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

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.

Lower-body negative pressure restores leg bone microvascular flow to supine levels during head-down tilt

2015 ◽  
Vol 119 (2) ◽  
pp. 101-109 ◽  
Author(s):  
Jamila H. Siamwala ◽  
Paul C. Lee ◽  
Brandon R. Macias ◽  
Alan R. Hargens
Keyword(s):  
Negative Pressure ◽  
Repeated Measures ◽  
Simulated Microgravity ◽  
Near Infrared ◽  
Lower Body Negative Pressure ◽  
Lower Body ◽  
Calf Circumference ◽  
Fluid Shift ◽  
Microvascular Flow ◽  
Flow Head

Skeletal unloading and cephalic fluid shifts in microgravity may alter the bone microvascular flow and may be associated with the 1-2% bone loss per month during spaceflight. The purpose of this study was to determine if lower-body negative pressure (LBNP) can prevent microgravity-induced alterations of tibial microvascular flow. Head-down tilt (HDT) simulates the cephalad fluid shift and microvascular flow responses that may occur in microgravity. We hypothesized that LBNP prevents HDT-induced increases in tibial microvascular flow. Tibial bone microvascular flow, oxygenation, and calf circumference were measured during 5 min sitting, 5 min supine, 5 min 15° HDT, and 10 min 15° HDT with 25 mmHg LBNP using photoplethysmography (PPG), near-infrared spectroscopy (NIRS), and strain-gauge plethysmography (SGP). Measurements were made simultaneously. Tibial microvascular flow increased by 36% with 5 min 15° HDT [2.2 ± 1.1 V; repeated-measures ANOVA (RMANOVA) P < 0.0001] from supine (1.4 ± 0.8 V). After 10 min of LBNP in the 15° HDT position, tibial microvascular flow returned to supine levels (1.1 ± 0.5 V; RMANOVA P < 0.001). Tibial oxygenation did not change significantly during sitting, supine, HDT, or HDT with LBNP. However, calf circumference decreased with 5 min 15° HDT (−0.7 ± 0.4 V; RMANOVA P < 0.0001) from supine (−0.5 ± 0.4 V). However, with LBNP calf circumference returned to supine levels (−0.4 ± 0.1 V; RMANOVA P = 0.002). These data establish that simulated microgravity increases tibial microvascular flow and LBNP prevents these increases. The results suggest that LBNP may provide a suitable countermeasure to normalize the bone microvascular flow during spaceflight.

Use of Lower Body Negative Pressure to Assess Changes in Heart Rate Response to Orthostatic-like Stress During 17 Weeks of Bed Rest

1994 ◽  
Vol 34 (6) ◽  
pp. 563-570 ◽  
Author(s):  
Claire M. Lathers ◽  
John B. Charles ◽  
Victor S. Schneider ◽  
Mary Anne B. Frey ◽  
Suzanne Fortney
Keyword(s):  
Heart Rate ◽  
Negative Pressure ◽  
Heart Rate Response ◽  
Lower Body Negative Pressure ◽  
Bed Rest ◽  
Lower Body

Upright exercise or supine lower body negative pressure exercise maintains exercise responses after bed rest

1997 ◽  
Vol 29 (7) ◽  
pp. 892-900 ◽  
Author(s):  
STUART M. C. LEE ◽  
BARBARA S. BENNETT ◽  
ALAN R. HARGENS ◽  
DONALD E. WATENPAUGH ◽  
RICHARD E. BALLARD ◽  
...  
Keyword(s):  
Negative Pressure ◽  
Lower Body Negative Pressure ◽  
Bed Rest ◽  
Lower Body

Supine Lower Body Negative Pressure Treadmill Exercise Maintains Upright Exercise Capacity In Women And Men After 30-d Bed Rest

2005 ◽  
Vol 37 (Supplement) ◽  
pp. S36
Author(s):  
Stuart M.C. Lee ◽  
Suzanne M. Schneider ◽  
Donald E. Watenpaugh ◽  
Wanda L. Boda ◽  
Brandon R. Macias ◽  
...  
Keyword(s):  
Exercise Capacity ◽  
Negative Pressure ◽  
Treadmill Exercise ◽  
Lower Body Negative Pressure ◽  
Bed Rest ◽  
Lower Body

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 Lower body negative pressure treadmill exercise as a countermeasure for bed rest-induced bone loss in female identical twins

Bone ◽  
2007 ◽  
Vol 40 (2) ◽  
pp. 529-537 ◽  
Author(s):  
Sara R. Zwart ◽  
Alan R. Hargens ◽  
Stuart M.C. Lee ◽  
Brandon R. Macias ◽  
Donald E. Watenpaugh ◽  
...  
Keyword(s):  
Bone Loss ◽  
Negative Pressure ◽  
Treadmill Exercise ◽  
Lower Body Negative Pressure ◽  
Bed Rest ◽  
Identical Twins ◽  
Lower Body

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

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.

Abstract 14436: Nightly Lower Body Negative Pressure Redistributes Blood Volume and Prevents Maladaptive Vascular Remodeling Induced by Microgravity

Circulation ◽  
2020 ◽  
Vol 142 (Suppl_3) ◽  
Author(s):  
Katrin A Dias ◽  
Christopher M Hearon ◽  
Gautam Babu ◽  
John E Marshall ◽  
James P Macnamara ◽  
...  
Keyword(s):  
Blood Volume ◽  
Negative Pressure ◽  
Vascular Remodeling ◽  
Lower Body Negative Pressure ◽  
Venous Pressure ◽  
Bed Rest ◽  
Lower Body ◽  
Long Duration ◽  
Sustained Reduction ◽  
Area And Volume

Introduction: During space flight and ground based simulations of microgravity, transmural distending pressure increases in resistance vessels above the level of the heart, causing maladaptive vascular remodeling over time. Lower body negative pressure (LBNP) mimics gravity by redistributing blood volume and reinstating hydrostatic gradients, and may preserve vascular structures above the heart while in microgravity. Methods: Ten healthy subjects (5 female, 29 ± 9 years) completed three days of supine (0°) bed rest with and without eight hours of nightly LBNP (-20mmHg) in a randomized, crossover design. Area and volume of the choroid, a highly vascularized layer of the eye sensitive to changes in hydrostatic gradients, were assessed using optical coherence tomography on the first and last day of bed rest. Central venous pressure (CVP) was measured during spontaneous breathing with a peripherally inserted central catheter. Results: CVP increased significantly from the seated to supine position (+9.1 ± 2.4mmHg, P < 0.001), leading to choroid engorgement over three days of supine bed rest (choroid area: +0.09 mm 2 95% CI 0.04 to 0.13, P = 0.0014; choroid volume: +0.37 mm 3 95% CI 0.19 to 0.55, P = 0.0011). Nightly LBNP caused a sustained reduction in supine CVP (5.7 ± 2.2mmHg to 1.2 ± 1.4mmHg, P < 0.001), indicating effective redistribution of blood volume and significantly attenuated the increase in choroid area (3.5% control vs. 0.9% LBNP, P = 0.0164) and volume (3.8% control vs. 1.8% LBNP, P = 0.0040) compared to control (Figure). Conclusions: Nightly LBNP caused caudal redistribution of blood volume that partially reinstated hydrostatic gradients and mitigated the increase in choroid area and volume by 74% and 53%, respectively. These findings illustrate that normalizing transmural distending pressures during simulated microgravity preserves vascularized structures above the level of the heart and may prevent adverse remodeling during long duration spaceflight.

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