Relationship between hours of CPAP use and achieving normal levels of sleepiness and daily functioning

Study Objectives: Evidence suggests that, to maintain treatment effects, nasal continuous positive airway pressure (CPAP) therapy for obstructive sleep apnea (OSA) needs to be used every night. What remains unknown is the nightly duration of use required to normalize functioning. This study, employing probit analyses and piecewise regression to estimate doseresponse functions, estimated likelihoods of return to normal levels of sleepiness and daily functioning relative to nightly duration of CPAP. Design: Multicenter, quasi-experimental study. Setting: Seven sleep centers in the United States and Canada. Participants: Patients with severe OSA (total cohort n = 149; the numbers of included participants from 85 - 120, depending on outcome analyzed.) Interventions: CPAP. Measurements and Results: Before treatment and again after 3 months of therapy, participants completed a day of testing that included measures of objective and subjective daytime sleepiness and functional status. There were significant differences in mean nightly CPAP duration between treatment responders and nonresponders across outcomes. Thresholds above which further improvements were less likely relative to nightly duration of CPAP were identified for Epworth Sleepiness Scale score (4 hours), Multiple Sleep Latency Test (6 hours), and Functional Outcomes associated with Sleepiness Questionnaire (7.5 hours). A linear dose-response relationship (P < 0.01) between increased use and achieving normal levels was shown for objective and subjective daytime sleepiness, but only up to 7 hours use for functional status. Conclusions: Our analyses suggest that a greater percentage of patients will achieve normal functioning with longer nightly CPAP durations, but what constitutes adequate use varies between different outcomes. Keywords: Obstructive sleep apnea, dose response, nightly duration, daytime sleepiness, quality of life, CPAP, adherence, daily functioning, alertness