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Seidler RD, Stern C, Basner M, Stahn AC, Wuyts FL, zu Eulenburg P. Future research directions to identify risks and mitigation strategies for neurostructural, ocular, and behavioral changes induced by human spaceflight: A NASA-ESA expert group consensus report. Front Neural Circuits 2022; 16:876789. [PMID: 35991346 PMCID: PMC9387435 DOI: 10.3389/fncir.2022.876789] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2022] [Accepted: 06/27/2022] [Indexed: 11/13/2022] Open
Abstract
A team of experts on the effects of the spaceflight environment on the brain and eye (SANS: Spaceflight-Associated Neuro-ocular Syndrome) was convened by NASA and ESA to (1) review spaceflight-associated structural and functional changes of the human brain and eye, and any interactions between the two; and (2) identify critical future research directions in this area to help characterize the risk and identify possible countermeasures and strategies to mitigate the spaceflight-induced brain and eye alterations. The experts identified 14 critical future research directions that would substantially advance our knowledge of the effects of spending prolonged periods of time in the spaceflight environment on SANS, as well as brain structure and function. They used a paired comparison approach to rank the relative importance of these 14 recommendations, which are discussed in detail in the main report and are summarized briefly below.
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Affiliation(s)
- Rachael D. Seidler
- Department of Applied Physiology & Kinesiology, Health and Human Performance, University of Florida, Gainesville, FL, United States
| | - Claudia Stern
- Department of Clinical Aerospace Medicine, German Aerospace Center (DLR) and ISS Operations and Astronauts Group, European Astronaut Centre, European Space Agency (ESA), Cologne, Germany
- *Correspondence: Claudia Stern,
| | - Mathias Basner
- Department of Psychiatry, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, United States
| | - Alexander C. Stahn
- Department of Psychiatry, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, United States
| | - Floris L. Wuyts
- Department of Physics, University of Antwerp, Antwerp, Belgium
- Laboratory for Equilibrium Investigations and Aerospace (LEIA), Antwerp, Belgium
| | - Peter zu Eulenburg
- German Vertigo and Balance Center, University Hospital, Ludwig-Maximilians-Universität München (LMU), Munich, Germany
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Nosikova I, Riabova A, Amirova L, Kitov V, Tomilovskaya E. NAIAD-2020: Characteristics of Motor Evoked Potentials After 3-Day Exposure to Dry Immersion in Women. Front Hum Neurosci 2021; 15:753259. [PMID: 34924980 PMCID: PMC8671694 DOI: 10.3389/fnhum.2021.753259] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2021] [Accepted: 11/15/2021] [Indexed: 11/13/2022] Open
Abstract
As female astronauts participate in space flight more and more frequently, there is a demand for research on how the female body adapts to the microgravity environment. In particular, there is very little research on how the neuromuscular system reacts to gravitational unloading in women. We aimed to estimate changes in motor evoked potentials (MEPs) in the lower leg muscles in women after 3-day exposure to Dry Immersion (DI), which is one of the most widely used ground models of microgravity. Six healthy female volunteers (mean age 30.17 ± 5.5 years) with a natural menstrual cycle participated in this experiment. MEPs were recorded from the gastrocnemius and soleus muscles twice before DI, on the day of DI completion, and 3 days after DI, during the recovery period. To evoke motor responses, transcranial and trans-spinal magnetic stimulation was applied. We showed that changes in MEP characteristics after DI exposure were different depending on the stimulation site, but were similar for both muscles. For trans-spinal stimulation, MEP thresholds decreased compared to baseline values, and amplitudes, on the contrary, increased, resembling the phenomenon of hypogravitational hyperreflexia. This finding is in line with data observed in other experiments on both male and female participants. MEPs to transcranial stimulation had an opposing dynamic, which may have resulted from the small group size and large inter-subject variability, or from hormonal fluctuations during the menstrual cycle. Central motor conduction time remained unchanged, suggesting that pyramidal tract conductibility was not affected by DI exposure. More research is needed to explore the underlying mechanisms.
