Brown C M, Hainsworth R
Institute for Cardiovascular Research, University of Leeds, UK.
Clin Auton Res. 1999 Apr;9(2):69-73. doi: 10.1007/BF02311762.
Orthostatic stress causes, in addition to venous pooling, a loss of plasma fluid from capillaries to the dependent tissues. The rate of this loss may be one of the factors determining orthostatic tolerance. In this study we assessed the use of a multichannel impedance plethysmograph for determining changes in volume in the calf, thigh, and abdominal segments, in asymptomatic volunteers and in patients shown to have poor tolerance to orthostatic stress. Impedance plethysmography showed, for leg segments, that following head-up tilt there was an initial rapid change in volume followed after 2 to 4 minutes by an almost linear change. Results from the abdominal segment were more variable. The rate of change of leg (thigh + calf) volume was significantly correlated with the estimated loss of plasma volume derived from the changes in the concentration of plasma protein, using Evans Blue dye as the marker. Comparison of results of leg filtration rates between patients and volunteers indicated that some of the patients had abnormally high filtration rates and suggests that impedance plethysmography may have a role in assessing the possible reasons for orthostatic intolerance.
除静脉淤积外，直立位应激还会导致血浆液体从毛细血管流失至下垂组织。这种流失速率可能是决定直立耐力的因素之一。在本研究中，我们评估了多通道阻抗体积描记法在无症状志愿者以及对直立位应激耐受性差的患者中用于测定小腿、大腿和腹部节段体积变化的情况。阻抗体积描记法显示，对于腿部节段，头高位倾斜后，体积最初会快速变化，2至4分钟后则出现几乎呈线性的变化。腹部节段的结果更具变异性。腿部（大腿 + 小腿）体积的变化速率与使用伊文思蓝染料作为标志物、根据血浆蛋白浓度变化估算的血浆体积损失显著相关。患者与志愿者腿部滤过率结果的比较表明，部分患者的滤过率异常高，这表明阻抗体积描记法可能在评估直立不耐受的可能原因方面具有一定作用。
