scholarly journals PlanHab: Hypoxia counteracts the erythropoietin suppression, but seems to exaggerate the plasma volume reduction induced by 3 weeks of bed rest

2016 ◽  
Vol 4 (7) ◽  
pp. e12760 ◽  
Author(s):  
Michail E. Keramidas ◽  
Igor B. Mekjavic ◽  
Roger Kölegård ◽  
Alexander Choukèr ◽  
Claudia Strewe ◽  
...  
Keyword(s):  
Plasma Volume ◽  
Bed Rest ◽  
Volume Reduction

Effect of head-down-tilt bed rest and hypovolemia on dynamic regulation of heart rate and blood pressure

2000 ◽  
Vol 279 (6) ◽  
pp. R2189-R2199 ◽  
Author(s):  
Ken-Ichi Iwasaki ◽  
Rong Zhang ◽  
Julie H. Zuckerman ◽  
James A. Pawelczyk ◽  
Benjamin D. Levine
Keyword(s):  
Blood Pressure ◽  
Heart Rate ◽  
Transfer Function ◽  
Stroke Volume ◽  
Plasma Volume ◽  
High Frequency ◽  
Function Analysis ◽  
Bed Rest ◽  
Baroreflex Control ◽  
Transfer Function Analysis

Adaptation to head-down-tilt bed rest leads to an apparent abnormality of baroreflex regulation of cardiac period. We hypothesized that this “deconditioning response” could primarily be a result of hypovolemia, rather than a unique adaptation of the autonomic nervous system to bed rest. To test this hypothesis, nine healthy subjects underwent 2 wk of −6° head-down bed rest. One year later, five of these same subjects underwent acute hypovolemia with furosemide to produce the same reductions in plasma volume observed after bed rest. We took advantage of power spectral and transfer function analysis to examine the dynamic relationship between blood pressure (BP) and R-R interval. We found that 1) there were no significant differences between these two interventions with respect to changes in numerous cardiovascular indices, including cardiac filling pressures, arterial pressure, cardiac output, or stroke volume; 2) normalized high-frequency (0.15–0.25 Hz) power of R-R interval variability decreased significantly after both conditions, consistent with similar degrees of vagal withdrawal; 3) transfer function gain (BP to R-R interval), used as an index of arterial-cardiac baroreflex sensitivity, decreased significantly to a similar extent after both conditions in the high-frequency range; the gain also decreased similarly when expressed as BP to heart rate × stroke volume, which provides an index of the ability of the baroreflex to alter BP by modifying systemic flow; and 4) however, the low-frequency (0.05–0.15 Hz) power of systolic BP variability decreased after bed rest (−22%) compared with an increase (+155%) after acute hypovolemia, suggesting a differential response for the regulation of vascular resistance (interaction, P < 0.05). The similarity of changes in the reflex control of the circulation under both conditions is consistent with the hypothesis that reductions in plasma volume may be largely responsible for the observed changes in cardiac baroreflex control after bed rest. However, changes in vasomotor function associated with these two conditions may be different and may suggest a cardiovascular remodeling after bed rest.

Changes in plasma volume during bed rest: effects of menstrual cycle and estrogen administration

1988 ◽  
Vol 65 (2) ◽  
pp. 525-533 ◽  
Author(s):  
S. M. Fortney ◽  
W. S. Beckett ◽  
A. J. Carpenter ◽  
J. Davis ◽  
H. Drew ◽  
...  
Keyword(s):  
Menstrual Cycle ◽  
Plasma Volume ◽  
Bed Rest ◽  
Transient Effects ◽  
Menstrual Cycles ◽  
Healthy Women ◽  
Exogenous Estrogen ◽  
Estrogen Administration ◽  
Estrogen Concentration

