Why does gender influence survival in obstructive sleep apnoea?

The study aim was to compare the mortality risk of men and women diagnosed with obstructive sleep apnoea (OSA) and started on treatment with continuous positive airway pressure (CPAP). From August to December 2003 we reviewed the hospital records of patients who had started on CPAP for OSA between July 1995 and June 1998. Mortality rates were compared between men and women. Associations with mortality risk were determined using univariate and multivariate Cox's proportional hazards regression. The sample comprised 292 men and 47 women. Eight percent of the men and 23% of the women died (p=0.003). Univariate analysis showed increased mortality risk was associated with female sex, greater age when CPAP was started, a pre-treatment minimum nocturnal oxygen saturation (SpO(2)) <75%, a higher Charlson comorbidity index score and discontinuation of CPAP treatment. Female sex remained associated with increased mortality independent of age, minimum SpO(2) and CPAP use, but was not independent of the Charlson score. Women diagnosed with OSA and treated with CPAP demonstrated a 3.44 greater mortality risk than men, mostly due to greater comorbidity.