Abstract： Objective To evaluate the clinical effect of regulating expiratory airway pressure of noninvasive ventilation(NIV)to treat overlap syndrome(OS)with respiratory failure by pressure titration in monitor during sleep.Method Individuals who met the following criteria were selected for the study:(1)OS with respiratory failure confiemed by polysomnogram(PSC)and pulmonary function tests;(2)ability to tolerate PSG tests all night;(3)lucid consciousness and spontaneous breathing upon awaken and(4)ability to tolerate NIV.The criteria of exclusion were:(1)frequent expectoration of blood or hemoptysis;(2)spontaneous pneumothorax;(3)severe prosopo-trauma or facial ulcer and(4)large amount of secretion in the airway.From August 2005 to Decentber 2008,27 patients were selected with two patients excluded.The remaining 25 patients treated with noninvasive bi-level positive airway pressure(BiPAP)were randomly assigned to titration group or control group.During sleep,the patients of titration group were put under the optimal expiratory airway pressure[EPAP,(8.8 ± 0.5)cmH2O]which was got from titration by AutoCPAP ventilator and the EPAP decreased immediately to 5 cmH2O when the patients wake up next day.In the patients of control group,the EPAP was maintained at 5 cm H2O round the clock.The degree of apnoea and the hypopnea index(AHI),the results of arterial blood gas analysis(pH,PaO2,PaCO2)in the morning,the lowest pulse oxygen saturation(SPO2LOW)and the arterial blood gas level at 10 am before and after ventilation,duration of taking off ventilator at night,complications of NIV,incidence of air leakage and invasive ventilation after NIV were comparatively analyzed between the two groups.Results Compared with the control group,the titration group showed a notably increase in the value of SPO2LOW[(25.9± 11.3)%vs.(14.9±8.4)%;P＜0.05].The PaO2 level was significantly higher in the titration group(29.4±4.4)mmHg than that in the control group(22.6 ± 2.1)mmHg(P＜0.0001);however,the PaCO2 level in the titration group(16.8 ±7.3)mmHg was not significant different from that in the control group(20.0±6.3)mmHg(P＞0.05).The PaO2 level at 10am in the titration group(28.9 ± 6.7)mmHg was not significant different from that in the control group(31.3 ± 7.7)mmHg(P＞0.05);however,the PaCO2 level in the titration group(23.3 ±5.7)mmHg was higher than that in the control group(18.2 ±5.0)mmHg(P＜0.05).Conclusions Regulating EPAP of NIV to treat overlap syndrome with respiratory failure by pressure titration in monitor during sleep was more effective at improving hypoxemia and carbon dioxide retention than traditional methods without adjusting the EPAP to the optimal level.The optimal didn't increase carbon dioxide retention at night,confirming that the method was safe.