Reduced orthostatic tolerance following 4 h head-down tilt

Butler, G. C.; Hua, Xing; Northey, David; Hughson, Richard L.

doi:10.1007/bf00635629

Cited by 47 publications

(28 citation statements)

References 8 publications

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“…Butler et al have found that only 4 h of HDBR modiWes cardiovascular responses to head-up tilt, with a marked increase in occurrence of presyncopal symptoms before 10 min of head-up tilt (Butler et al 1991). Khan et al observe that after 24 h of HDBR, the ability to augment the muscular sympathetic nerve activity at high levels of LBNP is reduced (Khan et al 2002).…”

Section: Discussionmentioning

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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Section: Discussionmentioning

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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“…Even though heart rate increased very little with Ϫ20 to Ϫ30 mmHg lower body negative pressure, MSNA is increased by lower body suction (23,31,38). It is possible that prolonged supine posture might have interacted with the lower body suction to modify the cardiovascular response, resulting in elevated heart rate, as has been observed after very short durations of slight head-down bed rest (2,25).…”

Section: Sympathetic Activation and Stress Responsementioning

confidence: 97%

Effect of acute sympathetic nervous system activation on flow-mediated dilation of brachial artery

Dyson

Shoemaker²,

Hughson

2006

American Journal of Physiology-Heart and Circulatory Physiology

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son. Effect of acute sympathetic nervous system activation on flowmediated dilation of brachial artery. Am J Physiol Heart Circ Physiol 290: H1446 -H1453, 2006. First published November 11, 2005 doi:10.1152/ajpheart.00771.2005.-We tested the hypothesis that flow-mediated dilation (FMD) of the brachial artery would be impaired by acute increases in sympathetic nervous system activity (SNA) in models where similar peak shear stress stimulus was achieved by varying the duration of forearm muscle ischemia. Eleven healthy young men were studied under four different conditions, each with its own control: lower body suction (LBS), cold pressor test (CPT), mental arithmetic task (MAT), and activation of muscle chemoreflex (MCR). The duration of ischemia before observation of FMD by ultrasound imaging was 5 min each for control, LBS, and CPT; 3 min for MAT; and 2-min for MCR. Peak shear rate was not different between control and any of the SNA conditions, although total shear in the first minute was reduced in MAT. MCR was the only condition in which brachial artery vasoconstriction was observed before forearm occlusion [4.38 (SD 0.53) vs. control 4.60 (SD 0.53) mm, P Ͻ 0.05]; however, diameter increased to the same absolute value as that of the control, so the percent FMD was greater for MCR . During SNA, the increase in plasma cortisol from baseline was significant only for MCR; the increase in plasma norepinephrine was significant for MCR, LBS, and CPT; and the increase in epinephrine was significant only for MCR. These results showed that the four models employed to achieve increases in SNA had different effects on baseline brachial artery diameter and that blunted FMD is not a general response to increased SNA. endothelium; shear stress; muscle chemoreflex; cold pressor test; mental stress FLOW-MEDIATED DILATION (FMD) is studied by high-resolution ultrasound imaging of the change in conduit artery vessel dimension in response to a sudden increase in blood flow after release of circulatory occlusion. When compared with that in healthy, young subjects, FMD is impaired in patients with coronary artery disease (27, 40), as well as essential (11, 28) and white-coat (13) hypertension. Reduced FMD reflects impaired endothelial function, which has been found to be an independent risk factor of coronary artery disease (6, 12). Some evidence suggests that FMD might also be impaired in apparently healthy subjects during an acute stress that elevates sympathetic nervous system activity (SNA) (18,24,35). However, these findings are not universal (17) and might depend on the nature of the stress and the experimental design. Lind et al. (24) concluded that acute increases in SNA with mental arithmetic and cold pressor tests impaired FMD when expressed relative to blood flow stimulus. Impaired FMD was also found during application of lower body suction (18), but a different study (17) of a mental arithmetic challenge reported enhanced FMD. Unfortunately, the magnitude of reactive hyperemia or shear stress was not measured in thi...

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“…A period of 4 days of HDT has been found sucient to induce orthostatic intolerance as con®rmed by the tilt-up test. It has been shown that development of orthostatic intolerance can be related to several factors such as: reduced plasma volume, decreased barore¯ex sensitivity, modi®-cation of the in¯uence of the sympathetic (increased) and parasympathetic (decreased) nervous systems, as well as reduced arterial vasomotor response and increased venous compliance, particularly in the lower limbs (Arbeille et al , 1995bBungo et al 1985;Butler et al 1991;Ganey et al 1985;Gharib et al 1992;Melchior and Fortney 1993;Piwinski et al 1994;Sigaudo et al 1996).…”

Section: Introductionmentioning

confidence: 97%

Femoral to cerebral arterial blood flow redistribution and femoral vein distension during orthostatic tests after 4 days in the head-down tilt position or confinement

Arbeille

Sigaudo

Traon³

et al. 1998

European Journal of Applied Physiology

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The first objective of this study was to confirm that 4 days of head-down tilt (HDT) were sufficient to induce orthostatic intolerance, and to check if 4 days of physical confinement may also induce orthostatic intolerance. Evidence of orthostatic intolerance during tilt-up tests was obtained from blood pressure and clinical criteria. The second objective was to quantify the arterial and venous changes associated with orthostatic intolerance and to check whether abnormal responses to the tilt test and lower body negative pressure (LBNP) may occur in the absence of blood pressure or clinical signs of orthostatic intolerance. The cerebral and lower limb arterial blood flow and vascular resistance, the flow redistribution between these two areas, and the femoral vein distension were assessed during tilt-up and LBNP by ultrasound. Eight subjects were given 4 days of HDT and, 1 month later, 4 days of physical confinement. Tilt and LBNP test were performed pre- and post-HDT and confinement. Orthostatic intolerance was significantly more frequent after HDT (63%) than after confinement (25%, P < 0.001). Cerebral haemodynamic responses to tilt-up and LBNP tests were similar pre- and post-HDT or confinement. Conversely, during both tilt and LBNP tests the femoral vascular resistances increased less (P < 0.002), and the femoral blood flow reduced less (P < 0.001) after HDT than before HDT or after confinement. The cerebral to femoral blood flow ratio increased less after HDT than before (P < 0.002) but remained unchanged before and after confinement. This ratio was significantly more disturbed in the subjects who did not complete the tilt test. The femoral superficial vein was more distended during post-HDT LBNP than pre-HDT or after confinement (P < 0.01). In conclusion, 4 days of HDT were enough to alter the lower limb arterial vasoconstriction and venous distensibility during tilt-up and LBNP, which reduced the flow redistribution in favour of the brain in all HDT subjects. Confinement did not alter significantly the haemodynamic responses to orthostatic tests. The cerebral to femoral blood flow ratio measured during LBNP was the best predictor of orthostatic intolerance.

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Reduced orthostatic tolerance following 4 h head-down tilt

Cited by 47 publications

References 8 publications

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

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

Effect of acute sympathetic nervous system activation on flow-mediated dilation of brachial artery

Femoral to cerebral arterial blood flow redistribution and femoral vein distension during orthostatic tests after 4 days in the head-down tilt position or confinement

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