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Turner R, Rasmussen P, Gatterer H, Tremblay JC, Roche J, Strapazzon G, Roveri G, Lawley J, Siebenmann C. Cerebral blood flow regulation in hypobaric hypoxia: role of haemoconcentration. J Physiol 2024. [PMID: 38687185 DOI: 10.1113/jp285169] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2023] [Accepted: 04/04/2024] [Indexed: 05/02/2024] Open
Abstract
During acute hypoxic exposure, cerebral blood flow (CBF) increases to compensate for the reduced arterial oxygen content (CaO2). Nevertheless, as exposure extends, both CaO2 and CBF progressively normalize. Haemoconcentration is the primary mechanism underlying the CaO2 restoration and may therefore explain, at least in part, the CBF normalization. Accordingly, we tested the hypothesis that reversing the haemoconcentration associated with extended hypoxic exposure returns CBF towards the values observed in acute hypoxia. Twenty-three healthy lowlanders (12 females) completed two identical 4-day sojourns in a hypobaric chamber, one in normoxia (NX) and one in hypobaric hypoxia (HH, 3500 m). CBF was measured by ultrasound after 1, 6, 12, 48 and 96 h and compared between sojourns to assess the time course of changes in CBF. In addition, CBF was measured at the end of the HH sojourn after hypervolaemic haemodilution. Compared with NX, CBF was increased in HH after 1 h (P = 0.001) but similar at all later time points (all P > 0.199). Haemoglobin concentration was higher in HH than NX from 12 h to 96 h (all P < 0.001). While haemodilution reduced haemoglobin concentration from 14.8 ± 1.0 to 13.9 ± 1.2 g·dl-1 (P < 0.001), it did not increase CBF (974 ± 282 to 872 ± 200 ml·min-1; P = 0.135). We thus conclude that, at least at this moderate altitude, haemoconcentration is not the primary mechanism underlying CBF normalization with acclimatization. These data ostensibly reflect the fact that CBF regulation at high altitude is a complex process that integrates physiological variables beyond CaO2. KEY POINTS: Acute hypoxia causes an increase in cerebral blood flow (CBF). However, as exposure extends, CBF progressively normalizes. We investigated whether hypoxia-induced haemoconcentration contributes to the normalization of CBF during extended hypoxia. Following 4 days of hypobaric hypoxic exposure (corresponding to 3500 m altitude), we measured CBF before and after abolishing hypoxia-induced haemoconcentration by hypervolaemic haemodilution. Contrary to our hypothesis, the haemodilution did not increase CBF in hypoxia. Our findings do not support haemoconcentration as a stimulus for the CBF normalization during extended hypoxia.
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Affiliation(s)
- Rachel Turner
- Institute of Mountain Emergency Medicine, Eurac Research, Bolzano, Italy
- Institut für Sportwissenschaft, Universität Innsbruck, Tyrol, Austria
| | | | - Hannes Gatterer
- Institute of Mountain Emergency Medicine, Eurac Research, Bolzano, Italy
| | - Joshua C Tremblay
- School of Sport and Health Sciences, Cardiff Metropolitan University, Wales, UK
| | - Johanna Roche
- Institute of Mountain Emergency Medicine, Eurac Research, Bolzano, Italy
| | - Giacomo Strapazzon
- Institute of Mountain Emergency Medicine, Eurac Research, Bolzano, Italy
| | - Giulia Roveri
- Institute of Mountain Emergency Medicine, Eurac Research, Bolzano, Italy
| | - Justin Lawley
- Institut für Sportwissenschaft, Universität Innsbruck, Tyrol, Austria
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Simpson LL, Stembridge M, Siebenmann C, Moore JP, Lawley JS. Mechanisms underpinning sympathoexcitation in hypoxia. J Physiol 2024. [PMID: 38533641 DOI: 10.1113/jp284579] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2023] [Accepted: 02/28/2024] [Indexed: 03/28/2024] Open
Abstract
Sympathoexcitation is a hallmark of hypoxic exposure, occurring acutely, as well as persisting in acclimatised lowland populations and with generational exposure in highland native populations of the Andean and Tibetan plateaus. The mechanisms mediating altitude sympathoexcitation are multifactorial, involving alterations in both peripheral autonomic reflexes and central neural pathways, and are dependent on the duration of exposure. Initially, hypoxia-induced sympathoexcitation appears to be an adaptive response, primarily mediated by regulatory reflex mechanisms concerned with preserving systemic and cerebral tissue O2 delivery and maintaining arterial blood pressure. However, as exposure continues, sympathoexcitation is further augmented above that observed with acute exposure, despite acclimatisation processes that restore arterial oxygen content (C a O 2 ${C_{{\mathrm{a}}{{\mathrm{O}}_{\mathrm{2}}}}}$ ). Under these conditions, sympathoexcitation may become maladaptive, giving rise to reduced vascular reactivity and mildly elevated blood pressure. Importantly, current evidence indicates the peripheral chemoreflex does not play a significant role in the augmentation of sympathoexcitation during altitude acclimatisation, although methodological limitations may underestimate its true contribution. Instead, processes that provide no obvious survival benefit in hypoxia appear to contribute, including elevated pulmonary arterial pressure. Nocturnal periodic breathing is also a potential mechanism contributing to altitude sympathoexcitation, although experimental studies are required. Despite recent advancements within the field, several areas remain unexplored, including the mechanisms responsible for the apparent normalisation of muscle sympathetic nerve activity during intermediate hypoxic exposures, the mechanisms accounting for persistent sympathoexcitation following descent from altitude and consideration of whether there are sex-based differences in sympathetic regulation at altitude.