Bed rest (BR) is associated with a decrease in plasma volume (PV), which may contribute to the impaired orthostatic and exercise tolerances seen immediately after BR. The purpose of this study was to determine whether increases in blood estrogen concentration, either during normal menstrual cycles or during exogenous estrogen administration, would attenuate this loss of PV. Nineteen healthy women (21-39 yr of age) completed the study. Twelve women underwent duplicate 11-day BR without estrogen supplementation. PV decreased significantly (P less than or equal to 0.01) during both BR's, from 2,531 +/- 113 to 2,027 +/- 102 ml during BR1 and from 2,445 +/- 115 to 2,244 +/- 96 ml during BR2. The women who began BR in the periovulatory stage of the menstrual cycle (n = 3), a time of elevated endogenous estrogens, had a transient delay in loss of PV during the first 5 days of BR. Women who began BR during other stages of the menstrual cycle (n = 17) showed the established trend to decrease PV primarily during the first few days of BR. Seven additional women underwent a single 12-day BR while taking estrogen supplementation (1.25 mg/day premarin). PV decreased during the first 4-5 days of BR, then returned toward the pre-BR level during the remainder of the BR (pre-BR PV, 2,525 +/- 149 ml; post-BR PV, 2,519 +/- 162 ml). Thus menstrual fluctuations in endogenous estrogens appear to have only small transient effects on the loss of PV during BR, whereas exogenous estrogen supplementation significantly attenuates PV loss.

scholarly journals Transcutaneous Electrical Acupuncture Stimulation as a Countermeasure against Cardiovascular Deconditioning during 4 days of Head-Down Bed Rest in Humans

2015 ◽  
Vol 33 (5) ◽  
pp. 381-387 ◽  
Author(s):  
Jing Sun ◽  
Xiaotao Li ◽  
Changbin Yang ◽  
Yongchun Wang ◽  
Fei Shi ◽  
...  
Keyword(s):  
Cardiac Function ◽  
Plasma Volume ◽  
Bed Rest ◽  
Control Group ◽  
Acupuncture Stimulation ◽  
Cardiovascular Deconditioning ◽  
Electrical Acupuncture ◽  
Before And After ◽  
Registration Number ◽  
Plasma Hormones

Objective Spaceflight is associated with cardiovascular deregulation. However, the influence of microgravity on the cardiovascular system and its mechanisms and countermeasures remain unknown. Our previous studies have demonstrated that transcutaneous electrical acupuncture stimulation (TEAS) is effective in improving orthostatic tolerance (OT). The purpose of this study was to determine if TEAS treatment can attenuate cardiovascular deconditioning induced by a 4-day −6° head-down bed rest (HDBR). Methods Fourteen healthy male subjects were randomly allocated to a control group (control, n=6, 4 days HDBR without countermeasures) and a TEAS treatment group (TEAS, n=8, 4 days HDBR with TEAS at Neiguan (PC6) for 30 min each day for 4 consecutive days during HDBR). OT, plasma hormones, plasma volume and heart rate variability were assessed before and after HDBR. Cardiac function and cerebral blood flow were measured before, during and after HDBR. Results The data showed that TEAS treatment mitigated the decrease in OT that was observed in the control group and cardiac function, alleviated autonomic dysfunction, and partially prevented plasma volume reduction after HDBR. Angiotensin II and aldosterone were significantly increased by 129.3% and 133.3% after HDBR in the TEAS group (p<0.05). Conclusions These results indicate that 30 min of daily TEAS treatment at PC6 is partially effective in maintaining OT, probably due to increased plasma volume-regulating hormones and activation of the peripheral sympathetic nervous system. TEAS treatment appears effective at reducing cardiovascular deconditioning induced by HDBR for 4 days. Trial Registration Number NCT02300207.

scholarly journals Moderate Exercise Based on Artificial Gravity Preserves Orthostatic Tolerance and Exercise Capacity During Short-Term Head-Down Bed Rest

