Pathophysiological Significance of Parasympathetic Nervous System in Essential Hypertension : A Study of Coefficient of Variation of RR Intervals (CVRR) on Electrocardiogram

The pathophysiological role of the parasympathetic nervous system on essential hypertension （EHT） has not been fully understood due to methodological limitations and difficulties. We introduce two parasympathetic index by the heart rate variability on electrocardiogram: coefficient of variation of RR （CVRR） and power spectral analysis for this purpose. CVRR at rest was examined in 73 patients with EHT and in 87 normotensive subjects （NT）, and the influences of a 60°head-up tilt （tilt） and the changes produced by infused norepinephrine （NE-R,0.2μg/kg/min） on CVRR were investigated. Comparative studies on CVRR and the high-frequency （HF） component of power spectral analysis on RR, calculated as an index of parasympathetic activity, revealed strong positive correlation between the two variables. Moreover, CVRR had the same negative linear correlation with age logarithmically both in NT and EHT, and no significant differences were found between the groups. Similar correlations were observed between age and HF. Following tilt, CVRR decreased significantly both in NT （n=12） and EHT （n=11）, a significant negative correlation between percentage changes of CVRR （%ΔCVRR） and pNE （%ΔpNE） were also observed in the two groups, and there were no significant differences between NT and EHT. The change in MAP （ΔMAP） was correlated positively with %ΔCVRR in both NT （n=20） and EHT （n=30） following NE-R, but the regression line in EHT shifted to a lower %ΔCVRR level compared with NT. A percentage change of CVRR and %ΔCVRR/ΔMAP were significantly lower in EHT than agematched NT. These results suggest that CVRR should be considerd as a reliable clinical index for the parasympathetic nervous system and that parasympathetic activity in interaction with sympathetic tone is impaired in EHT, which might be attributable to the mechanism of high blood pressure in essential hypertension.departmental bulletin pape