Blood volume expansion among blacks: an hypothesis.

Black persons are believed to have developed in a tropical environment and an expanded blood volume would have facilitated adaptation to such an environment. Throughout most of the first half of the life cycle blacks have slower heart rates than whites, and several lines of evidence suggest that heart rate is inversely related to blood volume. Review of blood volume studies in normotensive whites and normotensive blacks does not permit any conclusion concerning the blood volume hypothesis. Among patients with hypertension results of blood volume studies are inconsistent, but indirect evidence suggests that black patients with hypertension have greater plasma volume expansion than white patients with hypertension.