Compared with the extensive research in maximizing adherence to treatments in such chronic diseases as asthma and diabetes, research into increasing patient use of positive pressure devices is in its infancy. In addition, adherence research is generally focused on pharmaceutical treatments, not cumbersome devices such as CPAP machines and associated mask types. However, the measurement of treatment adherence in CPAP therapy is more precise than metrics used with most pharmaceutical interventions. Smart cards, modem, or web-based methodology can be used to obtain data regarding the nightly duration of therapy at effective pressure—that is, the amount of time the mask is applied directly to the patient.
Using this technology, we know that the pattern of adherence is established early, within the first week of treatment, and predicts long-term use (13
). Those who skip nights of treatment also use CPAP for shorter nightly durations—on average, 3 hours per night (13
). Failure to use CPAP on a nightly basis permits the reemergence of daytime sleepiness and neurobehavioral deficits, even with one skipped night of treatment (20
However, an important limitation to evaluating individual adherence to CPAP and developing interventions to promote its use is knowing the exact implications of greater or fewer hours of effective use. Do greater hours of CPAP use improve cardiovascular, neurobehavioral, and cognitive outcomes? Is there interindividual variation in the relationship between hours of CPAP use and outcomes? Large-scale studies on this question are currently being implemented. It is also important to recognize that there are many patients who refuse to consider treatment for sleep apnea because of the nature of CPAP as a mechanical mask– and machine-based therapy. This nonacceptance of therapy is therefore a crucial cause of nonadherence.
Whether using CPAP all night every night provides the best clinical outcomes has recently become the focus of several studies. It has been observed that improvements in symptoms, daytime sleepiness, neurological behavior, blood pressure, and quality of life occur with greater use (22
). Some studies suggest that even low levels of application provide some benefit (24
). For example, an examination of the effect of nightly duration on 5-year survival rates found that use greater than 1 hour per night significantly lowered mortality (28
). However, this study was unable to differentiate benefit with nightly CPAP use of between 1 and 6 hours and use of more than 6 hours per night. Other studies, however, have demonstrated a dose–response relationship (see
). Normal levels of subjective sleepiness, objective sleepiness, memory, and daily functioning have been achieved with more than 4, 6, more than 6, and 7.5 hours per night, respectively (24
). Moreover, patients with sleep apnea are eight times more likely to obtain normal scores on a visual memory task with CPAP use of more than 6 hours per night (26
) compared with those using it for shorter durations. Using a variety of clinical outcomes, this evidence suggests that any use is better than no use, but greater gains in clinical outcomes may be obtained with longer nightly durations of CPAP therapy. It also indicates that the definition of optimal use may be outcome specific (24
). Although it remains unclear why some patients benefit with less CPAP use than others, independent of the baseline apnea–hypopnea index or degree of obesity, it is important to interpret adequate use in terms of benefits achieved (24
Figure 1. Cumulative proportion of participants obtaining normal threshold values on the Epworth Sleepiness Scale (squares), Multiple Sleep Latency Test (triangles), and Functional Outcomes of Sleep Questionnaire (diamonds). CPAP = continuous positive airway (more ...)