The hematocrit (Hct) of awake hamsters was lowered to 90% of baseline by isovolemic hemodilution using hamster plasma to determine the acute effect of small changes in Hct and blood viscosity on systemic hemodynamics. Mean arterial blood pressure (MAP) increased, reaching a maximum of about 10% above baseline (8.6 ± 5.5 mmHg) when Hct decreased 8.4 ± 1.9%, p < 0.005. Cardiac output increased continuously with hemodilution. These conditions were reached at ~ 60 min after exchange transfusion, and remained stationary for 1 hr. Peripheral vascular resistance was approximately constant up to a decrease of Hct of about 10% and then fell continuously with lowering Hct. Vascular hindrance or vascular resistance independent of blood viscosity increased by about 20% and remained at this level up to an Hct decrease of 20%, indicating that the vasculature constricted with the lowered Hct. Results for the initial 2 hr period are opposite but continuous with previous findings with small increases in Hct. In conclusion, limited acute anemic conditions increase MAP during the initial period of 2 hr, an effect that is quantitatively similar but opposite to the acute increase of Hct during the same period.
- blood pressure
- Copyright © 2010, American Journal of Physiology - Heart and Circulatory Physiology