CLINICAL STUDIES
Noninvasive assessment of the cardiac baroreflex
Response to downward tilting and comparison with the phenylephrine method
Naohiko Takahashi, MD*,
Mikiko Nakagawa, MD ,
Tetsunori Saikawa, MD*,
Tatsuhiko Ooie, MD* ,
Tadafumi Akimitsu, MD*,
Koji Kaneda, MD*,
Masahide Hara, MD*,
Tetsu Iwao, MD,
Hidetoshi Yonemochi, MD,
Morio Ito, MD and
Toshiie Sakata, MD*
* Department of Internal Medicine I, School of Medicine, Oita Medical University, Oita, Japan
Department of Laboratory Medicine, School of Medicine, Oita Medical University, Oita, Japan
Manuscript received April 28, 1998;
revised manuscript received February 9, 1999,
accepted March 15, 1999.
Reprint requests and correspondence: Dr. Naohiko Takahashi, Department of Internal Medicine I, School of Medicine, Oita Medical University, 1-1 Idaigaoka, Hasama, Oita 879-5593, Japan
takanao{at}oita-med.ac.jp
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.
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Abbreviations and Acronyms
| | 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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