancy with fetal growth restriction and an increased cardiovascular risk in the adult offspring (Table). Oxidative stress decreases nitric oxide bioavailability, impairing perfusion and thereby the delivery of oxygen and nutrients to the developing conceptus. Maternal treatment with antioxidants in pregnancy complicated by oxidative stress restores nitric oxide bioavailability protecting perfusion. Therefore, in contrast with other treatments, such as maternal hyperoxygenation in pregnancy complicated by fetal growth restriction, maternal antioxidant therapy restores the delivery of all essential nutrients necessary for appropriate fetal growth and development. Initial studies of maternal treatment with the antioxidant vitamin C in hypoxic pregnancy have provided the necessary proof-of-principle findings to support that maternal antioxidant therapy can protect against fetal growth restriction and programmed cardiovascular dysfunction in adult offspring. More recent studies have enhanced the human translational potential of these ideas, showing that maternal treatment with the mitochondria-targeted antioxidant MitoQ in hypoxic pregnancy can offer improved protection on fetal growth and programmed heart disease in the adult offspring. In contrast with conventional antioxidants, maternal treatment with MitoQ protects against developmental programming of heart disease in adult offspring while maintaining the fetal brain-sparing response to chronic hypoxia, thereby ensuring concomitant protection of the developing cardiovascular and central nervous systems in progeny. Future studies should focus on the applicability of mitochondria-targeted therapy to the human clinical situation, evaluating its safety for mother and child.Dino Giussani is Professor of Developmental Cardiovascular Physiology and Medicine in the Department of Physiology, Development, and Neuroscience at the University of Cambridge; Professorial Fellow and Director of Studies in Medicine at Gonville and Caius College; a Lister Institute Fellow; and a Royal Society Wolfson Research Merit Award Holder.This work is supported by The British Heart Foundation (RG/17/8/32924) and the Medical Research Council UK (MR/V03362X/1). Both programs of research support Dr Giussani.None.


Family caregivers typically rely on community-based services and social support networks to supplement their caregiving of older adults with dementia (OAwD). In April 2020, the Singapore government implemented a partial lockdown to contain the spread of COVID-19. We assessed the policy's impact on the physical and mental health of caregivers and their OAwD. As part of a larger study, 30 caregivers were interviewed and rated the stress they experienced when caring for an OAwD during the partial lockdown. Qualitative analyses found significant behavioral changes in OAwD such as irritability, aggression and hallucinations, which led some caregivers to believe their dependents’ condition had deteriorated, as well as heightened levels of caregiving stress. Overall, our preliminary results suggested that although social distancing measures may be effective in containing the spread of COVID-19, these measures could lead to negative outcomes on vulnerable populations such as OAwD and their caregivers.