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Thoolen SJJ, Kuypers MI. External Hemorrhage Control Techniques for Human Space Exploration: Lessons from the Battlefield. Wilderness Environ Med 2023; 34:231-242. [PMID: 36906432 DOI: 10.1016/j.wem.2023.01.006] [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: 08/23/2022] [Revised: 01/11/2023] [Accepted: 01/12/2023] [Indexed: 03/11/2023]
Abstract
The past few decades of military experience have brought major advances in the prehospital care of patients with trauma. A focus on early hemorrhage control with aggressive use of tourniquets and hemostatic gauze is now generally accepted. This narrative literature review aims to discuss external hemorrhage control and the applicability of military concepts in space exploration. In space, environmental hazards, spacesuit removal, and limited crew training could cause significant time delays in providing initial trauma care. Cardiovascular and hematological adaptations to the microgravity environment are likely to reduce the ability to compensate, and resources for advanced resuscitation are limited. Any unscheduled emergency evacuation requires a patient to don a spacesuit, involves exposure to high G-forces upon re-entry into Earth's atmosphere, and costs a significant amount of time until a definitive care facility is reached. As a result, early hemorrhage control in space is critical. Safe implementation of hemostatic dressings and tourniquets seems feasible, but adequate training will be essential, and tourniquets are preferably converted to other methods of hemostasis in case of a prolonged medical evacuation. Other emerging approaches such as early tranexamic acid administration and more advanced techniques have shown promising results as well. For future exploration missions to the Moon and Mars, when evacuation is not possible, we look into what training or assistance tools would be helpful in managing the bleed at the point of injury.
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Affiliation(s)
- Stijn J J Thoolen
- Neural Systems Group, Massachusetts General Hospital, Harvard Medical School, Charlestown, MA; Centre for Human and Applied Physiological Sciences, King's College London, United Kingdom.
| | - Maybritt I Kuypers
- European Astronaut Centre, European Space Agency, Cologne, Germany; Department of Emergency Medicine, Amsterdam UMC, University of Amsterdam, the Netherlands
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Norsk P. Adaptation of the cardiovascular system to weightlessness: Surprises, paradoxes and implications for deep space missions. Acta Physiol (Oxf) 2020; 228:e13434. [PMID: 31872965 DOI: 10.1111/apha.13434] [Citation(s) in RCA: 48] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2019] [Revised: 12/18/2019] [Accepted: 12/18/2019] [Indexed: 01/02/2023]
Abstract
Weightlessness in space induces a fluid shift from the dependent to the cephalad parts of the body leading to distension of the cardiac chambers and an accumulation of blood in the veins of the head and neck. Surprisingly, central venous pressure (CVP) during the initial hours of spaceflight decreases compared to being horizontal supine on the ground. The explanation is that the thorax is expanded by weightlessness leading to a decrease in inter-pleural pressure (IPP), which exceeds the measured decrease in CVP. Thus, transmural CVP (TCVP = CVP - IPP) is increased indicating an augmented cardiac preload. Simultaneously, stroke volume and cardiac output (CO) are increased by 18%-26% within the initial weeks and more so by 35%-56% during the subsequent months of flight relative to in the upright posture on the ground. Mean arterial pressure (MAP) is decreased indicating a lower systemic vascular resistance (MAP/CO). It is therefore a surprise that sympathetic nerve activity is not suppressed in space and thus cannot be a mechanism for the systemic vasodilation, which still needs to be explored. Recent observations indicate that the fluid shift during long duration (months) flights is associated with increased retinal thickness that sometimes leads to optical disc oedema. Ocular and cerebral structural changes, increases in left atrial size and decreased flows with thrombi formation in the left internal jugular vein have also been observed. This is of concern for future long duration deep space missions because the health implications are unknown.
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Affiliation(s)
- Peter Norsk
- Center for Space Medicine & Department of Molecular Physiology and Biophysics Baylor College of Medicine Houston TX USA
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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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4
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Blood pressure regulation IV: adaptive responses to weightlessness. Eur J Appl Physiol 2014; 114:481-97. [PMID: 24390686 DOI: 10.1007/s00421-013-2797-2] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2013] [Accepted: 12/11/2013] [Indexed: 10/25/2022]
Abstract
During weightlessness, blood and fluids are immediately shifted from the lower to the upper body segments, and within the initial 2 weeks of spaceflight, brachial diastolic arterial pressure is reduced by 5 mmHg and even more so by some 10 mmHg from the first to the sixth month of flight. Blood pressure thus adapts in space to a level very similar to that of being supine on the ground. At the same time, stroke volume and cardiac output are increased and systemic vascular resistance decreased, whereas sympathetic nerve activity is kept surprisingly high and similar to when ground-based upright seated. This was not predicted from simulation models and indicates that dilatation of the arteriolar resistance vessels is caused by mechanisms other than a baroreflex-induced decrease in sympathetic nervous activity. Results of baroreflex studies in space indicate that compared to being ground-based supine, the carotid (vagal)-cardiac interaction is reduced and sympathetic nerve activity, heart rate and systemic vascular resistance response more pronounced during baroreflex inhibition by lower body negative pressure. The future challenge is to identify which spaceflight mechanism induces peripheral arteriolar dilatation, which could explain the decrease in blood pressure, the high sympathetic nerve activity and associated cardiovascular changes. It is also a challenge to determine the cardiovascular risk profile of astronauts during future long-duration deep space missions.
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Allison AL, Peres JC, Boettger C, Leonbacher U, Hastings PD, Shirtcliff EA. Fight, flight, or fall: Autonomic nervous system reactivity during skydiving. PERSONALITY AND INDIVIDUAL DIFFERENCES 2012. [DOI: 10.1016/j.paid.2012.03.019] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Norsk P, Christensen NJ. The paradox of systemic vasodilatation and sympathetic nervous stimulation in space. Respir Physiol Neurobiol 2009; 169 Suppl 1:S26-9. [DOI: 10.1016/j.resp.2009.07.020] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2009] [Revised: 07/24/2009] [Accepted: 07/25/2009] [Indexed: 10/20/2022]
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Graebe A, Schuck EL, Lensing P, Putcha L, Derendorf H. Physiological, pharmacokinetic, and pharmacodynamic changes in space. J Clin Pharmacol 2005; 44:837-53. [PMID: 15286087 DOI: 10.1177/0091270004267193] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Medications have been taken since the first Mercury flight in 1967 and, since then, have been used for several indications such as space motion sickness, sleeplessness, headache, nausea, vomiting, back pain, and congestion. As the duration of space missions get longer, it is even more likely that astronauts will encounter some of the acute illnesses that are frequently seen on Earth. Microgravity environment induces several physiological changes in the human body. These changes include cardiovascular degeneration, bone decalcification, decreased plasma volume, blood flow, lymphocyte and eosinophil levels, altered hormonal and electrolyte levels, muscle atrophy, decreased blood cell mass, increased immunoglobulin A and M levels, and a decrease in the amount of microsomal P-450 and the activity of some of its dependent enzymes. These changes may be expected to have severe implications on the pharmacokinetic and pharmacodynamic properties of drug substances.
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Affiliation(s)
- Annemarie Graebe
- Department of Pharmacy Practice and Administration, Ernest Mario School of Pharmacy, Rutgers, State University of New Jersey, USA
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8
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Xu K, Davis KL, Sytkowski AJ. Measurement of hemoglobin in long-term fixed erythroid cells: application development for cell science experiments in microgravity. METHODS IN CELL SCIENCE : AN OFFICIAL JOURNAL OF THE SOCIETY FOR IN VITRO BIOLOGY 2005; 25:247-52. [PMID: 15801171 DOI: 10.1007/s11022-004-2381-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Abstract
Studying the effects of microgravity on cell differentiation will enhance our understanding of fundamental biology and is indispensable for a sustained space program. Rauscher murine erythroleukemic cells were chosen as a model system to study erythroid cell differentiation aboard the International Space Station because these cells undergo differentiation in response to the natural inducer, erythropoietin, as well as various chemical-inducers. We have now developed a method to quantify hemoglobin in Rauscher cells after weeks of fixation and storage required for such space biology experiments. By exploiting the pseudoperoxidase activity of hemoglobin and by using reagents that yield a soluble chromophore that freely passes out of fixed cells, we developed a highly specific and sensitive assay applicable to cells fixed as long as 4 months.
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Affiliation(s)
- Kun Xu
- Laboratory for Cellular and Molecular Biology, Division of Hematology and Oncology, Beth Israel Deaconess Medical Center, Department of Medicine, Harvard Medical School, Boston, Massachusetts 02215, USA
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Kirkpatrick AW, Campbell MR, Jones JA, Broderick TJ, Ball CG, McBeth PB, McSwain NE, Hamilton DR, Holcomb JB. Extraterrestrial hemorrhage control: Terrestrial developments in technique, technology, and philosophy with applicability to traumatic hemorrhage control in long-duration spaceflight. J Am Coll Surg 2005; 200:64-76. [PMID: 15631922 DOI: 10.1016/j.jamcollsurg.2004.08.028] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2004] [Accepted: 08/27/2004] [Indexed: 12/27/2022]
Affiliation(s)
- Andrew W Kirkpatrick
- Departments of Critical Care Medicine and Surgery, and Calgary Brain Institute, Foothills Medical Centre, 1403 29th Street NW, Calgary, Alberta T2N 2T9, Canada.
