Skin surface cooling improves orthostatic tolerance following prolonged head-down bed rest

Prolonged exposure to microgravity, as well as its ground-based analog, head-down bed rest (HDBR), reduces orthostatic tolerance in humans. While skin surface cooling improves orthostatic tolerance, it remains unknown whether this could be an effective countermeasure to preserve orthostatic tolerance following HDBR. We therefore tested the hypothesis that skin surface cooling improves orthostatic tolerance after prolonged HDBR. Eight subjects (six men and two women) participated in the investigation. Orthostatic tolerance was determined using a progressive lower-body negative pressure (LBNP) tolerance test before HDBR during normothermic conditions and on day 16 or day 18 of 6° HDBR during normothermic and skin surface cooling conditions (randomized order post-HDBR). The thermal conditions were achieved by perfusing water (normothermia ∼34°C and skin surface cooling ∼12–15°C) through a tube-lined suit worn by each subject. Tolerance tests were performed after ∼30 min of the respective thermal stimulus. A cumulative stress index (CSI; mmHg LBNP·min) was determined for each LBNP protocol by summing the product of the applied negative pressure and the duration of LBNP at each stage. HDBR reduced normothermic orthostatic tolerance as indexed by a reduction in the CSI from 1,037 ± 96 mmHg·min to 574 ± 63 mmHg·min ( P < 0.05). After HDBR, skin surface cooling increased orthostatic tolerance (797 ± 77 mmHg·min) compared with normothermia ( P < 0.05). While the reduction in orthostatic tolerance following prolonged HDBR was not completely reversed by acute skin surface cooling, the identified improvements may serve as an important and effective countermeasure for individuals exposed to microgravity, as well as immobilized and bed-stricken individuals.

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Skin surface cooling improves orthostatic tolerance in normothermic individuals

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.00394.2003 ◽

2004 ◽

Vol 286 (1) ◽

pp. R199-R205 ◽

Cited By ~ 35

Author(s):

S. Durand ◽

J. Cui ◽

K. D. Williams ◽

C. G. Crandall

Keyword(s):

Cerebral Blood Flow Velocity ◽

Lower Body Negative Pressure ◽

Skin Surface ◽

Tolerance Test ◽

Stress Index ◽

Plasma Norepinephrine ◽

Orthostatic Tolerance ◽

Lower Body ◽

Surface Cooling ◽

Cumulative Stress

Previous studies suggest that skin surface cooling (SSC) preserves orthostatic tolerance; however, this hypothesis has not been experimentally tested. Thus the purpose of this project was to identify whether SSC improves orthostatic tolerance in otherwise normothermic individuals. Eight subjects underwent two presyncope limited graded lower-body negative pressure (LBNP) tolerance tests. On different days, and randomly assigned, LBNP tolerance was assessed under control conditions and during SSC (perfused 16°C water through tube-lined suit worn by each subject). Orthostatic tolerance was significantly elevated in each individual due to SSC, as evidenced by a significant increase in a standardized cumulative stress index (normothermia 564 ± 58 mmHg·min; SSC 752 ± 58 mmHg·min; P < 0.05). At most levels of LBNP, blood pressure during the SSC tolerance test was significantly greater than during the control test. Furthermore, the reduction in cerebral blood flow velocity was attenuated during some of the early stages of LBNP for the SSC trial. Plasma norepinephrine concentrations were significantly higher during LBNP with SSC, suggesting that SSC may improve orthostatic tolerance through increased sympathetic activity. These data demonstrate that SSC is effective in improving orthostatic tolerance in otherwise normothermic individuals.

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

Journal of Applied Physiology ◽

10.1152/japplphysiol.00835.2003 ◽

2004 ◽

Vol 96 (3) ◽

pp. 840-847 ◽

Cited By ~ 21

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.

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

Journal of Applied Physiology ◽

10.1152/japplphysiol.00132.2007 ◽

2007 ◽

Vol 103 (6) ◽

pp. 1964-1972 ◽

Cited By ~ 32

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.

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Skin Surface Cooling Improves Orthostatic Tolerance After Prolonged Head-Down Bed Rest

Medicine & Science in Sports & Exercise ◽

10.1249/01.mss.0000274260.62990.1b ◽

2007 ◽

Vol 39 (Supplement) ◽

pp. S324

Author(s):

David M. Keller ◽

David A. Low ◽

Scott L. Davis ◽

Kenichi Kimura ◽

Jonathan Wingo ◽

...

Keyword(s):

Bed Rest ◽

Skin Surface ◽

Orthostatic Tolerance ◽

Surface Cooling

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Lower-body negative pressure/ergometer exercise in bed rest: Effects on female orthostatic tolerance

Journal of Novel Physiotherapy and Rehabilitation ◽

10.29328/journal.jnpr.1001036 ◽

2020 ◽

Vol 4 (2) ◽

pp. 040-048

Author(s):

Wang Linjie ◽

Li Zhili ◽

Tan Cheng ◽

Wang Huijuan ◽

Zhou Xiangjie ◽

...

