Intra-night variation in apnea-hypopnea index affects diagnostics and prognostics of obstructive sleep apnea

BACKGROUND: Diagnostics of obstructive sleep apnea (OSA) is based on apnea-hypopnea index (AHI) determined as full-night average of occurred events. We investigate our hypothesis that intra-night variation in the frequency of obstructive events affects diagnostics and prognostics of OSA and should therefore be considered in clinical practice. METHODS: Polygraphic recordings of 1989 patients (mean follow-up 18.3 years) with suspected OSA were analyzed. Number and severity of individual obstructive events were calculated hourly for the first 6 h of sleep. OSA severity was determined based on the full-night AHI and AHI for the 2 h when the obstructive event frequency was highest (AHI(2h)). Hazard ratios for all-cause, cardiovascular, and non-cardiovascular mortalities were calculated for different OSA severity categories based on the full-night AHI and AHI(2h). RESULTS: Frequency and duration of obstructive events varied hour-by-hour increasing towards morning. Using AHI(2h) led to a statistically significant rearrangement of patients between the OSA severity categories. The use of AHI(2h) for severity classification showed clearer relationship between the OSA severity and mortality than the full-night AHI. CONCLUSIONS: Currently, the intra-night variation in frequency and severity of obstructive events is completely ignored by conventional, full-night AHI and considering this information could improve the diagnostics of OSA.