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Powers J, Bernstein D. The mouse as a model of cardiovascular adaptations to microgravity. J Appl Physiol (1985) 2004; 97:1686-92. [PMID: 15258130 DOI: 10.1152/japplphysiol.00925.2003] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
There are a multitude of physiological adaptations to microgravity, involving the cardiovascular, neuromuscular, and neuroendocrine systems. Some of these adaptations lead to cardiovascular deconditioning on return to normal gravity, posing a threat to human functional integrity after long-term spaceflight. Animal models of microgravity, e.g., tail suspension in rats, have yielded important information regarding the mechanism of these adaptations and have been useful in the design of countermeasures. The mouse could potentially be a useful experimental model, given its small size (smaller and lighter payload) and the powerful tools of experimental mouse genetics, which allow us to dissect mechanisms on a gene-specific basis. We show that the mouse demonstrates a wide range of cardiovascular responses to simulated microgravity, including alterations in heart rate, exercise capacity, peripheral arterial vasodilatory responsiveness, and baroreflex response. These responses are qualitatively similar to many of those demonstrated in humans during spaceflight and in rats using tail suspension, although there are some important differences. Thus the mouse has value as a model for studies of cardiovascular changes during microgravity; however, investigators must maintain an appreciation of important species differences.
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Affiliation(s)
- Jennifer Powers
- Division of Pediatric Cardiology, Department of Pediatrics, Stanford University, 750 Welch Rd., Suite 305, Palo Alto, CA 94304, USA
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Migeotte PF, Prisk GK, Paiva M. Microgravity alters respiratory sinus arrhythmia and short-term heart rate variability in humans. Am J Physiol Heart Circ Physiol 2003; 284:H1995-2006. [PMID: 12560205 DOI: 10.1152/ajpheart.00409.2002] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We studied heart rate (HR), heart rate variability (HRV), and respiratory sinus arrhythmia (RSA) in four male subjects before, during, and after 16 days of spaceflight. The electrocardiogram and respiration were recorded during two periods of 4 min controlled breathing at 7.5 and 15 breaths/min in standing and supine postures on the ground and in microgravity. Low (LF)- and high (HF)-frequency components of the short-term HRV (< or =3 min) were computed through Fourier spectral analysis of the R-R intervals. Early in microgravity, HR was decreased compared with both standing and supine positions and had returned to the supine value by the end of the flight. In microgravity, overall variability, the LF-to-HF ratio, and RSA amplitude and phase were similar to preflight supine values. Immediately postflight, HR increased by approximately 15% and remained elevated 15 days after landing. LF/HF was increased, suggesting an increased sympathetic control of HR standing. The overall variability and RSA amplitude in supine decreased postflight, suggesting that vagal tone decreased, which coupled with the decrease in RSA phase shift suggests that this was the result of an adaptation of autonomic control of HR to microgravity. In addition, these alterations persisted for at least 15 days after return to normal gravity (1G).
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Affiliation(s)
- P-F Migeotte
- Biomedical Physics Laboratory, Université Libre de Bruxelles, Belgium.
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12
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Naschitz JE, Sabo E, Naschitz S, Rosner I, Rozenbaum M, Fields M, Isseroff H, Priselac RM, Gaitini L, Eldar S, Zukerman E, Yeshurun D, Madelain F, Isseroff H. Hemodynamics instability score in chronic fatigue syndrome and in non-chronic fatigue syndrome. Semin Arthritis Rheum 2002; 32:141-8. [PMID: 12528078 DOI: 10.1053/sarh.2002.34608] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
OBJECTIVE In studying patients with chronic fatigue syndrome (CFS) we developed a method that confers numerical expression to the degree of blood pressure and heart rate lability, ie, the 'hemodynamic instability score' (HIS). The HIS in CFS patients differed significantly from healthy subjects. The present investigation compares the HIS in CFS, non-CFS chronic fatigue and patients with recurrent syncope. METHODS Patients with CFS (n = 21), non-CFS chronic fatigue (n = 24), syncope of unknown cause (n = 44), and their age and sex-matched healthy controls (n = 21) were evaluated with a standardized head-up tilt test (HUTT). Abnormal reactions (endpoints) on HUTT were classified 'clinical outcomes' (cardioinhibitory or vasodepressor reaction, orthostatic hypotension, postural tachycardia syndrome) and 'HIS endpoint', i.e. HIS >-0.98. RESULTS The highest incidence of endpoints was noted in patients with CFS (79%), followed by patients with syncope of unknown cause (46%), non-CFS chronic fatigue (35%), and healthy subjects (14%). Presyncope or syncope during tilt occurred in 38% of CFS patients, 21% of patients with non-CFS chronic fatigue, and 43% of patients with recurrent syncope. The average HIS values were: CFS = +2.02 (SD 4.07), non-CFS chronic fatigue = -2.89 (SD 3.64), syncope = -3.2 (SD 3.0), healthy = -2.48 (4.07). The odds ratios for CFS patients to have HIS >-0.98 was 8.8 compared with non-CFS chronic fatigue patients, 14.6 compared with recurrent syncope patients, and 34.8 compared with healthy subjects. CONCLUSION The cardiovascular reactivity in patients with CFS has certain features in common with the reactivity in patients with recurrent syncope or non-CFS chronic fatigue, such as the frequent occurrence of vasodepressor reaction, cardioinhibitory reaction, and postural tachycardia syndrome. Apart from to these shared responses, the large majority of CFS patients exhibit a particular abnormality which is characterized by HIS values >-0.98. Thus, HIS >-0.98 lends objective criteria to the assessment of CFS.
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Affiliation(s)
- Jochanan E Naschitz
- Departments of Internal Medicine A, Rheumatology, Anesthesiology, and Surgery, Bnai Zion Medical Center and Bruce Rappaport Faculty of Medicine, Technion-Israel Institute of Technology, Haifa, Israel
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Colvin GA, Lambert JF, Carlson JE, McAuliffe CI, Abedi M, Quesenberry PJ. Rhythmicity of engraftment and altered cell cycle kinetics of cytokine-cultured murine marrow in simulated microgravity compared with static cultures. In Vitro Cell Dev Biol Anim 2002; 38:343-51. [PMID: 12513122 DOI: 10.1290/1071-2690(2002)038<0343:roeaac>2.0.co;2] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Space flight with associated microgravity is complicated by "astronaut's anemia" and other hematologic abnormalities. Altered erythroid differentiation, red cell survival, plasma volume, and progenitor numbers have been reported. We studied the impact of microgravity on engraftable stem cells, culturing marrow cells in rotary wall vessel (RWV) culture chambers mimicking microgravity and in normal gravity nonadherent Teflon bottles. A quantitative competitive engraftment technique was assessed under both conditions in lethally irradiated hosts. We assessed 8-wk engraftable stem cells over a period spanning at least one cell cycle for cytokine (FLT-3 ligand, thrombopoietin [TPO], steel factor)-activated marrow stem cells. Engraftable stem cells were supported out to 56 h under microgravity conditions, and this support was superior to that seen in normal-gravity Teflon bottle cultures out to 40 h, with Teflon bottle culture support superior to RWV from 40 to 56 h. A nadir of stem cell number was seen at 40 h in Teflon and 48 h in RWV, suggesting altered marrow stem cell cycle kinetics under microgravity. This is the first study of engraftable stem cells under microgravity conditions, and the differences between microgravity and normal gravity cultures may present opportunities for unique future stem cell expansion strategies.
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Affiliation(s)
- Gerald A Colvin
- University of Massachusetts Cancer Center, Worcester, MA 01655, USA
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Wang SS, Good TA. Effect of culture in a rotating wall bioreactor on the physiology of differentiated neuron-like PC12 and SH-SY5Y cells. J Cell Biochem 2002; 83:574-84. [PMID: 11746501 DOI: 10.1002/jcb.1252] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
A variety of evidence suggests that nervous system function is altered during microgravity, however, assessing changes in neuronal physiology during space flight is a non-trivial task. We have used a rotating wall bioreactor with a high aspect ratio vessel (HARV), which simulates the microgravity environment, to investigate the how the viability, neurite extension, and signaling of differentiated neuron-like cells changes in different culture environments. We show that culture of differentiated PC12 and SH-SY5Y cells in the simulated microgravity HARV bioreactor resulted in high cell viability, moderate neurite extension, and cell aggregation accompanied by NO production. Neurite extension was less than that seen in static cultures, suggesting that less than optimal differentiation occurs in simulated microgravity relative to normal gravity. Cells grown in a mixed vessel under normal gravity (a spinner flask) had low viability, low neurite extension, and high glutamate release. This work demonstrates the feasibility of using a rotating wall bioreactor to explore the effects of simulated microgravity on differentiation and physiology of neuron-like cells.
