DIASTOLIC TIME - AN IMPORTANT DETERMINANT OF REGIONAL ARTERIAL BLOOD-FLOW

In unanesthetized dogs we measured heart rate, blood pressure, and ext ernal iliac, celiac, and renal artery flows on a beat-by-beat basis. A ll three flows fluctuated in synchrony with breathing. Although the fl uctuations in renal flow could to a large degree be explained by fluct uations in blood pressure, this was not the case in the external iliac artery where flow increased when pressure decreased and decreased whe n pressure increased. These paradoxical fluctuations in flow appear to be caused by respiratory fluctuations in heart rate, since we observe d a strong (r = 0.89) correlation between external iliac flow and the length of the preceding diastole. Single long diastolic periods, induc ed by atropine, were always followed by a beat of increased flow even though arterial pressure was constant. We conclude that diastolic time has a profound impact on blood flow during the next beat. Our data su pport a model of the arterial system in which backpressure to flow thr ough a bed is dependent on the amount of time for diastolic runoff int o the capillaries.