Abstract: Objective To analyze the effect of bi-level positive airway pressure(BiPAP) on the prognosis and vascular endothelial function of patients with obstructive sleep apnea hypopnea syndrome(OSAHS). 
Methods In total, 100 patients with OSAHS were included in the study, and randomly divided into observation group(n=50) and control group(n=50).The observation group was treated with BiPAP, while the control group was given routine treatment.Polysomnography(PSG) indexes(hypoventilation index, apnea index, apnea and hypopnea time, times of oxygen saturation below 90%, time of oxygen saturation below 90%), cardiopulmonary function brain natriuretic peptide(BNP), Tei index of the right ventricle, Tei index of the left ventricle, forced expiratory volume in one second/forced vital capacity(FEV1/FVC), forced expiratory volume in one second as a percentage of expected value(FEV1%pred), vascular endothelial function ［endothelin-1(ET-1), nitric oxide(NO), antithrombinⅢ(AT-Ⅲ)］ and quality of life were compared between two groups. 
Results The hypoventilation index, apnea index, apnea and hypopnea time, times of blood oxygen saturation below 90% and time indexes of blood oxygen saturation below 90% in the observation group were significantly lower than those in the control group(P＜0.05). After treatment, BNP and Tei index in the observation group were significantly lower than those before treatment and after treatment in the control group. FEV1/FVC and FEV1%pred in the observation group were significantly higher than those before and after treatment in the control group(P＜0.05). After treatment, ET-1 and AT-Ⅲ in the observation group were lower than those before treatment and after treatment in the control group, while NO in the observation group was higher than that before treatment and after treatment in the control group(P＜0.05). The scores of quality of life in the observation group were significantly higher than those in the control group(P＜0.05). 
Conclusion BiPAP treatment can improve the prognosis and vascular endothelial function of patients with OSAHS, showing definite curative effect.

Key words: sleep apnea, obstructive, continuous positive airway pressure, prognosis