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Affiliation(s)
- S S Wang
- Department of Chemical Engineering, Texas A&M University, College Station, TX 77843-3122, USA
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Levine BD, Pawelczyk JA, Ertl AC, Cox JF, Zuckerman JH, Diedrich A, Biaggioni I, Ray CA, Smith ML, Iwase S, Saito M, Sugiyama Y, Mano T, Zhang R, Iwasaki K, Lane LD, Buckey JC, Cooke WH, Baisch FJ, Eckberg DL, Blomqvist CG. Human muscle sympathetic neural and haemodynamic responses to tilt following spaceflight. J Physiol 2002; 538:331-40. [PMID: 11773340 PMCID: PMC2290017 DOI: 10.1113/jphysiol.2001.012575] [Citation(s) in RCA: 123] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2001] [Accepted: 09/12/2001] [Indexed: 11/08/2022] Open
Abstract
Orthostatic intolerance is common when astronauts return to Earth: after brief spaceflight, up to two-thirds are unable to remain standing for 10 min. Previous research suggests that susceptible individuals are unable to increase their systemic vascular resistance and plasma noradrenaline concentrations above pre-flight upright levels. In this study, we tested the hypothesis that adaptation to the microgravity of space impairs sympathetic neural responses to upright posture on Earth. We studied six astronauts approximately 72 and 23 days before and on landing day after the 16 day Neurolab space shuttle mission. We measured heart rate, arterial pressure and cardiac output, and calculated stroke volume and total peripheral resistance, during supine rest and 10 min of 60 deg upright tilt. Muscle sympathetic nerve activity was recorded in five subjects, as a direct measure of sympathetic nervous system responses. As in previous studies, mean (+/- S.E.M.) stroke volume was lower (46 +/- 5 vs. 76 +/- 3 ml, P = 0.017) and heart rate was higher (93 +/- 1 vs. 74 +/- 4 beats min(-1), P = 0.002) during tilt after spaceflight than before spaceflight. Total peripheral resistance during tilt post flight was higher in some, but not all astronauts (1674 +/- 256 vs. 1372 +/- 62 dynes s cm(-5), P = 0.32). No crew member exhibited orthostatic hypotension or presyncopal symptoms during the 10 min of postflight tilting. Muscle sympathetic nerve activity was higher post flight in all subjects, in supine (27 +/- 4 vs. 17 +/- 2 bursts min(-1), P = 0.04) and tilted (46 +/- 4 vs. 38 +/- 3 bursts min(-1), P = 0.01) positions. A strong (r(2) = 0.91-1.00) linear correlation between left ventricular stroke volume and muscle sympathetic nerve activity suggested that sympathetic responses were appropriate for the haemodynamic challenge of upright tilt and were unaffected by spaceflight. We conclude that after 16 days of spaceflight, muscle sympathetic nerve responses to upright tilt are normal.
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Affiliation(s)
- Benjamin D Levine
- Institute for Exercise and Environmental Medicine, Presbyterian Hospital of Dallas and the University of Texas Southwestern Medical Center at Dallas, Dallas, TX 75231, USA.
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Ertl AC, Diedrich A, Biaggioni I, Levine BD, Robertson RM, Cox JF, Zuckerman JH, Pawelczyk JA, Ray CA, Buckey JC, Lane LD, Shiavi R, Gaffney FA, Costa F, Holt C, Blomqvist CG, Eckberg DL, Baisch FJ, Robertson D. Human muscle sympathetic nerve activity and plasma noradrenaline kinetics in space. J Physiol 2002; 538:321-9. [PMID: 11773339 PMCID: PMC2290013 DOI: 10.1113/jphysiol.2001.012576] [Citation(s) in RCA: 94] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Astronauts returning from space have reduced red blood cell masses, hypovolaemia and orthostatic intolerance, marked by greater cardio-acceleration during standing than before spaceflight, and in some, orthostatic hypotension and presyncope. Adaptation of the sympathetic nervous system occurring during spaceflight may be responsible for these postflight alterations. We tested the hypotheses that exposure to microgravity reduces sympathetic neural outflow and impairs sympathetic neural responses to orthostatic stress. We measured heart rate, photoplethysmographic finger arterial pressure, peroneal nerve muscle sympathetic activity and plasma noradrenaline spillover and clearance, in male astronauts before, during (flight day 12 or 13) and after the 16 day Neurolab space shuttle mission. Measurements were made during supine rest and orthostatic stress, as simulated on Earth and in space by 7 min periods of 15 and 30 mmHg lower body suction. Mean (+/- S.E.M.) heart rates before lower body suction were similar pre-flight and in flight. Heart rate responses to -30 mmHg were greater in flight (from 56 +/- 4 to 72 +/- 4 beats min(-1)) than pre-flight (from 56 +/- 4 at rest to 62 +/- 4 beats min(-1), P < 0.05). Noradrenaline spillover and clearance were increased from pre-flight levels during baseline periods and during lower body suction, both in flight (n = 3) and on post-flight days 1 or 2 (n = 5, P < 0.05). In-flight baseline sympathetic nerve activity was increased above pre-flight levels (by 10-33 %) in the same three subjects in whom noradrenaline spillover and clearance were increased. The sympathetic response to 30 mmHg lower body suction was at pre-flight levels or higher in each subject (35 pre-flight vs. 40 bursts min(-1) in flight). No astronaut experienced presyncope during lower body suction in space (or during upright tilt following the Neurolab mission). We conclude that in space, baseline sympathetic neural outflow is increased moderately and sympathetic responses to lower body suction are exaggerated. Therefore, notwithstanding hypovolaemia, astronauts respond normally to simulated orthostatic stress and are able to maintain their arterial pressures at normal levels.
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Affiliation(s)
- Andrew C Ertl
- Vanderbilt University Medical Center, Nashville, TN, USA
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Goldstein DS, Eisenhofer G. Sympathetic Nervous System Physiology and Pathophysiology in Coping with the Environment. Compr Physiol 2001. [DOI: 10.1002/cphy.cp070402] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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Naschitz JE, Sabo E, Naschitz S, Shaviv N, Rosner I, Rozenbaum M, Gaitini L, Ahdoot A, Ahdoot M, Priselac RM, Eldar S, Zukerman E, Yeshurun D. Hemodynamic instability in chronic fatigue syndrome: indices and diagnostic significance. Semin Arthritis Rheum 2001; 31:199-208. [PMID: 11740800 DOI: 10.1053/sarh.2001.27738] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
OBJECTIVES To evaluate the cardiovascular response to postural challenge in patients with chronic fatigue syndrome (CFS) and to determine whether the degree of instability of the cardiovascular response may aid in diagnosing CFS. METHODS Patients with CFS (n = 25) and their age- and gender-matched healthy controls (n = 37), patients with fibromyalgia (n = 30), generalized anxiety disorder (n = 15), and essential hypertension (n = 20) were evaluated with the aid of a standardized tilt test. The blood pressure (BP) and heart rate (HR) were recorded during 10 minutes of recumbence and 30 minutes of head-up tilt. We designated BP changes as the differences between successive BP values and the last recumbent BP. The average and standard deviation (SD) were calculated. Time curves of BP differences were loaded into a computerized image analyzer, and their outline ratios and fractal dimensions were measured. HR changes were determined similarly. The average and SD of the parameters were calculated, and intergroup comparisons were performed. RESULTS On multivariate analysis, the independent predictors of CFS patients versus healthy controls were the fractal dimension of absolute values of the systolic BP changes (SYST-FD.abs), the standard deviation of the current values of the systolic BP changes (SYST-SD.cur), and the standard deviation of the current values of the heart rate changes (HR-SD.cur). The following equation was deduced to calculate the hemodynamic instability score (HIS) in the individual patient: HIS = 64.3303 + (SYST-FD.abs x -68.0135) + (SYST-SD.cur x 111.3726) + (HR-SD.cur x 60.4164). The best cutoff differentiating CFS from the healthy controls was -0.98. HIS values >-0.98 were associated with CFS (sensitivity 97%, specificity 97%). The HIS differed significantly between CFS and other groups (P <.0001) except for generalized anxiety disorder. Group averages (SD) of HIS were CFS = +3.72 (5.02), healthy = -4.62 (2.26), fibromyalgia = -3.27 (2.63), hypertension = -5.53 (2.24), and generalized anxiety disorder = +1.08 (5.2). CONCLUSION The HIS adds objective criteria confirming the diagnosis of CFS.
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Affiliation(s)
- J E Naschitz
- Department of Internal Medicine A, Bnai Zion Medical Center and Bruce Rappaport Faculty of Medicine, Technion-Israel Institute of Technology, Haifa, Israel
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Abstract
According to a classic hypothesis, weightlessness should promote the renal excretion rate of sodium and water and lead to a fluid- and electrolyte-depleted state. This hypothesis is based on experiments in which weightlessness has been simulated in humans by head-down bed rest and water immersion. However, after 5 to 6 days of space mission, the diuretic and natriuretic responses to an intravenous isotonic saline load were attenuated and plasma norepinephrine and renin concentrations increased compared with those of the acute supine position before flight. Renal fluid excretion after an oral water load was also attenuated in space. Similar decreases were not observed during head-down bed rest. Sympathetic activity is of major importance in regulating blood volume and renal function. Studies in space have indicated that, compared with that while in a supine position on Earth, sympathoadrenal activity is increased during space flights as measured using plasma concentration and urinary excretion of norepinephrine and epinephrine. The space-induced activation of antinatriuretic mechanisms and sympathoadrenal activity could have been caused by early in-flight reduction in total and central blood volume. The decreased plasma volume may be explained by such factors as redistribution of plasma from the lower to the upper body (thin legs and puffy face), reduced food intake, and decreased muscle activity. The decrease in plasma volume and the subsequent increase in sympathetic activity is due, at least in part, to the abrupt cessation of activity in large muscle groups during microgravity, which normally counteracts the effects of gravity in the upright posture. This would lead to accumulation of albumin and fluid in the interstitial space.
