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 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.

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 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.

Cardiac atrophy in women following bed rest

2007 ◽  
Vol 103 (1) ◽  
pp. 8-16 ◽  
Author(s):  
Todd A. Dorfman ◽  
Benjamin D. Levine ◽  
Tommy Tillery ◽  
Ronald M. Peshock ◽  
Jeff L. Hastings ◽  
...  
Keyword(s):  
Exercise Training ◽  
Female Athletes ◽  
Orthostatic Intolerance ◽  
Bed Rest ◽  
Major Axis ◽  
Left Ventricular ◽  
Protein Supplementation ◽  
Treadmill Running ◽  
Intermediate Phenotype ◽  
Cardiac Atrophy

Both chronic microgravity exposure and long-duration bed rest induce cardiac atrophy, which leads to reduced standing stroke volume and orthostatic intolerance. However, despite the fact that women appear to be more susceptible to postspaceflight presyncope and orthostatic hypotension than male astronauts, most previous high-resolution studies of cardiac morphology following microgravity have been performed only in men. Because female athletes have less physiological hypertrophy than male athletes, we reasoned that they also might have altered physiological cardiac atrophy after bed rest. Magnetic resonance imaging was performed in 24 healthy young women (32.1 ± 4 yr) to measure left ventricular (LV) and right ventricular (RV) mass, volumes, and morphology accurately before and after 60 days of 6° head-down tilt (HDT) bed rest. Subjects were matched and then randomly assigned to sedentary bed rest (controls, n = 8) or two treatment groups consisting of 1) exercise training using supine treadmill running within lower body negative pressure plus resistive training ( n = 8), or 2) protein (0.45 g·kg−1·day−1 increase) plus branched-chain amino acid (BCAA) (7.2 g/day) supplementation ( n = 8). After sedentary bed rest without nutritional supplementation, there were significant reductions in LV (96 ± 26 to 77 ± 25 ml; P = 0.03) and RV volumes (104 ± 33 to 86 ± 25 ml; P = 0.02), LV (2.2 ± 0.2 to 2.0 ± 0.2 g/kg; P = 0.003) and RV masses (0.8 ± 0.1 to 0.6 ± 0.1 g/kg; P < 0.001), and the length of the major axis of the LV (90 ± 6 to 84 ± 7 mm. P < 0.001), similar to what has been observed previously in men (8.0%; Perhonen MA, Franco F, Lane LD, Buckey JC, Blomqvist Zerwekh JE, Peshock RM, Weatherall PT, Levine BD. J Appl Physiol 91: 645–653, 2001). In contrast, there were no significant reductions in LV or RV volumes in the exercise-trained group, and the length of the major axis was preserved. Moreover, there were significant increases in LV (1.9 ± 0.4 to 2.3 ± 0.3 g/kg; P < 0.001) and RV masses (0.7 ± 0.1 to 0.8 ± 0.2 g/kg; P = 0.002), as well as mean wall thickness (9 ± 2 to 11 ± 1 mm; P = 0.02). The interaction between sedentary and exercise LV and RV masses was highly significant ( P < 0.0001). Protein and BCAA supplementation led to an intermediate phenotype with no change in LV or RV mass after bed rest, but there remained a significant reduction in LV volume (103 ± 14 to 80 ± 16 ml; P = 0.02) and major-axis length (91 ± 5 to 88 ± 7 mm; P = 0.003). All subjects lost an equivalent amount of body mass (3.4 ± 0.2 kg control; 3.1 ± 0.04 kg exercise; 2.8 ± 0.1 kg protein). Cardiac atrophy occurs in women similar to men following sedentary 60 days HDT bed rest. However, exercise training and, to a lesser extent, protein supplementation may be potential countermeasures to the cardiac atrophy associated with chronic unloading conditions such as in spaceflight and prolonged bed rest.

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.

