Description:
Examination of the indicator concentration curves after rapid injection of normal saline reveals the existence of transient damped oscillations followed by a new, relatively stable level of arterial blood density. We hypothesized that the variation in density could be used to estimate ACV. To address this issue we analyzed the variation of arterial hematocrit (Ht1) during the injection/infusion of 0.9% NaCl; and performed experiments to answer the question: what is the rate of the restoration of blood density, in other words, what is the rate of leakage of injected normal saline from active circulation if (a) the blood volume is elevated up to 50% of expected and (b) if blood is withdrawn up to 30% of expected BV.Male SD rats (n=15) were anesthetized and received an extracorporeal A‐V loop connecting the carotid artery and the jugular vein with a controlled flow rate (8ml/min). Transit time clamp‐on sensors, TS450 flowmeter and an automatic algorithm (Transonic Systems Inc.) were used to calculate the cardiac output and central and actively circulating blood volume following injection of isotonic saline (0.3ml) into the venous limb of the AV loop. Hemorrhage was done by controlled blood withdrawals(~30 ml/kg in 3–4 steps). Increase of ACV was performed by series of 15–20 injections of 0.5–1 ml of normal saline.Results(1) Analysis of Ht1 variations reveals if Htb/Ht1 is constant then 0.9% NaCl is an indicator for ACV determination; (2) The rate of leakage of injected normal saline from active circulation is ~ 1–3%/min in normal or hypovolemic states and is up to 10%/min if ACV is elevated up to 30% of expected baseline.