Vascular reactivity in obstructive sleep apnea syndrome

The obstructive sleep apnea syndrome (OSAS) is associated with cardiovascular disease and systemic hypertension. Because systemic arterial blood pressure is proportional to venodilation and venous return to the heart, we hypothesized that altered vascular responsiveness might exist in the veins of subjects with OSAS. We therefore investigated venodilator responses in awake, normotensive subjects with and without OSAS, using the dorsal hand vein compliance technique. Dose-response curves to bradykinin and nitroglycerin were obtained from 12 subjects with OSAS and 12 matched control subjects. Maximal dilation (E-max) to bradykinin was significantly lower in the OSAS group (62.1% +/- 26.1%) than in the control group (94.3% +/- 10.7%) (p < 0.005). Vasodilation to nitroglycerin tended to be lower in the OSAS group (78.6% +/- 31.8%) than the control group (100.3% +/- 12.9%), but this effect did not reach statistical significance. When six of the OSAS subjects were retested after 60 d of treatment with nasal continuous positive airway pressure (CPAP), E-max to bradykinin rose from 60.3% +/- 20.3% to 121.4% +/- 26.9% (p < 0.01). Vasodilation to nitroglycerin also increased, but this effect did not reach statistical significance. These results demonstrate that a blunted venodilatory responsiveness to bradykinin exists in OSAS. This effect appears to be reversible with nasal CPAP therapy.