SPONTANEOUS CARDIAC BAROREFLEX IN HUMANS - COMPARISON WITH DRUG-INDUCED RESPONSES

We compared two methods of assessment of baroreflex sensitivity in eig ht supine healthy volunteers during repeated baseline measurements and various conditions of cardiac autonomic blockade. The spontaneous bar oreflex method involved computer scanning of recordings of continuous finger arterial pressure and electrocardiogram to locate sequences of three or more beats in which pressure spontaneously increased or decre ased, with parallel changes in pulse intervals. The mean regression sl ope of all these sequences during each study condition was considered to represent the mean spontaneous baroreflex slope. In the drug-induce d method, sigmoidal curves were constructed from data obtained by bolu s injections of phenylephrine and nitroprusside; the tangents taken at the resting pressure of each of these curves were compared with the m ean spontaneous baroreflex slopes. The two methods yielded slopes that were highly correlated (r=.96, P<.001), with significant but similar intraindividual baseline variability. Atropine virtually eliminated th e baroreflex slope; subsequent addition of propranolol did not alter i t further. Propranolol or clonidine alone increased average baroreflex slope to the extent that they increased resting pulse interval (r=.69 to .83). The spontaneous baroreflex method provides a reliable, nonin vasive assessment of human vagal cardiac baroreflex sensitivity within its physiological operating range.