The carotid sinus baroreceptor reflex was studied in 15 healthy young men by a variable pressure neck suction chamber. Neck suction produced a reduction in blood pressure and an increase in RR interval, which were augmented by an increase of stimuli. Both responses occurred promptly and were attenuated with time. The reproducibility of the response was examined in 6 subjects. There were no differences in either hypotensive or bradycardiac responses between 2 runs separated by 1 hour, indicating

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... good short-term reproducibility. In a long-term reproducibility study involving 2 runs separated by 2 weeks, hypotensive responses showed similar changes, whereas bradycardiac responses showed a wide variation. Based on this good reproducibility of responses, the effects of diltiazem on baroreflex function were studied in 9 men. Following the administration of diltiazem (20mg, P.O.), the hypotensive responses to neck suction stimuli were significantly augmented compared to preadministration responses. On the other hand, diltiazem did not have a significant influence on heart rate responses. Thus, the present study shows that the neck chamber method is a feasible approach to studying the influence of given interventions on baroreflex function and demonstrates an enhancement of baroreflex-mediated hypotension by diltiazem.