Relationships between chronic hyperinsulinemia, heart rate variability andcircadian variation of blood pressure in obese hypertensive subjects

Aims : During insulin resistance, sympathetic nerve activity is increased. However insulin resistance is a common feature of obesity and essential hyp ertension, it is unclear if chronic hyperinsulinemia per se contributes to sympathetic overactivation. The purpose of our study was to explor the rela tionships between chronic hyperinsulinemia and heart rate variability (HRV) , a non-intensive tool to assess autonomic function, in obese and hypertens ive subjects. Methods : 24 hours Holter ECG for HRV time and frequency domain analysis wa s performed in 77 patients, mean age 53 +/- 10 years, 52 men and 25 women, free of diabetes, without beta-blockers, divided in four groups according t o three parameters, body mass index (BMI > 27 kg/m(2) in man and > 25 kg/m( 2) in woman defined obesity), arterial pressure and insulinemia (fasting in sulinemia > 25 mUI/L defined hyperinsulinemia): 27 patients obese, hyperten sive, with hyperinsulinemia; 28 patients obese, hypertensive, without hyper insulinemia; 12 patients non obese, hypertensive, without hyperinsulinemia; 10 patients obese, normotensive, without hyperinsulinemia. Results : In comparison with the three other groups, patients with hyperins ulinemia 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 sig nificant decrease (p < 0.005) of SD and the normalized power of the low fre quency (0.04-0.15 Hz) band, both indexes reflecting sympathetic modulation of HRV. In contrast, no significant difference was observed between the fou r groups for indexes of HRV reflecting parasympathetic tone. These relation s were independent of mean RR. Fasting insulinemia was significantly (p < 0 .0001) related with HRV in time domain (SDNN: r = -0.43; SD : r = -0.49) an d spectral domain (total spectrum: r = -0.49; low frequency: r = -0.52). Conclusion : Chronic hyperinsulinemia appears to be an important determinan t of HRV, particularly for the indexes reflecting sympathetic influence, in dependent of obesity and hypertension.