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.

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.

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 Orthostatic Intolerance Is Independent of the Degree of Autonomic Cardiovascular Adaptation after 60 Days of Head-Down Bed Rest

2015 ◽  
Vol 2015 ◽  
pp. 1-10 ◽  
Author(s):  
Jiexin Liu ◽  
Yongzhi Li ◽  
Bart Verheyden ◽  
Zhanghuang Chen ◽  
Jingyu Wang ◽  
...  
Keyword(s):  
Arterial Pressure ◽  
Orthostatic Intolerance ◽  
Low Frequency ◽  
Systolic Arterial Pressure ◽  
Bed Rest ◽  
Progressive Increase ◽  
Tilt Test ◽  
Sinus Arrhythmia ◽  
Before And After ◽  
Low Frequency Power

Spaceflight and head-down bed rest (HDBR) can induce the orthostatic intolerance (OI); the mechanisms remain to be clarified. The aim of this study was to determine whether or not OI after HDBR relates to the degree of autonomic cardiovascular adaptation. Fourteen volunteers were enrolled for 60 days of HDBR. A head-up tilt test (HUTT) was performed before and after HDBR. Our data revealed that, in all nonfainters, there was a progressive increase in heart rate over the course of HDBR, which remained higher until 12 days of recovery. The mean arterial pressure gradually increased until day 56 of HDBR and returned to baseline after 12 days of recovery. Respiratory sinus arrhythmia and baroreflex sensitivity decreased during HDBR and remained suppressed until 12 days of recovery. Low-frequency power of systolic arterial pressure increased during HDBR and remained elevated during recovery. Three subjects fainted during the HUTT after HDBR, in which systemic vascular resistance did not increase and remained lower until syncope. None of the circulatory patterns significantly differed between the fainters and the nonfainters at any time point. In conclusion, our data indicate that the impaired orthostatic tolerance after HDBR could not be distinguished by estimation of normal hemodynamic and/or neurocardiac data.

Abstract P192: Orthostatic Tolerance Before And After 60 Days Of Strict Head Down Tilt Bedrest With And Without Daily Artificial Gravity Training

Hypertension ◽  
2021 ◽  
Vol 78 (Suppl_1) ◽  
Author(s):  
Jan Hoenemann ◽  
Fabian Hoffmann ◽  
Stefan Moestl ◽  
Karten Heusser ◽  
Edwin Mulder ◽  
...  
Keyword(s):  
Stroke Volume ◽  
Plasma Volume ◽  
Orthostatic Intolerance ◽  
Lower Body Negative Pressure ◽  
Cardiovascular Responses ◽  
Pooled Analysis ◽  
Artificial Gravity ◽  
Control Group ◽  
Orthostatic Tolerance ◽  
Before And After

Background: Orthostatic intolerance occurs after space flight, immobilization and in patients with autonomic diseases, so there is a need for more effective countermeasures. We hypothesized that daily artificial gravity elicited through short-arm centrifugation attenuates plasma volume loss and orthostatic intolerance following 60 days of HDTBR, which models cardiovascular responses to weightlessness. Methods: We studied 24 healthy persons (8 women, 33.4±9.3 yr, 24.3±2.1 kg/m2) exposed to 60d HDTBR. Subjects were assigned to 30 min/d continuous short arm centrifugation (cAG), 6x5 min short arm centrifugation (iAG), or a control group (ctr, no countermeasures). Head-up tilt testing (15 min of 80°) followed by incremental lower body negative pressure (-10 mmHg every 3 min) until presyncope was performed before and at the end of HDTBR. Plasma volume was measured (CO rebreathing) 12-2 days before and after 56d of HDTBR. Stroke volume was measured by cMRI. Norepinephrine, epinephrine, aldosterone, and renine plasma levels were measured before and after HDTBR. Results: Time to presyncope decreased in all groups following bedrest (ctr: 22:56 min pre and 9:35 min post, cAG 15:34 min pre and 10:11 min post; iAG 14:56 min pre and 10:00 min post, p<0.001). The significant interaction (p=0.025) between bedrest and intervention was explained by greater baseline orthostatic tolerance time in the ctr. AG Data was pooled analysis. The reduction in stroke volume (ctr, pre: 93±19 ml, HDTBR: 69±13 ml, AG, pre: 88±20 ml, HDTBR: 67±17 ml) and plasma volume was similar (ctr, pre: 4155±1085 ml, HDTBR: 3855±1087 ml, AG, pre: 4114±1250 ml, HDTBR: 3674± 1313 ml). Catechols and aldosterone did not change significantly during bedrest. The increase in renine was similar between groups (ctr pre: 18±12 mE/L, HDTBR: 21±8 mE/L, AG pre: 21±10 mE/L, HDTBR: 31±12 mE/L). Conclusions: 30 min daily AG didn’t prevent a reduction in orthostatic tolerance following 60d HDTBR. Whether numerically smaller reductions in orthostatic tolerance in the AG groups indicate efficacy or result from baseline differences can’t be ascertained. A stronger AG stimulus or combination with other countermeasures might be required to maintain orthostatic tolerance and to attenuate the volume reduction.

