Respiratory arousal threshold among patients with isolated sleep apnea and with comorbid insomnia (COMISA)

Insomnia and obstructive sleep apnea (OSA) are common sleep disorders and frequently coexist (COMISA). Arousals from sleep may be a common link explaining the frequent comorbidity of both disorders. Respiratory arousal threshold (AT) is a physiologic measurement of the level of respiratory effort to trigger an arousal from sleep. The impact of COMISA on AT is not known. We hypothesized that a low AT is more common among COMISA than among patients with OSA without insomnia. Participants referred for OSA diagnosis underwent a type 3 sleep study and answered the insomnia severity index (ISI) questionnaire and the Epworth sleepiness scale. Participants with an ISI score ≥ 15 were defined as having insomnia. Sleep apnea was defined as an apnea hypopnea index (AHI) ≥ 15 events/h. Low AT was determined using a previously validated score based on 3 polysomnography variables (AHI, nadir SpO₂ and the frequency of hypopneas). OSA-only (n = 51) and COMISA (n = 52) participants had similar age (61[52-68] vs 60[53-65] years), body-mass index (31.3[27.7-36.2] vs 32.2[29.5-38.3] kg/m²) and OSA severity (40.2[27.5-60] vs 37.55[27.9-65.2] events/h): all p = NS. OSA-only group had significantly more males than the COMISA group (58% vs 33%, p = 0.013. The proportion of participants with a low AT among OSA-only and COMISA groups was similar (29 vs 33%, p = NS). The similar proportion of low AT among COMISA and patients with OSA suggests that the respiratory arousal threshold may not be related to the increased arousability of insomnia.