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Affiliation(s)
- Lydia L Simpson
- Department of Sport Science, Performance Physiology and Prevention, Universität Innsbruck, Innsbruck, Austria
| | - Mike Stembridge
- Cardiff School of Sport and Health Sciences, Cardiff Metropolitan University, Cardiff, UK
| | | | - Jonathan P Moore
- School of Psychology and Sport Science, Institute of Applied Human Physiology, Bangor University, Bangor, UK
| | - Justin S Lawley
- Department of Sport Science, Performance Physiology and Prevention, Universität Innsbruck, Innsbruck, Austria
- Institute of Mountain Emergency Medicine, EURAC Research, Bolzano, Italy
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Lindsey ML, Usselman CW, Ripplinger CM, Carter JR, DeLeon-Pennell KY. Sex as a biological variable for cardiovascular physiology. Am J Physiol Heart Circ Physiol 2024; 326:H459-H469. [PMID: 38099847 PMCID: PMC11219053 DOI: 10.1152/ajpheart.00727.2023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/20/2023] [Revised: 12/08/2023] [Accepted: 12/10/2023] [Indexed: 02/03/2024]
Abstract
There have been ongoing efforts by federal agencies and scientific communities since the early 1990s to incorporate sex and/or gender in all aspects of cardiovascular research. Scientific journals provide a critical function as change agents to influence transformation by encouraging submissions for topic areas, and by setting standards and expectations for articles submitted to the journal. As part of ongoing efforts to advance sex and gender in cardiovascular physiology research, the American Journal of Physiology-Heart and Circulatory Physiology recently launched a call for papers on Considering Sex as a Biological Variable. This call was an overwhelming success, resulting in 78 articles published in this collection. This review summarizes the major themes of the collection, including Sex as a Biological Variable Within: Endothelial Cell and Vascular Physiology, Cardiovascular Immunity and Inflammation, Metabolism and Mitochondrial Energy, Extracellular Matrix Turnover and Fibrosis, Neurohormonal Signaling, and Cardiovascular Clinical and Epidemiology Assessments. Several articles also focused on establishing rigor and reproducibility of key physiological measurements involved in cardiovascular health and disease, as well as recommendations and considerations for study design. Combined, these articles summarize our current understanding of sex and gender influences on cardiovascular physiology and pathophysiology and provide insight into future directions needed to further expand our knowledge.
