Relation of autonomic activity to plasminogen activator inhibitor-1 plasma concentration and the role of body mass index

We hypothesized an association between heart rate variability (HRV) and plasminogen activator inhibitor (PAI)-1 that would be affected by body mass index (BMI). We determined PAI-1 antigen in plasma and the low-frequency power, high-frequency power and the low-frequency/high-frequency power ratio from surface electrocardiogram data using spectral analysis in a sample of 116 black and white men and women (mean +/- SE age, 36.8 +/- 0.7 years). Regression equations controlled for age, gender, ethnicity, smoking status, blood pressure, and BMI. We specifically tested whether BMI would moderate or mediate the relationship between HRV and PAI-1. There were bivariate correlations between PAI-1 and low-frequency power (r= -0.24, P= 0.010), high-frequency power (r = -0.41, P < 0.001), and the low-frequency/highfrequency power ratio (r=0.19, P=0.042). High-frequency power emerged as an independent predictor of PAI-1 levels (beta = -0.20, P = 0.040; Delta R-2 = 0.027) after controlling for covariates. The BMI significantly mediated the relationship between PAI-1 levels and low-frequency power (t=-2.77, P= 0.006) and high-frequency power (t= -2.99, P= 0.003). In conclusion, reduced parasympathetic activity (i.e. decreased high-frequency power) accounted for a small but significant amount of the variance in elevated PAI-1 levels. More apparent, higher BMI explained a significant proportion of the variance in the relationship between depressed sympathetic and parasympathetic activity and elevated plasma PAI-1 concentration.