EFFECTS OF CPAP ON DAYTIME FUNCTIONS The Effect of CPAP in Normalizing Daytime Sleepiness , Quality of Life , and Neurocognitive Function in Patients with Moderate to Severe OSA

111 The Effect of CPAP on Neurobehavior in OSA—Antic et al CONTINUOUS POSITIVE AIRWAY PRESSURE (CPAP) HAS BEEN SHOWN TO REDUCE DAYTIME SLEEPINESS IN PATIENTS WITH OBSTRUCTIVE SLEEP APNEA (OSA) and is widely accepted as the most efficacious therapy for OSA. Patel and colleagues performed a meta-analysis showing that CPAP reduced the Epworth Sleepiness Scale (ESS) score an average of 2.9 points more than did placebo (P < 0.001) in patients with OSA. Patients with moderate to severe OSA had a greater fall in ESS than did those with mild OSA.1 What is less well understood is the dose-response relationship of CPAP treatment in patients with OSA and the proportion of patients who return to normal neurobehavioral function after CPAP therapy. These are important questions because it is known that CPAP adherence varies widely among patients.2 For example, in an early study, Weaver et al. reported that, among 32 patients using CPAP, half were consistent users, applying CPAP on more than 90% of nights for an average of 6.2 hours per night, whereas the other half were intermittent users who had a wide range of daily use, averaging 3.5 hours per night.3 In addition, although many patients present with excessive daytime sleepiness (EDS), this is a relatively nonspecific symptom.4 In the Sleep Heart Health study, the percentage of subjects with EDS, defined as an ESS score greater than 10, was increased from 21% in subjects with an AHI of less than 5 to 35% in those with an AHI of at least 30. Thus, many people without OSA were still subjectively reporting EDS.5 It is likely that, in a proportion of patients with OSA, sleep apnea may not be the dominant cause of sleepiness, and, thus, CPAP therapy may only partially improve EDS. In a population-based study, Bixler and colleagues6 found that depression was the most significant risk factor for EDS, followed by, in decreasing levels of importance, body mass index, age, typical sleep duration, diabetes, smoking, and finally OSA. The same group noted in an earlier study that obesity itself may be associated with EDS independent of OSA.7-9 Finally, recent evidence suggests that OSA may lead to permanent structural brain abnormalities.9,10 If these abnormalities EFFECTS OF CPAP ON DAYTIME FUNCTIONS