Microvascular endothelial function in patients with obstructive sleep apnea syndrome

Background: Obstructive sleep apnea syndrome (OSAS) is a novel risk factor for cardiovascular disease (CVD) and thought to be associated with endothelial dysfunction. Although many reports have demonstrated endothelial dysfunction of large conduit artery by flow-mediated dilatation in patients with OSAS, only a few reports have assessed microvascular endothelial function in OSAS patients. In this study, we investigated microvascular endothelial function by reactive hyperemia-peripheral arterial tonometry (RH-PAT) in patients with OSAS and assessed the effects of continuous positive airway pressure (CPAP) treatment on microvascular endothelial function. Methods: Twelve male patients with OSAS (51±13 yrs, body mass index [BMI]: 27.6±7.1 kg/m2, apnea hypopnea index [AHI]: 44±18/hr) and 12 male patients with CVD (54±13 yrs, BMI: 25.5±3.0 kg/m2) underwent an endothelial function test by RH-PAT using Endo-PAT 2000 before and 12 months after induction of CPAP treatment. Results: The baseline reactive hyperemia index (RHI) in patients with OSAS was similar to that in patients with CAD (1.78±0.48 vs 1.79±0.36, P=0.878). In patients with OSAS, the RHI increased 12 months after CPAP treatment (to 2.32±0.40; P=0.003). The change in RHI from baseline after CPAP treatment tended to have a negative correlation with the baseline 3% oxygen desaturation index (3% ODI) (R=-0.526, P=0.079) and was correlated negatively with the baseline AHI (R=-0.607, P=0.036). Conclusion: Microvascular endothelial function is impaired in patients with OSAS, but improves after CPAP treatment. In addition, the improvement of microvascular endothelial function through CPAP treatment was driven by mainly patients with mild to moderate OSAS at baseline.