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Affiliation(s)
- N J Christensen
- Division of Endocrinology, Herlev Hospital, University of Copenhagen, Copenhagen, Denmark
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20
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Pawelczyk JA, Zuckerman JH, Blomqvist CG, Levine BD. Regulation of muscle sympathetic nerve activity after bed rest deconditioning. Am J Physiol Heart Circ Physiol 2001; 280:H2230-9. [PMID: 11299226 DOI: 10.1152/ajpheart.2001.280.5.h2230] [Citation(s) in RCA: 72] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Cardiovascular deconditioning reduces orthostatic tolerance. To determine whether changes in autonomic function might produce this effect, we developed stimulus-response curves relating limb vascular resistance, muscle sympathetic nerve activity (MSNA), and pulmonary capillary wedge pressure (PCWP) with seven subjects before and after 18 days of -6 degrees head-down bed rest. Both lower body negative pressure (LBNP; -15 and -30 mmHg) and rapid saline infusion (15 and 30 ml/kg body wt) were used to produce a wide variation in PCWP. Orthostatic tolerance was assessed with graded LBNP to presyncope. Bed rest reduced LBNP tolerance from 23.9 +/- 2.1 to 21.2 +/- 1.5 min, respectively (means +/- SE, P = 0.02). The MSNA-PCWP relationship was unchanged after bed rest, though at any stage of the LBNP protocol PCWP was lower, and MSNA was greater. Thus bed rest deconditioning produced hypovolemia, causing a shift in operating point on the stimulus-response curve. The relationship between limb vascular resistance and MSNA was not significantly altered after bed rest. We conclude that bed rest deconditioning does not alter reflex control of MSNA, but may produce orthostatic intolerance through a combination of hypovolemia and cardiac atrophy.
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Affiliation(s)
- J A Pawelczyk
- Noll Physiological Research Center, The Pennsylvania State University, University Park, Pennsylvania 16802, USA.
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21
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Fortrat JO, Sigaudo D, Hughson RL, Maillet A, Yamamoto Y, Gharib C. Effect of prolonged head-down bed rest on complex cardiovascular dynamics. Auton Neurosci 2001; 86:192-201. [PMID: 11270097 DOI: 10.1016/s1566-0702(00)00212-5] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
We postulated that a change in complex dynamics of the cardiovascular system could be involved in the orthostatic intolerance observed after simulated weightlessness. Supine recordings of 1024 consecutive pulse intervals and systolic blood pressures were obtained on 7 subjects adapted to a 42 day head-down bed rest (day 22 and 42) but also before and 6 days after head-down bed rest (-6 degrees). Coarse graining spectral analysis was used to extract the non-harmonic (fractal) component from each time series. The power spectral densities of this fractal component are inversely proportional to their frequency (1/f beta). We fitted an inverse power law estimate to the fractal component to determine the spectral exponent beta. The complex dynamics of blood pressure and heart rate variability were also analyzed by correlation dimension and non-linear prediction. Bed rest induced orthostatic intolerance in 4 subjects. There was a significant increase in the spectral exponent beta of RR-interval variability during and after head-down bed rest (before: 1.039 +/- 0.090; during: 1.552 +/- 0.080 and 1.547 +/- 0.100; after: 1.428 +/- 0.040). Analysis of the blood pressure dynamics indicated lower correlation dimensions during head-down bed rest and higher coefficients of predictability after head-down bed rest. Complexity alterations of RR-interval and blood pressure variability were not linked with one another during head-down bed rest. These alterations seemed to be correlated with the orthostatic intolerance observed after bed rest. These results suggest a change of the integration level of cardiovascular autonomic regulation.
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Affiliation(s)
- J O Fortrat
- Faculté de Médecine Grange-Blanche, Laboratoire de Physiologie de l'Environnement, 8, Avenue Rockefeller, 69373 Lyon, France.
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22
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Kirkpatrick AW, Dulchavsky SA, Boulanger BR, Campbell MR, Hamilton DR, Dawson DL, Williams DR. Extraterrestrial resuscitation of hemorrhagic shock: fluids. THE JOURNAL OF TRAUMA 2001; 50:162-8. [PMID: 11231691 DOI: 10.1097/00005373-200101000-00036] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Affiliation(s)
- A W Kirkpatrick
- Vancouver Hospital & Health Sciences Centre, 3rd Floor, 855 W. 10th Avenue, Vancouver, British Columbia, Canada V5Z 1L7.
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Redman DA. Ruscus aculeatus (butcher's broom) as a potential treatment for orthostatic hypotension, with a case report. J Altern Complement Med 2000; 6:539-49. [PMID: 11152059 DOI: 10.1089/acm.2000.6.539] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
CONTEXT Chronic orthostatic hypotension (OH) is frequently a severely debilitating disease that affects large groups of the population with autonomic insufficiency--the elderly; patients with diabetes, Parkinson's disease, and chronic fatigue syndrome; and anyone on drugs that affect the autonomic nervous system. Unfortunately, even though more than 60 medications are currently being used to treat OH, none of them is particularly or consistently effective. Ruscus aculeatus, a phytotherapeutic agent that is well known in Europe, may, however, change this. Its vasoconstrictive and venotonic properties make it ideally suited to treat the pooling of blood in the limbs, lack of venous tone, and lack of neurally mediated vasoconstriction that frequently characterize OH. Although it has never been suggested as a treatment for OH, it already has a long, proven record of use in Europe for treating a variety of circulatory disorders. OBJECTIVE To provide evidence for what appears to be an effective, safe, inexpensive botanical therapy for OH and encourage further studies on the efficacy of Ruscus for OH patients. DESIGN Review of OH and therapies currently available for OH and evaluation of the properties of Ruscus aculeatus, its mechanism of action, and its suitability as a therapeutic agent for treatment of OH. RESULTS A review of the many pharmacologic and nonpharmacologic agents for treating OH reveals that all of the drug therapies are disappointing and marginally useful. Although nonpharmacologic management is preferred, in the many cases in which OH becomes debilitating, pharmacologic intervention becomes a last resort. But drug therapy may not always be necessary, because Ruscus aculeatus, a phytotherapeutic agent containing ruscogenins and flavonoids, may prove useful for the treatment of OH if denervation is not so advanced that it has compromised receptor activity at the venous wall. Ruscus aculeatus is an alpha-adrenergic agonist that causes venous constriction by directly activating postjunctional alpha1- and alpha2-receptors, in turn stimulating the release of noradrenaline at the level of the vascular wall. It also possesses venotonic properties: it reduces venous capacity and pooling of blood in the legs and exerts protective effects on capillaries, the vascular endothelium, and smooth muscle. Its flavonoid content strengthens blood vessels, reduces capillary fragility, and helps maintain healthy circulation. Unlike most of the drug therapies used to treat OH, Ruscus aculeatus does not cause supine hypertension. It also appears to do something no other therapy can offer--alleviate the worsening effects of OH in environmentally hot conditions. Finally, it is an extremely safe, inexpensive, over-the-counter botanical medicine. CONCLUSION With proven phlebotherapeutic properties, including vasoconstrictive action and venotonic properties, Ruscus aculeatus shows great promise for ameliorating the symptoms of OH and improving the quality of life for large groups in the population. It clearly deserves to be the object of wider research and study as a treatment for OH.
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Affiliation(s)
- D A Redman
- American University, Washington, DC, USA
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24
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Abstract
Urine output in astronauts following ingestion of an oral water load was low in space on the Russian space station Mir and less than during simulation by 6 degrees head-down bed rest. This surprising observation shows that the effects of gravity and weightlessness on fluid volume regulation are not well understood and that the head-down bed-rest model does not simulate the effects of weightlessness on renal water handling.
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MILLET CATHERINE, CUSTAUD MARCANTOINE, ALLEVARD ANNEMARIE, GHARIB CLAUDE, GAUQUELIN-KOCH GUILLEMETTE, FORTRAT JACQUESOLIVIER. Adaptations to a 7-day head-down bed rest with thigh cuffs. Med Sci Sports Exerc 2000. [DOI: 10.109710.1097/00005768-200010000-00014] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/01/2022]
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Custaud MA, Millet C, Frutoso J, Maillet A, Gauquelin G, Gharib C, Fortrat JO. No effect of venoconstrictive thigh cuffs on orthostatic hypotension induced by head-down bed rest. ACTA PHYSIOLOGICA SCANDINAVICA 2000; 170:77-85. [PMID: 11114945 DOI: 10.1046/j.1365-201x.2000.00763.x] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Orthostatic intolerance (OI) is the most serious symptom of cardiovascular deconditioning induced by head-down bed rest or weightlessness. Wearing venoconstrictive thigh cuffs is an empirical countermeasure used by Russian cosmonauts to limit the shift of fluid from the lower part of the body to the cardio-cephalic region. Our aim was to determine whether or not thigh cuffs help to prevent orthostatic hypotension induced by head-down bed rest. We studied the effect of thigh cuffs on eight healthy men. The cuffs were worn during the day for 7 days of head-down bed rest. We measured: orthostatic tolerance (stand tests and lower body negative pressure tests), plasma volume (Evans blue dilution), autonomic influences (plasma noradrenaline) and baroreflex sensitivity (spontaneous baroreflex slope). Thigh cuffs limited the loss of plasma volume (thigh cuffs: -201 +/- 37 mL vs. control: -345 +/- 42 mL, P < 0.05), the degree of tachycardia and reduction in the spontaneous baroreflex sensitivity induced by head-down bed rest. However, the impact of thigh cuffs was not sufficient to prevent OI (thigh cuffs: 7.0 min of standing time vs. control: 7.1 min). Decrease in absolute plasma volume and in baroreflex sensitivity are known to be important factors in the aetiology of OI induced by head-down bed rest. However, dealing with these factors, using thigh cuffs for example, is not sufficient to prevent OI. Other factors such as venous compliance, microcirculatory changes, peripheral arterial vasoconstriction and vestibular afferents must also be considered.