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 The Effects of Intermittent Hypoxic Training on Anaerobic and Aerobic Power in Boxers

2020 ◽  
Vol 17 (24) ◽  
pp. 9361
Author(s):  
Tadeusz Ambroży ◽  
Marcin Maciejczyk ◽  
Andrzej T. Klimek ◽  
Szczepan Wiecha ◽  
Arkadiusz Stanula ◽  
...  
Keyword(s):  
Peak Power ◽  
Anaerobic Power ◽  
Training Session ◽  
Endurance Performance ◽  
Peak Oxygen Uptake ◽  
Control Group ◽  
Intermittent Hypoxic Training ◽  
Time To Peak ◽  
Hypoxic Training ◽  
Before And After

Background: The aim of the study was to evaluate the effects of intermittent hypoxic training (IHT) on anaerobic and aerobic fitness in elite, national boxers. Methods: The study was conducted over a period of 6 weeks. It comprised 30 national championship boxers, divided into 2 groups: the experimental and control. Both groups performed the same boxing training twice a day (morning and afternoon training). In the afternoon, the experimental group performed training under normobaric conditions in a hypoxic chamber (IHT), while the control group undertook exercise in standard normoxic conditions. In both groups, before and after the 6-week programme, basic anthropometric indices as well as anaerobic (Wingate Test) and aerobic (graded test) fitness were assessed. Results: There was a significant increase in anaerobic peak power (988.2 vs. 1011.8 W), mean anaerobic power (741.1 vs. 764.8 W), total work (22.84 vs. 22.39 kJ), and a decrease in fatigue index (20.33 vs. 18.6 W·s−1) as well as time to peak power (5.01 vs. 4.72 s). Such changes were not observed in the control group. In both groups, no significant changes in endurance performance were noted after the training session – peak oxygen uptake did not significantly vary after IHT. Conclusions: Our results have practical application for coaches, as the IHT seems to be effective in improving anaerobic performance among boxers.

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).

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.

Kidney protection by pretreatment with free radical scavengers and allopurinol: Renal function at recirculation after warm ischaemia in rabbits

1986 ◽  
Vol 71 (3) ◽  
pp. 245-251 ◽  
Author(s):  
R. Hansson ◽  
S. Johansson ◽  
O. Jonsson ◽  
S. Pettersson ◽  
T. Scherstén ◽  
...  
Keyword(s):  
Superoxide Dismutase ◽  
Renal Function ◽  
Serum Creatinine ◽  
Kidney Tissue ◽  
Urine Osmolality ◽  
Free Radical Scavengers ◽  
Control Group ◽  
Creatinine Concentration ◽  
Pronounced Increase ◽  
Before And After

1. Renal function and morphology were studied before and after 60 min of renal ischaemia and contralateral nephrectomy in five groups of rabbits. The animals were pretreated with superoxide dismutase, catalase, allopurinol or mannitol. One group was not pretreated and served as a control. 2. A moderate transient increase in serum creatinine concentration was observed in the control rabbits, while a significantly less pronounced increase was noted after pretreatment with superoxide dismutase, catalase and mannitol. 3. Pretreatment with allopurinol did not significantly reduce the postoperative increase in serum creatinine and sodium excretion, but the urine osmolality returned to normal more rapidly than in the control group. 4. The appearance under the light microscope of kidney tissue taken from surviving rabbits was found to be normal irrespective of pretreatment. Severe tubular necrosis was observed in the kidneys from rabbits that died during the observation period.

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