Improvement in obstructive sleep apnea in the supine knees-up position.

We report a 38-year-old man with obstructive sleep apnea whose sleep-disordered breathing was substantially reduced by sleep in the supine, "knees-up" position, relative to his sleep in the customary supine, "knees-down" position. No obvious anatomic or pathophysiologic alterations explained this phenomenon. The effect was reproducible in the patient 4 years later. Potential mechanisms underlying such improvement, including alterations in upper airway/lung volume dependence and venous supply to upper airway vasculature, are discussed. This manipulation could be an important adjunctive treatment for a subset of obstructive sleep apnea patients demonstrating such an effect.