Phenylephrine bolus injection is an established technique to measure baroreflex sensitivity (BRS). This study quantified the relationship between the phenylephrine method and noninvasive measures of BRS and examined the effects of aging and hypertension on BRS. We also examined whether heart rate variability (HRV) provides as much information as does BRS.Methods
BRS was determined by phenylephrine bolus (BRSphe), amyl nitrite inhalation (BRSamyl), Valsalva maneuver (BRSVals) and by time (BRS(+)) and spectral domain analysis (BRSLFα, 004–015 Hz) of spontaneous blood pressure and R–R interval changes over the 5-min time period.Results
The phenylephrine method significantly correlated with other methods (BRSLFα R = 0.54, BRS(+)R = 0.55, BRSValsR = 0.43 and BRSamylR = 0.39; P ≤ 0.001). Each method underestimated the BRSphe by the factors 0.62, 0.64, 0.59 and 0.33, respectively; P value less than 0.001. Only BRSLFα was significantly different between normotensive and hypertensive patients in young [24.3 ± 1.4 (n = 40) vs. 12.2 ± 2.3 (n = 7)] and middle-aged [16.5 ± 1.1 (n = 71) vs. 10.8 ± 1.1 (n = 31) groups, respectively]. HRV in the high frequency band (0.15–0.40 Hz) was significantly lower in young hypertensive patients than in normal controls (26 ± 6.0 vs. 50 ± 2.4, P < 0.05).Conclusion
Although all methods correlated with the phenylephrine technique, none of them could be used interchangeably with that technique. BRSLFα detected the baroreflex loss of hypertension most clearly, and BRSamyl did not differ among groups.