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Affiliation(s)
- Merry L Lindsey
- School of Graduate Studies, Meharry Medical College, Nashville, Tennessee, United States
- Research Service, Nashville Veterans Affairs Medical Center, Nashville, Tennessee, United States
| | - Charlotte W Usselman
- Cardiovascular Health and Autonomic Regulation Laboratory, Department of Kinesiology and Physical Education, McGill University, Montreal, Quebec, Canada
| | - Crystal M Ripplinger
- Department of Pharmacology, UC Davis School of Medicine, Davis, California, United States
| | - Jason R Carter
- Robbins College of Health and Human Sciences, Baylor University, Waco, Texas, United States
| | - Kristine Y DeLeon-Pennell
- Division of Cardiology, Department of Medicine, School of Medicine, Medical University of South Carolina, Charleston, South Carolina, United States
- Research Service, Ralph H. Johnson Veterans Affairs Medical Center, Charleston, South Carolina, United States
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Siebenmann C, Roche J, Schlittler M, Simpson LL, Stembridge M. Regulation of haemoglobin concentration at high altitude. J Physiol 2023. [PMID: 38051656 DOI: 10.1113/jp284578] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2023] [Accepted: 11/21/2023] [Indexed: 12/07/2023] Open
Abstract
Lowlanders sojourning for more than 1 day at high altitude (HA) experience a reduction in plasma volume (PV) that increases haemoglobin concentration and thus restores arterial oxygen content. If the sojourn extends over weeks, an expansion of total red cell volume (RCV) occurs and contributes to the haemoconcentration. While the reduction in PV was classically attributed to an increased diuretic fluid loss, recent studies support fluid redistribution, rather than loss, as the underlying mechanism. The fluid redistribution is presumably driven by a disappearance of proteins from the circulation and the resulting reduction in oncotic pressure exerted by the plasma, although the fate of the disappearing proteins remains unclear. The RCV expansion is the result of an accelerated erythropoietic activity secondary to enhanced renal erythropoietin release, but a contribution of other mechanisms cannot be excluded. After return from HA, intravascular volumes return to normal values and the normalisation of RCV might involve selective destruction of newly formed erythrocytes, although this explanation has been strongly challenged by recent studies. In contrast to acclimatised lowlanders, native highlanders originating from the Tibetan and the Ethiopian plateaus present with a normal or only mildly elevated haemoglobin concentration. Genetic adaptations blunting the erythropoietic response to HA exposure have been proposed as an explanation for the absence of more pronounced haemoconcentration in these populations, but new evidence also supports a contribution of a larger than expected PV. The functional significance of the relatively low haemoglobin concentration in Tibetan and Ethiopian highlanders is incompletely understood and warrants further investigation.
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Affiliation(s)
| | - Johanna Roche
- Institute of Mountain Emergency Medicine, EURAC Research, Bolzano, Italy
| | - Maja Schlittler
- AO Research Institute Davos, Regenerative Orthopaedics Program, Davos, Switzerland
| | - Lydia L Simpson
- Department of Sport Science, Division of Performance Physiology and Prevention, Universität Innsbruck, Innsbruck, Austria
| | - Mike Stembridge
- Cardiff School of Sport and Health Sciences, Cardiff Metropolitan University, Cardiff, UK
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Zhu Y, Li Q, Wu Y, Peng X, Xiang X, Lau B, Tzang F, Liu L, Li T. Protective Effect of Modified Hemoglobin on Rabbits and Goats in High-Altitude Sickness. Adv Biol (Weinh) 2023; 7:e2200307. [PMID: 37097708 DOI: 10.1002/adbi.202200307] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2022] [Revised: 02/06/2023] [Indexed: 04/26/2023]
Abstract
The prevalence and severity of high-altitude sickness increases with increasing altitude. Prevention of hypoxia caused by high-altitude sickness is an urgent problem. As a novel oxygen-carrying fluid, modified hemoglobin can carry oxygen in a full oxygen partial pressure environment and release oxygen in a low oxygen partial pressure environment. It is unclear whether modified hemoglobin can improve hypoxic injury on a plateau. Using hypobaric chamber rabbit (5000 m) and plateau goat (3600 m) models, general behavioral scores and vital signs, hemodynamic, vital organ functions, and blood gas are measured. The results show that the general behavioral scores and vital signs decrease significantly in the hypobaric chamber or plateau, and the modified hemoglobin can effectively improve the general behavioral scores and vital signs in rabbits and goats, and reduce the degree of damage to vital organs. Further studies reveal that arterial partial pressure of oxygen (PaO2 ) and arterial oxygen saturation (SaO2 ) on the plateau decrease rapidly, and the modified hemoglobin could increase PaO2 and SaO2 ; thus, increasing the oxygen-carrying capacity. Moreover, modified hemoglobin has few side effects on hemodynamics and kidney injury. These results indicate that modified hemoglobin has a protective effect against high-altitude sickness.
