Individuals with obstructive sleep apnea-hypopnea syndrome (OSA) experience excessive daytime sleepiness and fatigue, decreased cognitive function and mood changes, resulting in significant, negative consequences in work and driving performance, and lowered quality of life (see review by [1
]). Therefore, the evaluation of OSA treatment on both nighttime and daytime consequences of OSA is critical.
The most obvious consequence and manifestation of untreated OSA are probably subjective sleepiness and high propensity to fall asleep during the daytime. Engleman and Douglas [2
] reviewed 29 studies that measured sleepiness and concluded that at least moderate impairments in terms of excessive daytime sleepiness are indicated in patients with OSA. Accumulating evidence suggests that the main causes of daytime sleepiness in patients with OSA are sleep fragmentation and sleep architecture disruptions [3
]. Some propose that sleepiness of patients with more severe OSA may be more related to the breathing disruptions and the associated nocturnal hypoxemia (e.g., [4
An association between OSA and mood disorders is revealed by studies reporting their comorbidity (e.g., [5
]). Previous studies also showed that individuals with OSA showed elevated scores on measures of depression, and 58% met the DSM criteria for depression [6
]. In the Wisconsin Sleep Cohort Study, longitudinal data demonstrated a dose-response association between OSA and depression in a community sample of 1408 participants [7
]. On the contrary, other studies do not find an association between OSA and psychological problems (e.g., [8
]). Authors like Cassel contend that the so-called personality change or psychological consequence of OSA is due to a misinterpretation of sleepiness by medical staff and the overlap of symptoms like fatigue between OSA and depression. The implication is that symptoms of fatigue and depression have to be distinguished in studies investigating mood in patients with OSA. Bardwell et al. [9
] concluded from their study that many of the previously reported links between mood and OSA dissipate after controlling for covariates such as age, BMI, and hypertension. But it should be noted that a strong relationship between OSA and mood was demonstrated even after potential confounds were controlled in a later study (see above) [5
The relationship between OSA and psychological problems is still uncertain, and the mechanisms of OSA-related mood symptoms are unknown. Depressive symptoms in patients with OSA have been proposed to be related to oxygen desaturation and nocturnal hypoxemia (e.g., [10
]) or to sleep fragmentation and excessive daytime sleepiness [11
]. It has also been shown that experimental sleep fragmentation produces significant mood symptoms [12
], supporting the potential effects of sleep disruption and daytime sleepiness on mood. However, it is difficult, if not impossible, for previous studies to distinguish the more direct effects of the illness itself (i.e., the hypoxic insults) and the indirect effects of daytime sleepiness on mood in patients with untreated OSA. Investigating stably treated individuals in which hypoxemia is eliminated or minimized would help elucidate the remaining effects of any persistent daytime sleepiness.
Continuous Positive Airway Pressure (CPAP) has been reported to be effective in improving subjective and objective measures of sleepiness in patients with OSA [13
], with therapeutic effects ranging from moderate to large [2
]. The average improvement for patients with severe OSA was 4.75 points on the Epworth Sleepiness Scale (ESS, [13
]). However, it is not uncommon for individual patients to continue to experience excessive daytime sleepiness with CPAP treatment (e.g., [4
]). A number of authors have reported improvements of psychological functioning after CPAP treatment (e.g., [15
]). Several placebo-controlled studies on the reversibility of psychopathology (mainly depression) have been conducted with mixed results [16
]. Sateia [18
] concluded that while the clinical impression suggests that OSA may be directly related to psychopathology and that treatments can reverse the impairments, the literature does not provide unequivocal support for these associations. In addition, another question that is left unanswered is whether the psychosocial functioning of stably treated patients is comparable to their peers without OSA.
The purpose of the current study was to investigate the relationship between any residual sleepiness or sleep issues and psychosocial functioning in individuals with stably treated OSA to understand their long-term outcomes. In order to ensure that the patients were indeed properly treated with CPAP, data on their pre-treatment status (i.e., PSG data, sleepiness scores, subjective sleep quality) were collected and compared with posttreatment data. Improvements on hypoxemia indices, sleepiness, and sleep quality were previously reported in an earlier paper focusing on cognitive functions [19
] and will be summarized in the results section. Here, we report in detail on how changes in sleepiness and sleep quality relate to psychosocial functioning posttreatment. The OSA group was also asked to rate their pre-treatment functional outcomes retrospectively to understand if and to what extent they perceived CPAP helped in terms of subjective daytime functions. We then investigated the predictors of the psychosocial functioning of individuals with treated OSA. Outcome variables included the mood measures and functional outcomes. Predictors examined were demographics, pre-treatment disease severity, and posttreatment sleep-related variables.
Based on the findings of previous studies, we hypothesized that (1) the OSA group will show improvements in their daytime sleepiness, sleep quality, and functional outcomes after CPAP treatment as compared to their pre-CPAP status; (2) current sleep variables would be more important in predicting psychosocial outcomes in individuals with stably treated OSA compared to pre-treatment diagnostic variables; (3) the associations between sleepiness, sleep quality, and psychosocial functioning would also apply to healthy age-matched controls.