Pronounced and rapid plasma volume reduction upon quiet standing as revealed by a novel approach to the determination of the intravascular volume change

Abstract

Plasma volume (PV) changes to 15 min quiet standing were analysed (Hb/Hct-alterations) in two studies (nine and 11 healthy males). Data confirmed and extended our findings that blood, arterial or venous, sampled on standing fails to reveal the induced overall haemoconcentration (PV loss). First, standing led to markedly incomplete mixing of blood between circulatory compartments. Secondly, with sampling of antecubital venous blood, haemoconcentration was strongly affected by regional plasma loss and, apparently equally important, by regional blood flow. These difficulties were circumvented, however, by the finding that the PV restitution (haemoconcentration) in the recumbent subject after standing fitted invariably a monoexponential function with striking precision. It allowed, by extrapolation, a seemingly superior definition of the PV reduction at the very end of standing as supported by the fact that PV changes from Hb/Hct and from IgM protein concentration changes were similar, refuting that Fcell-changes contributed to the pronounced Hb/Hct changes. The described novel approach revealed a nicely reproducible PV loss of no less than 692 +/- 46 mL (18.1 +/- 0.6%, Study I; 18.4 +/- 0.5%, Study II), or approximately 11% reduction of blood volume, showing that quiet standing leads to a much more rapid and haemodynamically important decrease in PV than reported previously. Yet, PV was virtually restored within 20 min of recumbency after standing, with 50% recovery within 6 min and regain of as much as 70 mL in the very first min. The latter data indicate that the body possesses a surprising capacity for rapid fluid transfer from the extra- to the intravascular space.

Water ingestion as prophylaxis against syncope

“…In addition, blood was taken for assay 1 minute after the onset of presyncope or syncope for estimation of plasma volume change. [13][14][15] Signals for blood pressure, the ECG, and bioimpedance were sampled at 500 Hz using Dataq model DI-220 and visualized using Windaq Proϩ software (Dataq Instruments Inc). Complete recordings of R-R interval, finger blood pressure values, and respiration were analyzed offline with a program based on PV-wave software (Visual Numerics Inc).…”

Relative Blood Volume Changes Underestimate Total Blood Volume Changes during Hemodialysis

“…This time interval was chosen to allow adequate distribution of the radioiodinated isotopes (15,16). For avoidance of the widely known influence of postural changes on blood volume (18) and F cell ratio (19,20), patients were placed in a supine position 20 min before blood sampling for erythrocyte labeling with 51 Cr and remained in this position until the study protocol was completed (from 100 min before the start of HD until the stop of HD). After completion of the erythrocyte labeling with 51 Cr, the patients' own blood supplemented with 125 I-albumin was administered.…”

Critical Evaluation of Blood Volume Measurements during Hemodialysis

“…Postural changes have a profound effect on plasma volume in healthy subjects [16] and in HD patients [17]. Upon standing, the hematocrit increases because of a decrease in plasma volume due to a fluid shift from the circulation to the interstitial tissue of the dependent regions of the body.…”