Body position and breathing abnormalities during sleep: a systematic study.

BACKGROUND: Until now, studies about body position and nocturnal breathing abnormalities have been restricted to comparing supine versus lateral positions. OBJECTIVES: In this retrospective study, we systematically evaluated the effect of body position on nocturnal breathing in 105 patients with a sleep apnea hypopnea syndrome (SAHS). METHODS: All the patients had an apnea hypopnea index > 10/h, as judged from polysomnography performed in the sleep laboratory. A thoracic sensor allowed to detect nine distinct body positions: supine (S), supine right (SR), right (R), prone right (PR), prone (P), prone left (PL), left (L), supine left (SL) and sitting upward (UP). Respiratory variables (number of obstructive, central and mixed apneas, of hypopneas and of desaturations, all expressed as an index per hour of total sleep time) were evaluated versus the body positions, using the non-parametric Kruskal-Wallis H method. Pairwise comparisons were performed using Mann-Whitney U tests. RESULTS: Most of the total sleep time (45%) was spent supine. A significant effect of body position was found for all the respiratory variables. Breathing was better in the intermediate SR and SL positions than S, and also better in PR and PL positions than, respectively, R and L. All the respiratory variables gradually improved when gradualling moving from the S to the P position. CONCLUSIONS: A nine position sensor, able to define intermediate positions in addition to the basic cardinal positions, is useful in the sleep laboratory. Using such a sensor, we found in SAHS patients that nocturnal breathing improves as a continuum from the S to the P position.