Motivation and Outcome Expectancies Predict Adherence to CPAP before Experience with CPAP

Introduction: Continuous Positive Airway Pressure (CPAP) can be an effective therapy for Obstructive Sleep Apnoea (OSA), but adherence is often poor. Biomedical indices explain little of the variance in CPAP use. This study tested a motivational model of adherence using psychological constructs. Methods: 77 consecutive patients (61% male, mean age = 55.25, mean RDI = 38.36) newly diagnosed with OSA who were NAIVE to CPAP, completed questionnaires assessing; outcome expectancy with treatment, self-efficacy, functional outcomes of sleepiness, apnoea beliefs and perceived risk of negative health outcomes. Physiological data from standard clinical diagnostic sleep study was obtained. Objective CPAP adherence was assessed at 3 months post-treatment initiation. Results: Patients used CPAP an average 4.57 hours per night. Physiological indices explained 10.4% (p > 0.05) of the variance in CPAP adherence, while risk and self-efficacy uniquely explained an additional 6.3% of the variance (p > 0.05). Outcome expectancies and functional outcomes of sleep added in the final model explained an additional significant unique proportion of the variance (15.3%), and in combination with the above steps explained a total of 32% of the variance in CPAP adherence (R = 0.566, p < 0.01). Conclusion: Results supported a hierarchical model of adherence. Functional outcomes of sleepiness and outcome expectancies before CPAP is first tried uniquely predicted adherence suggesting that psychological indices, rather than disease severity and physiological indices, are most important in patients’ adherence to effective therapy. Significant inter-relationships between variables at each hierarchical step suggest the need for more sophisticated statistical modelling in explaining motivation to use CPAP