Early detection of hypovolemia from directional arterial flow velocity.

The effect of hypovolemia on femoral artery vascular resistance and directional arterial flow velocity was determined in six mongrel dogs. Progressive withdrawal of blood was associated with an increase in femoral arterial resistance and reverse flow velocity and a decrease in forward flow velocity. The percentage increase in the ratio of peak reverse to peak forward flow velocity (Vr/Vf) varied in a positive linear fashion with the percent increase in femoral artery vascular resistance, (r = 0.69, P less than 0.001). The femoral arterial peripheral vascular resistance and peak Vr/Vf increased significantly before arterial pressure declined. These alterations in peak Vr/Vf occur early in the course of hypovolemia and are a sensitive index of extremity hemodynamics associated with hemorrhagic induced hypovolemia.