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Affiliation(s)
- M A Custaud
- Laboratoire de Physiologie de l'Environnement, Faculté de Médecine Lyon Grange-Blanche, 8 avenue Rockefeller, 69373 Lyon CEDEX 08, France
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27
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Millet C, Custaud MA, Allevard AM, Gharib C, Gauquelin-Koch G, Fortrat JO. Adaptations to a 7-day head-down bed rest with thigh cuffs. Med Sci Sports Exerc 2000; 32:1748-56. [PMID: 11039648 DOI: 10.1097/00005768-200010000-00014] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
PURPOSE Thigh cuffs were two elastic strips fixed at the upper part of each thigh, which limits the shift of fluid from the legs into the cardio-thoracic region. The purpose of this study was to examine the effects of thigh cuffs on hormonal and plasma volume responses and orthostatic tolerance during a 7-day head-down bed rest (HDBR). METHODS Orthostatic tolerance, plasma volume, total body water, blood volume-regulating hormones, and hydro-electrolyte responses were measured in eight healthy men (age range, 25-40 yr), using thigh cuffs 10 h daily during 7 d of -6 degrees HDBR. RESULTS Thigh cuffs worn during HDBR attenuated the decrease in plasma volume observed after HDBR (thigh cuffs: -5.85 +/- 0.95% vs control: -9.09 +/- 0.82%, P < or = 0.05). During this experiment, there was no significant change in total body water. Thus, the hypovolemia did not result from a loss of water but from a fluid shift from the blood compartment into the interstitial and/or intracellular compartment. Hormonal responses during HDBR and stand test were not modified by the thigh cuffs. Thigh cuffs had no significant effect on the clinical symptoms of orthostatic intolerance after HDBR. CONCLUSIONS Thigh cuffs worn during HDBR blunted the decrease in plasma volume but did not reduce orthostatic intolerance; thus, they are not a completely effective countermeasure. Furthermore, hypovolemia seems to be necessary but not sufficient to induce orthostatic intolerance after HDBR.
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Affiliation(s)
- C Millet
- Laboratoire de Physiologie de L'Environnement, Faculté de Médecine Lyon Grange-Blanche, France.
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28
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Naschitz JE, Rosner I, Rozenbaum M, Gaitini L, Bistritzki I, Zuckerman E, Sabo E, Yeshurun D. The capnography head-up tilt test for evaluation of chronic fatigue syndrome. Semin Arthritis Rheum 2000; 30:79-86. [PMID: 11071579 DOI: 10.1053/sarh.2000.9201] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
OBJECTIVES To compare the hemodynamic and ventilatory responses to autonomic challenge evoked by upright tilt table testing in patients with chronic fatigue syndrome (CFS) to healthy individuals. METHODS Thirty-two consecutive patients with CFS and 32 healthy volunteers were evaluated with the aid of the recently introduced capnography head-up tilt test (CHUTT). The main outcome measures were values of blood pressure (BP), heart rate (HR), respiratory rate (RR), and end-tidal pressure of co2 (ETPco2) recorded during recumbence and tilt. In addition, the end points of vasodepressor and cardioinhibitory reactions, hyperventilation (defined by ETPco2 <25 mm Hg) and the postural tachycardia syndrome, were recorded. RESULTS The BP, HR, RR, and ETPco2 recorded during recumbence were similar in both groups. During tilt, patients with CFS developed significantly lower systolic BP, diastolic BP, and ETPco2, and a significant rise in HR and RR (P<.01). In CFS patients, the postural tachycardia syndrome occurred in 44%, vasodepressor reaction in 41%, cardioinhibitory reaction in 13%, and hyperventilation in 31% of cases. One or more end points of the CHUTT were reached in 78% of patients with CFS but in none of the controls (P<.0001). CONCLUSIONS In most patients with CFS, a spectrum of abnormal homeostatic reactions is diagnosed with the aid of the CHUTT. Data provided by the CHUTT may reinforce the clinical diagnosis by adding objective and unbiased criteria to the subjective assessment of CFS.
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Affiliation(s)
- J E Naschitz
- Department of Internal Medicine A, Bnai Zion Medical Center and Bruce Rappaport Faculty of Medicine, Technion-Israel Institute of Technology, Haifa, Israel
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29
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Kamiya A, Iwase S, Michikami D, Fu Q, Mano T. Head-down bed rest alters sympathetic and cardiovascular responses to mental stress. Am J Physiol Regul Integr Comp Physiol 2000; 279:R440-7. [PMID: 10938230 DOI: 10.1152/ajpregu.2000.279.2.r440] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Astronauts usually work under much mental stress. However, it is unclear how and whether or not an exposure to microgravity affects physiological response to mental stress in humans. To examine effects of microgravity on vasomotor sympathetic and peripheral vasodilator responses to mental stress, we performed 10 min of mental arithmetic (MA) before and after 14 days of 6 degrees head-down bed rest (HDBR), a ground-based simulation of spaceflight. Total muscle sympathetic nerve activity (MSNA, measured by microneurography) slightly increased during MA before HDBR, and this increase was augmented after HDBR. Calf blood flow (measured by venous occlusion plethysmography) increased and calf vascular resistance (calculated by dividing mean blood pressure by calf blood flow) decreased during MA before HDBR, but these responses were abolished after HDBR. Increases in heart rate and mean blood pressure during MA were not different between before and after HDBR. These findings suggest that HDBR augmented vasomotor sympathoexcitation but attenuated vasodilatation in the calf muscle in response to mental stress.
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Affiliation(s)
- A Kamiya
- Department of Autonomic Neuroscience, Research Institute of Environmental Medicine, Nagoya University, Nagoya, Japan.
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30
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Iwase S, Sugiyama Y, Miwa C, Kamiya A, Mano T, Ohira Y, Shenkman B, Egorov AI, Kozlovskaya IB. Effects of three days of dry immersion on muscle sympathetic nerve activity and arterial blood pressure in humans. JOURNAL OF THE AUTONOMIC NERVOUS SYSTEM 2000; 79:156-64. [PMID: 10699647 DOI: 10.1016/s0165-1838(99)00076-4] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The present study was performed to determine how sympathetic function is altered by simulated microgravity, dry immersion for 3 days, and to elucidate the mechanism of post-spaceflight orthostatic intolerance in humans. Six healthy men aged 21-36 years old participated in the study. Before and after the dry immersion, subjects performed head-up tilt (HUT) test to 30 degrees and 60 degrees (5 min each) with recordings of muscle sympathetic nerve activity (MSNA, by microneurography), electrocardiogram, and arterial blood pressure (Finapres). Resting MSNA was increased after dry immersion from 23.7+/-3.2 to 40.9+/-3.0 bursts/min (p<0.005) without significant changes in resting heart rate (HR). MSNA responsiveness to orthostasis showed no significant difference but HR response was significantly augmented after dry immersion (p<0. 005). A significant diastolic blood pressure fall at 5th min of 60 degrees HUT was observed in five orthostatic tolerant subjects despite enough MSNA discharge after dry immersion. A subject suffered from presyncope at 2 min after 60 degrees HUT. He showed gradual blood pressure fall 10 s after 60 degrees HUT with initially well-maintained MSNA response and then with a gradually attenuated MSNA, followed by a sudden MSNA withdrawal and abrupt blood pressure drop. In conclusion, dry immersion increased MSNA without changing MSNA response to orthostasis, and resting HR, while increasing the HR response to orthostasis. Analyses of MSNA and blood pressure changes in orthostatic tolerant subjects and a subject with presyncope suggested that not only insufficient vasoconstriction to sympathetic stimuli, but also a central mechanism to induce a sympathetic withdrawal might play a role in the development of orthostatic intolerance after microgravity exposure.
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Affiliation(s)
- S Iwase
- Department of Autonomic Neuroscience, Research Institute of Environmental Medicine, Nagoya University, Furo-cho, Chiksa-ku, Nagoya, Japan.
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31
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Socci RR, Wang M, Thierry-Palmer M, Emmett N, Bayorh MA. Cardiovascular responses to simulated microgravity in Sprague-Dawley rats. Clin Exp Hypertens 2000; 22:155-64. [PMID: 10744356 DOI: 10.1081/ceh-100100069] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
Microgravity is known to induce orthostatic intolerance and baroreflex impairment in astronauts. Cardiovascular responses observed in 30 degrees head-down tilt rat models, whether 24 hr whole body suspension (WBS) or 7 day tail-suspension (TS), mimic observations made during exposure to microgravity. We evaluated the cardiovascular effects of simulated microgravity and the subsequent post-suspension in rats using the above models. Mean arterial pressure (MAP) of both WBS and TS rats did not change during suspension. In both models, MAP decreased post-suspension and this response lasted for 6 hrs. Salt-loaded animals did not show a post-suspension reduction in MAP. Plasma ionized calcium was decreased at 2 hr of WBS, with no change in sodium, potassium, magnesium, glucose, or hematocrit. Body weight changes were similar for all animals whether under suspension or control conditions. Both rat models demonstrate post-suspension hypotension and these results support the notion that salt-loading may have some beneficial effects in ameliorating this hypotension.
