Effects of nitroglycerin on fractal features of short-term heart rate and blood pressure variability

Abstract

Purpose. We investigated the effect of nitroglycerin(NTG) on fractal features of short-term heart rate variability (HRV) and blood pressure variability (BPV) using coarse-graining spectral analysis (CGSA).

Method. Nine healthy young volunteers participated in this study. Five-minute recordings of electrocardiogram and blood pressure estimated by photoplethysmograph were made during stepwise NTG infusions of 0.2, 0.4, 0.8, and 1.6 μg·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- and high-frequency) and nonharmonic (β of 1/f^β and %fractal) components.

Results. A statistically significant difference from the control period was observed during the maximum dose of NTG infusion, with decrease in mean blood pressure, shortening of mean R-R interval, and increase in plasma norepinephrine and epinephrine. The β in HRV increased significantly (0.89 ± 0.06 vs. 1.27 ± 0.13, P < 0.05). However, %fractal was not affected (47.9 ± 6.7 vs. 50.1 ± 4.0). Indicators of parasympathetic and sympathetic nervous system activity showed reduced and increased values, respectively. No change in BPV was observed for any measurement.

Conclusion. The data suggest that NTG significantly affected fractal features, as well as harmonic components, of short-term HRV. NTG had no effect on BPV, suggesting a different mechanism for genesis of 1/f^β fluctuation in BPV and HRV.