Abstract： Objective To investigate the possible association between residual sleepiness(RS)and central sleep apnea events in patients with obstructive sleep apnea syndrome(OSAS)following continuous positive airway pressure(CPAP)treatment,as well as the effects of adaptive servo-ventilation(ASV)on RS.Methods Following correct application of CPAP treatment and exclusion of other sleepiness-associated disorders,50 patients with mederate-to-severe OSAS were:recruited,including 26 patients with RS(RS group)and 24 patients without RS(control group).The treatment ofone month's auto-CPAP(AutoCPAP)followed by one week ASV with autoCS2 ventilator was performed.Comparisons were ntsde separately before treatment,on AutoCPAP and ASV treatments in beth groups of the following parameters:polysomnographic parameters including central sleep apnea index(CSAD,micro-arousal index(MAI),etc;daytime Epworth sleepiness score(ESS),and possibly sleepiness-associated factor,i.e.,plasma tumor necrosis factor-a (TNF-a).Plasma TNF-a levels were measured by enzynle linked immunosorbent assay(ELISA).t test and single factor analysis of variances were used for comparison between two groups and within group respectively.q test was used for couple comparison within group at 3 difierent stages.Pearson correlation test wag performed for correlation analysis between 2 variables.Results Before treatment there was no significant difference between two groups in apnea hypoapnea index(AHI),MAJ,minimal pulse oxygen saturation (minSpO2),ESS and plasma TNF-a levels(t:0.630、1.223、0.691、0.764 and 0.192,all P>0.05).However,the CSAI in RS group was significantly higherthan that in the control group[(7.19±1.75)times/h vs(3.37±1.04)times/h.t=4.097,P＜0.05)].After 1 month's AutoCPAP treatment there was a significant decrease in AHI,CSAJ,MAI and ESS in beth groups(q:0.87～112.55,all P＜0.05),but CSAI,MAI and ESS in the RS group than those in the control group[CSAI:(7.19±1.75)times/h vs(3.37±1.04)times/h,t=9.473,P＜0.05;MAI:(9.00±1.95)times/h vs(2.36±0.66)times/h,t=14.385.P＜0.05:ESS:9.54±0.51 vs 5.42±1.32.t=2.857,P＜0.05).On one weeks' ASV treatment there was such a further significant decrease in CSAI,MAI and daytime ESS in the RS group and the control group.In addition.compared with the plasma TNF-a level before treatment in the RS group,there was no statistical difference on AutoCPAP treatment but a significant decrease on ASV treatment.Plasma TNF-alevels were positively correlated with ESS(r=0.503.P＜0.01)and MAI(r=0.545,P＜0.01).Conclusions RS in OSAS patients following CPAP treatment was associated with their CSAI before and during treatment.By effectively eliminating CSA events with ASV.RS was significantly improved,which suggested that ASV was effective in treatment of RS.The elevation of plasma TNF-a level was correlated with the severity of sleepiness and may be involved in the pathogenesis of RS.