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-AHI4% ; (2) ≥3% fall in oxyhemoglobin saturation-AHI3% ; or (3) ≥3% fall in oxyhemoglobin saturation or an event-related arousal-AHI3%a .

RESULTS: In both cohorts, the prevalence of an AHI ≥30 events/h increased by 14% with AHI3%a , compared to AHI4% criteria. The percentage of women with an AHI <5 events/h decreased from 13.9% with AHI4% to 1.1% with the AHI3%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 AHI4% and AHI3% but not the AHI3%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 (AHI3%a ), a threshold of 30 events/h is appropriate to identify women, but not elderly individuals with increased risk of cardiovascular death.