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Harris KM, Petersen LG, Weber T. Reviving lower body negative pressure as a countermeasure to prevent pathological vascular and ocular changes in microgravity. NPJ Microgravity 2020; 6:38. [PMID: 33335101 PMCID: PMC7746725 DOI: 10.1038/s41526-020-00127-3] [Citation(s) in RCA: 20] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2020] [Accepted: 10/30/2020] [Indexed: 02/08/2023] Open
Abstract
Mitigation of spaceflight-related pathologies such as spaceflight-associated neuro-ocular syndrome (SANS) and the recently discovered risk of venous thrombosis must happen before deep space exploration can occur. Lower body negative pressure (LBNP) can simulate gravitational stress during spaceflight that is likely to counteract SANS and venous thrombosis, but the ideal dose and method of delivery have yet to be determined. We undertook a review of current LBNP literature and conducted a gap analysis to determine the steps needed to adapt LBNP for in-flight use. We found that to use LBNP in flight, it must be adapted to long time duration/low pressure use that should be compatible with crew activities. A lack of understanding of the etiology of the pathologies that LBNP can counteract hinders the application of LBNP as a countermeasure during spaceflight. Future research should aim at filling the knowledge gaps outlined in this review.
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Affiliation(s)
- Katie M Harris
- Faculty of Medicine, Memorial University of Newfoundland, St. John's, NL, Canada.
| | - Lonnie G Petersen
- Department of Mechanical and Aerospace Engineering, University of California San Diego, San Diego, CA, USA.,Department of Radiology, University of California San Diego, San Diego, CA, USA.,Department of Biomedical Science, University of Copenhagen, Copenhagen, Denmark
| | - Tobias Weber
- Space Medicine Team (HRE-OM), European Astronaut Centre (EAC), European Space Agency (ESA), Köln, Germany.,KBR GmbH, Köln, Germany
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Sandal PH, Kim D, Fiebig L, Winnard A, Caplan N, Green DA, Weber T. Effectiveness of nutritional countermeasures in microgravity and its ground-based analogues to ameliorate musculoskeletal and cardiopulmonary deconditioning-A Systematic Review. PLoS One 2020; 15:e0234412. [PMID: 32516346 PMCID: PMC7282646 DOI: 10.1371/journal.pone.0234412] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2020] [Accepted: 05/24/2020] [Indexed: 12/13/2022] Open
Abstract
A systematic review was performed to evaluate the effectiveness of nutrition as a standalone countermeasure to ameliorate the physiological adaptations of the musculoskeletal and cardiopulmonary systems associated with prolonged exposure to microgravity. A search strategy was developed to find all astronaut or human space flight bed rest simulation studies that compared individual nutritional countermeasures with non-intervention control groups. This systematic review followed the guidelines of the Cochrane Handbook for Systematic Reviews and tools created by the Aerospace Medicine Systematic Review Group for data extraction, quality assessment of studies and effect size. To ensure adequate reporting this systematic review followed the guidelines of the Preferred Reporting Items for Systematic Review and Meta-Analyses. A structured search was performed to screen for relevant articles. The initial search yielded 4031 studies of which 10 studies were eligible for final inclusion. Overall, the effect of nutritional countermeasure interventions on the investigated outcomes revealed that only one outcome was in favor of the intervention group, whereas six outcomes were in favor of the control group, and 43 outcomes showed no meaningful effect of nutritional countermeasure interventions at all. The main findings of this study were: (1) the heterogeneity of reported outcomes across studies, (2) the inconsistency of the methodology of the included studies (3) an absence of meaningful effects of standalone nutritional countermeasure interventions on musculoskeletal and cardiovascular outcomes, with a tendency towards detrimental effects on specific muscle outcomes associated with power in the lower extremities. This systematic review highlights the limited amount of studies investigating the effect of nutrition as a standalone countermeasure on operationally relevant outcome parameters. Therefore, based on the data available from the included studies in this systematic review, it cannot be expected that nutrition alone will be effective in maintaining musculoskeletal and cardiopulmonary integrity during space flight and bed rest.