2017 ◽  
pp. 567-580 ◽  
Author(s):  
X.-T. LI ◽  
C.-B. YANG ◽  
Y.-S. ZHU ◽  
J. SUN ◽  
F. SHI ◽  
...  
Keyword(s):  
Aerobic Exercise ◽  
Plasma Volume ◽  
Systolic Function ◽  
Bed Rest ◽  
Control Group ◽  
Orthostatic Tolerance ◽  
Short Term ◽  
Exercise Endurance ◽  
Physical Deconditioning ◽  
Cardiac Systolic Function

Numerous countermeasures have been proposed to minimize microgravity-induced physical deconditioning, but their benefits are limited. The present study aimed to investigate whether personalized aerobic exercise based on artificial gravity (AG) mitigates multisystem physical deconditioning. Fourteen men were assigned to the control group (n=6) and the countermeasure group (CM, n=8). Subjects in the CM group were exposed to AG (2 Gz at foot level) for 30 min twice daily, during which time cycling exercise of 80-95 % anaerobic threshold (AT) intensity was undertaken. Orthostatic tolerance (OT), exercise tests, and blood assays were determined before and after 4 days head-down bed rest (HDBR). Cardiac systolic function was measured every day. After HDBR, OT decreased to 50.9 % and 77.5 % of pre-HDBR values in control and CM groups, respectively. Exercise endurance, maximal oxygen consumption, and AT decreased to 96.5 %, 91.5 % and 91.8 % of pre-HDBR values, respectively, in the control group. Nevertheless, there were slight changes in the CM group. HDBR increased heart rate, sympathetic activity, and the pre-ejection period, but decreased plasma volume, parasympathetic activity and left-ventricular ejection time in the control group, whereas these effects were eliminated in the CM group. Aldosterone had no change in the control group but increased significantly in the CM group. Our study shows that 80-95 % AT aerobic exercise based on 2 Gz of AG preserves OT and exercise endurance, and affects body fluid regulation during short-term HDBR. The underlying mechanisms might involve maintained cardiac systolic function, preserved plasma volume, and improved sympathetic responses to orthostatic stress.

Fluid and electrolyte shifts during bed rest with isometric and isotonic exercise

1977 ◽  
Vol 42 (1) ◽  
pp. 59-66 ◽  
Author(s):  
J. E. Greenleaf ◽  
E. M. Bernauer ◽  
H. L. Young ◽  
J. T. Morse ◽  
R. W. Staley ◽  
...  
Keyword(s):  
Plasma Volume ◽  
Recovery Period ◽  
Extracellular Volume ◽  
Isometric Exercise ◽  
Bed Rest ◽  
The Other ◽  
Interstitial Volume ◽  
Isotonic Exercise ◽  
Exercise Regimen ◽  
Blood Cell And Plasma

Fluid and electrolyte shifts were measured in seven men (19–21 yr) during three 2-wk bed rest (BR) periods, each of which was separated by a 3-wk ambulatory recovery period. During two of the three BR periods they performed isometric exercise and isotonic exercise. No prescribed exercise was given during the other BR period. On day 4 of BR, plasma volume decreased (P less than 0.05) 441 ml (-12.6%) with no exercise, 396 ml (-11.3%) with isometric, and 262 ml (-7.8%) with isotonic exercise; the decreases (NS) of extracellular volume were -4.4%, -2.6%, and -2.7%, respectively. By day 13 of BR, plasma volume stabilized at the lower level with isometric and isotonic exercise and continued to decline with no exercise; but the extracellular volume returned to or above control levels due to an overshoot of the interstitial volume of +320 to +430 ml (2.0–2.7%) that was about equal to the plasma volume loss. During BR there were isocontent losses from the plasma of protein, albumin, globulin, urea N2, uric acid, creatinine, Na, Cl, osmolarity, P, and glucose that were not influenced by either exercise regimen. However, the blood, red blood cell, and plasma volumes, and the Ca and K contents were stabilized during BR by both exercise regimens. The results suggest that during BR, preservation of the extracellular volume takes precedence over maintenance of the plasma volume, and this mechanism is independent of the effects of isometric or isotonic exercise.

