Although causality cannot be discerned from these studies, intervention studies provide important clues. Means and colleagues9 showed that treatment of obstructive sleep apnea with continuous PAP reduced the depressive symptoms. Continuous PAP reduced depression scores in patients with major depression and obstructive sleep apnea who were already receiving optimal antidepressive pharmacotherapy.10 Furthermore, a systematic review of randomized trials of continuous PAP and obstructive sleep apnea showed improved mood following therapy.11
The mechanism(s) underlying the connection between SDB and psychiatric symptoms is a matter of debate. From a psychiatric perspective, one can conceptualize the relationship as stemming from a direct physiological consequence of the general medical condition (in this case, sleep deprivation and nocturnal hypoxia/hypercapnia). Therefore, the increased prevalence of depression with SDB would not be surprising given that such a relationship is seen in other diseases that produce hypoxia and impair quality of life (eg, chronic obstructive pulmonary disease).11,12 On the other hand, excessive sleepiness and fatigue as a result of sleep apnea produce significant social and personal problems and result in depression.13 Ishman and colleagues14 showed that the daytime sleepiness is a strong predictor of depressive symptoms in patients with SDB.
Sleep apnea and depression can be bridged conceptually by vital exhaustion. Vital exhaustion refers to a state characterized by elevated somatic and cognitive symptoms of depression without affective symptoms. Our group as well as others demonstrated that vital exhaustion profiles were affected in patients with SDB.15,16 Therefore, depressive manifestations in patients with sleep apnea may reflect the patients’ vital exhaustion, which differs dramatically from melancholic affective mood changes observed in more typical forms of depression and dysthymia. As such, depressive phenomena in patients who have sleep apnea should be more akin to depression secondary to chronic medical illness.
Anxiety disorders. An association between obstructive sleep apnea and anxiety has also been seen. Our data reveal a higher prevalence of clinically diagnosed anxiety associated with SDB.5 Yue and colleagues6 found higher anxiety scores in patients with SDB than in controls (measured by the General Severity Index).
Many years ago, researchers began discussing a link between PTSD and REM sleep behavior disorder (RBD).17,18 Under normal circumstances, the hypopolarization of alpha and gamma motor neurons during REM sleep maintains a func-tional paralysis that prevents the sleeper from enacting his or her dream content. In RBD, the mechanisms that produce REM-related atonia fail and fictive movements become real actions, sometimes resulting in serious injury. Combat veterans with PTSD seem especially vulnerable to REM atonia failure, and dream-enactment reports are more common than in the general population.