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 resistance syndrome are common in hypertensive patients. It is not known, however, whether abnormalities in HRV and BRS in hypertension are related to the insulin-resistance syndrome. Therefore, we compared HRV and BRS in hypertensive subjects with and without metabolic features of the insulin-resistance syndrome. HRV was analyzed using the autoregressive method from a 45-min electrocardiographic recording (15 min lying, sitting, and standing) and BRS using the Valsalva maneuver. The groups were matched for age, sex, and antihypertensive medication, and age- and 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) hypertriglyceridemia (fasting serum triglycerides > or =2.0 mmol/L), and 3) hyperinsulinemia (fasting serum insulin > or =12 mU/L). Standard deviation of RR intervals, total, very-low-, and low-frequency power of HRV were significantly lower in hypertensive subjects with insulin-resistance syndrome compared to hypertensive subjects without the syndrome and to normotensive controls (P < .001 for all), but the hypertensive group without the syndrome did not differ from the normotensive group. High-frequency power of HRV (P < .01) and BRS (P < .05) were reduced in both hypertensive groups compared to the normotensive group. In multiple regression analysis, systolic blood pressure (P < .01) and serum triglyceride level (P < .001) were independent predictors of reduced total power of HRV, but BRS was related only to systolic blood pressure (P < .01). Thus, most of the abnormalities in overall HRV seem to be confined to the subgroup of hypertensive subjects with insulin-resistance syndrome, but baroreflex and respiratory modulation of heart rate are impaired also in hypertensive subjects without metabolic features of insulin-resistance syndrome.