Keyword(s):

Negative Pressure ◽

Orthostatic Intolerance ◽

Lower Body Negative Pressure ◽

Bed Rest ◽

Tilt Test ◽

Control Group ◽

Orthostatic Tolerance ◽

Lower Body ◽

Interval Exercise ◽

Ergometer Exercise

Introduction: Alternatively using gradient lower-body negative pressure (LBNP) and ergometer exercise (LBNP + ergo) under a flight schedule framework was explored to detect its orthostatic capacity maintenance effects in female subjects after 15 days of -6° head-down bed rest (HDBR). Methods: Twenty-two female university students were divided into a control group (n = 8), an LBNP group (n = 7), and an LBNP + ergo group (n = 7). Ergometer exercise consisted of an interval exercise protocol with 2 min intervals alternating between 41% and 70% VO2max. Gradient LBNP was decompressed in 10 mm Hg intervals to -40 mmHg every 5 min. intermittent ergometer exercise and LBNP were alternatively performed. Tilt test was performed 2 days before HDBR (R-2), on the day of HDBR termination (R+1), and 5 days after HDBR (R+5). Results: Fifty percent of the participants (11/22) did not pass the tilt test on R+1. The orthostatic tolerance time decreased from 20 to 16.1 ± 2.1 min in the control group, to 10.0 ± 2.7 min in the LBNP group (p = 0.01) and to 16.3 ± 2.0 min in the LBNP + ergo group. The HRs and BPs were at similar level among three groups during tilt test on different test days. Compared with the control group, the LBNP + ergo group had higher SV and CO percentage changes at R+1(p < 0.023) and R+5 (p < 0.00001) during the tilt test. Conclusion: LBNP combined with ergometer exercises fails to prevent orthostatic intolerance but it induced some positive hemodynamic changes during tilt test after 15 days HDBR.

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Abstract 2197: The Multi-System Effect of Exercise Training During Prolonged Bed Rest Deconditioning: An Integrated Approach to Countermeasure Development for the Heart, Lungs, Muscle and Bones

Circulation ◽

10.1161/circ.118.suppl_18.s_682 ◽

2008 ◽

Vol 118 (suppl_18) ◽

Author(s):

Jeffrey Hastings ◽

Eric Pacini ◽

Felix Krainski ◽

Shigeki Shibata ◽

Manish Jain ◽

...

Keyword(s):

Exercise Training ◽

Exercise Capacity ◽

Orthostatic Intolerance ◽

Lower Body Negative Pressure ◽

Bed Rest ◽

Orthostatic Tolerance ◽

Volume Loading ◽

System Effect ◽

Cardiac Atrophy ◽

South Central

We propose to prevent the cardiac atrophy and orthostatic intolerance associated with prolonged bed rest using rowing ergometry/resistance training with aggressive volume loading on the day of testing. We hypothesize that prevention of cardiac atrophy will forestall cardiovascular deconditioning, leading to preserved exercise capacity and orthostatic tolerance. Twenty-four healthy subjects, ages 20 –55, were enrolled with 8 randomized to training (EX), 8 with training and volume loading (VOL), and 8 as sedentary (SED) controls. Testing included maximal upright exercise, orthostatic tolerance via graded lower body negative pressure (LBNP), cardiac MRI, as well as invasive cardiac pressure-volume measurements, performed at baseline and at the end of 5 weeks of 6° head down bedrest. Upright exercise capacity was preserved with training as measured by peak workrate and VO2max (EX/VOL: pre 195±46W, 34±7 ml/kg/min; post 202±42W, 33±4 ml/kg/min) but deteriorated in SED group (pre 171±55W, 34±8 ml/kg/min; post 145±51W, 27±7 ml/kg/min). MRI derived mass (% change: +6.3±9.9% EX/VOL vs. −5.5±3.7% SED) was increased by training. Exercise training appears to preserve LV chamber compliance (stiffness constants: EX/VOL: pre= 0.035±0.021, post = 0.036±0.029; SED: pre= 0.020±0.011, post = 0.028±0.007). Training also preserves hemodynamic variables measured at −40mmHg of LBNP, including stroke volume (EX: pre 44±12; post 38±9 ml, VOL: pre 49±30; post 45±29 ml, SED: pre 35±5; post 24±8 ml ). These preliminary data support our hypothesis that an optimized training program consisting of dynamic and resistance exercise can prevent part of the multisystem atrophy and orthostatic intolerance associated with prolonged bed rest. This defines a specific countermeasure that is practical, safe, and effective against the cardiovascular, muscle and bone deconditioning associated with prolonged bed rest. This information is relevant not only for astronauts exposed to long duration spaceflight, but also for patients with chronic reductions in physical activity, and those with disease processes that alter cardiac stiffness such as obesity, hypertension, heart failure or ischemic heart disease, plus normal aging and osteoporosis. This research has received full or partial funding support from the American Heart Association, AHA South Central Affiliate (Arkansas, New Mexico, Oklahoma & Texas).

