Recent advances in the physiology of cardiovascular reflexes, with special reference to hypotension.

The basic response of the carotid and aortic baroreceptor areas to pressure stimuli has been known for some years (Heymans and Neil, 1958); stimulation of these areas (acute hypertension) leads mainly to bradycardia and hypotension; reduction in receptor activity (acute hypertension) results in an increase in heart rate and an increase in arterial pressure. In this review, comments have been made on the inadequacy of the "control theory" approach in describing the details of such mechanisms. Some recent evidence is presented of the differences between the effects from stimulation of the carotid and aortic areas, of the modifying influences of efferent sympathetic nerves to the two receptor areas, and of some evidence for central nervous "control" of the reflexes. The responses of the reflexes in the complex situation of haemorrhage, together with possible reflex actions from the ventricles, are discussed.