Effects of nicardipine and diltiazem on fractal features of short-term heart rate variability--application of coarse graining spectral analysis.
OBJECTIVE
This study was designed to investigate the effects of nicardipine and diltiazem on the fractal features of short-term heart rate variability (HRV), using coarse graining spectral analysis (CGSA).


METHODS
Eighteen healthy volunteers participated in this study; they were divided into two groups according to the drug administered. Five-minute electrocardiogram and arterial pressure recordings were made during stepwise infusions of either nicardipine (0.4, 0.8, 1.6, and 3.2 microg.kg(-1).min(-1)) or diltiazem (2, 4, 8, and 16 microg.kg(-1).min(-1)) under rate-controlled breathing at 0.25 Hz. CGSA broke down the total power of the time series into harmonic (low frequency [0.0-0.15 Hz; LF] and high frequency [0.15-0.5 Hz; HF]) and nonharmonic (fractal) components. Cardiac sympathetic nervous system (SNS) and parasympathetic nervous system (PNS) activity indicators were evaluated as the ratios LF/HF and HF/TP (total spectral power), respectively. Fractal components were evaluated as %fractal and the spectral exponent beta of 1/f(beta).


RESULTS
Compared with control measurements, the maximum dose of nicardipine infusion caused a significant decrease in systolic arterial pressure, a significant increase in the mean heart rate, and a significant increase in plasma norepinephrine level, findings that were associated with significant increases in %fractal and beta values (54.2 +/- 13.3 vs 75.6 +/- 9.8, and 0.86 +/- 0.22 vs 1.32 +/- 0.46, respectively; P < 0.05). PNS and SNS indicators showed decreased and increased values, respectively. Diltiazem caused a reduction in arterial pressure; however, no other parameters, including the nonharmonic components of HRV, were affected by this drug.


CONCLUSIONS
These findings strongly suggest that nicardipine suppresses vagal cardiac neural outflow and activate the SNS, an action which, subsequently, causes changes in the fractal features of HRV. Although diltiazem reduces arterial pressure, it preserves the basic neural balance of the autonomic nervous system in regard to heart rate control.