HEART-RATE-VARIABILITY AND BAROREFLEX SENSITIVITY IN HYPERTENSIVE SUBJECTS WITH AND WITHOUT METABOLIC FEATURES OF INSULIN-RESISTANCE SYNDROME

Both abnormal autonomic control of heart rate, assessed by heart rate variability (HRV) and baroreflex sensitivity (BRS), and insulin resist ance syndrome are common in hypertensive patients. It is not known, ho wever, whether abnormalities in HRV and BRS in hypertension are relate d to the insulin-resistance syndrome. Therefore, we compared HRV and B RS in hypertensive subjects with and without metabolic features of the insulin-resistance syndrome. HRV was analyzed using the autoregressiv e method from a 45-min electrocardiographic recording (15 min lying, s itting, and standing) and BRS using the Valsalva maneuver. The groups were matched for age, sex, and antihypertensive medication, and age- a nd sex-matched normotensive subjects served as a control group (n = 69 in each group). The insulin-resistance syndrome was defined using the criteria of 1) hypertension (blood pressure > 160/90 mm Hg), 2) hyper triglyceridemia (fasting serum triglycerides greater than or equal to 2.0 mmol/L), and 3) hyperinsulinemia (fasting serum insulin greater th an or equal to 12 mU/L).Standard deviation of RR intervals, total, ver y-low-, and low-frequency power of HRV were significantly lower in hyp ertensive subjects with insulin-resistance syndrome compared to hypert ensive subjects without the syndrome and to normotensive controls (P < .001 for all), but the hypertensive group without the syndrome did no t differ from the normotensive group. High-frequency power of HRV (P < .01) and BRS (P < .05) were reduced in both hypertensive groups compa red to the normotensive group. In multiple regression analysis, systol ic blood pressure (P < .01) and serum triglyceride level (P < .001) we re independent predictors of reduced total power of HRV, but BRS was r elated only to systolic blood pressure (P < .01). Thus, most of the ab normalities in overall HRV seem to be confined to the subgroup of hype rtensive subjects with insulin-resistance syndrome, but baroreflex and respiratory modulation of heart rate are impaired also in hypertensiv e subjects without metabolic features of insulin-resistance syndrome. (C) 1998 American Journal of Hypertension, Ltd.