Lundvall J, Bjerkhoel P
Department of Clinical Physiology, Växjö Hospital, Sweden.
J Appl Physiol (1985). 1994 Nov;77(5):2155-62. doi: 10.1152/jappl.1994.77.5.2155.
The hypothesis was tested that the hemoconcentration observed during standing provides erroneous information about the induced plasma volume (PV) decline. Male volunteers (n = 10) stood quietly for 15 min after supine rest. On standing arterial hemoglobin (Hb) rose slowly to reach an increase of 5.9 +/- 0.3% (SE) after 15 min. Early after resuming the supine position, Hb increased further to 9.2 +/- 0.5% above control level and then declined gradually. Venous antecubital blood from the left arm supported horizontally at heart level in both the supine and standing positions (no hydrostatic load) showed very similar changes. However, Hb in venous blood collected during standing from the right arm held in the natural dependent position rose much more markedly than that in arterial blood and in venous blood from the horizontal arm (470 +/- 122, 105 +/- 24, and 55 +/- 7% greater increase at 5, 10, and 15 min, respectively). Taken together, these observations indicated that 1) analyses of arterial blood sampled from the standing subject grossly underestimated the prevailing "overall" hemoconcentration and PV decline, a phenomenon ascribed to incomplete mixing of blood between dependent and nondependent regions; 2) arterial blood sampled from the recumbent subject early (60 s) after completion of standing reflected the "true" overall intravascular hemoconcentration, with a calculated PV decline of no less than 511 +/- 27 ml, because the supine position facilitated proper mixing of blood between circulatory compartments; 3) data from common venous sampling from the dependent arm during standing primarily reflected a regional hemoconcentration (fluid loss) in the arm rather than PV decline; and 4) short-term quiet standing caused a more prominent and hemodynamically important decrease in PV than usually believed.
该假设得到了验证，即站立期间观察到的血液浓缩会提供有关诱导血浆量（PV）下降的错误信息。男性志愿者（n = 10）在仰卧休息后安静站立15分钟。站立时动脉血红蛋白（Hb）缓慢上升，15分钟后增加5.9±0.3%（标准误）。恢复仰卧位后早期，Hb进一步升高至比对照水平高9.2±0.5%，然后逐渐下降。在仰卧位和站立位时，左臂水平支撑在心脏水平（无静水压负荷）的肘前静脉血显示出非常相似的变化。然而，站立期间从自然下垂的右臂采集的静脉血中的Hb升高比动脉血和水平手臂的静脉血中更为明显（在5、10和15分钟时分别增加470±122%、105±24%和55±7%）。综上所述，这些观察结果表明：1）对站立受试者采集的动脉血进行分析严重低估了当时的“总体”血液浓缩和PV下降，这种现象归因于血液在下垂和非下垂区域之间的混合不完全；2）站立完成后早期（60秒）从卧位受试者采集的动脉血反映了“真正”的总体血管内血液浓缩，计算出的PV下降不少于511±27毫升，因为仰卧位促进了循环腔室之间血液的适当混合；3）站立期间从下垂手臂进行的普通静脉采样数据主要反映了手臂的局部血液浓缩（液体流失）而非PV下降；4）短期安静站立导致PV下降比通常认为的更为显著且在血液动力学上更重要。
