Impact of different hypopnea definitions on obstructive sleep apnea severity and cardiovascular mortality risk in women and elderly individuals

Objective To assess the impact of three hypopnea definitions on the severity classification of obstructive sleep apnea (OSA) and its association with cardiovascular mortality risk in women and elderly individuals. Methods We analyzed two Spanish clinical cohorts (1116 women and 939 elderly individuals) who were studied for suspicion of OSA between 1998 and 2007. A calibration model was used to apply different definitions of hypopnea to our two cohorts. Hypopnea was defined as a 30–90% reduction in oronasal flow for ≥10 s followed by (1) ≥4% fall in oxyhemoglobin saturation—AHI_4%; (2) ≥3% fall in oxyhemoglobin saturation—AHI_3%; or (3) ≥3% fall in oxyhemoglobin saturation or an event-related arousal—AHI_3%a. Results In both cohorts, the prevalence of an AHI ≥30 events/h increased by 14% with AHI_3%a, compared to AHI_4% criteria. The percentage of women with an AHI <5 events/h decreased from 13.9% with AHI_4% to 1.1% with the AHI_3%a definition. In fully adjusted multivariable analyses, AHI ≥30 events/h was associated with increased cardiovascular mortality risk in women, regardless of the hypopnea definition, and in elderly individuals diagnosed using the AHI_4% and AHI_3% but not the AHI_3%a definition. Conclusions Our findings suggest that hypopnea definitions substantially influence OSA prevalence and severity classification, and also affect the association with cardiovascular outcomes. With the currently recommended criterion (AHI_3%a), a threshold of 30 events/h is appropriate to identify women, but not elderly individuals with increased risk of cardiovascular death.