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

https://doi.org/10.1016/S0735-1097(99)00158-8Get rights and content
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Abstract

OBJECTIVES

We studied the relation between changes in systolic blood pressure 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 bolus injections of phenylephrine. Several noninvasive methods proposed to assess 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 electrocardiogram was simultaneously recorded. After 20 min of 70° upright tilting, the table was returned to supine position at a speed of 3.2°/s. Subsequently, BRS was assessed using an intravenous bolus injection of phenylephrine (2 to 3 μg/kg). Heart rate variability under resting conditions also was analyzed.

RESULTS

In all subjects, a beat to beat systolic blood pressure increase associated with corresponding RR interval lengthening was observed during downward tilting as well as during phenylephrine administration. During both testing procedures, these two variables showed linear correlation, and the slope of regression line during downward tilting (DT-BRS) correlated significantly with Phe-BRS (r = 0.79, p = 0.0003). The DT- and Phe-BRS also correlated 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 an assessment of reflex cardiac vagal function comparable to that obtained by the phenylephrine method.

Abbreviations

BRS
baroreflex sensitivity
DT-BRS
baroreflex sensitivity measured by the downward tilting method
ECG
electrocardiogram
HF
high frequency (0.15 to 0.45 Hz)
HRV
heart rate variability
LF
low frequency (0.04 to 0.15 Hz)
Phe-BRS
baroreflex sensitivity measured by the phenylephrine method

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