Cardiorespiratory deconditioning with static and dynamic leg exercise during bed rest

1976 ◽  
Vol 41 (6) ◽  
pp. 905-909 ◽  
Author(s):  
R. W. Stremel ◽  
V. A. Convertino ◽  
E. M. Bernauer ◽  
J. E. Greenleaf
Keyword(s):  
Heart Rate ◽  
Plasma Volume ◽  
Rest Period ◽  
Bed Rest ◽  
Bicycle Ergometer ◽  
Dynamic Exercise ◽  
Maximal Heart Rate ◽  
Leg Extension ◽  
Ergometer Exercise ◽  
Extension Force

Bed rest deconditioning was assessed in seven healthy men (19–22 yr) following three 14-day periods of controlled activity during recumbencyby measuring submaximal and maximal oxygen uptake (VO2), ventilation (VE), heart rate, and plasma volume. Exercise regimens were performed in the supine position and included a) two 30-min periods daily of intermittent staticexercise at 21% of maximal leg extension force, and b) two 30-min periods of dynamic bicycle ergometer exercise daily at 68% of VO2max. No prescribed exercise was performed during the third bed rest period. Compared with their respective pre-bed rest control values, VO2max decreased (P less than 0.05) under all exercise conditions; -12.3% with no exercise, -9.2% with dynamic exercise, but only -4.8% with static exercise. Maximal heart rate was increased by 3.3% to 4.9% (P less than 0.05) under the three exercise conditions, while plasma volume decreased (P less than 0.05) -15.1% with no exercise and -10.1% with static, but only -7.8% (NS) with dynamic exercise. Sinceneither the static nor dynamic exercise training regimes minimized the changes in all the variables studied, some combination of these two types of exercise may be necessary for maximum protection from the effects of the bed deconditioning.

Reduced baroreflex control of heart period after bed rest is normalized by acute plasma volume restoration

2004 ◽  
Vol 287 (5) ◽  
pp. R1256-R1262 ◽  
Author(s):  
Ken-ichi Iwasaki ◽  
Rong Zhang ◽  
Merja A. Perhonen ◽  
Julie H. Zuckerman ◽  
Benjamin D. Levine
Keyword(s):  
Blood Pressure ◽  
Transfer Function ◽  
Plasma Volume ◽  
Bed Rest ◽  
Left Ventricular ◽  
Spontaneous Respiration ◽  
Baroreflex Control ◽  
Baroreflex Function ◽  
Transfer Function Gain ◽  
Cardiac Period

Adaptation to spaceflight or head-down-tilt bed rest leads to hypovolemia and an apparent abnormality of baroreflex regulation of cardiac period. In a previous study, we demonstrated that both chronic (2 wk) head-down-tilt bed rest and acute induced hypovolemia led to similar impairments in spontaneous baroreflex control of cardiac period, suggesting that a reduction in plasma volume may be responsible for this abnormality after bed rest. Therefore we hypothesized that this reduced “baroreflex function” could be restored by intravenous volume infusion equivalent to the reduction in plasma volume after bed rest. Six healthy subjects underwent 2 wk of −6° head-down bed rest. Beat-by-beat arterial blood pressure and ECG were recorded during 6 min of spontaneous respiration and fixed-rate breathing (0.2 Hz), and transfer function analysis between systolic blood pressure and R-R interval was performed. Plasma volume was measured with Evans blue dye, and cardiac filling pressures were directly measured (Swan-Ganz catheter). After bed rest, studies were repeated before and after plasma volume restoration, with which both plasma volume and left ventricular end-diastolic pressure were restored to pre-bed rest levels by intravenous dextran40 infusion (288 ± 31 ml). Transfer function gain in the high-frequency range, used as an index of vagally mediated arterial-cardiac baroreflex function, decreased significantly (13.4 ± 3.1 to 8.1 ± 2.9 ms/mmHg, P < 0.05) after bed rest. However, reduced transfer function gain was normalized to the pre-bed rest level (12.2 ± 3.6 ms/mmHg) after precise plasma volume restoration. This result confirms that reductions in plasma volume, rather than a unique autonomic nervous system adaptation to bed rest, are largely responsible for the observed changes in spontaneous arterial-cardiac baroreflex function after bed rest.