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Affiliation(s)
- R R Socci
- Department of Pharmacology/Toxicology, Morehouse School of Medicine, Atlanta, GA 30310-1495, USA
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Arbeille P, Herault S, Fomina G, Roumy J, Alferova I, Gharib C. Influences of thigh cuffs on the cardiovascular system during 7-day head-down bed rest. J Appl Physiol (1985) 1999. [DOI: 10.115210.1152/jappl.1999.87.6.2168] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022] Open
Abstract
Thigh cuffs, presently named “bracelets,” consist of two straps fixed to the upper part of each thigh, applying a pressure of 30 mmHg. The objective was to evaluate the cardiac, arterial, and venous changes in a group of subjects in head-down tilt (HDT) for 7 days by using thigh cuffs during the daytime, and in a control group not using cuffs. The cardiovascular parameters were measured by echography and Doppler. Seven days in HDT reduced stroke volume in both groups (−10%; P < 0.05). Lower limb vascular resistance decreased more in the cuff group than in the control group (−29 vs. −4%; P < 0.05). Cerebral resistance increased in the control group only (+6%; P < 0.05). The jugular vein increased (+45%; P < 0.05) and femoral and popliteal veins decreased in cross-sectional area in both groups (−45 and −8%, respectively; P < 0.05). Carotid diameter tended to decrease (−5%; not significant) in both groups. Heart rate, blood pressure, cardiac output, and total resistance did not change significantly. After 8 h with thigh cuffs, the cardiac and arterial parameters had recovered their pre-HDT level except for blood pressure (+6%; P < 0.05). Jugular vein size decreased from the pre-HDT level (−21%; P < 0.05), and femoral and popliteal vein size increased (+110 and +136%, respectively; P < 0.05). The thigh cuffs had no effect on the development of orthostatic intolerance during the 7 days in HDT.
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Affiliation(s)
- P. Arbeille
- Unité Médecine et Physiologie Spatiale, Departement de Médecine Nucléaire et Ultrasons, Centres Hospitaliers Universitaires Trousseau, 37044 Tours, France
| | - S. Herault
- Unité Médecine et Physiologie Spatiale, Departement de Médecine Nucléaire et Ultrasons, Centres Hospitaliers Universitaires Trousseau, 37044 Tours, France
| | - G. Fomina
- Institute of Biomedical Problems, 123007 Moscow, Russia; and
| | - J. Roumy
- Unité Médecine et Physiologie Spatiale, Departement de Médecine Nucléaire et Ultrasons, Centres Hospitaliers Universitaires Trousseau, 37044 Tours, France
| | - I. Alferova
- Institute of Biomedical Problems, 123007 Moscow, Russia; and
| | - C. Gharib
- Laboratoire Physiologie de l'Environnement, Faculté de Médecine Grange Blanche, 69373 Lyon, France
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Arbeille P, Herault S, Fomina G, Roumy J, Alferova I, Gharib C. Influences of thigh cuffs on the cardiovascular system during 7-day head-down bed rest. J Appl Physiol (1985) 1999; 87:2168-76. [PMID: 10601164 DOI: 10.1152/jappl.1999.87.6.2168] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Thigh cuffs, presently named "bracelets," consist of two straps fixed to the upper part of each thigh, applying a pressure of 30 mmHg. The objective was to evaluate the cardiac, arterial, and venous changes in a group of subjects in head-down tilt (HDT) for 7 days by using thigh cuffs during the daytime, and in a control group not using cuffs. The cardiovascular parameters were measured by echography and Doppler. Seven days in HDT reduced stroke volume in both groups (-10%; P < 0.05). Lower limb vascular resistance decreased more in the cuff group than in the control group (-29 vs. -4%; P < 0.05). Cerebral resistance increased in the control group only (+6%; P < 0.05). The jugular vein increased (+45%; P < 0.05) and femoral and popliteal veins decreased in cross-sectional area in both groups (-45 and -8%, respectively; P < 0.05). Carotid diameter tended to decrease (-5%; not significant) in both groups. Heart rate, blood pressure, cardiac output, and total resistance did not change significantly. After 8 h with thigh cuffs, the cardiac and arterial parameters had recovered their pre-HDT level except for blood pressure (+6%; P < 0.05). Jugular vein size decreased from the pre-HDT level (-21%; P < 0.05), and femoral and popliteal vein size increased (+110 and +136%, respectively; P < 0.05). The thigh cuffs had no effect on the development of orthostatic intolerance during the 7 days in HDT.
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Affiliation(s)
- P Arbeille
- Unité Médecine et Physiologie Spatiale, Departement de Médecine Nucléaire et Ultrasons, Centres Hospitaliers Universitaires Trousseau, 37044 Tours, France.
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Barbe P, Galitzky J, Thalamas C, Langin D, Lafontan M, Senard JM, Berlan M. Increase in epinephrine-induced responsiveness during microgravity simulated by head-down bed rest in humans. J Appl Physiol (1985) 1999; 87:1614-20. [PMID: 10562599 DOI: 10.1152/jappl.1999.87.5.1614] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The epinephrine (Epi)-induced effects on the sympathetic nervous system (SNS) and metabolic functions were studied in men before and during a decrease in SNS activity achieved through simulated microgravity. Epi was infused at 3 graded rates (0.01, 0.02, and 0. 03 microg. kg(-1). min(-1) for 40 min each) before and on the fifth day of head-down bed rest (HDBR). The effects of Epi on the SNS (assessed by plasma norepinephrine levels and spectral analysis of systolic blood pressure and heart rate variability), on plasma levels of glycerol, nonesterified fatty acids (NEFA), glucose and insulin, and on energy expenditure were evaluated. HDBR decreased urinary norepinephrine excretion (28.1 +/- 4.2 vs. 51.5 +/- 9.1 microg/24 h) and spectral variability of systolic blood pressure in the midfrequency range (16.3 +/- 1.9 vs. 24.5 +/- 0.9 normalized units). Epi increased norepinephrine plasma levels (P < 0.01) and spectral variability of systolic blood pressure (P < 0.009) during, but not before, HDBR. No modification of Epi-induced changes in heart rate and systolic and diastolic blood pressures were observed during HDBR. Epi increased plasma glucose, insulin, and NEFA levels before and during HDBR. During HDBR, the Epi-induced increase in plasma glycerol and lactate levels was more pronounced than before HDBR (P < 0.005 and P < 0.001, respectively). Epi-induced energy expenditure was higher during HDBR (P < 0.02). Our data suggest that the increased effects of Epi during simulated microgravity could be related to both the increased SNS response to Epi infusion and/or to the beta-adrenergic receptor sensitization of end organs, particularly in adipose tissue and skeletal muscle.
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Affiliation(s)
- P Barbe
- Laboratoire de Pharmacologie Médicale et Clinique, Institut National de la Santé et de la Recherche Médicale U-317, 31073 Toulouse Cedex, France
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Shoemaker JK, Hogeman CS, Sinoway LI. Contributions of MSNA and stroke volume to orthostatic intolerance following bed rest. THE AMERICAN JOURNAL OF PHYSIOLOGY 1999; 277:R1084-90. [PMID: 10516248 DOI: 10.1152/ajpregu.1999.277.4.r1084] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We examined whether the altered orthostatic tolerance following 14 days of head-down tilt bed rest (HDBR) was related to inadequate sympathetic outflow or to excessive reductions in cardiac output during a 10- to 15-min head-up tilt (HUT) test. Heart rate, blood pressure (BP, Finapres), muscle sympathetic nerve activity (MSNA, microneurography), and stroke volume blood velocity (SVV, Doppler ultrasound) were assessed during supine 30 degrees (5 min) and 60 degrees (5-10 min) HUT positions in 15 individuals who successfully completed the pre-HDBR test without evidence of orthostatic intolerance. Subjects were classified as being orthostatically tolerant (OT, n = 9) or intolerant (OI, n = 6) following the post-HDBR test. MSNA, BP, and SVV during supine and HUT postures were not altered in the OT group. Hypotension during 60 degrees HUT in the post-bed rest test for the OI group (P < 0.05) was associated with a blunted increase in MSNA (P < 0.05). SVV was reduced following HDBR in the OI group (main effect of HDBR, P < 0.02). The data support the hypothesis that bed rest-induced orthostatic intolerance is related to an inadequate increase in sympathetic discharge that cannot compensate for a greater postural reduction in stroke volume.
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Affiliation(s)
- J K Shoemaker
- Section of Cardiology, Pennsylvania State University College of Medicine, Milton S. Hershey Medical Center, Hershey 17033, Pennsylvania, USA.
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Bouzeghrane F, Somody L, Gallo-Bona N, Gauquelin-Koch G, Gharib C, Fagette S. Effect of a 14-day hindlimb suspension on beta-adrenoreceptors in rats. COMPARATIVE BIOCHEMISTRY AND PHYSIOLOGY. PART C, PHARMACOLOGY, TOXICOLOGY & ENDOCRINOLOGY 1999; 123:95-102. [PMID: 10390061 DOI: 10.1016/s0742-8413(99)00015-8] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Exposure to long-term simulated microgravity exhibits reduced sympathetic nervous system activity. This study tested the hypothesis that the hypersensitivity of adrenoreceptors would explain partly many other features of the hemodynamic consequences of return from space. The biochemical properties of the beta adrenoreceptors (betaAR) were determined using 125I-cyanopindolol (125I-CYP) binding in three rat groups: (1) The first experimental group consisted of 24 h-restrained orthostatic rats in the horizontal position, to test the early effect of the attachment to the suspension device; (2) the second experimental group consisted of 24 h-restrained antiorthostatic rats, to test the early effect of the suspension; (3) the third experimental group consisted of 14 day-restrained antiorthostatic rats, to test the long term effect of the suspension. The study was performed in two organs involved in blood pressure regulation, i.e. the heart (atria and ventricles were separated) and kidneys. The Scatchard analysis of 125I-cyanopindolol binding in both organs indicated no significant alterations in the dissociation constant (Kd) and the maximum binding capacity (Bmax) in the three experimental groups. These results do not allow the conclusion about the SNS adaptation pattern to simulated microgravity. Thus, the hypothesis that betaAR are involved in the cardiovascular adaptation to simulated microgravity is not verified in this model where, as a matter of fact, cardiovascular deconditioning is not verified even if this model is widely used.
