In the article, we propose a comprehensive methodology of value chain analysis in the international input–output framework that introduces a new measure of value chain participation and an extended typology of value chains, with the novel inclusion of domestic value chain to address the extent of fragmentation of purely domestic production. This allows for the simultaneous analysis of both global and domestic production fragmentation, the complex patterns of their evolution and their impact on economic development. The main contribution of the proposed methodology is conceptual: it permits the measurement of all value chain paths that pass through each country-sector from production to final consumption, whether the path includes downstream linkages, upstream linkages or their combination. Empirical application of this methodology shows the importance of including domestic fragmentation in value chain analysis: The fragmentation of both global and domestic levels of production has a significant positive correlation with economic growth. This implies that the effects of global production fragmentation must be analysed together with the changing structure of the fragmentation of domestic production to obtain the whole picture, one that might provide important information for policymaking and industrial policy. In recent decades, the growing complexity of the division of labour has been reflected in the fact that ever more production is occurring within value chains, both at home and abroad. Theoretical and empirical approaches to the analysis of value chains have advanced rapidly, yet are very eclectic and heterogeneous. The earliest definitions of commodity chains7In this article, we present a new methodology for measuring different value chain participation rates in the international input–output framework. Compared to the most widely used measurement of value chain participation introduced by Wang et al. , we makesimultaneously. Creating a single consistent variable on the country-sector level that measures the overall level of participation in value chains enables the empirical testing of many research theses that were previously either limited to the aggregate level or had to be articulated separately in terms of measuring the impacts of upstream and downstream value chain integration.First, our methodology creates a single and consistent measurement of value chain participation on the country-sector level, as opposed to the two (upstream and downstream) participation rates that feature in Wang’s methodology. The argumentation and logic used to derive a single value chain participation share on the country-sector level is very similar to the approach of Arto et al. , which cSecond, our methodology allows extensions of the value chain typology that are not possible with Wang’s approach to the decomposition of production activities or with export decompositions. We introduce a novel measure of the domestic value chain participation rate to measure the share of production which represents the extent of the fragmentation of domestic production. In place of a single and undifferentiated domestic component, we distinguish domestic production, which is fragmented (involving measurable cooperation among domestic firms), and domestic production, which is not fragmented . This makes our concept of the domestic value chain a completely new and different concept compared to Wang’s domestic component, which does not distinguish the two and combines both categories within a single undifferentiated concept. While Wang’s share of the domestic component is only a simple residual—a negation of the share of the fragmentation of global production and the global Ricardian trade share that does not provide information about the nature of the domestic economy, our novel methodology allows us to measure the extent of fragmentation of domestic production in addition to the usual study of the fragmentation of international production.We aim to use our approach to provide methodological tools that facilitate exploration of the complex interrelationship of global and domestic value chains and their evolution over time. We believe this will add to understanding of the diverse patterns of the structural integration of various countries/sectors and the different effects of such patterns on economic development. While this is primarily a methodological contribution, we shall use elementary empirical data to try to show the possible link between the level of fragmentation of global and domestic production and overall economic growth.The article is structured as follows: In Sect. The most recent macroeconomic analyses of global value chains rely on the international input–output methodology. As international I–O data are essentially an integrated standard accounting data set harmonised on the sectoral level, information is lacking on the typology of value chain governance. This means the international I–O database cannot be the sole source for the study of production networks, which theoretically differ from purely open trade transactions by including at least some level of hierarchy, and which investigate the local embedding of production linkages Buckley . HoweverEarly I–O measures of the GVC structure were simple upstream and downstream indicators that corresponded to the measure of distance to final demand (upstream) and the Leontief measure of backward linkage (downstream) and were often referred to as the length of a value chain . Fally  and AntrThe existing dominant conceptualisation of GVC participation measures is largely based on the work of Johnson and Noguera , who proa priori criteria, such as “at least two cross-border transactions” or “at least one cross-border production sharing transaction”. The reviewed literature has contributed to better understanding of value chains and their I–O applied research, but still suffers two shortcomings that we try to address and improve with our approach.The development of I–O participation share measures of value chains, which are the primary interest of this article, evolved simultaneously with the development of methodologies of decomposing trade in value added  a single particular country-sector. The logic of our approach is very similar to that of Arto et al. . It is important to note that any such criteria are arbitrary and potential multiplicity of such criteria and hence value chain typologies can coexist and offer researchers some leeway in their empirical applications.o et al.  for combmentclass2pt{minimApplying this methodology, we show that increasing fragmentation of global production in recent decades has been a general trend for most countries (with a backlash in later years), but different institutional arrangements and structural economic positions led to various types of global economic integration, bringing diverse effects for domestic fragmentation. With our methodology, we shall empirically demonstrate that in many countries with high growth and ever stronger global integration domestic fragmentation also increased. However, one can find cases where domestic fragmentation stagnated or even declined whereas fragmentation of the global value chain increased. The different types of integration in global value chains are the outcome of several structural and institutional developments.We understand a value chain as a series of stages in the production of a product or service for the end user, where each stage adds value and the total value of the end product is the sum of the value added in each stage. For a value chain to exist, there must be at least two separate production stages. The existing GVC framework is analytically and empirically based on the idea that value is created in the production process and added to the value already present in the intermediate goods being used. The old value  is only transferred to the new product, while the newly created value is added linearly to the transferred value. The same idea also lies behind the elimination of double counting in standard gross trade statistics and exploration of the hidden underlying trade in value added, which provides insight into the international structure of trade  and aims to capture the upstream and downstream value chain linkages see Fig. .14 In thTo conceptualise and measure the value chain structure of each specific smallest unit of analysis (country-sector), we introduce the value chain path concept. From the perspective of a firm, a value chain path is a series of transactions between firms that lead from a value-adding process to final demand. While currently no data exist that would account for every transaction between all firmsOur goal of deriving a single value chain participation share measure on the country-sector level requires the derivation of an object able to track the value passing through a specific country-sector in focus along all possible paths from its origin to its end use. In this way, we decompose the value that forms part of the production process of a given country-sector along all its paths, which not only include the downstream paths leading to the country-sector under study and the upstream paths leading from it to final consumption, but also, and above all, the paths that combine upstream and downstream linkages and pass through that country-sector. In general, any value share can originate in any country-sector, and the same value share can also reach final consumption as a product of any country-sector. Compared to the approach of Johnson and Noguera, we add a third dimensionThe value chain tree of each country-sector is defined as the structure of the value chain paths, where this country-sector is the siphon via which the value chain paths pass. We show that each unit of analysis (country-sector) has a unique value chain structure that represents its structural position in the economy. Its output can be decomposed along every possible path within its value chain tree—i.e. along every value chain path that has its primary origin in any country-sector, passes through downstream linkages to the production stage of the country-sector which defines the value chain tree (the siphon), and ends in final consumption through upstream linkages as the final product of any country-sector.Understanding the structure of value chains by empirically measuring all such paths of each country-sector  is already an end in itself and can help with further understanding of the economy and its changing structure in terms of global integration, its specific regional and sectoral forms, and the complex interactions between domestic and global production fragmentation.The object of disaggregation is a country-sector’s total output. Each country-sector’s total output is disaggregated along both downstream and upstream linkages that are unique to its specific value chain structure. Downstream disaggregation represents all possible value chain paths from the origin of production and upstream disaggregation all possible paths to satisfy the final demand, both with respect to the unique value chain tree of each country-sector. In this way, we disaggregate the same object—the total output of each country-sector—simultaneously along its downstream and upstream paths.In contrast to approaches based on the matrix of value-added exports  and the final destination  are replaced by a single index for each country-sector for more transparent notation. Since we are no longer working in the k), one for the final stage country-sector (j) and one to characterise the country-sector value chain tree—the country-sector representing the siphon through which the value chain paths pass (i).18We derive our disaggregation within the static international Leontief demand-driven model. W:Upstream output decomposition W represents the upstream output decomposition along all upstream value chain paths. Its element i that reaches final consumption as the end product of country-sector j, along all possible