Noninvasive assessment of the cardiac baroreflex: Response to downward tilting and comparison with the phenylephrine method

OBJECTIVES We studied the relation between changes in systolic blood pressu re and RR interval during downward tilting in comparison with assessment of baroreflex sensitivity (BRS) measured by the phenylephrine method (Phe-BRS ) and with measures of heart rate variability (HRV). BACKGROUND The method most extensively used for assessing BRS involves bolu s injections of phenylephrine. Several noninvasive methods proposed to asse ss BRS have not been widely applied in the clinical setting. METHODS Sixteen healthy male volunteers were studied (mean age +/- SD 27.5 +/- 4.6 years). Arterial blood pressure using tonometry and electrocardiogr am was simultaneously recorded. Alter 20 min of 70 degrees upright tilting, the table was returned to supine position at a speed of 3.2 degrees/s. Sub sequently, BRS was assessed using an intravenous bolus injection of phenyle phrine (2 to 3 mu g/kg). Heart rate variability under resting conditions al so was analyzed. RESULTS In all subjects, a beat to beat systolic blood pressure increase as sociated with corresponding RR interval lengthening was observed during dow nward tilting as well as during phenplephrine administration. During both t esting procedures, these two variables showed linear correlation, and the s lope of regression line during downward tilting (DT-BRS) correlated signifi cantly with Phe-BRS (r = 0.79, p = 0.0003). The DT- and Phe-BRS also correl ated significantly with the high frequency component of resting HRV (r = 0. 70, p = 0.0023 for DT-BRS; r = 0.58, p = 0.0185 for Phe-BRS). CONCLUSIONS We conclude that in a small homogeneous group DT-BRS provided a n assessment of reflex cardiac vagal function comparable to that obtained b y the phenylephrine method. (C) 1999 by the American College of Cardiology.