Shvartz E, Convertino V A, Keil L C, Haines R F
J Appl Physiol Respir Environ Exerc Physiol. 1981 Dec;51(6):1404-10. doi: 10.1152/jappl.1981.51.6.1404.
A tilt-table test was administered to five young men before (test 1) and after (test 2) 8 days of heat acclimation (2-h daily exercise at 50% VO2max at 40 degrees db, 30 degrees C wb) and to five other young men before and after the same exercise at 24 degrees C to determine fluid-electrolyte and endocrine responses in orthostasis in fainters and nonfainters. Half of the 10 subjects showed improved orthostatic reactions from test 1 to test 2 (disappearance of nausea and dizziness and improved heart rate and blood pressure), and the other 5 subjects showed no improvement. The improvement, especially in the nonfainters, was related to increases in posttilt plasma volume (PV) and plasma concentration of potassium. During test 1, plasma renin activity (PRA) increased five times from supine to orthostatis, with a corresponding increase in plasma vasopressin (ADH) of 50 times. The corresponding increases in test 2 were lower by 50 and 75% compared with those occurring in test 1 for PRA and ADH, respectively. PRA was five times higher in nonfainters than in fainters in test 1, whereas ADH showed an opposite trend. The orthostatic-induced increase in ADH seems to be related to volume control independent of PRA. This increase is reduced with improvement in orthostatic reactions, probably because of an increase in PV.
对五名年轻男性在热适应8天之前（测试1）和之后（测试2）进行了倾斜试验（每天在40℃干球温度、30℃湿球温度下以50%最大摄氧量进行2小时运动），并对另外五名年轻男性在24℃下进行相同运动之前和之后进行倾斜试验，以确定晕厥者和非晕厥者在直立状态下的体液电解质和内分泌反应。10名受试者中有一半从测试1到测试2直立反应有所改善（恶心和头晕消失，心率和血压改善），另外5名受试者没有改善。这种改善，尤其是在非晕厥者中，与倾斜后血浆容量（PV）增加和血浆钾浓度增加有关。在测试1期间，血浆肾素活性（PRA）从仰卧位到直立位增加了五倍，血浆血管加压素（ADH）相应增加了50倍。在测试2中，PRA和ADH的相应增加分别比测试1中的增加低50%和75%。在测试1中，非晕厥者的PRA比晕厥者高五倍，而ADH则呈现相反趋势。直立位引起的ADH增加似乎与独立于PRA的容量控制有关。随着直立反应的改善，这种增加会减少，可能是因为PV增加。
