Circulatory effects of carotid sinus stimulation and changes in blood volume distribution in hypertensive man

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Abstract
In 8 patients with moderate hypertension and 8 normotensive subjects, the circulatory effects of high and low pressure baroreceptor stimulation was studied. Intrathoracic low pressure receptors were stimulated by changes in blood volume distribution using lower body negative pressure (LBNP) and lower body positive pressure (LBPP). The carotid sinus was stimulated by sinusoidal neck suction. Blood pressure, central venous pressure, heart rate, cardiac output and forearm blood flow were recorded. During LBNP and LBPP changes in central blood volume, reflected in changes in central venous pressure, induced significantly greater changes in cardiac output and forearm blood flow in the hypertensive subjects. In both normotensive and hypertensive subjects mean arterial blood pressure was essentially unchanged during LBNP and a slight increase was found during LBPP. Heart rate and blood pressure response to stimulation of the carotid sinus decreased with increasing resting mean arterial pressure. Impairment of reflex adjustments via arterial baroreceptors, possibly in particular to dynamic stimuli, rather than via intrathoracic low pressure baroreceptors, is suggested in subjects with moderate hypertension.