Time course of blood volume change with carbon monoxide inhalation and its contribution to the overall cardiovascular response.

Adult male Sprague-Dawley rats inhaled 500 ppm CO continuously for 42 days in order to examine the blood volume response in a time course manner. Plasma volume as measured by Evan's blue dye dilution technique did not change significantly from the control value of 3.96% of body weight (BW). Total blood volume estimated using plasma volume and hematocrit increased steadily from 7.34% of BW to 11.69%, almost entirely as the result of a more than 2-fold increase in erythrocyte mass (3.42% increased to 7.55%). Absolute blood volume increased from 28.51 ml to 58.26 ml; normal growth contributed to this increase, i.e. BW increased from 350.0 g to 499.1 g. "Real hematocrit" determined by dye dilution increased from 46.5% to 64.6%, reaching a near-equilibrium level within 15 days. Hemoglobin concentration increased from 13.68 g/dl to 20.07 g/dl, and erythrocyte count increased from 6,150,000 per cubic mm to 9,140,000 per cubic mm. Minor changes in erythrocyte indices (i.e. mean corpuscular hemoglobin concentration and mean corpuscular volume) occurred during the 42 days. Concurrently, the weight of right ventricle increased more than left ventricle + septum, reflecting somewhat greater right-sided cardiomegaly. Increases in both ventricles were correlated with changes in blood volume and hematocrit. Plasma atrial natriuretic peptide activity increased 2.5 fold after 15 and 30 days of CO exposure, possibly reflecting increasing atrial stretch caused by increased blood volume. Like the polycythemic hypervolemic state of chronic hypoxic hypoxia, blood volume in CO hypoxia increases solely through addition of erythrocytes.