Body position during sleep influences the severity of obstructive sleep apnea (OSA). The AHI is the number of times per hour of sleep that the airway temporarily collapses at the level of the tongue or soft palate. In a significant number of individuals with OSA, the severity of the condition as measured by the apnea-hypopnea index (AHI), increases in the supine (back) position and lowers in the lateral (side) position. This is called positional OSA.