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Affiliation(s)
- F Bouzeghrane
- Laboratoire de Neurobiologie, Institut des Sciences de la Nature, Université des Sciences et de la Technologie Houari Boumédiene, Alger, Algeria
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Shoemaker JK, McQuillan PM, Sinoway LI. Upright posture reduces forearm blood flow early in exercise. THE AMERICAN JOURNAL OF PHYSIOLOGY 1999; 276:R1434-42. [PMID: 10233037 DOI: 10.1152/ajpregu.1999.276.5.r1434] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The hypothesis that upright posture could modulate forearm blood flow (FBF) early in exercise was tested in six subjects. Both single (2-s duration) and repeated (1-s work/2-s rest cadence for 12 contractions) handgrip contractions (12 kg) were performed in the supine and 70 degrees head-up tilt (HUT) positions. The arm was maintained at heart level to diminish myogenic effects. Baseline brachial artery diameters were assessed at rest in each position. Brachial artery mean blood velocity (MBV; Doppler) and mean arterial pressure (MAP) (Finapres) were measured continuously to calculate FBF and vascular conductance. MAP was not changed with posture. Antecubital venous pressure (Pv) was reduced in HUT (4.55 +/- 1.3 mmHg) compared with supine (11.3 +/- 1.9 mmHg) (P < 0.01). For the repeated contractions, total excess FBF (TEF) was reduced in the HUT position compared with supine (P < 0.02). With the single contractions, peak FBF, peak vascular conductance, and TEF during 30 s after release of the contraction were reduced in the HUT position compared with supine (P < 0.01). Sympathetic blockade augmented the FBF response to a single contraction in HUT (P < 0.05) and tended to increase this response while supine (P = 0.08). However, sympathetic blockade did not attenuate the effect of HUT on peak FBF and TEF after the single contractions. Raising the arm above heart level while supine, to diminish Pv, resulted in FBF dynamics that were similar to those observed during HUT. Alternatively, lowering the arm while in HUT to restore Pv to supine levels restored the peak FBF and vascular conductance responses, but not TEF response, after a single contraction. It was concluded that upright posture diminishes the hyperemic response early in exercise. The data demonstrate that sympathetic constriction restrains the hyperemic response to a single contraction but does not modulate the postural reduction in postcontraction hyperemia. Therefore, the attenuated blood flow response in the HUT posture was largely related to factors associated with diminished venous pressures and not sympathetic vasoconstriction.
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Affiliation(s)
- J K Shoemaker
- Section of Cardiology, The Pennsylvania State University College of Medicine, The Milton S. Hershey Medical Center, Hershey, Pennsylvania 17033, USA.
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38
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Schondorf R, Freeman R. The Importance of Orthostatic Intolerance in the Chronic Fatigue Syndrome. Am J Med Sci 1999. [DOI: 10.1016/s0002-9629(15)40485-9] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
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Abstract
Chronic fatigue syndrome (CFS) or myalgic encephalomyelitis is a clinically defined syndrome characterized by persistent or relapsing debilitating fatigue for longer than 6 months in the absence of any definable medical diagnosis. The cause of this syndrome is unknown. Symptoms of orthostatic intolerance, such as disabling fatigue, dizziness, diminished concentration, tremulousness, and nausea, are often found in patients with CFS. In this review, we critically evaluate the relationship between orthostatic intolerance and CFS. Particular emphasis is placed on clinical diagnosis, laboratory testing, pathophysiology, and therapeutic management. It is hoped that this review will provide a stimulus for further study of this complex and disabling condition.
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Affiliation(s)
- R Schondorf
- Dept. of Neurology, McGill University, Sir Mortimer B. Davis Jewish General Hospital, Montreal, Quebec, Canada.
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Fortrat JO, Somody L, Gharib C. Autonomic control of cardiovascular dynamics during weightlessness. BRAIN RESEARCH. BRAIN RESEARCH REVIEWS 1998; 28:66-72. [PMID: 9795141 DOI: 10.1016/s0165-0173(98)00027-7] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Measuring cardiovascular dynamics is a new method of assessing the autonomic regulation of the cardiovascular system, it provides an easily-implemented non-invasive way of monitoring the effects of weightlessness on this regulatory function. The major findings of studies on cardiovascular dynamics during actual or simulated weightlessness are presented, taking into account the recent consensus on this approach. Future improvements of these studies are discussed.
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Affiliation(s)
- J O Fortrat
- Laboratoire de Physiologie de l'Environnement, Faculté de Médecine Lyon Grange-Blanche, 8, avenue Rockefeller 69373, Lyon Cedex 08, France.
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Koenig SC, Convertino VA, Fanton JW, Reister CA, Gaffney FA, Ludwig DA, Krotov VP, Trambovetsky EV, Latham RD. Evidence for increased cardiac compliance during exposure to simulated microgravity. THE AMERICAN JOURNAL OF PHYSIOLOGY 1998; 275:R1343-52. [PMID: 9756567 DOI: 10.1152/ajpregu.1998.275.4.r1343] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We measured hemodynamic responses during 4 days of head-down tilt (HDT) and during graded lower body negative pressure (LBNP) in invasively instrumented rhesus monkeys to test the hypotheses that exposure to simulated microgravity increases cardiac compliance and that decreased stroke volume, cardiac output, and orthostatic tolerance are associated with reduced left ventricular peak dP/dt. Six monkeys underwent two 4-day (96 h) experimental conditions separated by 9 days of ambulatory activities in a crossover counterbalance design: 1) continuous exposure to 10 degrees HDT and 2) approximately 12-14 h per day of 80 degrees head-up tilt and 10-12 h supine (control condition). Each animal underwent measurements of central venous pressure (CVP), left ventricular and aortic pressures, stroke volume, esophageal pressure (EsP), plasma volume, alpha1- and beta1-adrenergic responsiveness, and tolerance to LBNP. HDT induced a hypovolemic and hypoadrenergic state with reduced LBNP tolerance compared with the control condition. Decreased LBNP tolerance with HDT was associated with reduced stroke volume, cardiac output, and peak dP/dt. Compared with the control condition, a 34% reduction in CVP (P = 0.010) and no change in left ventricular end-diastolic area during HDT was associated with increased ventricular compliance (P = 0.0053). Increased cardiac compliance could not be explained by reduced intrathoracic pressure since EsP was unaltered by HDT. Our data provide the first direct evidence that increased cardiac compliance was associated with headward fluid shifts similar to those induced by exposure to spaceflight and that reduced orthostatic tolerance was associated with lower cardiac contractility.
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Affiliation(s)
- S C Koenig
- Physiology Research Branch, Clinical Sciences Division, Brooks Air Force Base, Texas 78235, USA
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42
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Sigaudo D, Fortrat JO, Allevard AM, Maillet A, Cottet-Emard JM, Vouillarmet A, Hughson RL, Gauquelin-Koch G, Gharib C. Changes in the sympathetic nervous system induced by 42 days of head-down bed rest. THE AMERICAN JOURNAL OF PHYSIOLOGY 1998; 274:H1875-84. [PMID: 9841515 DOI: 10.1152/ajpheart.1998.274.6.h1875] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Changes in autonomic nervous system activity could be linked to the orthostatic intolerance (OI) that individuals suffer after a spaceflight or head-down bed rest (HDBR). We examined this possibility by assessing the sympathetic nervous system activity during 42 days of HDBR in seven healthy men. Heart rate variability was studied with the use of power spectral analysis, which provided indicators of the sympathetic (SNSi) and parasympathetic (PNSi) nervous system influences on the heart. Urinary catecholamines and the spontaneous baroreflex sensitivity were measured. Urinary catecholamines decreased by 21.3%, showing a decrease in SNSi. Heart rate variability was greatly reduced during 42 days of HDBR with a drop in PNSi but with no significant changes in SNSi. The baroreflex sensitivity was greatly reduced (30.7%) on day 42 of HDBR. These results suggest a dissociation between the catecholamine response and the SNSi of the heart rate. This dissociation could be the consequence of an increase in beta-adrenergic receptor density and/or activity induced by a decrease in catecholamines during HDBR. The subjects who suffered from OI also had a greater sympathetic response and much lower baroreflex sensitivity when supine than those who finished the stand test. However, the mean response of all subjects indicated that the sympathetic activity (catecholamine excretion) was probably slightly inhibited during HDBR and could contribute to OI.
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Affiliation(s)
- D Sigaudo
- Laboratoire de Physiologie de l'Environnement (Groupement d'Interet Public Exercice), Faculte de Medecine Lyon Grange-Blanche, F-69373 Lyon Cedex 08, France
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43
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Shoemaker JK, Hogeman CS, Silber DH, Gray K, Herr M, Sinoway LI. Head-down-tilt bed rest alters forearm vasodilator and vasoconstrictor responses. J Appl Physiol (1985) 1998; 84:1756-62. [PMID: 9572827 DOI: 10.1152/jappl.1998.84.5.1756] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
To test the hypothesis that head-down-tilt bed rest (HDBR) for 14 days alters vascular reactivity to vasodilatory and vasoconstrictor stimuli, the reactive hyperemic forearm blood flow (RHBF, measured by venous occlusion plethysmography) and mean arterial pressure (MAP, measured by Finapres) responses after 10 min of circulatory arrest were measured in a control trial (n = 20) and when sympathetic discharge was increased by a cold pressor test (RHBF + cold pressor test; n = 10). Vascular conductance (VC) was calculated (VC = RHBF/MAP). In the control trial, peak RHBF at 5 s after circulatory arrest (34.1 +/- 2.5 vs. 48.9 +/- 4.3 ml . 100 ml-1 . min-1) and VC (0.34 +/- 0.02 vs. 0.53 +/- 0.05 ml . 100 ml-1 . min-1 . mmHg-1) were reduced in the post- compared with the pre-HDBR tests (P < 0. 05). Total excess RHBF over 3 min was diminished in the post- compared with the pre-HDBR trial (84.8 vs. 117 ml/100 ml, P < 0.002). The ability of the cold pressor test to lower forearm blood flow was less in the post- than in the pre-HDBR test (P < 0.05), despite similar increases in MAP. These data suggest that regulation of vascular dilation and the interaction between dilatory and constrictor influences were altered with bed rest.