upstream production fragmentation paths in the economy. The ith row of W represents the disaggregation of the total output of the ith country-sector into output shares according to its final production stages that account for all direct and indirect paths of the upstream value transfers leading to the full realisation of total output (by being used directly or indirectly by other country-sectors as intermediate productive consumption). Each ith row of W may thus be characterised as a discrete probability distribution. On one hand, the upstream output shares of each country-sector i add up consistently to 1: ith country-sector will eventually be consumed as the final product of country-sector j, along any upstream value chain path.The matrix For the downstream part, we begin with identity:Z:Downstream output decomposition Z represents the downstream output decomposition along all downstream value chain paths. Its element i that is primarily created in country-sector k, along any possible downstream production fragmentation path in the economy. The ith column of Z represents the disaggregation of the total output of the ith country-sector into output shares, which represent all direct and indirect paths of the downstream value transfer from each country-sector that has contributed to the production of its output (through the direct or indirect production of intermediate productive consumption used by i). Each ith column of Z may thus be characterised as a discrete probability distribution. On one hand, the downstream output shares of the individual country-sectors i add up consistently to 1: ith country-sector was produced by country-sector k, along any downstream value chain path.The matrix W and Z, may appear as two sides of the same coin—similar to forward and backward decomposition, which has largely been exhausted in the international input–output literature. However, if we focus on a single country-sector (i), the ith column of Z and the ith row of W represent two probability distributions that take the transfers in the value chain into account, which result in two completely different and independent types of information. The ith column of Z contains information on the downstream structure of the value chain of the respective ith country-sector and the ith row of W contains information on the upstream structure of the value chain of the respective ith country-sector. For a given ith country-sector, the two probability distributions are asymmetrical. Most importantly, both probability distributions relate to the same object of investigation—the total output of country-sector i.The two matrices presented, W matrix in terms of shares of total output  downstream. The same object  is then distributed along the upstream value chain paths (as determined by the ith row of W) until it reaches final consumption along an upstream value chain path.Using the total output of each country-sector seems to be the only way to disaggregate the same object into its upstream and downstream value chains. The object of decomposition of the upstream part  of a certain country-sector can be either its total output or total value added (even its export). However, the same is not possible for the downstream part . The object of decomposition of the downstream part of a certain country-sector can only be its total output, which also makes up the totality of value-added shares along the whole downstream value chain.l output , 3.5 andAll input–output analyses assume the homogeneity of the smallest classification object (country-sector in our case). The level of detail of the data corresponds to the level of detail of the sector (and country) classification and within a country-sector there is no further information and quite strict homogeneity assumptions apply. We use the assumption of the homogeneity of production of each country-sector to combine the two probability distributions.ith country-sector, which was primarily produced by country-sector k. Due to the homogeneity of the total output of the ith country-sector, the ith country-sector reaches final consumption as a product of j, but also the probability that a random part of any share of the output of the ith country-sector reaches final consumption as a product of j. Since ith country-sector’s total output, its upstream decomposition is clearly and uniquely defined by the ith row of w.ith country-sector is primarily produced in k and reaches final consumption as the product of j along any value chain path  passing through i. In other words, it represents the share of the total output of i that was produced by k and reached final consumption as a product of j. A simple multiplication of probabilities requires that the two events—a random portion of the total output of i produced by k and a random portion of the total output of i completed for consumption by j—are statistically independent. First, if certain parts of the total output of a particular country-sector were to behave differently from certain other parts of the same output, this would violate the homogeneity assumption, which is the basic assumption of the input–output structure and methodology. Second, at the level of economic theory it is relatively easy to argue about the statistical independence of the structure of upstream and downstream value chains: Nothing about the downstream structure of production in the ith country-sector implies anything about its upstream structure and vice versa. Both are calculated independently and provide completely different information: the downstream decomposition gives information about the inputs produced by other country-sectors used directly or indirectly in the production process of the ith country-sector, and the upstream decomposition gives information about how the product of the ith country-sector is consumed either directly or as part of the final product of other country-sectors.The product ith column of Z) and upstream value chain (ith row of W) thus span an entire matrix of total output shares that capture the value chain tree structure of the ith country-sector. We combine them with the direct product that defines the matrix of the value chain tree for each country-sector (i) by multiplying each element of ith column of Z) by each element of ith row of W).Two separate vectors which disaggregate the value chain paths of the downstream  along any value chain path, be it a downstream value chain path, an upstream value chain path or any combination of both paths at the same time.ith country-sector. The total output of i is not only disaggregated along all possible paths leading from any country-sector of origin via country-sector i to any country-sector of final stage production  to value realisation , which passes through the production stage of the i is determined by the Leontief technical coefficients i , and then sent as an intermediate to i) and a final destination of production  as well as all possible origins and final stage destinations, results in a unit:ith country-sector. Based on this property, we will decompose the value chain structure of each country-sector separately in the following section.A certain value chain path share of the total output of post festum.i along different downstream and upstream paths. When we refer to a value chain, we refer to the specific share of value (share of output) that corresponds to a particular value chain path. PathThe framework of the international I–O analysis allows the separate analysis of final transactions to consumers and transactions between companies. Based on this characteristic, we propose a typology of value chains based solely on the structure of linkages between enterprises, while adding a further decomposition with regard to different possible transactions to reach the final consumption Domestic value chain at least 1 domestic production-sharing transaction and involves only domestic production-sharing transactions along its path.Domestic value chain (DVC) is a value that involvesGlobal value chain at least 1 cross-border production-sharing transaction along its path. We further distinguish two types of global value chains: simple and complex.Global value chain (GVC) is a value that involvesSimple global value chainexactly 1 cross-border production-sharing transaction anywhere along its path.Simple global value chain (SGVC) is a value that involves Complex global value chain more than 1 cross-border production-sharing transaction along its path.Complex global value chain (CGVC) is a value that involvesNo value chaindoes not involve any production-sharing transactions and has no value chain path within production.No value chain (NVC) is a value that A few brief comments are appropriate on our definitions and their interpretation. No material product or service belongs to a single classification of value chain, and no enterprise can be considered part of a single type of value chain. The output of each enterprise belongs to a variety of value chain paths. In general, one part of the output comprises many cross-border transactions, another part only domestic transactions, and yet another part their relatively complex interrelationship. Each product (or country-sector in our case) can be assigned different shares of the value chain paths. These shares are objects that provide information about the structure of the economy. For example, virtually no enterprise could be classified exclusively as part of a no value chain, but some enterprises that provide services (e.g. domestic services) have a relatively high share of output that has no value chain path, especially in services, where salaries account for almost all of the enterprise’s expenditure and where their product directly satisfies final demand. On one hand, enterprises that specialise in intermediate goods are always part of a value chain, whether domestic or global. On the other hand, even modern industries such as food-processing and pharmaceuticals, also have a certain  share of value added that is not part of any value chain , corresponding to the share of domestic value added in these industries that is also directly consumed . The value chain shares and their changes are the object that provide information about the structure of the economy, whether on the sector or country level. As the economy develops, the division of labour also increases, which corresponds to the growing fragmentation of production, in particular international production fragmentation, and a decrease in shares where there is limited or no value chain fragmentation. Compared to the existing typology of value chains, this revised typology allows for analysis of the relationship between global and domestic fragmentation, which might prove especially relevant for the policies of developing countries.Our value chain typology is established according to criteria along the entire value chain. For this reason, we disaggregate the value chain tree matrices A), which allows us to decompose the Leontief inverse in the following way:I obviously represents that part of the output which contains no production-sharing transactions—no value chain linkages. In the upstream part, it represents the share of total output that directly satisfies final demand , while in the downstream part it represents the direct value added of the country-sector whose production is being decomposed . at least 1 domestic production-sharing transaction and contains only domestic production-sharing transactions.at least 1 production-sharing transaction and contains exactly one cross-border production-sharing transaction somewhere along its value chain path. This can be demonstrated by paraphrasing the part as all possible combinations of a single cross-border transaction among any possible set of domestic production-sharing transactions that occur before or after the single cross-border production-sharing transaction: at least two or more production-sharing transactions, of which at least two