Mild obstructive sleep apnoea in females: post hoc analysis of the MERGE randomised controlled trial

Background A post hoc analysis of the MERGE trial was conducted, to investigate whether sex differences are evident at the mildest end of the disease spectrum, for symptoms associated with obstructive sleep apnoea (OSA) and the response to continuous positive airway pressure (CPAP) treatment. Methods MERGE participants with mild OSA (apnoea-hypopnoea index 5-15 events.h(-1); American Academy of Sleep Medicine 2012 criteria) were randomised to either CPAP plus standard care (sleep hygiene counselling) or standard care alone for 3 months. Quality of life (QoL) was measured by questionnaires completed before and after the 3 months. This post hoc analysis of participants of the MERGE trial compared the symptom presentation, and response to CPAP, between the sexes. Results 233 patients were included; 71 (30%) were female. Females were more symptomatic at baseline in all QoL questionnaires. Specifically, females had lower 36-item Short-Form Health Survey (SF-36) Vitality scores (mean +/- SD 39.1 +/- 10.1 versus 44.8 +/- 10.3) and higher Epworth Sleepiness Scale (ESS) scores (mean +/- SD 11.0 +/- 4.2 versus 9.5 +/- 4.4). Both sexes experienced snoring, but more females reported fatigue and more males reported witnessed apnoeas. All symptoms improved with CPAP for both sexes; however, females had larger improvements in SF-36 Vitality scores, which was the primary outcome of the MERGE trial (mean change 9.4 (95% CI 6.8-12.0) versus 6.0 (95% CI 4.3-7.7); p=0.034), and ESS (mean change - 4.1 (95% CI -5.1- -3.0) versus -2.5 (95% CI -3.1- -1.8); p=0.015), after adjustment for baseline scores and CPAP usage. Conclusions Sex differences are apparent in patients with mild OSA. Females experience worse QoL symptoms than males at presentation to the sleep clinic; however, these improve significantly with CPAP treatment.