Changes in size and compliance of the calf after 30 days of simulated microgravity

1989 ◽  
Vol 66 (3) ◽  
pp. 1509-1512 ◽  
Author(s):  
V. A. Convertino ◽  
D. F. Doerr ◽  
S. L. Stein
Keyword(s):  
Simulated Microgravity ◽  
Orthostatic Intolerance ◽  
Bed Rest ◽  
Calf Muscle ◽  
Venous Compliance ◽  
Cross Sectional ◽  
Percent Change ◽  
Long Duration ◽  
Before And After ◽  
Muscle Compartment

Increased leg venous compliance may contribute to postflight orthostatic intolerance in astronauts. We reported that leg compliance was inversely related to the size of the muscle compartment. The purpose of this study was to test the hypothesis that reduced muscle compartment after long-duration exposure to microgravity would cause increased leg compliance. Eight men, 31–45 yr old, were measured for vascular compliance of the calf and serial circumferences of the calf before and after 30 days of continuous 6 degrees head-down bed rest. Cross-sectional areas (CSA) of muscle, fat, and bone compartments in the calf were determined before and after bed rest by computed tomography. From before to after bed rest, calculated calf volume (cm3) decreased (P less than 0.05) from 1,682 +/- 83 to 1,516 +/- 76. Calf muscle compartment CSA (cm2) also decreased (P less than 0.05) from 74.2 +/- 3.6 to 70.6 +/- 3.4; calf compliance (ml.100 ml-1.mmHg-1.100) increased (P less than 0.05) from 3.9 +/- .7 to 4.9 +/- .5. The percent change in calf compliance after bed rest was significantly correlated with changes in calf muscle compartment CSA (r = 0.72, P less than 0.05). The increased leg compliance observed after exposure to simulated microgravity can be partially explained by reduced muscle compartment. Countermeasures designed to minimize muscle atrophy in the lower extremities may be effective in ameliorating increased venous compliance and orthostatic intolerance after spaceflight.

Role of individual predisposition in orthostatic intolerance before and after simulated microgravity

2004 ◽  
Vol 96 (5) ◽  
pp. 1714-1722 ◽  
Author(s):  
S. M. Grenon ◽  
S. Hurwitz ◽  
N. Sheynberg ◽  
X. Xiao ◽  
C. D. Ramsdell ◽  
...  
Keyword(s):  
Nervous System ◽  
Parasympathetic Nervous System ◽  
Orthostatic Intolerance ◽  
Bed Rest ◽  
Serum Cortisol ◽  
Compensatory Mechanisms ◽  
Venous Compliance ◽  
Baseline Serum ◽  
Stand Test ◽  
Before And After

Orthostatic intolerance (OI) is a major problem after spaceflight. Its etiology remains uncertain, but reports have pointed toward an individual susceptibility to OI. We hypothesized that individual predisposition plays an important role in post-bed rest OI. Twenty-four healthy male subjects were equilibrated on a constant diet, after which they underwent tilt-stand test (pre-TST). They then completed 14-16 days of head-down-tilt bed rest, and 14 of the subjects underwent repeat tilt-stand test (post-TST). During various phases, the following were performed: 24-h urine collections and hormonal measurements, plethysmography, and cardiovascular system identification (a noninvasive method to assess autonomic function and separately quantify parasympathetic and sympathetic responsiveness). Development of presyncope or syncope defined OI. During pre-TST, 11 subjects were intolerant and 13 were tolerant. At baseline, intolerant subjects had lower serum aldosterone ( P < 0.01), higher excretion of potassium ( P = 0.01), lower leg venous compliance ( P = 0.03), higher supine parasympathetic responsiveness ( P = 0.02), and lower standing sympathetic responsiveness ( P = 0.048). Of the 14 subjects who completed post-TST, 9 were intolerant and 5 were tolerant. Intolerant subjects had lower baseline serum cortisol ( P = 0.03) and a higher sodium level ( P = 0.02) compared with tolerant subjects. Thus several physiological characteristics were associated with increased susceptibility to OI. We propose a new model for OI, whereby individuals with greater leg venous compliance recruit compensatory mechanisms (activation of the renin-angiotensin-aldosterone system and sympathetic nervous system, and withdrawal of the parasympathetic nervous system) in the face of daily postural challenges, which places them at an advantage to face orthostatic stress. With head-down-tilt bed rest, the stimulus to recruit compensatory mechanisms disappears, and differences between the two subgroups attenuate.