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Affiliation(s)
- Yu Zhu
- State Key Laboratory of Trauma, Burns, and Combined Injury, Department of Shock and Transfusion, Research Institute of Surgery, Daping Hospital, Army Medical University, Chongqing, 400042, China
| | - Qinghui Li
- State Key Laboratory of Trauma, Burns, and Combined Injury, Department of Shock and Transfusion, Research Institute of Surgery, Daping Hospital, Army Medical University, Chongqing, 400042, China
| | - Yue Wu
- State Key Laboratory of Trauma, Burns, and Combined Injury, Department of Shock and Transfusion, Research Institute of Surgery, Daping Hospital, Army Medical University, Chongqing, 400042, China
| | - Xiaoyong Peng
- State Key Laboratory of Trauma, Burns, and Combined Injury, Department of Shock and Transfusion, Research Institute of Surgery, Daping Hospital, Army Medical University, Chongqing, 400042, China
| | - Xinming Xiang
- State Key Laboratory of Trauma, Burns, and Combined Injury, Department of Shock and Transfusion, Research Institute of Surgery, Daping Hospital, Army Medical University, Chongqing, 400042, China
| | - Billy Lau
- New Beta Innovation Limited, Kowloon Bay, Hong Kong, Hong Kong SAR, 999077, China
| | - Feichuen Tzang
- New Beta Innovation Limited, Kowloon Bay, Hong Kong, Hong Kong SAR, 999077, China
| | - Liangming Liu
- State Key Laboratory of Trauma, Burns, and Combined Injury, Department of Shock and Transfusion, Research Institute of Surgery, Daping Hospital, Army Medical University, Chongqing, 400042, China
| | - Tao Li
- State Key Laboratory of Trauma, Burns, and Combined Injury, Department of Shock and Transfusion, Research Institute of Surgery, Daping Hospital, Army Medical University, Chongqing, 400042, China
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Kammerer T, Walzl A, Müller T, Groene P, Roveri G, Turner R, Roche J, Gatterer H, Siebenmann C, Schäfer ST. Effects of Hypobaric Hypoxia on Coagulation in Healthy Subjects Exposed to 3,500 m Altitude. High Alt Med Biol 2023; 24:94-103. [PMID: 37339401 DOI: 10.1089/ham.2022.0154] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/22/2023] Open
Abstract
Kammerer, Tobias, Anna Walzl, Thomas Müller, Philipp Groene, Giulia Roveri, Rachel Turner, Johanna Roche, Hannes Gatterer, Christoph Siebenmann, and Simon T. Schäfer. Effects of hypobaric hypoxia on coagulation in healthy subjects exposed to 3,500 m altitude. High Alt Med Biol. 24:94-103, 2023. Background: Hypoxia is discussed as a trigger for prothrombotic changes both in intensive care and high altitude medicine. This research study aimed to evaluate the effect of isolated hypobaric hypoxia (HH) on coagulation in females in a highly standardized setting. Methods: Twelve healthy female subjects were studied under HH (equivalent to 3,500 m) and normoxia (NX) during two 4-day sojourns, in a strictly controlled crossover design. Nutrition, fluid intake, hormonal status (i.e., menstrual cycle variation), and physical stress were standardized. Functional coagulation and blood lysis were measured by viscoelastometry and compared between HH and NX. In addition, plasma-based coagulation tests (PBCTs), namely prothrombin time, activated partial thromboplastin time, fibrinogen, factor VIII coagulation activity (FVIII:C), von Willebrand factor antigen (vWF:Ag), and von Willebrand factor ristocetin cofactor activity (vWF:RCo) were measured. Results: Neither for Viscoelastic Haemostatic Assays nor for PBCTs significant changes were found for HH compared with NX (all p > 0.05). Specifically, the lysis ability, as well as clotting time, clot formation, clot amplitude, and maximum clot firmness unchanged were similar between HH and NX. This also applied to all other variables. Conclusion: We demonstrate that moderate HH per se has no influence on blood coagulation in healthy females.
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Affiliation(s)
- Tobias Kammerer
- Department of Anaesthesiology and Intensive Care Medicine, Faculty of Medicine and University Hospital Cologne, University of Cologne, Cologne, Germany
- Department of Anaesthesiology, Ludwig-Maximilians-University Munich, Munich, Germany
| | - Anna Walzl
- Department of Anaesthesiology, Ludwig-Maximilians-University Munich, Munich, Germany
| | - Thomas Müller
- Department of Laboratory Medicine, Hospital Voecklabruck, Voecklabruck, Austria
| | - Philipp Groene
- Department of Anaesthesiology, Ludwig-Maximilians-University Munich, Munich, Germany
| | - Giulia Roveri
- Eurac Research, Institute of Mountain Emergency Medicine, Bolzano, Italy
- Department of Pathophysiology and Transplantation, University of Milan, Milan, Italy
| | - Rachel Turner
- Eurac Research, Institute of Mountain Emergency Medicine, Bolzano, Italy
| | - Johanna Roche
- Eurac Research, Institute of Mountain Emergency Medicine, Bolzano, Italy