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Affiliation(s)
- Peter H. Sandal
- Space Medicine Team, European Astronaut Centre, European Space Agency, Köln, Germany
| | - David Kim
- Space Medicine Team, European Astronaut Centre, European Space Agency, Köln, Germany
- Faculty of Medicine, University of British Columbia, Vancouver, Canada
| | - Leonie Fiebig
- Space Medicine Team, European Astronaut Centre, European Space Agency, Köln, Germany
- Institute of Biomechanics und Orthopaedics, German Sport University, Cologne, Germany
| | - Andrew Winnard
- Faculty of Health and Life Sciences, Northumbria University, Newcastle upon Tyne, United Kingdom
| | - Nick Caplan
- Faculty of Health and Life Sciences, Northumbria University, Newcastle upon Tyne, United Kingdom
| | - David A. Green
- Space Medicine Team, European Astronaut Centre, European Space Agency, Köln, Germany
- Centre of Human & Applied Physiological Sciences, King’s College London, London, United Kingdom
- KBR GmbH, Köln, Germany
| | - Tobias Weber
- Space Medicine Team, European Astronaut Centre, European Space Agency, Köln, Germany
- KBR GmbH, Köln, Germany
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Ogoh S, Hirasawa A, de Abreu S, Denise P, Normand H. Internal carotid, external carotid and vertebral artery blood flow responses to 3 days of head-out dry immersion. Exp Physiol 2017; 102:1278-1287. [DOI: 10.1113/ep086507] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2017] [Accepted: 07/18/2017] [Indexed: 01/23/2023]
Affiliation(s)
- Shigehiko Ogoh
- Department of Biomedical Engineering; Toyo University; Kawagoe-Shi Saitama Japan
| | - Ai Hirasawa
- Faculty of Health Science, Department of Health and Welfare; Kyorin University; Mitaka-shi Tokyo Japan
| | - Steven de Abreu
- Normandie University, Unicaen; Inserm Comete; Chu Caen France
| | - Pierre Denise
- Normandie University, Unicaen; Inserm Comete; Chu Caen France
| | - Hervé Normand
- Normandie University, Unicaen; Inserm Comete; Chu Caen France
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Habazettl H, Stahn A, Nitsche A, Nordine M, Pries AR, Gunga HC, Opatz O. Microvascular responses to (hyper-)gravitational stress by short-arm human centrifuge: arteriolar vasoconstriction and venous pooling. Eur J Appl Physiol 2015; 116:57-65. [PMID: 26280651 DOI: 10.1007/s00421-015-3241-6] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2014] [Accepted: 08/08/2015] [Indexed: 10/23/2022]
Abstract
PURPOSE We hypothesized that lower body microvessels are particularly challenged during exposure to gravity and hypergravity leading to failure of resistance vessels to withstand excessive transmural pressure during hypergravitation and gravitation-dependent microvascular blood pooling. METHODS Using a short-arm human centrifuge (SAHC), 12 subjects were exposed to +1Gz, +2Gz and +1Gz, all at foot level, for 4 min each. Laser Doppler imaging and near-infrared spectroscopy were used to measure skin perfusion and tissue haemoglobin concentrations, respectively. RESULTS Pretibial skin perfusion decreased by 19% during +1Gz and remained at this level during +2Gz. In the dilated area, skin perfusion increased by 24 and 35% during +1Gz and +2Gz, respectively. In the upper arm, oxygenated haemoglobin (Hb) decreased, while deoxy Hb increased with little change in total Hb. In the calf muscle, O2Hb and deoxy Hb increased, resulting in total Hb increase by 7.5 ± 1.4 and 26.6 ± 2.6 µmol/L at +1Gz and +2Gz, respectively. The dynamics of Hb increase suggests a fast and a slow component. CONCLUSION Despite transmural pressures well beyond the upper myogenic control limit, intact lower body resistance vessels withstand these pressures up to +2Gz, suggesting that myogenic control may contribute only little to increased vascular resistance. The fast component of increasing total Hb indicates microvascular blood pooling contributing to soft tissue capacitance. Future research will have to address possible alterations of these acute adaptations to gravity after deconditioning by exposure to micro-g.
