Fig. 4From: Quantitative effects of head rotation angle on apnea hypopnea index in positional obstructive sleep apnea – a preliminary case seriesForce of gravity acting on oropharyngeal tissue to compress upper airway when head is supine compared to laterally rotated head (A). Proposed “Safe Sleep Region” of head rotation angles to reduce apnea - hypopnea index in positional OSA patients (B)Back to article page