| | - Hannes Gatterer
- Eurac Research, Institute of Mountain Emergency Medicine, Bolzano, Italy
- Institute for Sports Medicine, Alpine Medicine and Health Tourism (ISAG), UMIT TIROL-Private University for Health Sciences and Health Technology, Hall in Tirol, Austria
| | | | - Simon T Schäfer
- Department of Anaesthesiology, Ludwig-Maximilians-University Munich, Munich, Germany
- Department of Anesthesia, Intensive Care Medicine, Emergency Medicine and Pain Therapy, University Hospital, Carl-von-Ossietzky University Oldenburg, Klinikum Oldenburg AöR, Oldenburg, Germany
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Gatterer H, Roche J, Turner R, Vinetti G, Roveri G, Schlittler M, Kob M, Walzl A, Dal Cappello T, Debevec T, Siebenmann C. Changes in body mass, appetite-related hormones, and appetite sensation in women during 4 days of hypobaric hypoxic exposure equivalent to 3,500-m altitude. J Appl Physiol (1985) 2023; 134:133-141. [PMID: 36476162 PMCID: PMC9829471 DOI: 10.1152/japplphysiol.00369.2022] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Altitude exposure may suppress appetite and hence provide a viable weight-loss strategy. While changes in food intake and availability as well as physical activity may contribute to altered appetite at altitude, herein we aimed to investigate the isolated effects of hypobaric hypoxia on appetite regulation and sensation. Twelve healthy women (age: 24.0 ± 4.2 years, body mass: 60.6 ± 7.0 kg) completed two 4-day sojourns in a hypobaric chamber, one in normoxia [PB = 761 mmHg, 262 m (NX)] and one in hypobaric hypoxia [PB = 493 mmHg (HH)] equivalent to 3,500-m altitude. Energy intake was standardized 4 days prior and throughout both sojourns. Plasma concentrations of leptin, acylated ghrelin, cholecystokinin (CCK), and cytokine growth differentiation factor 15 (GDF15) were determined every morning. Before and after breakfast, lunch, and dinner, appetite was assessed using visual analog scales. Body mass was significantly decreased following HH but not NX (-0.71 ± 0.32 kg vs. -0.05 ± 0.54 kg, condition: P < 0.001). Compared to NX, acylated ghrelin decreased throughout the HH sojourn (condition × time: P = 0.020), while leptin was higher throughout the entire HH sojourn (condition: P < 0.001). No differences were observed in CCK and GDF15 between the sojourns. Feelings of satiety and fullness were higher (condition: P < 0.001 and P = 0.013, respectively), whereas prospective food consumption was lower in HH than in NX (condition: P < 0.001). Our findings suggest that hypoxia exerts an anorexigenic effect on appetite-regulating hormones, suppresses subjective appetite sensation, and can induce weight loss in young healthy women. Among the investigated hormones, acylated ghrelin and leptin most likely explain the observed HH-induced appetite suppression.NEW & NOTEWORTHY This study investigated the effects of hypoxia on appetite regulation in women while strictly controlling for diet, physical activity, menstrual cycle, and environmental conditions. In young women, 4 days of altitude exposure (3,500 m) decreases body weight and circulating acylated ghrelin levels while preserving leptin concentrations. In line with the hormonal changes, altitude exposure induces alterations in appetite sensation, consisting of a decreased feeling of hunger and prospective food intake and an increased feeling of fullness and satiety.
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Affiliation(s)
- Hannes Gatterer
- 1Institute of Mountain Emergency Medicine, Eurac Research, Bolzano, Italy,2Institute for Sports Medicine, Alpine Medicine and Health Tourism (ISAG), UMIT TIROL–Private University for Health Sciences and Health Technology, Hall in Tirol, Austria
| | - Johanna Roche
- 1Institute of Mountain Emergency Medicine, Eurac Research, Bolzano, Italy
| | - Rachel Turner
- 1Institute of Mountain Emergency Medicine, Eurac Research, Bolzano, Italy
| | - Giovanni Vinetti
- 1Institute of Mountain Emergency Medicine, Eurac Research, Bolzano, Italy
| | - Giulia Roveri
- 1Institute of Mountain Emergency Medicine, Eurac Research, Bolzano, Italy,3Department of Pathophysiology and Transplantation, University of Milan, Milan, Italy
| | - Maja Schlittler
- 1Institute of Mountain Emergency Medicine, Eurac Research, Bolzano, Italy
| | - Michael Kob
- 4Division of Clinical Nutrition, Bolzano Regional Hospital, Bolzano, Italy
| | - Anna Walzl
- 5Department of Anaesthesiology, University Hospital, LMU Munich, Munich, Germany
| | - Tomas Dal Cappello
- 1Institute of Mountain Emergency Medicine, Eurac Research, Bolzano, Italy
| | - Tadej Debevec
- 6Faculty of Sport, University of Ljubljana, Ljubljana, Slovenia,7Department of Automation, Biocybernetics, and Robotics, Jožef Stefan Institute, Ljubljana, Slovenia
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