Relationships of chronic hyperinsulinemia, heart rate variability, and circadian variation of blood pressure in obese hypertensive subjects

Background:During insulin resistance, sympathetic nerve activity is increased. However insulin resistance is a common feature of obesity and essential hypertension, it is unclear if chronic hyperinsulinemia per se contributes to sympathetic overactivation. The purpose of our study was to explore the relationship between hyperinsulinemia and heart rate variability (HRV), a noninvasive tool to assess autonomic function, in obese and hypertensive subjects. Methods:24-hour Holter ECG for HRV time and frequency domain analysis was performed in 77 patients: mean age 53 ± 10 years; 52 men and 25 women; free of diabetes; without beta-blockers. The patient were divided into four groups according to three parameters, body mass index (BMI > 27 kg/m2 in the men and > 25 kg/m2 in the women defined obesity), arterial pressure, and insulinemia (fasting insulinemia > 25 mUI/L defined hyperinsulinemia). Twenty-seven patients were obese, hypertensive, with hyperinsulinemia; 28 patients obese, hypertensive, without hyperinsulinemia; 12 patients nonobese, hypertensive, without hyperinsulinemia; 10 patients obese, normotensive, without hyperinsulinemia. Results:In comparison with the three other groups, patients with hyperinsulinemia showed a significant decrease (P < 0.05) of SDNN and the power of total spectrum (0.01–1 Hz) band, which are indexes of global HRV, and a significant decrease (P < 0.005) of SD and the normalized power of the low frequency (0.04–0.15 Hz) band, both indexes reflecting sympathetic modulation of HRV. In contrast, no significant difference was observed among the four groups for indexes of HRV reflecting parasympathetic tone. These relations were independent of mean R-R. Fasting insulinemia was significantly (P < 0.0001) related with HRV in time domain (SDNN: r =−0.43; SD: r =-0.49) and spectral domain (total spectrum: r =−0.49; low frequency: r =−0.52). Conclusion:Chronic hyperinsulinemia appears to be an important determinant of HRV, particularly for the indexes reflecting sympathetic influence, independent of obesity and hypertension. A.N.E. 1999;4(3):316–324