Changes in Pharyngeal Cross-Sectional Area with Posture and Application of Continuous Positive Airway Pressure in Patients with Obstructive Sleep Apnea

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Abstract
In attempt to elucidate whether changes in posture (from sitting to supine) result in reduction in pharyngeal area, thus promoting pharyngeal occlusion during sleep in so predisposed persons, we studied 12 snoring apneic patients and 6 snoring nonapneic control subjects. In all subjects, we employed acoustic reflection technique to measure pharyngeal area at FRC sitting and supine. We also examined changes in pharyngeal area resulting from the application of positive intrapharyngeal pressure in sitting and supine posture. We found that (1) pharyngeal cross-sectional area at FRC was similar in both groups, (2) decrease in pharyngeal area with assumption of supine posture was also similar in both groups (21 .+-. 11% in patients with OSA versus 15 .+-. 13% in nonapneic control subjects), and (3) pharyngeal distensibility was significantly higher in apneic snorers than in nonapneic control subjects (0.090 .+-. 0.039 cm H2O-1 in apneic snorers versus 0.032 .+-. 0.027 cm H2O-1 in nonapneic control subjects; p < 0.005). We conclude that changes in posture alone are not sufficient to convert a snorer into a patient with OSA; however, when physiologic abnormalities ("floppy" pharynx) are superimposed on postural reduction in pharyngeal area, airway occlusion results.