Pathophysiology of orthostatic hypotension after bed rest: paradoxical sympathetic withdrawal

2003 ◽  
Vol 285 (3) ◽  
pp. H1158-H1167 ◽  
Author(s):  
Atsunori Kamiya ◽  
Daisaku Michikami ◽  
Qi Fu ◽  
Satoshi Iwase ◽  
Junichiro Hayano ◽  
...  
Keyword(s):  
Blood Pressure ◽  
Orthostatic Hypotension ◽  
Plasma Volume ◽  
Sympathetic Nerve ◽  
Sympathetic Nerve Activity ◽  
Muscle Sympathetic Nerve Activity ◽  
Bed Rest ◽  
Clinical Syndrome ◽  
Tilt Test ◽  
Nerve Activity

Although orthostatic hypotension is a common clinical syndrome after spaceflight and its ground-based simulation model, 6° head-down bed rest (HDBR), the pathophysiology remains unclear. The authors' hypothesis that a decrease in sympathetic nerve activity is the major pathophysiology underlying orthostatic hypotension after HDBR was tested in a study involving 14-day HDBR in 22 healthy subjects who showed no orthostatic hypotension during 15-min 60° head-up tilt test (HUT) at baseline. After HDBR, 10 of 22 subjects demonstrated orthostatic hypotension during 60° HUT. In subjects with orthostatic hypotension, total activity of muscle sympathetic nerve activity (MSNA) increased less during the first minute of 60° HUT after HDBR (314% of resting supine activity) than before HDBR (523% of resting supine activity, P < 0.05) despite HDBR-induced reduction in plasma volume (13% of plasma volume before HDBR). The postural increase in total MSNA continued during several more minutes of 60° HUT while arterial pressure was maintained. Thereafter, however, total MSNA was paradoxically suppressed by 104% of the resting supine level at the last minute of HUT ( P < 0.05 vs. earlier 60° HUT periods). The suppression of total MSNA was accompanied by a 22 ± 4-mmHg decrease in mean blood pressure (systolic blood pressure <80 mmHg). In contrast, orthostatic activation of total MSNA was preserved throughout 60° HUT in subjects who did not develop orthostatic hypotension. These data support the hypothesis that a decrease in sympathetic nerve activity is the major pathophysiological factor underlying orthostatic hypotension after HDBR. It appears that the diminished sympathetic activity, in combination with other factors associated with HDBR (e.g., hypovolemia), may predispose some individuals to postural hypotension.

Blood volume, bleeding volume and tolerance to hemorrhage in the splenectomized dog

1958 ◽  
Vol 196 (1) ◽  
pp. 176-178 ◽  
Author(s):  
Thomas H. Allen ◽  
Richard A. Walzer ◽  
Kirsten Gregersen ◽  
Magnus I. Gregersen
Keyword(s):  
Blood Volume ◽  
Plasma Volume ◽  
Volume Of Fluid ◽  
Volume Reduction ◽  
Critical Range ◽  
Bleeding Volume ◽  
Replacement Procedure ◽  
Initial Blood ◽  
Blood Volumes

The relation between blood volume reduction and survival was studied in 28 experiments on 20 splenectomized dogs using Walcott's bleed-out and replacement procedure for adjusting the blood volume to the critical range. Plasma volume was measured with T-1824 and blood volume calculated using the Fcells factor of 0.87. Control blood volumes averaged 95 ml/kg in the lean dogs and 78 ml/kg in medium fat dogs. However, the bleeding percentage (bleeding volume as percentage of blood volume) was nearly the same in both groups with an over-all average of 57%. Fifty per cent survival was computed to occur at 66% of the initial blood volume, the critical range extending from 62 to 74%. The volume of fluid replaced by compensatory dilution averaged 10% of the control blood volume.

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