are cross-border production-sharing transactions. This logically follows from the fact that parts (1), (2) and (3) cover the total output that contains less than two cross-border transactions, and that the full Leontief inverse covers the total output.First, we investigate the decomposition of only a single Leontief inverse  and only then do we analyse the decomposition of all value chain paths characterised by the two Leontief inverses. The international I–O data have a specific block matrix structure in which the block diagonal elements represent domestic production-sharing transactions and the block off-diagonal elements represent international production-sharing transactions , and a matrix consisting only of the value that has no value chain path.We proceed by disaggregating all of the value chain paths as they are structured in the value chain tree matrices. Using the decomposition of the Leontief inverse that we disaggregated in the previous subsection and inserting it into Eq. Domestic value chain tree ith country-sector final stage (no upstream path), the second part (ith country-sector (no downstream path) that is transferred via the upstream domestic value chain (upstream domestic path), and the third part . All three cases meet the definition of a domestic value chain.The domestic value chain tree represents all value chain paths of the output of each country-sector which, according to Definition Global value chain tree The global value chain tree represents all paths of the output of the individual country-sector, which form part of global value chains according to Definition Simple global value chain tree Complex global value chain tree The complex global value chain tree represents all paths of the output of individual country-sectors that form part of complex global value chains as defined in 5.2 The first element . Domestic consumption here refers to the country-sector in which the last stage of production took place and not the country-sector whose value chain we are analysing. Each country-sector has a unique value chain and a specific structure of value chain paths. The completion of each value chain path by a transaction to the consumer can be achieved by an additional cross-border transaction of exporting the final product or consumption in the country where the product was finalised. Such a further decomposition of the value chain paths allows a more detailed analysis of the value chains.F, which can be decomposed into its cross-border and domestic flows to final consumers  is represented by a single measure  that covers the extent of overall value chain fragmentation, as opposed to separate downstream and upstream indicators.Due to the limitations of the paper and its chiefly methodological focus, we present only some very basic empirical results. First, we show the global averages of value chain participation rates based on WIOD 2016 data and the global average participation rates for the manufacturing and service sectors separately Figs.  and 4. UAs the data for the world average conceal large differences between countries, we also show the value chain participation shares of manufacturing for China, the USA and the average of the economically most integrated new EU members—3 Baltic and 4 Visegrad countries Figs. , 6 and 7Finally, we use the fact that we have created uniform participation rates by performing a simple between-effects regression to test the relationship between the level of domestic and global fragmentation and economic growth measured by GDP per capita. Since short-term productivity fluctuations can hardly be explained by an economic structure expressed in value chain shares, we use a cross-sectional approach to test the long-term effects of different levels of domestic or global fragmentation on economic growth. Our observations relate to the 43 countries included in the WIOD 2016 data, and the variables are their average annual growth, the average DVC and GVC shares, with the average logarithm of GDP per capita as a control for convergence, the average logarithm of the annual population as a control for the size of the country, and the EU control dummy for potential EU specifics. The main regression equation with between effects is derived in the usual way out of a general panel data model:To ensure a consistent estimator, The regression results are shown in Table We have proposed a new methodology for measuring the participation shares of different types of value chains in the international input–output framework. We addressed the lack of a consistent unitary measure of value chain integration on the country-sector level by proposing a new concept of the value chain tree for each country-sector, covering all value chain paths from value creation (downstream linkages) through a single country-sector to final consumption (upstream linkages) simultaneously. By capturing the structure of all value chains in a series of value chain tree matrices, we add a new mathematical object that serves as a basis for deriving the proposed new indicator of value chain participation, which we contribute to the existing collection of indicators.post festum differentiation is also derived based on the last transaction to the final consumer.This methodology allows us to introduce an extended typology of value chains by distinguishing and disaggregating all production activity into the following types: no value chain, domestic value chain, and global value chain—further differentiated into simple and complex global value chains. The most important new conceptual subdivision in the extended typology relates to the subdivision of the existing ’domestic component’ into a no value chain and a domestic value chain. This subdivision, which is only possible with the proposed methodology, provides a better representation of domestic production interdependencies and permits comparative analyses of the simultaneous development of domestic and foreign production interdependencies, thereby enabling aggregated analyses of domestic and global production fragmentation and its interrelated development as influenced by outsourcing or offshoring. Another big change introduced by the new typology is its fundamental production-related character: all distinctions between different types of value chains are made only with regard to  production fragmentation, with a separate examination of the transaction to the final consumer—which may or may not be cross-border. This affirms the concept of value chain as related primarily to the fragmentation of production, while the The proposed methodology and typology of value chains provides researchers with new opportunities to conduct future research on different levels of disaggregation, be it comparative geographical analysis  or observing the evolution of value chains in different sectoral disaggregations. The preliminary illustration of the new methodology, which attempts to link both domestic and global production fragmentation with long-term growth rates, shows a positive correlation between both global and domestic production fragmentation with economic growth. This result may indicate that it is the general complexity of the division of labour, reflected in the general fragmentation of production, that is chiefly correlated with growth, irrespective of its global or domestic nature. Accordingly, the proposed measure and the new typology of value chains, in particular the novel conceptualisation of domestic value chain fragmentation, could bring to light important information that has been concealed in the existing typology, which conceptualises the domestic component only as a negation of the global value chain and thus did not allow research with explicit questions concerning domestic integration. The complex development of globalisation in recent decades and the shifts of late towards the localisation and regionalisation of economic integration caused by political, economic and external factors make this new approach increasingly relevant. The proposed measure, particularly in conjunction with data from other sources, could further deepen the theoretical discussion and empirical investigations.In conclusion, we believe that our new methodological approach and the new extended typology of value chains associated with it provide fertile grounds for obtaining deeper insights into different types of value chains as well as a broader set of tools of use for various extensions of research.


As leadless pacing (LP) use is expected to increase, it becomes increasingly essential that operators become familiar with the tools and techniques needed to retrieve an LP successfully. The purpose of this review is to describe a stepwise approach for the successful retrieval of tine-based LP devices, including ways to minimize complications. The Micra™ Transcatheter Pacing study, the LEADLESS II trial, and multiple real-world investigations have demonstrated the efficacy of LPs in comparison with traditional transvenous devices.4 Until recently, LPs were implanted in patients with an infrequent need for pacing or in those with permanent atrial fibrillation and complete atrioventricular block.The leadless pacemaker (LP) is the most recent technological advancement in the pacemaker industry.9 An inadequately placed LP with suboptimal pacing parameters or an embolized LP will need to be retrieved.13 Although the true incidence of LP dislodgment is unknown, more than 50 cases have already been reported in the literature involving retrieval of the Micra™ TPS.11 As the use of LPs is expected to grow, it will be increasingly essential that operators become familiar with the tools and techniques needed to retrieve an LP successfully. A considerable worldwide multicenter experience has suggested that multiple approaches can be used to remove an LP.10 The purpose of this review is to describe a stepwise approach for the successful retrieval of an LP. Particular emphasis will be given to the retrieval of free-floating devices in the heart or pulmonary vasculature.Multiple studies have reported high rates of procedural success and LP implantation.14 In the event of a dislodgment or embolization, retrieval of the LP is important to minimize the risk of thromboembolic complications. A second indication for device retrieval is the observation of suboptimal pacing parameters during the implant procedure.11 Any device with inadequate pacing parameters at the time of implant is expected to have a high risk of device dislodgment and should be immediately retrieved. Recapturing the device during the initial implant procedure minimizes the risk of vascular access complications incurred at the time of a subsequent procedure. Additionally, some of the equipment required for device retrieval is used during the implant procedure.There are multiple reasons for why retrieval of an LP may be required. One of the most feared complications involving the use of an LP is device dislodgment. A dislodged device can either remain in the RV or embolize to the pulmonary vasculature.16 In cases involving transvenous lead extractions in the setting of bacteremia or device-related infections, current practice standards support a waiting period ranging from 72 hours to 14 days between extraction and device reimplantation.17 Traditionally, these patients received a temporary transvenous pacemaker or a temporary externalized pacemaker while they completed a course of antibiotics, often in a hospitalized setting. An alternative strategy involves implanting an LP, which allows for early discharge and the completion of antibiotics in the outpatient setting.17 After the infection issue has been resolved, patients in need of atrial pacing, cardiac resynchronization, or those who had implantable cardioverter-defibrillators extracted can be reimplanted with permanent transvenous devices. These cases represent the third indication for LP retrieval. Finally, although extremely rare, a fourth indication for