Cardiovascular changes in awake dogs caused by suddenly induced aortic hypertension

Cardiovascular adaptation to the sudden inflation of a balloon in the descending aorta was investigated in intact awake, standing dogs. The balloon inflation raised pressure in the arterial bed proximal from the balloon. Initially, it lowered heart rate and cardiac output. After 4 sec, heart rate and cardiac output began increasing again and within the next 14 sec, these functions returned almost to the control values. The restoration of cardiac output was associated with a further rise in aortic pressure. These findings are consistent with the hypothesis that the prime circulatory adaptation to a hindrance to arterial flow is restoration of blood flow even though this requires a further elevation of arterial pressure. The demands of the tissues for an adequate supply of blood appear to override the inhibitory baroreceptor reflexes. The circulatory changes observed under conditions of attenuated parasympathetic inhibition and under conditions of attenuated beta-adrenergic stimulation were consistent with this interpretation. The findings suggest that arterial hyertension may involve a comparable adaptation of cardiac output in patients whose blood flow is hindered by pathologically narrowed arterioles.