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Affiliation(s)
- H Habazettl
- Institute of Physiology, Charité-University Medicine Berlin, Charitéplatz 1, 10117, Berlin, Germany. .,German Heart Institute Berlin, Berlin, Germany. .,Center for Space Medicine Berlin, Berlin, Germany.
| | - Alexander Stahn
- Institute of Physiology, Charité-University Medicine Berlin, Charitéplatz 1, 10117, Berlin, Germany.,Center for Space Medicine Berlin, Berlin, Germany
| | - Andrea Nitsche
- Institute of Aerospace Medicine, German Aerospace Center, Cologne, Germany
| | - Michael Nordine
- Institute of Physiology, Charité-University Medicine Berlin, Charitéplatz 1, 10117, Berlin, Germany.,Center for Space Medicine Berlin, Berlin, Germany
| | - A R Pries
- Institute of Physiology, Charité-University Medicine Berlin, Charitéplatz 1, 10117, Berlin, Germany.,Center for Cardiovascular Research, Charité-University Medicine Berlin, Berlin, Germany
| | - H-C Gunga
- Institute of Physiology, Charité-University Medicine Berlin, Charitéplatz 1, 10117, Berlin, Germany.,Center for Space Medicine Berlin, Berlin, Germany
| | - O Opatz
- Institute of Physiology, Charité-University Medicine Berlin, Charitéplatz 1, 10117, Berlin, Germany.,Center for Space Medicine Berlin, Berlin, Germany
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Adami A, Pizzinelli P, Bringard A, Capelli C, Malacarne M, Lucini D, Simunič B, Pišot R, Ferretti G. Cardiovascular re-adjustments and baroreflex response during clinical reambulation procedure at the end of 35-day bed rest in humans. Appl Physiol Nutr Metab 2013; 38:673-80. [DOI: 10.1139/apnm-2012-0396] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
During the reambulation procedure after 35-day head-down tilt bed rest (HDTBR) for 9 men, we recorded for the first time heart rate (HR; with electrocardiogram) and arterial pressure profiles (fingertip plethysmography) for 5 min in HDTBR and horizontal (SUP) positions, followed by 12 min in standing position, during which 4 subjects fainted (intolerant, INT) and were laid horizontal again (Recovery). We computed: mean arterial pressure (P¯; pressure profiles integral mean), stroke volume (SV; obtained with Modelflow method), and cardiac output (Q̇; SV × HR). All cardiovascular data remained stable in HDTBR and SUP for both groups (EXP). Taking the upright posture, EXP showed a decrease in SV and an increase in HR, becoming significantly different from SUP within 1 min. Further evolution of these parameters kept Q̇ stable in both groups until the second minute of standing. Afterward, in INT, P̄ precipitated without further HR increases: SV stopped being corrected and Q̇ reached 2.9 ± 0.4 L·min−1 at the last 15 s of standing. Sudden drop in P̄ allowed identification of a low-pressure threshold in INT (70.7 ± 12.9 mm Hg), after which syncope occurred within 80 s. During Recovery, baroreflex curves showed a flat phase (P̄ increase, HR stable), followed by a steep phase (P̄ increased, HR decreased, starting when P̄ was 84.5 ± 12.5 mm Hg and Q̇ was 9.6 ± 1.5 L·min−1). INT, in contrast with tolerant subjects, did not sustain standing because HR was unable to correct for the P̄ drop. These results indicate a major role for impaired arterial baroreflexes in the onset of orthostatic intolerance.