Effects of simulated microgravity on closed-loop cardiovascular regulation and orthostatic intolerance: analysis by means of system identification

2004 ◽  
Vol 96 (2) ◽  
pp. 489-497 ◽  
Author(s):  
Xinshu Xiao ◽  
Ramakrishna Mukkamala ◽  
Natalie Sheynberg ◽  
S. Marlene Grenon ◽  
Michael D. Ehrman ◽  
...  
Keyword(s):  
System Identification ◽  
Simulated Microgravity ◽  
Closed Loop ◽  
Orthostatic Intolerance ◽  
Bed Rest ◽  
Model Parameters ◽  
Primary Concern ◽  
Loop Model ◽  
Before And After ◽  
Coupling Mechanisms

Microgravity-induced orthostatic intolerance (OI) continues to be a primary concern for the human space program. To test the hypothesis that exposure to simulated microgravity significantly alters autonomic nervous control and, thus, contributes to increased incidence of OI, we employed the cardiovascular system identification (CSI) technique to evaluate quantitatively parasympathetic and sympathetic regulation of heart rate (HR). The CSI method analyzes second-to-second fluctuations in noninvasively measured HR, arterial blood pressure, and instantaneous lung volume. The coupling mechanisms between these signals are characterized by using a closed-loop model. Parameters reflecting parasympathetic and sympathetic responsiveness with regard to HR regulation can be extracted from the identified coupling mechanisms. We analyzed data collected from 29 human subjects before and after 16 days of head-down-tilt bed rest (simulated microgravity). Statistical analyses showed that parasympathetic and sympathetic responsiveness was impaired by bed rest. A lower sympathetic responsiveness and a higher parasympathetic responsiveness measured before bed rest identified individuals at greater risk of OI before and after bed rest. We propose an algorithm to predict OI after bed rest from measures obtained before bed rest.

A NEW MODEL FOR THE ROLE OF INDIVIDUAL PREDISPOSITION IN ORTHOSTATIC INTOLERANCE BEFORE AND AFTER EXPOSURE TO SIMULATED MICROGRAVITY.

2004 ◽  
Vol 52 ◽  
pp. S384-S385
Author(s):  
S. M. Grenon ◽  
N. Sheynberg ◽  
X. Xiao ◽  
C. D. Ramsdell ◽  
S. Hurwitz ◽  
...  
Keyword(s):  
Simulated Microgravity ◽  
Orthostatic Intolerance ◽  
New Model ◽  
Before And After

scholarly journals Effect of intermittent hypoxic training on orthostatic tolerance in humans before and after simulated microgravity

2020 ◽  
Author(s):  
VP Katuntsev ◽  
TV Sukhostavtseva ◽  
AN Kotov ◽  
MV Baranov
Keyword(s):  
Orthostatic Intolerance ◽  
Bed Rest ◽  
Daily Basis ◽  
Tilt Test ◽  
Control Group ◽  
Orthostatic Tolerance ◽  
Pronounced Increase ◽  
Intermittent Hypoxic Training ◽  
Hypoxic Training ◽  
Before And After

Reduced orthostatic tolerance (OT) is a serious concern facing space medicine. This work sought to evaluate the effects of intermittent hypoxic training (IHT) on OT in humans before and after 3 days of head-down bed rest (HDBR) used to model microgravity. The study was carried out in 16 male volunteers aged 18 to 40 years and included 2 series of experiments with 11-day and 21-day IHT administered on a daily basis. During the first IHT session, the concentration of oxygen in the inspired gas mixture was 10%; for other sessions it was adjusted to 9%. OT was assessed by a 20-minute-long orthostatic tilt test (OTT) conducted before and after HDBR. Before HDBR, orthostatic intolerance was observed in 3 participants, while after HDBR, it was observed in 9 of 16 volunteers (p < 0.05). During OTT conducted after HDBR, the heart rate (HR) exceeded control values by 26.8% (p < 0.01). Preexposure to any of the applied IHT regimens led to a reduction in the number of volunteers with orthostatic intolerance. After the 11-day IHT program, there was a less pronounced increase in HR during OTT before HDBR; with the extended IHT regimen, less pronounced changes were observed for HR, systolic, diastolic and mean blood pressure (BP). The increase in HR during OTT after HDBR was significantly lower in the group that had completed the 11-day IHT program, while BP remained stable. The changes in HR and systolic BP were less pronounced in the group that had completed the 21-day IHT program than in the control group (p < 0.05). Thus, IHT reduced the risk of orthostatic disorders and mitigated changes in cardiovascular parameters during the orthostatic test.

scholarly journals Decreased otolith-mediated vestibular response in 25 astronauts induced by long-duration spaceflight

2016 ◽  
Vol 115 (6) ◽  
pp. 3045-3051 ◽  
Author(s):  
Emma Hallgren ◽  
Ludmila Kornilova ◽  
Erik Fransen ◽  
Dmitrii Glukhikh ◽  
Steven T. Moore ◽  
...  
Keyword(s):  
Orthostatic Intolerance ◽  
Balance Control ◽  
Head Tilt ◽  
Otolith Organs ◽  
Negative Effects ◽  
Spatial Disorientation ◽  
Long Duration ◽  
Before And After ◽  
Ocular Counterrolling ◽  
Otolith System