removing an LP is in the setting of an infection of the LP itself. Although the incidence of LP infection is exceedingly low due to the lack of a subcutaneous pocket and transvenous leads, the absence of direct contact between the operator and the device, and the parylene coating on the device, limited reports in the literature of retrieval for this indication do exist.18A third indication for retrieval is in situations where the LP is used as a bridge to a permanent device in patients requiring prolonged antibiotics following the extraction of infected cardiac implantable devices.The Micra™ TPS is the only LP currently available; thus, the following techniques will focus on percutaneous retrieval of the Micra™ TPS. There are three commonly employed approaches for retrieving this device.Each of the percutaneous approaches involves using a Micra™ TPS access sheath, which has 27-Fr and 23-Fr outer and inner diameters.Successful retrieval of a Micra™ TPS requires the use of a snare. The snare loop diameter and the snare catheter size are essential factors to consider when choosing between the various techniques for Micra™ retrieval. When snaring through the 23-Fr Micra™ delivery catheter during the initial implant procedure, the largest snare loop diameter that can be used is 5 mm. In contrast, snares with larger loop diameters can be used if the retrieval is performed using a steerable sheath through the 27-Fr (outer diameter) Micra™ delivery sheath. and 1B. Once the snare is around the body of the device, it can be tightened and gradually retracted back to capture the retrieval feature of the LP . The snare is then cinched and secured by placing hemostatic forceps on the back end. At this point, the LP can be pulled to the edge of the delivery cup and both the device and the delivery catheter assembly are then brought into the outer Micra™ delivery sheath as a unit. This allows the LP to be safely removed from the body.If the retrieval is performed during the initial procedure, the Micra™ delivery catheter can be used. This technique involves advancing a 5-mm loop snare through the Micra™ delivery catheter. Once the delivery catheter is in close proximity to the LP, the snare can be advanced over the LP body. To facilitate advancing the snare over the LP, both the right anterior oblique (RAO) and left anterior oblique (LAO) projections should be used 10There are several limitations to using this technique. First, a 7-mm snare loop is the maximal snare size that can be advanced through the Micra™ delivery catheter but can be challenging to engage the LP. Second, the Micra™ TPS delivery catheter has limited steerability, given that the deflection is unidirectional. This limited steerability can hinder adequate coaxial alignment of the catheter with the LP. Despite these limitations, the use of a Micra™ delivery catheter for retrieval has been reported to be successful in an extensive multicenter international experience.. Although the use of a steerable sheath is an additional cost, this is a preferred approach for retrieval.The most commonly employed approach for retrieving an LP involves the use of an 8.5-Fr steerable sheath  inside the 27-Fr Micra™ delivery sheath. A 16-Fr or 14-Fr sheath must be placed inside the 27-Fr sheath prior to inserting the smaller 8.5-Fr steerable sheath to prevent back bleeding from the hemostatic valve. Once the steerable sheath is inside the 27-Fr Micra™ delivery sheath, the system can be advanced into the RV. The 8.5-Fr steerable sheath allows for the use of a larger loop snare (20–30 mm is recommended). The steerable sheath can be brought close to the LP, which facilitates snaring the LP, again using multiple fluoroscopic projections. After the snare has successfully encircled the LP body, it is brought back onto the retrieval feature and tightened. The snare is then withdrawn to the end of the steerable sheath. The LP and the steerable sheath assembly are then brought into the 27-Fr sheath. At this point, the steerable sheath, the LP, and the inner 14- or 16-Fr sheath can be removed from the 27-Fr sheath as a unit. If the LP becomes entrapped in the hemostatic valve of the 27-Fr sheath, the entire apparatus, including the 27-Fr sheath, can be removed from the groin as one unit to prevent dislodgment of the LP in the venous circulation Retrieval of an LP from the pulmonary arterial vasculature requires the use of additional equipment such as a 5-Fr multipurpose catheter . Depending on the location of the embolized LP and the size of the steerable sheath, the sheath can be advanced distally into the pulmonary vasculature. The closer the sheath is positioned to the embolized LP, the easier it is to align the sheath with the LP. Depending on the LP location in the pulmonary vascular bed, however, it can be challenging to bring the sheath in close approximation to the device due to the steerable sheath (72-cm working length). If the steerable sheath is not long enough, a multipurpose catheter should be advanced over a Glidewire™  into the pulmonary artery. After the multipurpose catheter is near the LP, the guidewire can be removed. At this point, a snare can be advanced through the multipurpose catheter and onto the LP. If possible, the snare should be advanced over the body of the LP.–5. Limitations of this method include potential damage to the pulmonic valve leaflets if the LP is snared in such a fashion that the tines become entangled in the valve apparatus as the device is withdrawn across the valve. While all three of these approaches involve removing the LP through the tricuspid valve, this is the only approach that risks damage to both valves.Occasionally, depending on the embolized LP orientation, the snare may capture one of the LP tines. The snare can be tightened after it has encircled the body of the LP or one of the tines. The multipurpose catheter can then be pulled more proximally into the main pulmonary artery. Two of the authors (M. R. A. and R. S. A.) have successfully used a multipurpose catheter to retrieve an LP from the right pulmonary artery using this technique. In this case, the snare was cinched around one of the tines and was successfully brought into the right atrium. The LP dislodged in the right atrium during an attempt to withdraw it into the 27-Fr sheath. Subsequently, the snare was advanced over the body of the LP and tightened around the retrieval feature, which allowed for a successful retrieval 19 The majority of the patients were able to receive a newer LP with excellent pacing parameters. Long-term follow-up of patients after retrieval was not reported.11Published experience reports 100% safety during the retrieval procedure.20 It is critical to deploy the LP in the heavily trabeculated area of the interventricular septum. The identification of a heavily trabeculated septum is achieved using an iodinated contrast injection in the RAO and LAO views. Ideally, there should be sufficient trabeculations on the superior, anterior, and inferior aspects of the delivery catheter tip. After the LP is deployed in the trabeculated septal area, a good pull-and-hold test should be performed. During this test, the cup of the delivery catheter should come closer to the LP with a visible stretch on at least two of the four tines of the LP.There are multiple steps during LP deployment that can help to minimize the risk of device dislodgment. Most importantly, the deployment site should be confirmed in both RAO and LAO views prior to deploying the device.The use of LPs is steadily increasing. Although the need for retrieval is infrequent, the skill and familiarity with the required equipment are necessary for any physician who implants these devices. Although multiple approaches can be employed to retrieve an LP, commonly used approaches involve using a steerable sheath and snares of variable loop diameter. Familiarity with the use of snares, in particular, is an essential skillset to successfully and safely retrieve an LP.


With ever increasingly complex healthcare settings, technology enhanced simulation (TES) is well positioned to explore all perspectives to enhance patient safety and patient outcomes. Analysis from a Safety-II stance requires identification of human adjustments in daily work that are key to maintaining safety. The aim of this paper is to describe an approach to explore the consequences of human variability from a Safety-II perspective and describe the added value of this to TES.The reader is guided through a novel application of functional resonance analysis methodology (FRAM), a method to analyse how a system or activity is affected by human variability, to explore human adaptations observed in in situ simulations (ISS). The structured applicability of this novel approach to TES is described by application to empirical data from the standardised ISS management of paediatric time critical head injuries (TCHI).A case series is presented to illustrate the step-wise observation of key timings during ISSs, the construction of FRAM models and the visualisation of the propagation of human adaptations through the FRAM models. The key functions/actions that ensure the propagation are visible, as are the sequelae of the adaptations.The approach as described in this paper is a first step to illuminating how to explore, analyse and observe the consequences of positive and negative human adaptations within simulated complex systems. This provides TES with a structured methodology to visualise and reflect upon both Safety-I and Safety-II perspectives to enhance patient safety and patient outcomes.The online version contains supplementary material available at 10.1186/s41077-021-00166-0. For over 20 years now, technology enhanced simulation (TES) has been a lightning-rod to promote reflection , and disHistorically, TES and debriefing strategies have transitioned from exploring individual knowledge, skill or behaviour deficits, to embrace complexity and provide opportunities for improvement with a systems focused approach , 8. ConcThe TES approach to identifying gaps, or deficits, that in turn stimulate the implementation of mitigation strategies, and the improvement of patient safety, can be interpreted as ensuring a state of safety where “as few things as possible go wrong”. From this perspective TES as a pedagogy, can be viewed as aligned to aspects of Safety-I thinking ; howeverIn addition to identifying gaps, TES groups have also approached the challenges of understanding and promoting deeper reflection on things that go right . One TESThere is a need for a methodology that supports TES practitioners, safety scientists and human factors practitioners to bridge the current gap of how to see and analyse events systematically, when events go right and when they go wrong, taking into account the complexities of the real world. This would then afford the opportunity to embed variations in human practice into future real-life designs, should the adaptations prove beneficial.An approach developed outside of healthcare to analyse how a system or activity is affected by human variability is the functional resonance analysis method (FRAM) . AlthougUsing this approach, it is possible to compare and contrast how a system actually operates with different human adaptations of practice (WAD) against how it might have been designed to operate (WAI) and observe the impact of variabilities in the different interactions on the outcomes. This is achieved by detailing the WAD and reflecting this against WAI . The FRAIn this paper, we introduce a novel application of the FRAM and describe how the methodology can now work in conjunction with TES to explore in-depth the human adaptations evident in healthcare simulations. The study has taken advantage of a recent enhancement of the FRAM methodology, termed the FRAM model interpreter (FMI) , which sThis application of FRAM thus systematically interrogates the effects of variability in the interactions of