Objective To evaluate the clinical effect of bilevel positive airway pressure ( BiPAP) ventilation via nasal/ mouth mask in elderly patients with respiratory failure secondary to the overlap syndrome ( OS). 目的探讨经口鼻面罩双水平气道正压通气(BiPAP)对老年重叠综合征(OS)并发呼吸衰竭患者的治疗作用。