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Affiliation(s)
- Alessandra Adami
- Département de Neuroscience Fondamentales, Centre Médical Universitaire, Université de Genève, 1 Rue Michel Servet, CH-1211 Genève 4, Switzerland
| | - Paolo Pizzinelli
- Dipartimento di Scienze Cliniche, Ospedale L. Sacco, Università di Milano, via GB. Grassi 74, Milano, Italia
| | - Aurélien Bringard
- Département de Neuroscience Fondamentales, Centre Médical Universitaire, Université de Genève, 1 Rue Michel Servet, CH-1211 Genève 4, Switzerland
| | - Carlo Capelli
- Dipartimento di Scienze Neurologiche, Neuropsicologiche, Morfologiche e Motorie, Facoltà di Scienze Motorie, Università di Verona, via F. Casorati, 54, 37100 Verona, Italia
| | - Mara Malacarne
- Dipartimento di Scienze Cliniche, Ospedale L. Sacco, Università di Milano, via GB. Grassi 74, Milano, Italia
| | - Daniela Lucini
- Dipartimento di Scienze Cliniche, Ospedale L. Sacco, Università di Milano, via GB. Grassi 74, Milano, Italia
| | - Boštjan Simunič
- Institute of Kinesiology Research, Science and Research Center, University of Primorska, Koper, Garibaldijeva street 1, 6000 Koper, Slovenia
| | - Rado Pišot
- Institute of Kinesiology Research, Science and Research Center, University of Primorska, Koper, Garibaldijeva street 1, 6000 Koper, Slovenia
| | - Guido Ferretti
- Département de Neuroscience Fondamentales, Centre Médical Universitaire, Université de Genève, 1 Rue Michel Servet, CH-1211 Genève 4, Switzerland
- Dipartimento di Scienze Biomediche e Biotecnologie, Facoltà di Medicina, Università di Brescia, Viale Europa 11, 25123 Brescia, Italia
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Yuan M, Coupé M, Bai Y, Gauquelin-Koch G, Jiang S, Aubry P, Wan Y, Custaud MA, Li Y, Arbeille P. Peripheral arterial and venous response to tilt test after a 60-day bedrest with and without countermeasures (ES-IBREP). PLoS One 2012; 7:e32854. [PMID: 22412933 PMCID: PMC3296756 DOI: 10.1371/journal.pone.0032854] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2011] [Accepted: 01/31/2012] [Indexed: 12/03/2022] Open
Abstract
We quantified the impact of 60-day head-down bed rest (HDBR) with countermeasures on arterial and venous response to tilt. Methods: Twenty-one males: 7 control (Con), 7 resistive vibration exercise (RVE) and 7 Chinese herb (Herb) were assessed. Subjects were identified as finisher (F) or non-finishers (NF) at the post-HDBR 20-min tilt test. The cerebral (MCA), femoral (FEM) arterial flow velocity and leg vascular resistance (FRI), the portal vein section (PV), the flow redistribution ratios (MCA/FEM; MCA/PV), the tibial (Tib), gastrocnemius (Gast), and saphenous (Saph) vein sections were measured by echography and Doppler ultrasonography. Arterial and venous parameters were measured at 3-min pre-tilt in the supine position, and at 1 min before the end of the tilt. Results: At post-HDBR tilt, MCA decreased more compared with pre-HDBR tilt in the Con, RVE, and Herb groups, the MCA/FEM tended to decrease in the Con and Herb groups (not significant) but remained stable in the RVE gr. FRI dropped in the Con gr, but remained stable in the Herb gr and increased in the RVE gr. PV decreased less in the Con and Herb groups but remained unchanged in the RVE gr. MCA/PV decreased in the Con and Herb groups, but increased to a similar extent in the RVE gr. Gast section significantly increased more in the Con gr only, whereas Tib section increased more in the Con and Herb groups but not in the RVE gr. The percent change in Saph section was similar at pre- and post-HDBR tilt. Conclusion: In the Con gr, vasoconstriction was reduced in leg and splanchnic areas. RVE and Herb contributed to prevent the loss of vasoconstriction in both areas, but the effect of RVE was higher. RVE and Herb contributed to limit Gast distension whereas only RVE had a protective effect on the Tib.
