Variations in the density of blood during hemorrhage

Abstract

It is known that hematocrit of the whole body (Htb) and venous or systemic hematocrit (Ht1) are different. The cell factor(ratio of whole body to venous Hct) F_c= Htb/Ht1. is around 0.85. Thus one can expect a drop in blood density during blood loss. Since the delivery of O2 (DO2) is proportional to cardiac output x Ht1; the variation of F_c reflects both the redistribution of (a) blood volume toward central circulation, to increase venous return and (b) RBC toward central circulation for the partially restoration of Ht1, the variation/stability of F_c could be a mechanism for compensation of variations of DO2.The aim of this study is to present a method of estimation of Htb/Ht1 during blood loss and to analyze variation of Htb/Ht1 during this challenge.Male Sprague‐Dawley rats (n=55) were hemorrhaged in 3–4 steps with 7 ml/kg body weight withdrawal of blood at each step. An arterio‐venous extracorporeal catheter (priming volume 0.8ml) was connected the carotid artery and jugular vein. Clamp on transit time sensors, TS450 flowmeter and an automatic algorithm (Transonic Systems Inc.) were used to calculate the cardiac output and blood volumes such as central blood volume and actively circulating blood volume.ResultsThe drop in blood density is proportional to F_cell and inversely proportional to the circulating blood volume. A linear drop in density during first and second withdrawals indicates the constancy of F_cell. After completion of the blood withdrawal the Htb/Ht1 was on average, slightly elevated (7% +/−6%), possibly due to the starting of refilling of intravascular volume.