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Attenuated sympathetic nerve responses after 24 hours of bed rest

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.00862.2001 ◽

2002 ◽

Vol 282 (6) ◽

pp. H2210-H2215 ◽

Cited By ~ 15

Author(s):

Mazhar H. Khan ◽

Allen R. Kunselman ◽

Urs A. Leuenberger ◽

William R. Davidson ◽

Chester A. Ray ◽

...

Keyword(s):

Cardiac Output ◽

Negative Pressure ◽

Sympathetic Nerve ◽

Sympathetic Nerve Activity ◽

Lower Body Negative Pressure ◽

Muscle Sympathetic Nerve Activity ◽

Bed Rest ◽

Nerve Activity ◽

Before And After ◽

Reduced Rate

Bed rest reduces orthostatic tolerance. Despite decades of study, the cause of this phenomenon remains unclear. In this report we examined hemodynamic and sympathetic nerve responses to graded lower body negative pressure (LBNP) before and after 24 h of bed rest. LBNP allows for baroreceptor disengagement in a graded fashion. We measured heart rate (HR), cardiac output (HR × stroke volume obtained by echo Doppler), and muscle sympathetic nerve activity (MSNA) during a progressive and graded LBNP paradigm. Negative pressure was increased by 10 mmHg every 3 min until presyncope or completion of −60 mmHg. After bed rest, LBNP tolerance was reduced in 11 of 13 subjects ( P < .023), HR was greater ( P< .002), cardiac output was unchanged, and the ability to augment MSNA at high levels of LBNP was reduced (rate of rise for 30- to 60-mmHg LBNP before bed rest 0.073 bursts · min−1 · mmHg−1; after bed rest 0.035 bursts · min−1 · mmHg−1; P < 0.016). These findings suggest that 24 h of bed rest reduces sympathetic nerve responses to LBNP.

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Daily generation of a footward fluid shift attenuates ocular changes associated with head-down tilt bed rest

Journal of Applied Physiology ◽

10.1152/japplphysiol.00250.2020 ◽

2020 ◽

Vol 129 (5) ◽

pp. 1220-1231

Author(s):

Justin S. Lawley ◽

Gautam Babu ◽

Sylvan L. J. E. Janssen ◽

Lonnie G. Petersen ◽

Christopher M. Hearon ◽

...

Keyword(s):

Negative Pressure ◽

Lower Body Negative Pressure ◽

Bed Rest ◽

Lower Body ◽

Fluid Shift ◽

Gravitational Gradients ◽

Ocular Changes

Choroid measurements appear to be sensitive to changes in gravitational gradients, as well as periods of head-down tilt (HDT) bed rest, suggesting that they are potential indicators of early ocular remodeling and could serve to evaluate the efficacy of countermeasures for SANS. Eight hours of lower body negative pressure (LBNP) daily attenuates the choroid expansion associated with 3 days of strict −6° HDT bed rest, indicating that LBNP may be an effective countermeasure for SANS.

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Hemodynamic Strategies in Blood Pressure Regulation During Orthostatic Challenge in Women

Canadian Journal of Applied Physiology ◽

10.1139/h97-023 ◽

1997 ◽

Vol 22 (4) ◽

pp. 351-367

Author(s):

Tania L. Culham ◽

Gabrielle K. Savard

Keyword(s):

Blood Pressure ◽

Arterial Pressure ◽

Stroke Volume ◽

Negative Pressure ◽

Lower Body Negative Pressure ◽

Peripheral Resistance ◽

Orthostatic Tolerance ◽

Lower Body ◽

Orthostatic Challenge ◽

Carotid Baroreflex

Several studies indicate that carotid baroreflex responsiveness is a good predictor of orthostatic tolerance. Two groups of healthy women with high (HI) and low (LO) carotid baroreflex responsiveness were studied (a) to determine any differences in the level of orthostatic tolerance of the two groups, and (b) to study the hemodynamic strategies used by HI and LO responders to regulate arterial pressure during the orthostatic challenge of lower body negative pressure (LBNP). Orthostatic tolerance was similar between the two groups, whereas the hemodynamic strategies recruited to maintain blood pressure at −40 mmHg LBNP differed: HI responders exhibited greater LBNP-induced decreases in stroke volume and cardiac output, as well as a greater increase in peripheral resistance compared to LO responders (p < .05). In addition, a significant increase in plasma renin activity during LBNP was found in the HI responders only. No significant between-group differences were found in arterial and cardiopulmonary control of vascular resistance or arterial haroreflex control of heart rate during LBNP. Key words: arterial pressure, carotid baroreceptor, lower body negative pressure, orthostatic tolerance, stroke volume

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