Effect of sleep position and sleep stage on the collapsibility of the upper airways in patients with sleep apnea

Collapsibility of the upper airways has been identified as an important pat hogenic factor in obstructive sleep apnea (OSA). Objective measures of coll apsibility are pharyngeal critical pressure (Pcrit) and resistance of the u pstream segment (Rus). To systematically determine the effects of sleep sta ge and body position we investigated 16 male subjects suffering from OSA. W e compared the measures in light sleep, slow-wave sleep, REM sleep and supi ne vs. lateral positions. The pressure-flow relationship of the upper airwa ys has been evaluated by simultaneous readings of maximal inspiratory airfl ow (Vimax) and nasal pressure (p-nCPAP). With two-factor repeated measures ANOVA on those 7 patients which had all 6 situations we found a significant influence of body position on Pcrit (p<0.05) whereas there was no signific ant influence of sleep stage and no significant interaction between body po sition and sleep stage. When comparing the body positions Pcrit was higher in the supine than in the lateral positions. During light sleep Pcrit decre ased from 0.6 +/- 0.8 cm H2O (supine) to -2.2+/-3.6 cm H2O (lateral) (p<0.0 1), during slow-wave sleep Pcrit decreased from 0.3+/-1.4 cm H2O (supine) t o -1.7+/-2.6 (lateral) (p<0.05) and during REM sleep it decreased from 1.2/-1.5 cm H2O to -2.0+/-2.2 cm H2O (p<0.05). Changes in Pus revealed no body position nor sleep-stage dependence. Comparing the different body position s Pus was only significantly higher in the lateral position during REM slee p (p<0.05). The results indicate that collapsibility of the upper airways i s not mediated by sleep stages but is strongly influenced by body position. As a consequence lower nCPAP pressure is needed during lateral positions c ompared to supine positions.