The information coming from the vestibular otolith organs is important for the brain when reflexively making appropriate visual and spinal corrections to maintain balance. Symptoms related to failed balance control and navigation are commonly observed in astronauts returning from space. To investigate the effect of microgravity exposure on the otoliths, we studied the otolith-mediated responses elicited by centrifugation in a group of 25 astronauts before and after 6 mo of spaceflight. Ocular counterrolling (OCR) is an otolith-driven reflex that is sensitive to head tilt with regard to gravity and tilts of the gravito-inertial acceleration vector during centrifugation. When comparing pre- and postflight OCR, we found a statistically significant decrease of the OCR response upon return. Nine days after return, the OCR was back at preflight level, indicating a full recovery. Our large study sample allows for more general physiological conclusions about the effect of prolonged microgravity on the otolith system. A deconditioned otolith system is thought to be the cause of several of the negative effects seen in returning astronauts, such as spatial disorientation and orthostatic intolerance. This knowledge should be taken into account for future long-term space missions.

46 A NEW MODEL FOR THE ROLE OF INDIVIDUAL PREDISPOSITION IN ORTHOSTATIC INTOLERANCE BEFORE AND AFTER EXPOSURE TO SIMULATED MICROGRAVITY.

2004 ◽  
Vol 52 (Suppl 2) ◽  
pp. S384.6-S385
Author(s):  
S. M. Grenon ◽  
N. Sheynberg ◽  
X. Xiao ◽  
C. D. Ramsdell ◽  
S. Hurwitz ◽  
...  
Keyword(s):  
Simulated Microgravity ◽  
Orthostatic Intolerance ◽  
New Model ◽  
Before And After

Effects of 18 days of bed rest on leg and arm venous properties

2004 ◽  
Vol 96 (3) ◽  
pp. 840-847 ◽  
Author(s):  
M. W. P. Bleeker ◽  
P. C. E. De Groot ◽  
J. A. Pawelczyk ◽  
M. T. E. Hopman ◽  
B. D. Levine
Keyword(s):  
Orthostatic Intolerance ◽  
Lower Body Negative Pressure ◽  
Bed Rest ◽  
Venous Occlusion ◽  
Stress Index ◽  
Orthostatic Tolerance ◽  
Venous Compliance ◽  
Venous Flow ◽  
Gravitational Gradients ◽  
Small Change

Venous function may be altered by bed rest deconditioning. Yet the contribution of altered venous compliance to the orthostatic intolerance observed after bed rest is uncertain. The purpose of this study was to assess the effect of 18 days of bed rest on leg and arm (respectively large and small change in gravitational gradients and use patterns) venous properties. We hypothesized that the magnitude of these venous changes would be related to orthostatic intolerance. Eleven healthy subjects (10 men, 1 woman) participated in the study. Before (pre) and after (post) 18 days of 6° head-down tilt bed rest, strain gauge venous occlusion plethysmography was used to assess limb venous vascular characteristics. Leg venous compliance was significantly decreased after bed rest (pre: 0.048 ± 0.007 ml·100 ml-1·mmHg-1, post: 0.033 ± 0.007 ml·100 ml-1·mmHg-1; P < 0.01), whereas arm compliance did not change. Leg venous flow resistance increased significantly after bed rest (pre: 1.73 ± 1.08 mmHg·ml-1·100 ml·min, post: 3.10 ± 1.00 mmHg·ml-1·100 ml·min; P < 0.05). Maximal lower body negative pressure tolerance, which was expressed as cumulative stress index (pressure·time), decreased in all subjects after bed rest (pre: 932 mmHg·min, post: 747 mmHg·min). The decrease in orthostatic tolerance was not related to changes in leg venous compliance. In conclusion, this study demonstrates that after bed rest, leg venous compliance is reduced and leg venous outflow resistance is enhanced. However, these changes are not related to measures of orthostatic tolerance; therefore, alterations in venous compliance do not to play a major role in orthostatic intolerance after 18 days of head-down tilt bed rest.

Lower body negative pressure exercise plus brief postexercise lower body negative pressure improve post-bed rest orthostatic tolerance

2007 ◽  
Vol 103 (6) ◽  
pp. 1964-1972 ◽  
Author(s):  
Donald E. Watenpaugh ◽  
Deborah D. O'Leary ◽  
Suzanne M. Schneider ◽  
Stuart M. C. Lee ◽  
Brandon R. Macias ◽  
...  
Keyword(s):  
Negative Pressure ◽  
Acute Exercise ◽  
Treadmill Exercise ◽  
Orthostatic Intolerance ◽  
Lower Body Negative Pressure ◽  
Bed Rest ◽  
Orthostatic Tolerance ◽  
Lower Body ◽  
Before And After ◽  
Head Up Tilt