critical functions. This provides a structured analysis of the downstream effects of the “what if” phenomena of human variability. As such, we have termed this “Structured What If–FRAM”, SWI-FRAM. The aim of this paper is to guide the reader through the SWI-FRAM approach and describe the added value of exploring the consequences of human variability from a Safety-II perspective to TES.In order to demonstrate the structured applicability of SWI-FRAM to in situ simulation (ISS), we present a case series exploration of empirical data from the ISS management of paediatric time critical head injuries (TCHI), using the SWI-FRAM approach. Paediatric trauma systems are recognised as complex systems and globally many ISS programs aim to improve the patient safety and outcomes of paediatric TCHI .Data collection took place in the emergency department of ten UK hospitals. Ethics approval was sought but not deemed necessary, in accordance with UK Health Research Authority guidelines. Informed consent was obtained from all participants in this study. All data sources were de-identified and stored in accordance with UK research guidelines. This study utilised the Reporting Guidelines for Health Care Simulation Research .The process for development of SWI-FRAM models from ISSs Fig.  is descrStructured observation of key timings of ISSsConstruction of FRAM models of WAI and WADVerification of the models then visualisation of the observed variability propagation through the FRAM models of WAD.The process had three steps:Twenty standardised ISSs were performed in 10 UK emergency departments following an established protocol . Each siVideo recordings of each simulation were independently reviewed by two researchers . Each video was observed for standardised key timing events deemed likely to impact patient outcomes agreed by a consensus panel of experts (INSPIRE Trauma group) .The observed key events and timings in the 20 simulations are shown in Table A full description of FRAM is outside the remit of this paper, the reader is directed to a short introduction to the ideas and steps in FRAM modelling  created the FRAM model of WAI, using the same evidence based guidelines for the management of paediatric TCHI, as used in the construction of the standardised ISS scenario.Initially, a FRAM model of WAI of all the functions involved in the TCHI management was constructed  both subject matter experts in simulation and management of paediatric TCHI. During these sessions, the research team members who did not create the FRAM models had opportunity to verify that the FRAMs captured the critical elements of the management of TCHI that was of interest .The FMI software  was usedThe FMI software  was thenThe observed variability of management of TCHI in the ISS recordings are presented as a case series of FRAM models of WAD. The FRAM models of WAD selected in the case series each depict a different adaptation from the FRAM model of WAI, evident by observing the ISS recordings.In this section, we present the FRAM model of WAI and the simplified version. We also present the observed variability of management of TCHI in the ISS recordings, as a case series of FRAM models of WAD. The FRAM models of WAD selected in the case series each depict a different adaptation from the FRAM model of WAI, evident by observing the ISS recordings. We then show how the SWI-FRAM approach provides the opportunity to visualise the consequences of variability around key functions, as the effects propagate through the system. In order to do so, the reader is directed to the videos provided in supplementary online files The focused FRAM model of WAI for the ISS management of a standardised scenario of a 7-year-old child presenting with evolving signs of raised intracranial pressure, a unilateral fixed dilated pupil and a depressed level of consciousness, following a road traffic accident (RTA) is shown in Fig. In this FRAM model, the functions performed by key team members are identified by different colouration; orange is the trauma team leader (TTL), red is the emergency department specialist trainee doctor, and blue is the anaesthetic doctor.In this model, all the functions in this simplified version of the WAI management of a paediatric TCHI and how they are coupled can be observed. The inter-relationship of the components of the primary survey, namely the airway, breathing, cardiovascular, disability / neurological assessment and exposure (ABCDE) assessment can be visualised. The entire FRAM model of WAI is available online (supplementary file In this case (ISS number 15), the TTL (orange functions) performs the primary survey as per WAI to determine the injury pattern and necessary immediate actions and declares to the team the presence of a head injury , the TTL coordinates the primary survey but decides to assess the neurological status of the child herself. This function is normally performed by a specialist trainee, with the TTL standing back. The primary survey is completed, the injury pattern determined and the TTL declares to the team the presence of a head injury Fig. , the carIn this case (ISS number 12), the TTL coordinates the primary survey and leads a team huddle with the team and states aloud the ABCDE findings. The TTL then declares to the team the presence of a blown pupil, decides to intubate and declares the need to manage intracranial pressure issues Fig. . This adIn this ISS (number 11), the primary survey commences and the there is no initial D (disability) assessment Fig. . This isThe structural integrity of all of the FRAM models was verified. To demonstrate this, the reader is directed to the online supplementary video of the FRAM models of WAI in this paper  shown in Fig. By observing SWI-FRAM models, the variability of functions in terms of precision and timing observed in the ISS cases Table  can be sThe SWI-FRAM reveals the flow of the functions that occurs leading to the determining the pattern of injury, the problem declaration and the subsequent actions  an holistic overview, (2) a depth of understanding of critical functions within the system, (3) a visualisation of non-linear interrelationships between functions, (4) the ability to observe the downstream effects of the variability of upstream functions inherent in different simulations, (5) the opportunity to discuss and develop interventions that embrace the complexity to enhance the safety and performance of the system explored. In addition to the visual models, the log report output provided by the software also provides information in a format that speaks to organisational learning goals.The holistic overview provided by SWI-FRAM models includes the ability to systematically step through every part of a complex system visually, for example the FRAM model of WAI,  and work-as-done (WAD) and the SWI-FRAM approach.Additional file 3. WAI.Additional file 4. WAI CAS.Additional file 5. focused WAI.Additional file 6. SWI-FRAM WAD.


This paper examines the field of energy-based medical therapies based on the analysis of patents. We define the field as the use of external stimuli to achieve biomedical modifications to treat disease and to increase health. Based upon distinct sets of patents, the field is subdivided into sub-domains for each energy category used to achieve the stimulation: electrical, magnetic, microwave, ultrasound, and optical. Previously developed techniques are used to retrieve the relevant patents for each of the stimulation modes and to determine main paths along the trajectory followed by each sub-domain. The patent sets are analyzed to determine key assignees, number of patents, and dates of emergence of the sub-domains. The sub-domains are found to be largely independent as to patent assignees. Electrical and magnetic stimulation patents emerged earliest in the 1970s and microwave most recently around 1990. The annual rate of improvement of all sub-domains (12–85%) is found to be significantly higher than one we find for an aggregate pharmaceutical domain (5%). Overall, the results suggest an increasingly important role for energy-based therapies in the future of medicine. Electroceuticals is a burgeoning therapeutic field of bioelectrical and bioelectronics medicine, in which electrical energy is utilized to stimulate electrical pathways in the body to modify biological functions or pathological processes in the body , 2. AlthA survey of the literature  demonstrThe goal of the research reported here is to make an objective analysis of stimulation therapies and their future potential for healthcare, including what relative impact they might have. In particular, we use patent data to begin to assess some important questions in this technological area. These questions are:How should researchers meaningfully decompose the overall area?How fast is this area (and its sub-areas) improving?What have been the key developmental steps in each of the subareas over the past decade or two?How important might this therapy form be for the future of health care and what other therapies might it affect?Regarding the first of these questions, there is no generally accepted decomposition, but at least three ways for decomposition can be considered. One is to decompose according to the organ system or disease being treated by the stimulation. The second is to differentiate only between brain stimulation and peripheral nerve stimulation. The third method—found most fruitful with patents in this work—is to decompose based upon the energy form used in the stimulation therapy. Neither decomposing by the organ system nor by brain vs. periphery stimulation was found to be effective frameworks for obtaining separate sets of patents for each technology—a necessary step in our overall research. Using this energy-based framework, we decompose the stimulation therapies into five domains: electrical, magnetic, microwave, optical, and ultrasound. Although microwave and optical energy are both electromagnetic energy-based, we treat them as different. This is because their frequencies are vastly different in the electromagnetic spectrum, and their tissue stimulation mechanisms (described in subsequent paragraphs) are distinct as well, thus leading to a significant difference in treatment modalities.via patent set analysis so we could compare that strongly established medical therapy path with the energy-based therapies focused upon in this research. Since these methods are applicable to sets of patents, they are not capable of identifying specific future details of therapies. Their value lies in aiding strategic and/or policy decisions such as resource allocations to different areas or personnel and other investments to make in public or private research and development activities.Our second research question involves the rate of improvement of the overall area and the constituent subareas. Methods for making such assessments from patent sets have been developed by Benson and Magee , 15 and The following section covers the methodological details; here, we present a brief description of each of these energy-based therapeutic approaches and the distinctions among them.Electrical energy-based therapeutic technologies achieve their therapeutic outcomes by administering electrical current to excitable cells and tissues , 24–26. Transcranial direct current stimulation, a viable non-invasive alternative technology, allows reversible modulation of activity, in particular brain regions, and involves the application of weak electrical current  for a short duration using two (or more) electrodes, anodes, and cathodes on the scalp of the subject, in which one functions as the target electrode and the other as the reference electrode. The target electrode could be either the anode or the cathode, depending on the application , 38. TheVagus nerve stimulation targets the vagus nerve, a mixed parasympathetic nerve, containing ~80% sensory and 20% motor efferent fibers. With extensive