The influence of arterial pressure changes on blood volume replacement after acute hemorrhage in the alert rat

Abstract

The fluid content of circulating blood was followed continuously by conductometric measurement of large vein hematocrit in the alert rat. Arterial pressure was registered simultaneously. 2.5-23% of the determined blood volume was withdrawn rapidly and the changes of fluid content (delta v) calculated. Determinations of plasma protein showed that calculated delta v(delta vapp) may exceed true delta v due to transvascular fluid inflow by maximally 38%. A very fast phase of fluid inflow into the circulation (delta vfapp, within 1 min) was observed at the beginning, followed by a slow phase (delta vsapp), the magnitude of both being proportional to the concomitant arterial pressure drop (delta p). At delta p = 0, delta vfapp was 20% of the volume of blood withdrawn, total replacement (delta vfapp + delta vsapp = volume withdrawn) being complete in 60 min. At delta p = -20 mm Hg the figures were 40% and 20 min, respectively. Experiments on splenectomized animals showed essentially the same relations, excepting that delta vsapp may have been underestimated in normal rats. An arterial pressure rise after hemorrhage may attenuate complete replacement. The results are discussed in terms of capillary fluid conductivity. Thus CFC may be in the order of 0.029 ml/min x mm Hg x 100 g.

Continuous simultaneous measurement of plasma protein concentration and hematocrit in the alert rat. A short preliminary report

“…As mentioned, the method was developed in order to substantiate the results of experiments in which very rapid transvascular fluid movements were demonstrated essentially by blood conductometry (3,4,5). For the most part this has successfully been done qualitatively in the present experiments.…”

“…In previous papers (3,4,5), conductometrically measured hematocrit (hct) was monitored as an indicator of fluid content of blood flowing in various parts of the circulatory system of the rat. The assumption of a correlation between hct changes and transvascular fluid movements was substantiated by occasional determination of both hct and total plasma protein in situations where sufficiently large and sustained changes took place for reliable measurements.…”

Volume control during periodic changes of blood volume in the alert rat

“…As in previous papers (1,2), in which it was shown that very rapid changes of protein concentration accompany hematoerit changes in acute hemorrhage, changes of plasma volume were followed by continuous registration of large vein hematocrit by means of conductometry while producing in the present experiments pulsatile changes of blood volume of various fixed amplitudes and period lengths, thus varying blood withdrawal rates within wide limits. Beside hct, arterial pressure and heart rate were determined for assessment of their influences on fluid exchange between the two compartments of extracellular space.…”

“…The conductivity cell was calibrated during these and previous experiments to deliver hematocrit values by repeated determinations of packed cell volume in 30-40 ~tl samples of blood passing the cell during the experiment. Details of all procedures have been reported (1,2).…”

“…Since Av was linearly related to the magnitude of non-hypotensive blood volume reduction in a series of experiments with quasi static measurements of Av after random (not time-controlled) blood withdrawals (2), it may be suspected that the rate of blood volume decrease in hemorrhage may not play an important part in the rapid phase of blood volume replacement. The demonstration of such a non-dependence on rate would shed some light on the properties of the volume receptors (6) and perhaps of the low pressure circulatory system itself.…”