HYPERDYNAMIC CIRCULATION AND THE INSULIN RESISTANCE SYNDROME (SYNDROME-X)

The insulin resistance syndrome ("syndrome X") consists of hyperinsulinemia, glucose intolerance, dyslipidemia, and hypertension, although the inclusion of hypertension has been challenged. Insulin has biological effects that could produce a hyperdynamic circulation. We therefore postulated that an insulin-induced hyperdynamic circulation is an early feature of the insulin resistance syndrome and that this circulatory abnormality leads to later fixed hypertension. The San Antonio Heart Study cohort, a population-based cohort of 3,301 Mexican Americans and 1,857 non-Hispanic whites, was used to define individuals who were hyperdynamic (pulse pressure and heart rate in the upper quartile of their respective distributions), intermediate, and hypodynamic (pulse pressure and heart rate in the bottom quartile). The characteristics of the insulin resistance syndrome were then examined according to these three hemodynamic categories. We also examined the 8-year incidence of hypertension and of type II diabetes according to these hemodynamic categories. A hyperdynamic circulation was associated with statistically significant increases in body mass index (BMI) (p<0.001), subscapular-to-triceps skinfold ratio (p=0.042), triglyceride (p=0.002), 2-hour glucose (p=0.002), and fasting and 2-hour insulin (p=0.019 and 0.006). When hemodynamic status was examined separately in lean (BMI <27 kg/m2) and obese (BMI greater-than-or-equal-to 27 kg/m2) individuals, the above effects persisted, although they were somewhat attenuated. The odds ratio for the hyperdynamic state as a predictor of future hypertension was 1.66, although this was not statistically significant (p=0304). The odds ratio for predicting future type II diabetes was 3.97, which was statistically significant (p=0.047). Hyperdynamic individuals display many of the features of the insulin resistance syndrome, although hyperdynamic circulation was not predictive of future hypertension. It was, however, highly predictive of type II diabetes, itself a principal outcome of the insulin resistance syndrome.