branches and sub-branches, the vagus nerve innervates many parts of the human body, ranging from ear, larynx, pharynx, bronchi, lungs, heart, and esophagus, the stomach proximal and descending colon, duodenum, and pancreas , 39, 40,In magnetic energy-based therapeutic technologies, extracorporeal coils  produce a magnetic field pulse, which penetrates the tissue and bone with minimal attenuation and induces eddy currents in the underlying superficial neuronal tissue (which has charged particles), following the induction principle of Faraday , 42. TheMicrowave and radiofrequency-based technologies achieve their therapeutic outcomes by heating the target tissue to a cytotoxic level such that the tissue gets ablated (destroyed) or coagulated. In microwave ablation, an alternating electromagnetic field is applied to a tissue to heat it through the mechanism of dielectric heating with the tissue functioning as the dielectric , 56. SeeOptical energy-based therapeutic technologies achieve their outcomes by activating biological compounds, cells, and tissues. The activation can occur through dislodging a compound that becomes biochemically active and binding to a downstream effector. An alternative approach is the activation of a light-sensitive protein such as channelrhodopsin, which can then excite the cell to express the opsin –60. DepeUltrasound-based therapeutic technologies achieve their therapeutic outcomes through thermal and mechanical effects produced by ultrasound radiation . ThermalThe current research utilizes patents granted by US Patent and Trademark Office (USPTO) to single out six sets of patents as the key data: The first five sets represent the five energy-based therapeutic domains, and the sixth set represents pharmaceutical technologies as a broad category or single domain. These patents sets were constructed using the classification overlap method (COM) and Patsnap patent database , 15 to dThe procedure utilizes US patent classification (UPC) and international patent classification systems (IPC) and typically includes the following steps: (1) identifying a seed patent set using keywords that describe the technological domain of interest; (2) binning the patents in the seed set into IPC (or CPC) and UPC classes; (3) calculating mean-precision-recall (MPR) value for each class, and then ranking classes using these values (this is repeated for the UPC classes); (4) pairing top IPC (or CPC) and UPC classes and retrieving new sets of patents that are listed in both of the top classes from each classification system; (5) reading a sample of patents from these sets to determine the relevancy of these patent sets for the technological domain in question and choosing the best set. The seed sets may also be found using other means such as a list of patents, inventors, or assignees who are known to work in the technological domain. The primary goal of the seed set is to find the relevant IPC (or CPC) classes and UPC classes in the two patent classification systems and use these classes to determine the patents relevant to the domain. Sometimes, when the classes or subclasses do not provide sufficient resolution, keywords may also be used additionally as filters to obtain a more relevant set of patents. To determine the relevancy of a patent set, a sample of 300 patents for each domain is read by two readers independently. Out of the 300 patents, the first 100 patents included those which had received the highest numbers of forward citations in the first 3 years after they were granted, and another 200 patents were randomly selected from the remaining patents in the patent set for the domain in consideration. Publications by Benson and Magee , 15 provThe current study utilized the commercial patent database PatSnap, which provides patents granted by the USPTO from 1970 onwards in an electronic format. This study considered all utility patents granted from January 1, 1970 to February 15, 2017 to retrieve patents relevant to each domain. The seed patent set for each technological domain was decomposed into UPC and IPC classes. The top five UPC and IPC classes (or subclasses) with the highest MPR values were utilized to operationalize the overlap (common patents) between the two classification systems. The electrical therapeutic domain has more than 4,600 patents, the largest among the five domains. The microwave/RF and optical have about 1,200 patents, 1/4 of the number of patents in the electrical therapeutic domain. The magnetic and ultrasound therapeutic domains have about 700 and 400 patents, respectively, one-seventh and one-twelfth the number of patents in the largest patent set. Even the smallest set for ultrasound is large enough to allow a reliable study of the domain , 15. Thenot common to any of the other four domains. Note that the percentage of patents that are common between different therapeutic domains is very low, with the highest value being only 1.5% for microwave/RF therapeutic  with the ultrasound therapeutic domain, suggesting a high degree of independence between the five therapeutic domains. This degree of independence is also reflected by the high values in the diagonal cells or all the focal domains.The common patents are quantified as the percentage of patents common between two patent sets, with each patent set representing a technology domain. The extent of commonality between two different patent sets representing different technological domains indicates the degree of independence between the two domains and indicates whether we can treat these separately. In those cases where commonality is larger, it also implies that patents might have applications in different functional areas. The heat map in all patents relevant to a particular anatomical system . Consequently, the size of the patent sets was much higher than the ones we had for energy-based therapeutics  as a context and as a baseline to compare their annual improvement rates with those of energy-based therapeutic domains. It should be noted that these domains are not the primary subject of this study. We utilized the patent sets developed by Guo, Park, and Magee for these pharmaceutical domains , using t compare , 2. The not common with other domains. Both Alzheimer's and Parkinson's diseases (A and PD) and respiratory diseases (RD) domains have close to 50% of the patients common with cardiovascular diseases (CVD). However, between A and PD and RD domains, common patents are only in the low 20%. It is not surprising to see such overlap, as it is a common practice in the pharmaceutical industry for a given treatment to have multiple disease applications . The higher the number of pathways passing through the focal patent, the higher the centrality of the patent, indicating the importance of the patent. Interpreting each patent as introducing some original technological knowledge, the centrality provides an indication of the significance of the original knowledge introduced by the focal patent for the downstream patents. As an extension of the method, Triulzi et al. (k). They have concluded this finding with a Monte Carlo cross-validation exercise between empirically observed k for the 30 diverse technological domains  for the five energy-based therapeutic domains and the aggregate pharmaceutical domain.where readable number of significant patents in the domain and to enable the identification of technology clusters within the domain. Hummon and Doreian  structuring the citation network from Step 2 into layers after defining start and end points, (3.b) calculating knowledge persistence of each patent in the domain patent set by considering backward and forward citations of each patent, (3.c) and identifying the patents with global (GP) and local (LP) persistence equal to or >0.3 and 0.8, respectively, as high-persistence patents. The GP of a patent estimates the importance of a patent in the entire network, whereas the LP estimates the importance of the patent in each layer. The local persistence (LP) plays a significant role in identifying and retaining important patents, which are recent but have not had a chance to enable the evolution of their lineage. In Step 4, the main paths are traced backward and forward, originating from the high-persistent patents. Often, it is necessary to connect main pathways traversing through high-persistent patents with low-persistent patents to make the main pathways continuous. As a final note, it should be noted that, in Step 2, the citation network is created only among patents in the domain patent set, and any citations outside the patent set are ignored. In contrast, the citation network constructed in the computation of centrality of patents  includes all the utility patents in the USPTO system. The readers are referred to prior publications for methodological details as well as for applications of the method to other domains , 22, 23.Patent activity in a technological domain indicates the level of interest in the technological domain and helps to identify when patenting activity accelerates. not among the five most active assignees in In the magnetic therapeutic domain, four of the five most central patents  of the five most central patents in the domain, plus the 10th patent  of energy-based therapeutic domains (blue bars) and the aggregate pharmaceutical therapeutic domain (orange bar) in descending order. The k values are computed using the regression model (described in the Data and Methods section) from the mean normalized centrality of the patent set for a given technological domain. The k value for the aggregate pharmaceutical domain is presented to provide a baseline and a context for comparison to allow some assessment of the growth potential of energy-based therapeutic modalities. The k values for the aggregate pharmaceutical domain are 5% . Earlier analysis of the uncertainty in the k estimates . The results on significant clusters and important contributing patents for the five energy-based therapeutic domains are presented below.Main paths for each of the five domains of interest are presented next. The nodes represent the patents in the domain, and the edges represent the citations, proxy for the flow of knowledge. The larger nodes in yellow color are high-persistent patents, while the smaller gray nodes are low-persistent patents, which are used to connect the high-persistent patents to construct the main paths. The time axis is shown below the main path, and the position of the patent along the time axis indicates the year in which it was granted. The nodes are labeled in ascending temporal order from left to right, with the oldest patent labeled as 1, followed by newer patents toward the right. This labeling scheme is used to show the sequence in which the patents in the main paths were granted. The table below the graphics lists the node labels and patent numbers in the main paths.The main paths for the electrical domain show two dominant clusters  related to flexible illuminators and US6443978 (node 20) related to optical-stimulation of tissue—linking OP1 cluster. US8475506 (node 25) from Lockheed Martin is an additional key patent in this OP2 cluster for stimulation of nerve tissue and utilizes an array of two or more vertical-cavity surface-emitting lasers (VCSELs) to stimulate human tissue. The patent cluster OP3 is primarily concerned with the treatment of skin ailments such as vascular and pigmented lesions in the skin using laser energy. Although the OP3 cluster began independently in the 1980s, it had significant interaction with OP2 later in 1990s, leveraging the work of, and linking to, OP2 through US4556001 (node 8) on photodynamic therapy and much later on the photo-cosmetic device for skin and the light energy head with higher efficiency. The nodes 16 (US6027495 for diode laser treatment of vascular and pigmented skin lesions), 23 (US8182473 photo-cosmetic device with phase-change-based subsystem for cooling tissue), and 24 (US8328796 