Study objectives: To assess the benefit of NCPAP in OSA and its relation to the degree of use of NCPAP.
Design: Randomised parallel controlled one month study comparing NCPAP set at therapeutic levels of pressure, with NCPAP set at sub-therapeutic pressure levels.
Setting: Teaching hospital sleep clinic and laboratory
Subjects: 101 men referred for investigation of possible OSA who were sleepy (Epworth Sleepiness Score > or = 10) and had > or = 10/hr of >4% dips in SaO2 due to OSA.
Outcome measures: Baseline and one month measures of Epworth Sleepiness Score (ESS), Maintenance of Wakefulness Test (MWT), and the Energy/Vitality dimension of the SF-36 (health status questionnaire). Correlation of these outcome measures with NCPAP usage.
Results: All outcome measures improved significantly more in the therapeutic, compared to the sub-therapeutic, group (e.g. ESS 15.0 to 13.0 on sub-therapeutic, and 15.5 to 7.0 on therapeutic, p<1x10(-6)). The degree of improvement correlated significantly with NCPAP usage in the therapeutic group (ESS, r=-0.60; MWT, r=0.55) but insignificantly in the sub-therapeutic group (ESS, r=-0.15; MWT, r=-0.06). Sub-therapeutic NCPAP did not improve OSA severity and acted as a control.
Conclusions: NCPAP is clearly effective in relieving the sleepiness of OSA compared to a control group identical in every way, except for receiving a nasal pressure inadequate to control the OSA.