LAUSR

The recognition of bidirectional relationships between obstructive sleep apnea (OSA) and post-traumatic stress disorder (PTSD) among active military service members and US veterans continues to grow [1]. The prevalence of PTSD may be as high as 25% among recently deployed military personnel while the incidence of OSA has shown a 6-fold increase in recent years [2, 3]. Encountering service members presenting with co-occurring symptoms of OSA and PTSD is commonplace in sleep clinics and can pose unique diagnostic and treatment challenges [1, 4]. Importantly, untreated OSA may worsen some PTSD symptoms (i.e., nightmares, insomnia) and may increase the risk for suicidal ideation [5]. However, other core symptoms of PTSD (i.e., hyperarousal) may represent a significant barrier to positive airway pressure (PAP) adherence [5]. Comorbid insomnia is frequently diagnosed in military personnel with OSA but its impact on PAP use is less clear as opposed to civilians with comorbid insomnia who have poorer PAP adherence [6–8]. A recent audit by the Office of the Inspector General found that the Veterans Health Administration had increased its spending on PAP devices and supplies by 59% over 5 years (to $234 million annually) [9]. However, 46% of veterans showed profiles of inconsistent and infrequent PAP use (i.e., < 50% of nights). Therefore, it is integral to develop a comprehensive understanding of predictors of PAP use, and to pursue multidisciplinary interventions to improve PAP acceptance and adherence among service members. Toward this end, recent studies have sought to understand the heterogeneity of OSA and treatment effectiveness by assessing anatomical and physiological traits [10]. These physiological factors include high loop gain, dampened pharyngeal muscle responsiveness during sleep, and low respiratory arousal threshold (greater propensity to arouse to respiratory stimuli). Low respiratory arousal threshold (ArTH) inhibits the sufficient accumulation of respiratory stimuli (i.e., carbon dioxide) and resulting recruitment of pharyngeal dilator muscles to stabilize breathing during sleep [11]. This propensity toward repetitive arousals, a potentially modifiable trait [10], has also sparked interest in its impact on treatment outcomes. For example, Zinchuk et al. recently examined the prevalence and correlates of ArTH in 940 US male veterans [12]. A low ArTH was observed in 38% of this sample and was associated with lower body mass index (BMI), older age, and antidepressant prescription. Interestingly, low ArTH was also associated with reduced long-term PAP adherence among non-obese patients, but not obese patients. Although this study identified important factors, it relied on medical records for mental health diagnoses and a mix of self-reported/documented long-term PAP adherence. Thus, a more comprehensive understanding of the heterogeneity of physiological traits of OSA among military service members with psychiatric comorbidities may assist in personalizing therapy and optimizing PAP adherence. In this issue of Sleep and Breathing, El Solh and colleagues define the prevalence of indirectly measured low ArTH in a sample of middle-aged male veterans with OSA and PTSD, * Douglas M. Wallace [email protected]