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Affiliation(s)
- J K Shoemaker
- Section of Cardiology, The Milton S. Hershey Medical Center, The Pennsylvania State University College of Medicine 17033, USA
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Convertino VA, Ludwig DA, Gray BD, Vernikos J. Effects of exposure to simulated microgravity on neuronal catecholamine release and blood pressure responses to norepinephrine and angiotensin. Clin Auton Res 1998; 8:101-10. [PMID: 9613800 DOI: 10.1007/bf02267820] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
We tested the hypothesis that exposure to microgravity reduces the neuronal release of catecholamines and blood pressure responses to norepinephrine and angiotensin. Eight men underwent 30 days of 6 degrees head-down tilt (HDT) bedrest to simulate exposure to microgravity. Plasma norepinephrine and mean arterial blood pressure (MAP) were measured before and after a cold pressor test (CPT) and graded norepinephrine infusion (8, 16 and 32 ng/kg/min) on day 6 of a baseline control period (C6) and on days 14 and 27 of HDT. MAP and plasma angiotensin II (Ang-II) were measured during graded Ang-II infusion (1, 2 and 4 ng/kg/min) on C8 and days 16 and 29 of HDT. Baseline total circulating norepinephrine was reduced from 1017ng during the baseline control period to 610 ng at day 14 and 673ng at day 27 of HDT, confirming a hypoadrenergic state. An elevation of norepinephrine (+178 ng) to the CPT during the baseline control period was eliminated by HDT days 14 and 27. During norepinephrine infusion, similar elevations in plasma norepinephrine (7.7 pg/ml/ng/kg/min) caused similar elevations in MAP (0.12 mmHg/ng/kg/min) across all test days. Ang-II infusion produced higher levels of plasma Ang-II during HDT (47.3 pg/ml) than during baseline control (35.5 pg/ml), while producing similar corresponding elevations in blood pressure. While vascular responsiveness to norepinephrine appears unaffected, impaired neuronal release of norepinephrine and reduced vascular responsiveness to Ang-II might contribute to the lessened capacity to vasoconstrict after spaceflight. The time course of alterations indicates effects that occur within two weeks of exposure.
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Affiliation(s)
- V A Convertino
- Flight Stress Protection Division, Air Force Research Laboratory, Brooks Air Force Base, Texas 78235-5104, USA
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45
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Shoemaker JK, Hogeman CS, Leuenberger UA, Herr MD, Gray K, Silber DH, Sinoway LI. Sympathetic discharge and vascular resistance after bed rest. J Appl Physiol (1985) 1998; 84:612-7. [PMID: 9475873 DOI: 10.1152/jappl.1998.84.2.612] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
The effect of -6 degrees head-down-tilt bed rest (HDBR) for 14 days on supine sympathetic discharge and cardiovascular hemodynamics at rest was assessed. Mean arterial pressure, heart rate (n = 25), muscle sympathetic nerve activity (MSNA; n = 16) burst frequency, and forearm blood flow (n = 14) were measured, and forearm vascular resistance (FVR) was calculated. Stroke distance, our index of stroke volume, was derived from measurements of aortic mean blood velocity (Doppler) and R-R interval (n = 7). With these data, an index of total peripheral resistance was determined. Heart rate at rest was greater in the post (71 +/- 2 beats/min)- compared with the pre-HDBR test (66 +/- 2 beats/min; P < 0.003), but mean arterial pressure was unchanged. Aortic stroke distance during post-HDBR (15.5 +/- 1.1 cm/beat) was reduced from pre-HDBR levels (20.0 +/- 1.5 cm/beat) (P < 0.03). Also, MSNA burst frequency was reduced in the post (16.7 +/- 2.8 beats/min)- compared with the pre (25.2 +/- 2.6 beats/min)-HDBR condition (P < 0.01). Bed rest did not alter forearm blood flow, FVR, or total peripheral resistance. Thus reductions in MSNA with HDBR were not associated with a decrease in FVR.
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Affiliation(s)
- J K Shoemaker
- Division of Cardiology, Pennsylvania State University College of Medicine, Hershey 17033, USA
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Levine BD, Zuckerman JH, Pawelczyk JA. Cardiac atrophy after bed-rest deconditioning: a nonneural mechanism for orthostatic intolerance. Circulation 1997; 96:517-25. [PMID: 9244220 DOI: 10.1161/01.cir.96.2.517] [Citation(s) in RCA: 240] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
BACKGROUND The cardiovascular adaptation to bed rest leads to orthostatic intolerance, characterized by an excessive fall in stroke volume (SV) in the upright position. We hypothesized that this large fall in SV is due to a change in cardiac mechanics. METHODS AND RESULTS We measured pulmonary capillary wedge pressure (PCWP), SV, left ventricular end-diastolic volume (LVEDV), and left ventricular mass (by echocardiography) at rest, during lower-body negative pressure, and after saline infusion before and after 2 weeks of bed rest with -6 degrees head-down tilt (n=12 subjects aged 24+/-5 years). Pressure (P)-volume (V) curves were modeled exponentially by P=ae(kV)+b and logarithmically by P=-Sln[(Vm-V)/(Vm-V0)], where V0 indicates volume at P=0, and the constants k and S were used as indices of normalized chamber stiffness. Dynamic stiffness (dP/dV) was calculated at baseline LVEDV. The slope of the line relating SV to PCWP during lower-body negative pressure characterized the steepness of the Starling curve. We also measured plasma volume (with Evans blue dye) and maximal orthostatic tolerance. Bed rest led to a reduction in plasma volume (17%), baseline PCWP (18%), SV (12%), LVEDV (16%), V0 (33%), and orthostatic tolerance (24%) (all P<.05). The slope of the SV/PCWP curve increased from 4.6+/-0.4 to 8.8+/-0.9 mL/mm Hg (P<.01) owing to a parallel leftward shift in the P-V curve. Normalized chamber stiffness was unchanged, but dP/dV was reduced by 50% at baseline LVEDV, and cardiac mass tended to be reduced by 5% (P<.10). CONCLUSIONS Two weeks of head-down-tilt bed rest leads to a smaller, less distensible left ventricle but a shift to a more compliant portion of the P-V curve. This results in a steeper Starling relationship, which contributes to orthostatic intolerance by causing an excessive reduction in SV during orthostasis.
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Affiliation(s)
- B D Levine
- Institute for Exercise and Environmental Medicine, Presbyterian Hospital of Dallas, Tex 75321, USA.
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47
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Abstract
The universality of gravity (1 g) in our daily lives makes it difficult to appreciate its importance in morphology and physiology. Bone and muscle support systems were created, cellular pumps developed, neurons organised and receptors and transducers of gravitational force to biologically relevant signals evolved under 1g gravity. Spaceflight provides the only microgravity environment where systematic experimentation can expand our basic understanding of gravitational physiology and perhaps provide new insights into normal physiology and disease processes. These include the surprising extent of our body's dependence on perceptual information, and understanding the effect and importance of forces generated within the body's weightbearing structures such as muscle and bones. Beyond this exciting prospect is the importance of this work towards opening the solar system for human exploration. Although both appear promising, we are only just beginning to taste what lies ahead.
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Affiliation(s)
- J Vernikos
- National Aeronautics and Space Administration, Headquarters, Washington, DC 20546-0001, USA
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48
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Robertson D, Jacob G, Ertl A, Shannon J, Mosqueda-Garcia R, Robertson RM, Biaggioni I. Clinical models of cardiovascular regulation after weightlessness. Med Sci Sports Exerc 1996; 28:S80-4. [PMID: 8897409 DOI: 10.1097/00005768-199610000-00038] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
After several days in microgravity, return to earth is attended by alterations in cardiovascular function. The mechanisms underlying these effects are inadequately understood. Three clinical disorders of autonomic function represent possible models of this abnormal cardiovascular function after spaceflight. They are pure autonomic failure, baroreflex failure, and orthostatic intolerance. In pure autonomic failure, virtually complete loss of sympathetic and parasympathetic function occurs along with profound and immediate orthostatic hypotension. In baroreflex failure, various degrees of debuffering of blood pressure occur. In acute and complete baroreflex failure, there is usually severe hypertension and tachycardia, while with less complete and more chronic baroreflex impairment, orthostatic abnormalities may be more apparent. In orthostatic intolerance, blood pressure fall is minor, but orthostatic symptoms are prominent and tachycardia frequently occurs. Only careful autonomic studies of human subjects in the microgravity environment will permit us to determine which of these models most closely reflects the pathophysiology brought on by a period of time in the microgravity environment.
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Affiliation(s)
- D Robertson
- Department of Medicine, Vanderbilt University, Nashville, TN 37232-2195, USA
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