HEART-RATE-VARIABILITY IN SYSTEMIC HYPERTENSION

Low heart rate (HR) variability is a risk factor for cardiac mortality in various patient populations, but it has not been well established whether patients with long-standing hypertension have abnormalities in the autonomic modulation of HR, Time and frequency domain measures of HR variability were compared in randomly selected, age-matched popula tions of 188 normotensive and 168 hypertensive males (mean age 50 +/- 6 years for both). The standard deviation of the RR intervals was lowe r in the hypertensive subjects than in the normotensive ones (52 +/- 1 9 vs 59 +/- 20 mss; p <0.01), and the very low and low-frequency spect ral components of HR variability analyzed as absolute units were reduc ed in the hypertensive patients relative to the normotensive controls (p <0.001 for both). Hypertensive subjects also had blunted changes of the normalized low- and high-frequency components in response to an u pright (sitting) posture (NS) as compared with normotensive subjects ( p <0.001 for both), Multiple regression analysis showed the standard d eviation of the RR intervals to be predicted most strongly by systolic blood pressure, both in the patients with hypertension (beta - 0.20, p = 0.01) and in the normotensive subjects (beta - 0.28, p = 0.0002), After adjustment for the baseline differences in blood pressure and bo dy moss index, none of the absolute measures of the HR variability or the responses of the normalized units of HR variability to a change in the body posture differed between the hypertensive subjects and normo tensive controls, These data show that long-standing hypertension resu lts in reduced overall HR variability and blunted autonomic responses to a change in body pasture, Altered autonomic modulation of HR in hyp ertension is mainly due to elevated blood pressure and obesity in male s with long-standing hypertension as compared with normotensive subjec ts.