Spontaneous Cardiac Baroreflex in Humans

Abstract

We compared two methods of assessment of baroreflex sensitivity in eight supine healthy volunteers during repeated baseline measurements and various conditions of cardiac autonomic blockade. The spontaneous baroreflex 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 decreased, with parallel changes in pulse intervals. The mean regression slope of all these sequences during each study condition was considered to represent the mean spontaneous baroreflex slope. In the drug-induced method, sigmoidal curves were constructed from data obtained by bolus injections of phenylephrine and nitroprusside; the tangents taken at the resting pressure of each of these curves were compared with the mean 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 the baroreflex slope; subsequent addition of propranolol did not alter it 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, noninvasive assessment of human vagal cardiac baroreflex sensitivity within its physiological operating range.

Validity and variability of xBRS: instantaneous cardiac baroreflex sensitivity

“…1995)). Rescaled nitroprusside (SNP) – phenylephrine (Phe) response data allow the generation of a sigmoidal cardiac baroreflex curve.…”

“…(1995) were reanalyzed. In brief, having obtained approval from the ethics committee of the Hospices Civils de Lyon and signed informed consent of the volunteers, eight healthy, normotensive, male physicians, aged 25–46 years, of average height and build were studied.…”

“…1995). In short, three sessions were scheduled for each subject in the morning of 3 days separated by approximately 2 weeks.…”

“…We sought to establish this by teaming up with Dr. Quintin and his group who had published on a BRS‐study (Parlow et al. 1995) with eight healthy subjects. They had used phenylephrine (Phe) and nitroprusside (SNP) bolus injections to determine the gold standard of BRS‐measurements (Smyth et al.…”

“…1969) and the “tangent method” or TG‐BRS (Parlow et al. 1995) reference value from the combination of those two. Moreover, the injections had been repeated under autonomic blockade with atropine, propranolol and clonidine, whereby different heart rates and different vagal/sympathetic effector balances had been established.…”