Exercise plus volume loading prevents orthostatic intolerance but not reduction in cerebral blood flow velocity after bed rest

2012 ◽  
Vol 302 (2) ◽  
pp. H489-H497 ◽  
Author(s):  
Sung-Moon Jeong ◽  
Shigeki Shibata ◽  
Benjamin D. Levine ◽  
Rong Zhang
Keyword(s):  
Blood Flow ◽  
Cerebral Blood Flow ◽  
Cerebral Blood Flow Velocity ◽  
Orthostatic Intolerance ◽  
Bed Rest ◽  
Left Ventricular ◽  
Stress Index ◽  
Control Group ◽  
Orthostatic Tolerance ◽  
Volume Loading

This study tested the hypothesis that reduction in cerebral blood flow (CBF) during orthostatic stress after bed rest can be ameliorated with volume loading, exercise, or both. Transcranial Doppler was used to measure changes in CBF velocity during lower body negative pressure (LBNP) before and after an 18-day bed rest in 33 healthy subjects. Subjects were assigned into four groups with similar age and sex: 1) supine cycling during bed rest (Exercise group; n = 7), 2) volume loading with Dextran infusion after bed rest to restore reduced left ventricular filling pressure (Dextran group; n = 7), 3) exercise combined with volume loading to prevent orthostatic intolerance (Ex-Dex group; n = 7), and 4) a control group ( n = 12). LBNP tolerance was measured using a cumulative stress index (CSI). After bed rest, CBF velocity was reduced at a lower level of LBNP in the Control group, and the magnitude of reduction was greater in the Ex-Dex group. However, reduction in orthostatic tolerance was prevented in the Ex-Dex group. Notably, volume loading alone prevented greater reductions in CBF velocity after bed rest, but CSI was reduced still by 25%. Finally, decreases in CBF velocity during LBNP were correlated with reduction in cardiac output under all conditions ( r2 = 0.86; P = < 0.001). Taken together, these findings demonstrate that volume loading alone can ameliorate reductions in CBF during LBNP. However, the lack of associations between changes in CBF velocity and orthostatic tolerance suggests that reductions in CBF during LBNP under steady-state conditions by itself are unlikely to be a primary factor leading to orthostatic intolerance.

scholarly journals Supine cycling plus volume loading prevent cardiovascular deconditioning during bed rest

2010 ◽  
Vol 108 (5) ◽  
pp. 1177-1186 ◽  
Author(s):  
Shigeki Shibata ◽  
Merja Perhonen ◽  
Benjamin D. Levine
Keyword(s):  
Exercise Training ◽  
Exercise Capacity ◽  
Orthostatic Intolerance ◽  
Lower Body Negative Pressure ◽  
Bed Rest ◽  
Left Ventricular ◽  
Orthostatic Tolerance ◽  
Volume Loading ◽  
Cardiac Atrophy ◽  
Cardiac Filling

There are two possible mechanisms contributing to the excessive fall of stroke volume (and its contribution to orthostatic intolerance) in the upright position after bed rest or spaceflight: reduced cardiac filling due to hypovolemia and/or a less distensible heart due to cardiac atrophy. We hypothesized that preservation of cardiac mechanical function by exercise training, plus normalization of cardiac filling with volume infusion, would prevent orthostatic intolerance after bed rest. Eighteen men and three women were assigned to 1) exercise countermeasure ( n = 14) and 2) no exercise countermeasure ( n = 7) groups during bed rest. Bed rest occurred in the 6° head-down tilt position for 18 days. The exercise regimen was prescribed to compensate for the estimated cardiac work reduction between bed rest and ambulatory periods. At the end of bed rest, the subjects were further divided into two additional groups for post-bed rest testing: 1) volume loading with intravenous dextran to normalize cardiac filling pressure and 2) no volume loading. Dextran infusion was given to half of the exercise group and all of the sedentary group after bed rest, leading ultimately to three groups: 1) exercise plus volume infusion; 2) exercise alone; and 3) volume infusion alone. Exercise training alone preserved left ventricular mass and distensibility as well as upright exercise capacity, but lower body negative pressure (LBNP) tolerance was still depressed. LBNP tolerance was maintained only when exercise training was accompanied by dextran infusion. Dextran infusion alone following bed rest without exercise maintained neither orthostatic tolerance nor upright exercise capacity. We conclude that daily supine cycle exercise sufficient to prevent cardiac atrophy can prevent orthostatic intolerance after bed rest only when combined with plasma volume restoration. This maintenance of orthostatic tolerance was achieved by neither exercise nor dextran infusion alone. Cardiac atrophy and hypovolemia are likely to contribute independently to orthostatic intolerance after bed rest.

scholarly journals Effect of rowing ergometry and oral volume loading on cardiovascular structure and function during bed rest