Orthostatic intolerance follows actual weightlessness and weightlessness simulated by bed rest. Orthostasis immediately after acute exercise imposes greater cardiovascular stress than orthostasis without prior exercise. We hypothesized that 5 min/day of simulated orthostasis [supine lower body negative pressure (LBNP)] immediately following LBNP exercise maintains orthostatic tolerance during bed rest. Identical twins (14 women, 16 men) underwent 30 days of 6° head-down tilt bed rest. One of each pair was randomly selected as a control, and their sibling performed 40 min/day of treadmill exercise while supine in 53 mmHg (SD 4) [7.05 kPa (SD 0.50)] LBNP. LBNP continued for 5 min after exercise stopped. Head-up tilt at 60° plus graded LBNP assessed orthostatic tolerance before and after bed rest. Hemodynamic measurements accompanied these tests. Bed rest decreased orthostatic tolerance time to a greater extent in control [34% (SD 10)] than in countermeasure subjects [13% (SD 20); P < 0.004]. Controls exhibited cardiac stroke volume reduction and relative cardioacceleration typically seen after bed rest, yet no such changes occurred in the countermeasure group. These findings demonstrate that 40 min/day of supine LBNP treadmill exercise followed immediately by 5 min of resting LBNP attenuates, but does not fully prevent, the orthostatic intolerance associated with 30 days of bed rest. We speculate that longer postexercise LBNP may improve results. Together with our earlier related studies, these ground-based results support spaceflight evaluation of postexercise orthostatic stress as a time-efficient countermeasure against postflight orthostatic intolerance.

scholarly journals Vascular adaptation to microgravity: what have we learned?

2001 ◽  
Vol 91 (6) ◽  
pp. 2415-2430 ◽  
Author(s):  
Li-Fan Zhang
Keyword(s):  
Structure Function ◽  
Rat Model ◽  
Animal Studies ◽  
Simulated Microgravity ◽  
Orthostatic Intolerance ◽  
Peripheral Resistance ◽  
Bed Rest ◽  
Cerebral Vasculature ◽  
Future Studies ◽  
Vascular Adaptation

Findings from recent bed rest and spaceflight human studies have indicated that the inability to adequately elevate the peripheral resistance and the altered autoregulation of cerebral vasculature are important factors in postflight orthostatic intolerance. Animal studies with rat model have revealed that simulated microgravity may induce upward and downward regulations in the structure, function, and innervation of the cerebral and hindquarter vessels. These findings substantiate in general the hypothesis that microgravity-induced redistribution of transmural pressures and flows across and within the arterial vasculature may well initiate differential adaptations of vessels in different anatomic regions. Understanding of the mechanisms involved in vascular adaptation to microgravity is also important for the development of multisystem countermeasures. However, future studies will be required to further ascertain the peripheral effector mechanism of postflight cardiovascular dysfunction.

scholarly journals Orthostatic Intolerance Is Independent of the Degree of Autonomic Cardiovascular Adaptation after 60 Days of Head-Down Bed Rest

2015 ◽  
Vol 2015 ◽  
pp. 1-10 ◽  
Author(s):  
Jiexin Liu ◽  
Yongzhi Li ◽  
Bart Verheyden ◽  
Zhanghuang Chen ◽  
Jingyu Wang ◽  
...  
Keyword(s):  
Arterial Pressure ◽  
Orthostatic Intolerance ◽  
Low Frequency ◽  
Systolic Arterial Pressure ◽  
Bed Rest ◽  
Progressive Increase ◽  
Tilt Test ◽  
Sinus Arrhythmia ◽  
Before And After ◽  
Low Frequency Power

Spaceflight and head-down bed rest (HDBR) can induce the orthostatic intolerance (OI); the mechanisms remain to be clarified. The aim of this study was to determine whether or not OI after HDBR relates to the degree of autonomic cardiovascular adaptation. Fourteen volunteers were enrolled for 60 days of HDBR. A head-up tilt test (HUTT) was performed before and after HDBR. Our data revealed that, in all nonfainters, there was a progressive increase in heart rate over the course of HDBR, which remained higher until 12 days of recovery. The mean arterial pressure gradually increased until day 56 of HDBR and returned to baseline after 12 days of recovery. Respiratory sinus arrhythmia and baroreflex sensitivity decreased during HDBR and remained suppressed until 12 days of recovery. Low-frequency power of systolic arterial pressure increased during HDBR and remained elevated during recovery. Three subjects fainted during the HUTT after HDBR, in which systemic vascular resistance did not increase and remained lower until syncope. None of the circulatory patterns significantly differed between the fainters and the nonfainters at any time point. In conclusion, our data indicate that the impaired orthostatic tolerance after HDBR could not be distinguished by estimation of normal hemodynamic and/or neurocardiac data.

Sign in / Sign up

Export Citation Format

Share Document