Orthostatic intolerance during a 13-day bed rest does not result from increased leg compliance

1993 ◽  
Vol 74 (1) ◽  
pp. 286-292 ◽  
Author(s):  
F. M. Melchior ◽  
S. M. Fortney
Keyword(s):  
Orthostatic Intolerance ◽  
Lower Body Negative Pressure ◽  
Bed Rest ◽  
Venous Occlusion ◽  
Orthostatic Tolerance ◽  
Lower Body ◽  
Pressure Test ◽  
Before And After ◽  
Negative Pressure Test ◽  
The Relationship

Increased leg compliance (LC) has been proposed as a mechanism for orthostatic intolerance after spaceflight or bed rest. Using venous occlusion plethysmography with mercury-in-Silastic strain gauge, we evaluated LC before, during, and after a 13-day head-down (-6 degrees) bed rest in 10 men. LC was measured by the relationship between the increased calf areas (in cm2) at thigh cuff occlusions of 20, 30, 50, 70, and 80 mmHg. Orthostatic tolerance was evaluated by a presyncopal-limited lower body negative pressure test (PSL-LBNP) before and after bed rest. The 10 subjects were divided into TOL (n = 5) and INT (n = 5) groups for which the orthostatic tolerance was similar and lower after bed rest, respectively. For TOL (INT) before bed rest, calf area increases were 2.2 +/- 0.5 (SE) (1.3 +/- 0.4), 3.5 +/- 0.7 (2.3 +/- 0.5), 5.0 +/- 0.9 (3.5 +/- 0.6), 5.6 +/- 0.9 (4.4 +/- 0.6), and 6.4 +/- 1.1 (4.7 +/- 0.6) cm2 for thigh occlusion pressures of 20, 30, 50, 70, and 80 mmHg, respectively. Neither for INT nor for TOL were these results significantly changed by bed rest. These results suggest that other mechanisms than increased LC have to be taken into account to explain the decreased orthostatic tolerance induced by this 13-day bed rest.

scholarly journals Regulation of muscle sympathetic nerve activity after bed rest deconditioning

2001 ◽  
Vol 280 (5) ◽  
pp. H2230-H2239 ◽  
Author(s):  
James A. Pawelczyk ◽  
Julie H. Zuckerman ◽  
C. Gunnar Blomqvist ◽  
Benjamin D. Levine
Keyword(s):  
Vascular Resistance ◽  
Sympathetic Nerve ◽  
Sympathetic Nerve Activity ◽  
Orthostatic Intolerance ◽  
Lower Body Negative Pressure ◽  
Muscle Sympathetic Nerve Activity ◽  
Bed Rest ◽  
Orthostatic Tolerance ◽  
Nerve Activity ◽  
Stimulus Response

Cardiovascular deconditioning reduces orthostatic tolerance. To determine whether changes in autonomic function might produce this effect, we developed stimulus-response curves relating limb vascular resistance, muscle sympathetic nerve activity (MSNA), and pulmonary capillary wedge pressure (PCWP) with seven subjects before and after 18 days of −6° head-down bed rest. Both lower body negative pressure (LBNP; −15 and −30 mmHg) and rapid saline infusion (15 and 30 ml/kg body wt) were used to produce a wide variation in PCWP. Orthostatic tolerance was assessed with graded LBNP to presyncope. Bed rest reduced LBNP tolerance from 23.9 ± 2.1 to 21.2 ± 1.5 min, respectively (means ± SE, P= 0.02). The MSNA-PCWP relationship was unchanged after bed rest, though at any stage of the LBNP protocol PCWP was lower, and MSNA was greater. Thus bed rest deconditioning produced hypovolemia, causing a shift in operating point on the stimulus-response curve. The relationship between limb vascular resistance and MSNA was not significantly altered after bed rest. We conclude that bed rest deconditioning does not alter reflex control of MSNA, but may produce orthostatic intolerance through a combination of hypovolemia and cardiac atrophy.

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.

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