Orthostatic tolerance and spontaneous baroreflex sensitivity in men versus women after 7 days of head-down bed rest

Custaud, Marc‐Antoine; Neto, Edmundo Pereira de Souza; Abry, Patrice; Flandrin, Patrick; Millet, Catherine; Duvareille, Monique; Fortrat, Jacques‐Olivier; Gharib, Claude

doi:10.1016/s1566-0702(02)00132-7

Cited by 62 publications

(59 citation statements)

References 29 publications

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“…Consistent with the literature (3,15,48), resting MAP was lower and resting HR was higher in females compared with males (Table 2). In addition, both HU groups exhibited a resting tachycardia compared with the CC animals.…”

Section: Resultssupporting

confidence: 91%

Hindlimb unloading and female gender attenuate baroreflex-mediated sympathoexcitation

Foley¹,

Mueller²,

Hasser³

et al. 2005

American Journal of Physiology-Regulatory, Integrative and Comp

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-Exposure to a period of microgravity or bed rest produces several physiological adaptations. These changes, which include an increased incidence of orthostatic intolerance, have an impact when people return to a 1G environment or resume an upright posture. Compared with males, females appear more susceptible to orthostatic intolerance after exposure to real or simulated microgravity. Decreased arterial baroreflex compensation may contribute to orthostatic intolerance. We hypothesized that female rats would exhibit a greater reduction in arterial baroreflex function after hindlimb unloading (HU) compared with male rats. Mean arterial pressure (MAP), heart rate (HR), and renal sympathetic nerve activity (RSNA) were recorded in conscious animals after 13-15 days of HU. Baseline HR was elevated in female rats, and HU increased HR in both genders. Consistent with previous results in males, baroreflex-mediated activation of RSNA was blunted by HU in both genders. Maximum RSNA in response to decreases in MAP was reduced by HU (male control 513 Ϯ 42%, n ϭ 11; male HU 346 Ϯ 38%, n ϭ 13; female control 359 Ϯ 44%, n ϭ 10; female HU 260 Ϯ 43%, n ϭ 10). Maximum baroreflex increase in RSNA was lower in females compared with males in both control and HU rats. Both female gender and HU attenuated baroreflex-mediated increases in sympathetic activity. The combined effects of HU and gender resulted in reduced baroreflex sympathetic reserve in females compared with males and could contribute to the greater incidence of orthostatic intolerance in females after exposure to spaceflight or bed rest. simulated microgravity; sympathetic nervous system; bed rest; deconditioning; hindlimb unweighting PROLONGED EXPOSURE TO MICROGRAVITY or bed rest results in a series of adaptations and changes including a central shift in body fluids, followed by a reduction in total blood and plasma volume, and muscle atrophy (46). Upon return to a 1G environment or to normal activity, individuals display resting tachycardia, decreased exercise capacity, and increased incidence of orthostatic intolerance (6,17,19). The mechanisms that account for these changes are still unresolved, although cardiac atrophy (39), altered vascular reactivity (17, 32), hypovolemia (47), and altered baroreflex control of sympathetic nerve activity (11, 18, 48) have been suggested, and all potentially contribute. In addition, females appear to be less tolerant of the negative effects of returning from spaceflight or a period of bed rest, because females exhibit a greater incidence of orthostatic intolerance after spaceflight compared with men (23, 48). The mechanisms that account for the greater susceptibility of women to the effects of microgravity and bed rest are unknown.The physiological response to an orthostatic challenge requires several compensatory mechanisms to maintain blood pressure and cerebral perfusion, including baroreflex-mediated increases in heart rate (HR) and vascular resistance (40). The arterial baroreceptor reflex is the primary controller of beat-tobe...

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Section: Resultssupporting

confidence: 91%

Hindlimb unloading and female gender attenuate baroreflex-mediated sympathoexcitation

Foley¹,

Mueller²,

Hasser³

et al. 2005

American Journal of Physiology-Regulatory, Integrative and Comp

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“…A decrease in plasma volume of 10-20% over the Wrst 30 days is a consistent Wnding for HDBR studies ranging from 30 to 90 days in male volunteers (Fortney et al 1988(Fortney et al , 1994Traon et al 1995;Custaud et al 2002;Belin de Chantemele et al 2004a). There have been few previous investigations of the eVects of HDBR on BV in women compared to men, and all such studies were of relatively short duration.…”

Section: Discussionmentioning

confidence: 58%

“…Several factors contribute to orthostatic intolerance: moderate hypovolemia (Buckey et al 1996;Custaud et al 2002), decreased stroke volume (Buckey et al 1996), myocardial atrophy (Levine et al 1997), reduced baroreXex sensitivity (Sigaudo-Roussel et al 2002) and increased distensibility of lower extremity blood vessels (Convertino et al 1989;Belin de Chantemele et al 2004b). Furthermore, females have a lower orthostatic tolerance than males (Convertino 1998;Fu et al 2004).…”

mentioning

confidence: 99%

WISE-2005: effect of aerobic and resistive exercises on orthostatic tolerance during 60 days bed rest in women

