Endothelial dysfunction and C-reactive protein in relation with the severity of obstructive sleep apnea syndrome

Study Objectives: To investigate flow-mediated dilatation (FMD) and C-reactive protein (CRP) levels in patients with obstructive sleep apnea syndrome (OSAS) in relation with the severity of respiratory disturbances and hypoxemia. Design: After subjects had completed nocturnal polysomnography, FMD was measured in the brachial artery, and blood samples were obtained to determine serum CRP levels. Setting: Sleep laboratory in Seoul National University Bundang Hospital. Patients: Ninety men: 22 normal controls, 28 subjects with mild to moderate OSAS, and 40 with severe OSAS. Measurements and Results: FMD was found to be correlated with oxygen desaturation index (ODI), percentage of time below 90% O-2 saturation, average 0 2 saturation, lowest 0 2 saturation, systolic blood pressure, apnea hypopnea index (AHI), and body mass index. In addition, CRP was correlated with body mass index, waist-to-hip ratio, neck circumference, diastolic pressure, average O-2 saturation and percentage of time below 90% O-2 saturation but not with AHI. Stepwise multiple regression showed that the ODI was a significant determinant of FMD (adjusted R-2 = 10%, beta = -0.33, P < 0.01). In addition, body mass index (beta = 0.25, P < 0.05) and waist-to-hip ratio (beta = 0.21, P < 0.05) were found to be significantly correlated with CRP (adjusted R-2 = 12%, P < 0.05), independently of other factors. There was no correlation between FMD and CRP. Conclusion: As a marker of nocturnal hypoxemia, ODI rather than AHI might better explain the relationship between OSAS and FMD. Because body mass index and waist-to-hip ratio were identified as risk factors of high serum CRP in OSAS, obesity should be considered when predicting cardiovascular complications in OSAS.