Effects of elevated-hematocrit levels on pulmonary circulation in conscious sheep.

We investigated the effects of stepwise hematocrit (Ht) increase on pulmonary circulation in conscious sheep (n = 7). The Ht was increased by an isovolumic exchange transfusion of blood with centrifuged red cells. By increasing the Ht-values, both systemic (PSA) and pulmonary artery pressures (PPA) were increased, with the degree of PPA increment greater than that of PSA. Cardiac output (CO) was slightly decreased by increasing the Ht. Also, A-V difference values of blood oxygen tension were reduced with elevation of the Ht values. The ratio of the right ventricular work rate (RVW) to the left one (LVW), RVW/LVW, was shown to increase remarkably with increased Ht. This increase was considered to be supporting evidence for the right ventricular hypertrophy in high altitude acclimatization. A strong positive correlation was observed between Ht and blood viscosity. It was thus confirmed that Ht effect was greater in pulmonary circulation than in systemic circulation.