et al. 2009

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Cardiovascular deconditioning after long duration spaceXight is especially challenging in women who have a lower orthostatic tolerance (OT) compared with men. We hypothesized that an exercise prescription, combining supine aerobic treadmill exercise in a lower body negative pressure (LBNP) chamber followed by 10 min of resting LBNP, three to four times a week, and Xywheel resistive training every third day would maintain orthostatic tolerance (OT) in women during a 60-day head-down-tilt bed rest (HDBR). Sixteen women were assigned to two groups (exercise, control). Pre and post HDBR OT was assessed with a tilt/LBNP test until presyncope. OT time (mean § SE) decreased from 17.5 § 1.0 min to 9.1 § 1.5 min (¡50 § 6%) in control group (P < 0.001) and from 19.3 § 1.3 min to 13.0 § 1.9 min (¡35 § 7%) in exercise group (P < 0.001), with no signiWcant diVerence in OT time between the two groups after HDBR (P = 0.13). Nevertheless, compared with controls post HDBR, exercisers had a lower heart rate during supine rest (mean § SE, 71 § 3 vs. 85 § 4, P < 0.01), a slower increase in heart rate and a slower decrease in stroke volume over the course of tilt/ LBNP test (P < 0.05). Blood volume (mean § SE) decreased in controls (¡9 § 2%, P < 0.01) but was maintained in exercisers (¡4 § 3%, P = 0.17).Our results suggest that the combined exercise countermeasure did not signiWcantly improve OT but protected blood volume and cardiovascular response to sub tolerance levels of orthostatic stress.

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“…Custaud et al (11) in 2002 showed that six out of eight subjects had an abnormal response (POTS) following a 7-day strict HDT. Thus a strong cardiovascular deconditioning was observed in both groups after 60 days of HDT together with the impairment of the baroreflex sensitivity and of the autonomic balance.…”

Section: Limitationsmentioning

confidence: 99%

Low-magnitude whole body vibration with resistive exercise as a countermeasure against cardiovascular deconditioning after 60 days of head-down bed rest

Coupé

Yuan

Demiot³

et al. 2011

American Journal of Physiology-Regulatory, Integrative and Comp

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YH. Low-magnitude whole body vibration with resistive exercise as a countermeasure against cardiovascular deconditioning after 60 days of head-down bed rest. Am J Physiol Regul Integr Comp Physiol 301: R1748 -R1754, 2011. First published September 7, 2011 doi:10.1152/ajpregu.00234.2011.-Whole body vibration with resistive exercise is a promising countermeasure against some weightlessness-induced dysfunctions. Our objective was to study whether the combination of low-magnitude whole body vibration with a resistive exercise can prevent the cardiovascular deconditioning induced by a nonstrict 60-day head-down bed rest (Earth Star International Bed Rest Experiment Project). Fourteen healthy men participated in this study. We recorded electrocardiograms and blood pressure waves by means of a noninvasive beat-by-beat measurement system (Cardiospace, integrated by Centre National d'Etudes Spatiales and Astronaut Center of China) during an orthostatic test (20 min of 75-degree head-up tilt test) before and immediately after bed rest. We estimated heart rate, blood pressure, cardiac output, stroke volume, total peripheral resistance, baroreflex sensitivity, and heart rate variability. Low-magnitude whole body vibration with resistive exercise prevented an increase of the sympathetic index (reflecting the sympathovagal balance of cardiac autonomic control) and limited the decrease of the spontaneous baroreflex sensitivity induced by 60 days of head-down bed rest. However, this countermeasure had very little effect on cardiac hemodynamics and did not improve the orthostatic tolerance. This combined countermeasure did not efficiently prevent orthostatic intolerance but prevents changes in the autonomic nervous system associated with cardiovascular deconditioning. The underlying mechanisms remain hypothetical but might involve cutaneous and muscular mechanoreceptors. autonomic nervous system; cardiovascular deconditioning; baroreflex; hemodynamic; head-up tilt test DAILY GRAVITATIONAL STRESS is necessary to maintain the cardiovascular system in a healthy state. Orthostatic challenge induces cardiac, hormonal, autonomic, macrocirculatory, and microcirculatory responses. A chronic decrease in the gravitational stress (i.e., bed rest or a weightlessness environment) impairs the cardiovascular system with a deconditioning syndrome leading to orthostatic intolerance (9). Several countermeasures were developed and tested against this orthostatic intolerance. Although aerobic exercise (24) and lower-body negative pressure (23) appear to be beneficial against orthostatic intolerance (however, not fully prevented), resistive exercise alone showed only slight effects or even no effects (3). Whole body vibration has been proposed as a countermeasure to prevent muscle and bone deconditioning induced by bed rest and an environment of weightlessness (2). A recent study (41) compared the effects of whole body vibration associated with resistive exercise versus resistive exercise alone on the vascular changes induced by 60-day bed rest. I...

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Orthostatic tolerance and spontaneous baroreflex sensitivity in men versus women after 7 days of head-down bed rest

Cited by 62 publications

References 29 publications

Hindlimb unloading and female gender attenuate baroreflex-mediated sympathoexcitation

Hindlimb unloading and female gender attenuate baroreflex-mediated sympathoexcitation

WISE-2005: effect of aerobic and resistive exercises on orthostatic tolerance during 60 days bed rest in women

Low-magnitude whole body vibration with resistive exercise as a countermeasure against cardiovascular deconditioning after 60 days of head-down bed rest

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