2012 ◽  
Vol 112 (10) ◽  
pp. 1735-1743 ◽  
Author(s):  
Jeffrey L. Hastings ◽  
Felix Krainski ◽  
Peter G. Snell ◽  
Eric L. Pacini ◽  
Manish Jain ◽  
...  
Keyword(s):  
Strength Training ◽  
Orthostatic Intolerance ◽  
Bed Rest ◽  
Left Ventricular ◽  
Cardiac Mass ◽  
Orthostatic Tolerance ◽  
Volume Loading ◽  
Cardiac Atrophy ◽  
Volume Load ◽  
Rowing Ergometry

This study examined the effectiveness of a short-duration but high-intensity exercise countermeasure in combination with a novel oral volume load in preventing bed rest deconditioning and orthostatic intolerance. Bed rest reduces work capacity and orthostatic tolerance due in part to cardiac atrophy and decreased stroke volume. Twenty seven healthy subjects completed 5 wk of −6 degree head down bed rest. Eighteen were randomized to daily rowing ergometry and biweekly strength training while nine remained sedentary. Measurements included cardiac mass, invasive pressure-volume relations, maximal upright exercise capacity, and orthostatic tolerance. Before post-bed rest orthostatic tolerance and exercise testing, nine exercise subjects were given 2 days of fludrocortisone and increased salt. Sedentary bed rest led to cardiac atrophy (125 ± 23 vs. 115 ± 20 g; P < 0.001); however, exercise preserved cardiac mass (128 ± 38 vs. 137 ± 34 g; P = 0.002). Exercise training preserved left ventricular chamber compliance, whereas sedentary bed rest increased stiffness (180 ± 170%, P = 0.032). Orthostatic tolerance was preserved only when exercise was combined with volume loading (−10 ± 22%, P = 0.169) but not with exercise (−14 ± 43%, P = 0.047) or sedentary bed rest (−24 ± 26%, P = 0.035) alone. Rowing and supplemental strength training prevent cardiovascular deconditioning during prolonged bed rest. When combined with an oral volume load, orthostatic tolerance is also preserved. This combined countermeasure may be an ideal strategy for prolonged spaceflight, or patients with orthostatic intolerance.

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 ◽  
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).

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.

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.

Cerebral blood flow velocity in humans exposed to 24 h of head-down tilt

1993 ◽  
Vol 74 (6) ◽  
pp. 3046-3051 ◽  
Author(s):  
Y. Kawai ◽  
G. Murthy ◽  
D. E. Watenpaugh ◽  
G. A. Breit ◽  
C. W. Deroshia ◽  
...  
Keyword(s):  
Blood Flow ◽  
Cerebral Blood Flow ◽  
Linear Regression ◽  
Cerebral Blood Flow Velocity ◽  
Bed Rest ◽  
Healthy Male ◽  
Increased Risk ◽  
The Right ◽  
Male Subjects ◽  
Peak Value

This study investigates cerebral blood flow (CBF) velocity in humans before, during, and after 24 h of 6 degree head-down tilt (HDT), which is a currently accepted experimental model to simulate microgravity. CBF velocity was measured by use of the transcranial Doppler technique in the right middle cerebral artery of eight healthy male subjects. Mean CBF velocity increased from the pre-HDT upright seated baseline value of 55.5 +/- 3.7 (SE) cm/s to 61.5 +/- 3.3 cm/s at 0.5 h of HDT (P < 0.05), reached a peak value of 63.2 +/- 4.1 cm/s at 3 h of HDT, and remained significantly above the pre-HDT baseline for > or = 6 h of HDT. During upright seated recovery (1–5 h post-HDT), mean CBF velocity decreased to 87% of the pre-HDT baseline value (P < 0.05). Mean CBF velocity correlated well with calculated intracranial arterial pressure (IAP) (r = 0.54, P < 0.001). As analyzed by linear regression, mean CBF velocity = 29.6 + 0.32IAP. These results suggest that HDT increases CBF velocity by increasing IAP during several hours after the onset of microgravity. Importantly, the decrease in CBF velocity after HDT may be responsible, in part, for the increased risk of syncope observed in subjects after prolonged bed rest and also in astronauts returning to Earth.

scholarly journals Perturbed and spontaneous regional cerebral blood flow responses to changes in blood pressure after high-level spinal cord injury: the effect of midodrine

2014 ◽  
Vol 116 (6) ◽  
pp. 645-653 ◽  
Author(s):  
Aaron A. Phillips ◽  
Andrei V. Krassioukov ◽  
Philip N. Ainslie ◽  
Darren E. R. Warburton
Keyword(s):  
Blood Pressure ◽  
Spinal Cord ◽  
Spinal Cord Injury ◽  
Blood Flow ◽  
Cerebral Blood Flow ◽  
Orthostatic Intolerance ◽  
Function Analysis ◽  
Orthostatic Tolerance ◽  
Transfer Function Analysis ◽  
Cord Injury

