Reflex cardiovascular regulation in humans.

Although studies of the cardiovascular control exerted by arterial baroreceptors in man are limited by technical and ethical problems, the variable-pressure neck-chamber technique has provided a considerable amount of information about this topic. This paper focuses on the carotid baroreceptor reflex as evaluated by studies using the neck-chamber technique and examines this control in a number of physiological and pathophysiological states. The results of these studies suggest that in normotensive subjects the set-point of the reflex is located eccentrically toward its saturation, which makes this homeostatic mechanism more effective in counteracting a blood-pressure fall than a blood-pressure rise. They also suggest that the concept of an impairment of the arterial baroreflex in aging, exercise, and hypertension, though valid for the baroreceptor control of heart rate, is no longer tenable for the baroreceptor control of arterial pressure. The paper also reviews in humans the effects of arterial baroreceptors on regional circulations and on the excretion of humoral substances such as renin, and compares them with those of the cardiopulmonary receptors. It is suggested that the latter predominate over the former in the reflex modulation of plasma-renin activity, and that this is part of a homeostatic mechanism for blood-volume control.