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Affiliation(s)
- Ming Yuan
- State Key Laboratory of Space Medicine Fundamentals and Application, China Astronaut Research and Training Center, Beijing, China
| | - Mickael Coupé
- Unité Mixte de Recherche, Centre National de la Recherche Scientifique, Institut National de la Santé et de la Recherche Médicale, Faculté de Médecine d'Angers, Angers, France
| | - Yanqiang Bai
- State Key Laboratory of Space Medicine Fundamentals and Application, China Astronaut Research and Training Center, Beijing, China
| | | | - Shizhong Jiang
- State Key Laboratory of Space Medicine Fundamentals and Application, China Astronaut Research and Training Center, Beijing, China
| | | | - Yumin Wan
- State Key Laboratory of Space Medicine Fundamentals and Application, China Astronaut Research and Training Center, Beijing, China
| | - Marc-Antoine Custaud
- Unité Mixte de Recherche, Centre National de la Recherche Scientifique, Institut National de la Santé et de la Recherche Médicale, Faculté de Médecine d'Angers, Angers, France
| | - Yinghui Li
- State Key Laboratory of Space Medicine Fundamentals and Application, China Astronaut Research and Training Center, Beijing, China
- * E-mail: (PA); (YL)
| | - Philippe Arbeille
- UMPS-CERCOM Médecine Physiologie spatiale, Universite-Hôpital Trousseau, Tours, France
- * E-mail: (PA); (YL)
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Artificial gravity with ergometric exercise preserves the cardiac, but not cerebrovascular, functions during 4days of head-down bed rest. Cytokine 2011; 56:648-55. [DOI: 10.1016/j.cyto.2011.09.004] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2011] [Revised: 07/19/2011] [Accepted: 09/02/2011] [Indexed: 11/20/2022]
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Temporal artery flow response during the last minute of a head up tilt test, in relation with orthostatic intolerance after a 60 day head-down bedrest. PLoS One 2011; 6:e22963. [PMID: 22073117 PMCID: PMC3202520 DOI: 10.1371/journal.pone.0022963] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2011] [Accepted: 07/03/2011] [Indexed: 11/24/2022] Open
Abstract
Objective Check if the Temporal flow response to Tilt could provide early hemodynamic pattern in the minutes preceding a syncope during the Tilt test performed after a 60-d head down bedrest (HDBR). Method Twenty-one men divided into 3 groups [Control (Con), Resistive Vibration (RVE) and Chinese Herb (Herb)] underwent a 60 day HDBR. Pre and Post HDBR a 20 min Tilt identified Finishers (F) and Non Finishers (NF). Cerebral (MCA), Temporal (TEMP), Femoral (FEM) flow velocity, were measured by Doppler during the Tilt. Blood pressure (BP) was measured by arm cuff and cardiopress. Results and Discussion Four of the 21 subjects were NF at the post HDBR Tilt test (Con gr:2, RVE gr: 1, Herb gr: 1). At 1 min and 10 s before end of Tilt in NF gr, FEM flow decreased less and MCA decreased more at post HDBR Tilt compared to pre (p<0.05), while in the F gr they changed similarly as pre. In NF gr: TEMP flow decreased more at post HDBR Tilt compared to pre, but only at 10 s before the end of Tilt (P<0.05). During the last 10 s a negative TEMP diastolic component appeared which induced a drop in mean velocity until Tilt arrest. Conclusion The sudden drop in TEMP flow with onset of a negative diastolic flow preceding the decrease in MCA flow confirm that the TEMP vascular resistance respond more directly than the cerebral one to the cardiac output redistribution and that this response occur several seconds before syncope.
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