Individuals with spinal cord injury (SCI) above the T6 spinal segment suffer from orthostatic intolerance. How cerebral blood flow (CBF) responds to orthostatic challenges in SCI is poorly understood. Furthermore, it is unclear how interventions meant to improve orthostatic tolerance in SCI influence CBF. This study aimed to examine 1) the acute regional CBF responses to rapid changes in blood pressure (BP) during orthostatic stress in individuals with SCI and able-bodied (AB) individuals; and 2) the effect of midodrine (alpha1-agonist) on orthostatic tolerance and CBF regulation in SCI. Ten individuals with SCI >T6, and 10 age- and sex-matched AB controls had beat-by-beat BP and middle and posterior cerebral artery blood velocity (MCAv, PCAv, respectively) recorded during a progressive tilt-test to quantify the acute CBF response and orthostatic tolerance. Dynamic MCAv and PCAv to BP relationships were evaluated continuously in the time domain and frequency domain (via transfer function analysis). The SCI group was tested again after administration of 10 mg midodrine to elevate BP. Coherence (i.e., linearity) was elevated in SCI between BP-MCAv and BP-PCAv by 35% and 22%, respectively, compared with AB, whereas SCI BP-PCAv gain (i.e., magnitudinal relationship) was reduced 30% compared with AB (all P < 0.05). The acute (i.e., 0–30 s after tilt) MCAv and PCAv responses were similar between groups. In individuals with SCI, midodrine led to improved PCAv responses 30–60 s following tilt (10 ± 3% vs. 4 ± 2% decline; P < 0.05), and a 59% improvement in orthostatic tolerance ( P < 0.01). The vertebrobasilar region may be particularly susceptible to hypoperfusion in SCI, leading to increased orthostatic intolerance.

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.

scholarly journals Phenylephrine alteration of cerebral blood flow during orthostasis: effect on n-back performance in chronic fatigue syndrome

2014 ◽  
Vol 117 (10) ◽  
pp. 1157-1164 ◽  
Author(s):  
Marvin S. Medow ◽  
Shilpa Sood ◽  
Zachary Messer ◽  
Seli Dzogbeta ◽  
Courtney Terilli ◽  
...  
Keyword(s):  
Blood Flow ◽  
Cerebral Blood Flow ◽  
Chronic Fatigue Syndrome ◽  
Cerebral Blood Flow Velocity ◽  
Orthostatic Intolerance ◽  
Chronic Fatigue ◽  
Neurocognitive Deficits ◽  
Significant Drop ◽  
Control Subjects ◽  
Fatigue Syndrome

Chronic fatigue syndrome (CFS) with orthostatic intolerance is characterized by neurocognitive deficits and impaired working memory, concentration, and information processing. In CFS, upright tilting [head-up tilt (HUT)] caused decreased cerebral blood flow velocity (CBFv) related to hyperventilation/hypocapnia and impaired cerebral autoregulation; increasing orthostatic stress resulted in decreased neurocognition. We loaded the baroreflex with phenylephrine to prevent hyperventilation and performed n-back neurocognition testing in 11 control subjects and 15 CFS patients. HUT caused a significant increase in heart rate (109.4 ± 3.9 vs. 77.2 ± 1.6 beats/min, P < 0.05) and respiratory rate (20.9 ± 1.7 vs. 14.2 ± 1.2 breaths/min, P < 0.05) and decrease in end-tidal CO2 (ETCO2; 42.8 ± 1.2 vs. 33.9 ± 1.1 Torr, P < 0.05) in CFS vs. control. HUT caused CBFv to decrease 8.7% in control subjects but fell 22.5% in CFS. In CFS, phenylephrine prevented the HUT-induced hyperventilation/hypocapnia and the significant drop in CBFv with HUT (−8.1% vs. −22.5% untreated). There was no difference in control subject n-back normalized response time (nRT) comparing supine to HUT (106.1 ± 6.9 vs. 97.6 ± 7.1 ms at n = 4), and no difference comparing control to CFS while supine (97.1 ± 7.1 vs 96.5 ± 3.9 ms at n = 4). However, HUT of CFS subjects caused a significant increase in nRT (148.0 ± 9.3 vs. 96.4 ± 6.0 ms at n = 4) compared with supine. Phenylephrine significantly reduced the HUT-induced increase in nRT in CFS to levels similar to supine (114.6 ± 7.1 vs. 114.6 ± 9.3 ms at n = 4). Compared with control subjects, CFS subjects are more sensitive both to orthostatic challenge and to baroreflex/chemoreflex-mediated interventions. Increasing blood pressure with phenylephrine can alter CBFv. In CFS subjects, mitigation of the HUT-induced CBFv decrease with phenylephrine has a beneficial effect on n-back outcome.

Sign in / Sign up

Export Citation Format

Share Document