Impairment of skin vasoconstrictive response to sympathetic activation in obese patients: influence of rheological disorders.

Alterations of cardiac vagosympathetic activity have been suggested in obesity. We have previously shown that the skin vasoconstrictive response to sympathetic activation is reduced in non-insulin-dependent diabetic patients. The present study investigates the skin vasoconstrictive response to sympathetic activation in nondiabetic obese patients and the influence of clinical and rheological factors. Fifty-seven obese and 18 healthy women were investigated. The resting cutaneous blood flow (CBF) and CBF response to three tests that activate the sympathetic nervous system (deep breathing, Valsalva maneuver, and sitting to standing) were measured by a laser Doppler device. The red blood cell (RBC) filtration index (FI) and RBC aggregation were measured using a Hanss hemorrheometer and a Myrenne aggregometer (Myrenne, Roetgen, Germany), respectively. Resting CBF was not significantly different in obese and control subjects. The vasoconstrictive response to the deep-breathing and sitting-to-standing tests expressed as the decrease in CBF was significantly lower in obese patients versus controls (43.9% +/- 3.1% v 73.7% +/- 17.9%, P = .01, and 67.1% +/- 3.8% v 89.8% +/- 12.0%, P = .02, respectively). The spontaneous basal CBF variations and the downward slope of the CBF reduction during the Valsalva and sitting-to-standing tests correlated negatively with age in obese patients (P = .042, .022, and .008, respectively). During the sitting-to-standing test, the percent change in CBF correlated positively with RBC aggregation at a shear rate of 0 and 3 s(-1) (P = .011 and .017, respectively). In conclusion, (1) CBF assessment by laser Doppler flowmetry is an effective noninvasive method to investigate sympathetic nervous function in obese patients; (2) obesity is associated with a significant reduction in the vasoconstrictive response to two tests for sympathetic activation, the deep-breathing and sitting-to-standing tests; (3) the severity of this reduction increases with age; and (4) RBC aggregation may contribute to the increase in the vasoconstrictive response and may thus increase the risk of widespread cardiovascular disease.