Insulin resistance and alterations of cardiac vagal activity in obese subjects

We have previously shown that alterations of vagal control of heart rate Va riations are found in more than half of non diabetic obese subjects (Int J Obes 1995) and are associated with a more severe insulin resistance in noni nsulin dependent diabetic patients (Metabolism 1998). The aim of this study was to examine whether parasympathetic alterations are also associated wit h a more severe insulin resistance in non diabetic obese subjects. 245 obese subjects (BMI=34.2+/-0.4 kg/m(2)) aged 38.6+/-0.8 years, with a n ormal oral glucose tolerance test were included. Parasympathetic activity w as evaluated by heart rate variations during three standardised tests : Val salva, deep-breathing and active lying-to-standing, with age being taken in to account. The Valsalva maneuver was abnormal in 17.5%, the deep-breathing test in 18% and the lying-to-standing test in 30.3% of the cases. One hund red and thirty subjects (52.1%) had at least one abnormal test. Compared wi th those with three normal tests, the obese subjects with parasympathetic a lterations had very similar BMI and blood pressure, but significantly highe r values of heart rate (75.5+/-1.4 vs 71.3+/-1.1 beats/min, p=0.02), fastin g blood glucose (5.0+/-0.1 vs 4.8+/-0.1 mmol/L, p=0.03) and plasma insulin (98+/-6 vs 82+/-4 pmol/L, p=0.03). In the whole series of obese subjects, h eart rate variations during the deep-breathing and lying-to-standing tests correlated negatively with blood glucose (p=0.001 and p=0.03 respectively), and during the deep-breathing test they correlated negatively with the wai st/hip ratio (p=0.004). This data suggests that cardiac parasympathetic alterations should take par t in the insulin-resistance syndrome and might account for the poor cardiov ascular prognosis linked to this syndrome.