Positional sensitivity as a confounder in diagnosis of severity of obstructive sleep apnea

The apnea-hypopnea index (AHI) is used to grade obstructive sleep apnea (OSA) into mild, moderate, and severe forms. Obstructive events are most common in the supine position. The amount of supine sleep thus influences total AHI. Our aim was to determine the prevalence of position-dependent OSA (POSA) and its relation to OSA severity classification as recommended by the American Academy of Sleep Medicine (AASM).

Two hundred sixty-five subjects were recruited from primary care hypertension clinics. Whole-night respiratory recordings were performed to determine the AHI in the supine and non-supine positions, respectively. POSA was defined as supine AHI twice the non-supine AHI with supine AHI ≥5.

Fifty-three percent had POSA, 22% had non-position-dependent OSA, and 25% had normal respiration. By AASM classification, 81 subjects did not have OSA, but 42% of them had some degree of obstruction when supine, and 5 subjects would have been classified as moderate-severe if they had only slept supine. Conversely, of the 53 classified as mild OSA, 30% would have changed to a more severe classification if they had exclusively slept supine.

POSA was common both in subjects that by AASM classification had OSA as well as those without. The severity of OSA, as defined by AASM, could be dependent on supine time in a substantial amount of subjects.