Hypovolemia and neurovascular control during orthostatic stress

被引:75
作者
Kimmerly, DS [1 ]
Shoemaker, JK [1 ]
机构
[1] Univ Western Ontario, Sch Kinesiol, Neurovasc Res Lab, London, ON N6A 3K7, Canada
来源
AMERICAN JOURNAL OF PHYSIOLOGY-HEART AND CIRCULATORY PHYSIOLOGY | 2002年 / 282卷 / 02期
关键词
baroreflex; muscle sympathetic nerve activity; Doppler ultrasound; lower body negative pressure; vascular resistance; spironolactone;
D O I
10.1152/ajpheart.00535.2001
中图分类号
R5 [内科学];
学科分类号
1002 ; 100201 ;
摘要
Humans exposed to real or simulated microgravity experience decrements in blood pressure regulation during orthostatic stress that may be related to autonomic dysregulation and/or hypovolemia. We examined the hypothesis that hypovolemia, without the deconditioning effects of bed rest or spaceflight, would augment the sympathoneural and vasomotor response to graded orthostatic stress. Radial artery blood pressure (tonometry), stroke volume (SV), brachial blood flow (Doppler ultrasound), heart rate (electrocardiogram), peroneal muscle sympathetic nerve activity (MSNA; microneurography), and estimated central venous pressure (CVP) were recorded during five levels (-5, -10, -15, -20 and -40 mmHg) of randomly assigned lower body negative pressure (LBNP) (n = 8). Forearm (FVR) and total peripheral vascular resistance (TPR) were calculated. The test was repeated under randomly assigned placebo (normovolemia) or diuretic (spironolactone: 100 mg/day, 3 days) (hypovolemia) conditions. The diuretic produced an similar to16% reduction in plasma volume. Compared with normovolemia, SV and cardiac output were reduced by similar to12% and similar to10% at baseline and during LBNP after the diuretic. During hypovolemia, there was an upward shift in the %DeltaMSNA/DeltaCVP, DeltaFVR/DeltaCVP, and DeltaTPR/DeltaCVP relationships during 0 to -20 mmHg LBNP. In contrast to normovolemia, blood pressure increased at -40 mmHg LBNP during hypovolemia due to larger gains in the %DeltaMSNA/DeltaCVP and DeltaTPR/DeltaCVP relationships. It was concluded that acute hypovolemia augmented the neurovascular component of blood pressure control during moderate orthostasis, effectively compensating for decrements in SV and cardiac output.
引用
收藏
页码:H645 / H655
页数:11
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