light energy head incorporating efficient means for minimizing backscattering) are additional key inventions in this main path for the OP3 cluster.The main paths for the optical therapeutic domain are shown in The main paths for the ultrasound therapeutic domain are shown in The specific inventions underlying energy-based therapeutics are quite broad and interactive with an even wider range of other technologies. This is seen in the main path results since this technique only considers a select set of high-persistence patents, which the technique identifies as having important longer-lasting effects on the development within the domain. Even with this much smaller set of patents, The main path analysis of the electrical therapeutic domain  shows thThe main path analysis shows that the magnetic therapeutic domain  was centThe main path analysis of the microwave/RF therapeutic domain  has a siThe main path analysis of the optical therapeutic domain  exhibitsMain path analysis of ultrasound therapeutics shows four clusters , with thIn summary, the discussion presented above demonstrates (1) that the clusters identified as important by the main path analysis are the ones that are significant therapeutically and (2) that neuromodulation is now the most important area in the electrical, magnetic, optical, and ultrasound areas. The microwave main path is the only one that exhibits a single group, and it is associated with ablation. These four domains active in neuromodulation appear to be producing competing and complementary therapeutics.In addition to the main path results, which, as just discussed, are found to be related to therapy trends, this research has provided estimates of performance improvement rates for the five energy-based stimulation domains and a comparable rate for pharmaceuticals. We note again that the high-centrality patents important in showing high rate domains are not the same as the high-persistence patents signaling important within-domain trends. In general, differences in performance improvement rates are the key factor in technological change, which occurs when a faster-improving technology achieves equal or better value in a given application than a more slowly improving incumbent technology . The impThe highest improvement rate identified in this study is for the microwave stimulation domain, the value of 88% improvement per year is higher than any other medical domain yet studied but is not as high as software-dominated domains identified by Benson and Magee  nor as hThere are several indicated therapies change phenomena that are consistent with, and thus potentially explained by, the rate differences we have observed. We note that the techniques used in this research are reliable indicators of the rate of improvement of a technology domain and can indicate which technology area is likely to dominate in the future. However, they are not capable of defining future technological or therapeutic developments  in any further detail as a clinical science and regulatory practice also have a strong influence on development dynamics. All the conclusions are, nonetheless, useful from a resource allocation point of view and thus are of value for strategists and policymakers. We now discuss four rate difference findings with strategic impact. First, the fastest improving domain (microwave) is the only main path with a singular cluster, and this is consistent with a fast-improving domain. Indeed, the initial patents within this main path show microwave technology quickly dominate other RF stimulation technologies as would be expected if microwaves were improving at a faster rate than competitors. A possible second therapy change could be if microwave stimulation begins to replace the other energy-based stimulation domains. However, it will only dominate other stimulation domains when and if it can be adapted for effective usage in other areas. It is not clear to us if this will be possible for cardiac or for nerve stimulation that is becoming the dominant application in other domains. However, if this can be done, microwave stimulation for cardiac and nerve stimulation could be a dominant future therapy.The third practical implication of our observed improvement rates is that bone and tissue growth by magnetic stimulation (MG1 in the main path) did not continue beyond the early 2000s but ultrasound bone and wound healing did continue until around 2010. The higher improvement rate for ultrasound (42%) vs. magnetic (14%) is a likely explanation for this difference.The fourth and somewhat speculative but potentially very important practical implication of our findings involves pharmaceuticals vs. energy-based therapies. The overall substantially higher rates of improvement for energy-based therapeutics relative to the currently dominant therapy of pharmaceuticals could foreshadow a major transition in medicine. This might particularly apply to developments in the fastest improving domain (microwave/RF) where a major application aim found in the main path was for cancer tumor removal . However, the advent of energy-based therapies might well be in roles that enhance or modify pharmaceuticals rather than replace them. A study looking at such possibilities would be very valuable to those who care about large transitions in medical therapies.all the patents across the globe, we reason that our patent sets include important patents globally and thus provide a sound basis for analysis and broad insights useful in the context of US and internationally.We conclude with a discussion of a limitation of our study. Our study utilizes only patents granted by the USPTO. These include patents filed by US institutions as well as by international institutions. We believe that the patents filed at the USPTO by international institutions should be important as the applicants are going outside their native patent jurisdiction  for patent protection in the US at a considerable cost. Although the patent sets for the five energy-based therapeutic domains do not include The original contributions presented in the study are included in the article/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. The reviewer HY declared a shared affiliation, with no collaboration, with the authors to the handling editor at the time of the review.All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.


Passive multistatic radars have gained a lot of interest in recent years as they offer many benefits contrary to conventional radars. Here in this research, our aim is detection of target in a passive multistatic radar system. The system contains a single transmitter and multiple spatially distributed receivers comprised of both the surveillance and reference antennas. The system consists of two main parts: 1. Local receiver, and 2. Fusion center. Each local receiver detects the signal, processes it, and passes the information to the fusion center for final detection. To take the advantage of spatial diversity, we apply major fusion techniques consisting of hard fusion and soft fusion for the case of multistatic passive radars. Hard fusion techniques are analyzed for the case of different local radar detectors. In terms of soft fusion, a blind technique called equal gain soft fusion technique with random matrix theory-based local detector is analytically and theoretically analyzed under null hypothesis along with the calculation of detection threshold. Furthermore, six novel random matrix theory-based soft fusion techniques are proposed. All the techniques are blind in nature and hence do not require any knowledge of transmitted signal or channel information. Simulation results illustrate that proposed fusion techniques increase detection performance to a reasonable extent compared to other blind fusion techniques. Passive radars have been an emerging field for researchers since last many years. They have many additional perks in contrast to active radars; the noteworthy one is the reduced cost of implementation since they use transmitters like FM broadcasting signals, television transmission signals, or can be mobile phone signals. Therefore, no extra hardware for signal generation is needed ,2. AnothA radar system with multiple receivers and multiple illuminators (IOs) is called a passive multistatic radar system. Multiple input Multiple output (MIMO) radars are passive multistatic radars, exploiting multiple IOs and multiple receivers, spatially separated to each other . In geneThe IOs are non-cooperative in nature, making the transmitted signal unknown to the receiver. Therefore, matched filters that are commonly used for detection in radar systems are not a good choice. However, we have multiple receivers, spatially distributed, collecting echos of the target simultaneously in a passive multistatic radar system. The correlation that exists between these echos can be used for detecting the targets. To exploit this correlation, we have used a mathematical tool called Random Matrix theory (RMT). The theory mainly deals with different forms of random matrices and the properties of eigenvalues and eigenvectors obtained from the sample covariance matrices (SCM). In our research, we have used singular values to design six novel soft fusion techniques. RMT has been used, as it has evolved as an excellent tool that can be used in signal processing . MoreoveOne of the hot topics of research in radar, sonar, and communication engineering like cognitive radios is detection ,11. DeteP nodes cooperates by sharing their own local sensing decisions on a target’s presence. The local sensor’s local decisions can be either soft or hard decisions. A global verdict on the target’s presence is then made by fusing the data received from all the local nodes. The central unit where the decision is made is known as the fusion center, and the fusion is done by using an appropriate fusion strategy.In communication theory, when spatially separated multiple receivers observe a common phenomenon, this is known as fusion. It has been widely used in cooperative spectrum sensing . In fusiDifferent types of transmission impairments are very common to occur during the process of spectrum sensing. This includes rigorous fading , issues In this paper, we exploit spatial diversity by using multiple receivers in a multistatic passive radar system; each receiver acts as a local detector. The local decision is sent to the fusion center, where fusion techniques are applied, and a final decision about detection is made.A framework for data fusion in multistatic radar systems with hard and soft fusion methods.Proposal of novel soft fusion techniques based on random matrix theories for improving the detection performance.Theoretical treatment of a known soft-decision fusion method “the equal gain combining” method.Simulations of known hard-decision fusion and soft decision fusion techniques and comparing the detection performance.The main contributions of this paper are:The performance of the system is increased in the recent past by deploying multiple receivers. MIMO radar is an excellent example of multiple receivers. An intensive study on distributed MIMO radars, a sort of multistatic radar, has been presented in . As compPassive multistatic radars can also be referred to a distributed systems where original signals received at the local detectors are sent to a fusion center for the final decision. In cognitive radio networks, fusion methods have been widely used for cooperative spectrum sensing to detect primary user . For thiSoft fusion has the potential to adapt, with a trade-off, i.e., increase data size being transmitted to the fusion center. Soft fusion-based techniques are commonly used in the cognitive radio environment. In , a novelIn cognitive radios, the prevailing soft fusion method mainly weighs measured power received from secondary users and designs optimal weight coefficients for various channels. In , for sloSingular values decomposition (SVD) is a broadly used signal processing tool . In deteThe research work in this paper adopts the idea of fusion techniques and proposes new soft-fusion methods that outperform other methods in the literature.Cooperative sensing for target detection in radar system is a two-level decision process to decide on the presence of a target in the environment. The first level of decision-making is at the receiver node known as the local detector whereas the second level of decision making takes place at the fusion center. The complete system model of local detector and fusion center has been explained in the following sub-sections.P is the total number of local detectors present in the system, hence, the detection problem can be formulated as the following hypothesis test,s and r describes the surveillance channels and reference channels, respectively. The terms M samples, normalized and unknown. It is noteworthy that distinguishing the pulses from one another for the formulated problem is only possible when there is perfect time synchronization between the transmitter and receiver. Commercial transmitters can achieve this kind of perfect synchronization by following certain mechanisms. However, in this paper, we have considered the case of perfect time synchronization.Our system model mainly consists of a single static target and multiple receivers, as depicted in ctively, . MoreoveN time snapshots at the Converting Equations  and 2)  2) into The local decisions made by the local receiver nodes are hard decisions with a binary representation of In soft fusion, each local detector will receive the signal and apply the local test statistics. When applying the fusion framework on multistatic radars, the local detector’s test statistic serves as a soft local decision. Therefore, in this section, we will present all the local detectors we have considered for analysis and comparison purposes. Suppose we receive information at the To design a framework for data fusion in multistatic radars, we have analyzed the fusion techniques for the case of different local detectors already present in the literature. The details of the local detector considered are as follows.M is the highest rank that can be obtained. The degree of freedom (DF) of the SSVD detector is Here, in this paper, SSVD , a recenA singular vectors-based detector is expressed in . The detThe most commonly applied method for detecting a target in passive radar is cross-correlation, where we cross-correlate the data received from the surveillance and the reference channels, respectively. The mathematical expression for the detector is given by,In this research, we consider a perfect case of the detector. It serves as a benchmark to compare the performance of other detectors. This detector is not a very practical case as it considers the transmitted signal to be known. The detector is called the clairvoyant detector. The test statistic of the clairvoyant detector is given by,The second decision process in target detection is performed at the fusion center after receiving all the local decisions from the local detectors. The final detection is done by fusing (depending on the reporting strategy) the received data and deciding upon the target’s presence. The mechanism of fusion done can be hard fusion or soft fusion. We categorize the fusing site into hard fusion-based detection or soft fusion-based detection depending on the first level’s strategy.Once we have local decisions made by the local detectors with a binary representation as explained in Given that The detection performance of the Q-out-of-P fusion technique can be easily analyzed by considering the detection and the false alarm probabilities of the local decisions from the local detector. Suppose if Q = 1 and the AND rule is implemented by letting Furthermore, two of the well-known logical operators, the OR function and the AND function, have also been used for the hard fusion decision. These two functions are special cases of the Q-out-of-P rule. The OR rule is implemented by letting In this paper, we have analyzed Q-out-of-P, AND, and OR cases of hard fusion. Here, we choose SSVD  as a locP = 1. As observed from P = 1).We start by implementing Q-out-of-P-based fusion by keeping a constant probability of detection Next, we analyze hard fusion for ‘OR’ and ‘AND’ schemes. This scenario is considered for two different cases (1) when all the detectors have a variable probability of detection (2) when all the detectors have a constant probability of detection. Both cases are explained as follows.Suppose if OR fusionAND fusionThe second case we consider is when the probability of detection is the same for all the local receivers. In this case, miss detection and false alarm probabilities for the OR and AND-based data fusion strategies becomes P. We have analyzed the results when the number of local detectors P are 1, 3, and 5. Here, we also monitor the performance of SSVD detector for various degrees of freedom (DF). We can observe the decreased performance as the degree of freedom is increased. The performance degrades due to the addition of noise vectors as the number of singular vectors increases by increasing the degree of freedom. Furthermore, the OR strategy displays better detection performance at the cost of the false alarm probability. In contrast, the AND strategy shows better false alarm performance at the expense of the detection probability. We can also observe the detector’s enhanced performance with an increasing number of local detectors P, regardless of the variable probability of detection.In In the next section, we will focus on applying soft fusion techniques for passive multistatic radars.As we know, in soft fusion, the local detector transmits the sensed data directly to the fusion center, and the fusion center combines the information to decide upon the presence of the target. Suppose the information at the To analyze the soft fusion in a passive multistatic radar case, SVD has been used as a local detector. SVD is chosen among all detectors because, from the observation made in p. Hence, the fusion test statistics becomeEqual Gain is the most straight forward yet most commonly used blind soft fusion technique. In this technique, we consider fusing all the detectors by assigning equal weights We calculate test statistics for each receiver for both the null hypothesis and the alternate hypothesis and pass it to the fusion center, where the fusion center sums them up with equal weights.P are the number of local detectors in the system. In this section, a closed-form expression for the threshold determining equal gain fusion decision has been calculated, specifically when an SVD detector, given by Equation  has beenribution  with degIt is noteworthy that the detection threshold is independent of received signal power and SNR, which is a highly desirable feature of Radar detection.In In the analysis phase, we observed that the performance of the technique equal gain fusion could be improved upon, as this fusion method gives equal weights to each local detector. It does not exploit the fact that some local detectors may receive a better signal than others. As in practical cases, signal attenuation for each receiver is not constant, and hence the resulting signal-to-noise ratio in the surveillance channel may vary for each local receiver. If the received signal contains signal and noise, then the largest singular value primarily reflects the power concentration of the initially transmitted signal. Hence, we utilize the singular values embedded inside the received signal.In particular, we propose two main fusion techniques based on singular values and four more designs that are precisely the variations of the first two proposed techniques.The combination of maximum singular value and trace obtained from the sample covariance matrix of the received signal matrix plays a vital role in various hypothesis testing problems, both in statistics and in signal processing. This combination can contribute to fusion decision by sensing the amount of signal in each local detector. Considering this, the weights defined in Equation  can be eAnother significant result from random matrix theory is the condition number method. The condition number method represents the ratio of the largest and smallest eigenvalue. In our second proposed algorithm, inspired by this method, we use the ratio of the largest and smallest singular value obtained by the singular value decomposition of received data matrix. Hence, the weights This technique is a variation of proposed technique 1. In this technique, we have applied the logarithmic function to the base 10 on proposed technique 1. Generally, the logarithm is a slowly increasing function, and it compresses large-scale data. The mathematical expression of this technique is given byThe exponential function is one of the most critical functions in mathematics. It increases rapidly, so here in this technique, we have analyzed its effect when applied on singular values divided by its trace. Mathematically, we can express it asIn this fusion technique, instead of applying the exponential on a ratio, we apply it on the largest singular value present in the singular value matrix, given byIn this technique, we have applied the logarithmic function to the base ten on largest singular value present. The mathematical expression of the method is as follows:In this section, numerical simulation results are provided to verify the analysis done so far and evaluate the performance of the proposed techniques. In In hard fusion-based detection, the local detector transmits its binary decisions on the presence of a target in the environment to the fusion center. This process has no liberty to use any other detection technique except the mentioned Q-out-of-P, AND, and OR techniques. Therefore, the advancement that can be done is minimal. However, we can use an optimal local detector that can improve the whole system’s detection performance. For this purpose, we have exploited some recently developed radar detector and analyzed them in the framework of hard fusion.u, any periodic waveform can be used. Here, we have considered simple unit norm sinusoidal wave.The details of detectors we consider for performance analysis are given in The complementary receiver operating characteristics curves for the Q-out-of-P hard fusion technique for different local detectors is depicted in We also analyze local detector’s performance in hard fusion framework when the SNR of the surveillance channel increases. In In In In In this paper, we have done a detailed analysis of the application of hard and soft fusion techniques for multistatic passive radars. Hard fusion techniques were analyzed for different local detectors. Among all the detectors, the particular case of SSVD detector, also known as SVD detector, showed the best performance. Moreover, hard fusion techniques were also analyzed for the case when the probability Of detection is constant and when the probability of detection is not constant. Additionally, we have studied the performance of equal gain soft fusion while considering SVD as a local detector. We derived an approximate expression for the detection threshold under the null hypothesis. Furthermore, we compared existing soft and hard fusion techniques and determined that the soft fusion techniques perform better than hard fusion techniques. Lastly, based on our research, we proposed some novel singular value-based soft fusion techniques. We demonstrated that the proposed techniques could significantly outperform the classical equal gain fusion when used in passive multistatic radar systems.In the future, we will expand our research specifically for the case of multiple targets. Moreover, our preliminary results demonstrate improvement in detection performance using novel soft fusion techniques, and we will develop the analysis for these techniques in our future work.