The International Classification of Sleep Disorders (ICSD-3) defines obesity hypoventilation syndrome (OHS) as the triad of obesity (body mass index [BMI] >30 kg/m 2 ), daytime hypoventilation (PaCO 2 levels >45 mmHg), and sleep-disordered breathing in the absence of other neuromuscular, mechanical, and metabolic reasons for hypoventilation. 1 Several studies have assessed the differences between male and female OHS patients. A study involving 144 patients 2 revealed that OHS was more prevalent in women. Moreover, women had significantly more comorbidities, such as diabetes mellitus, hypertension, and hypothyroidism, than men. In another large, longitudinal cohort study from Sweden involving 1527 OHS patients under home mechanical ventilation, the female patients were reportedly older, more obese, and more hypercapnic than males. Emergency noninvasive ventilation (NIV) was more frequently performed for female than male patients. The 5-year survival rates of both sexes were similar. 3 However, 21% of the male patients and 28% of the female patients were initially diagnosed with chronic obstructive pulmonary disease (COPD). Ideally, they should have been excluded from the cohort (according to ICSD-3).This study aimed to assess the differences in clinical presentation, comorbidities, adherence to NIV, and prognosis between male and female OHS patients.
| METHODSThis was a retrospective, cross-sectional, and longitudinal review of OHS patients under an established cohort of "NIV patients" at the Department of Sleep Medicine at the Royal Infirmary of Edinburgh, Edinburgh (2004-2017. OHS was defined as obesity (BMI > 30 kg/m 2 ) and daytime hypoventilation (PaCO 2 > 45 mmHg) on arterial blood gas breathing room air. Patients with other causes of type 2 respiratory failure, such as COPD (FEV1/FVC ratio < 70%), neuromuscular disorders, and chest wall disorders, were excluded.The baseline demographics, clinical characteristics, and comorbidities, including diabetes mellitus, hypertension, cancer, and smoking history, were obtained from the records. Coronary vascular disease was defined as a history of angina pectoris or myocardial infarction. Heart failure was defined as having echocardiogram abnormalities or clinical symptoms consistent with heart failure, treated with two medications, such as diuretics and beta-blockers. Sleep parameters included the apnea-hypopnea index and Epworth sleepiness score questionnaire. The causes and number of hospital admissions and all-cause mortality were also recorded.
