- diagnosing of moderate or severe sleep apnea (OSA) on the basis of apnoea-hypopnea index (AHI) in polysomnography. AHI was defined by the total number of apnoea's and hypopneas per hour of sleep. The severity of OSA was determined as: mild (AHI 5-15), moderate (AHI 15 - 30) and severe (AHI ≥ 30)