Anatomy of pharynx in patients with obstructive sleep apnea and in normal subjects

Shiroh Isono 1 , John E. Remmers 2 , Atsuko Tanaka 1 , Yasuhide Sho 1 , Jiro Sato 1 , and Takashi Nishino 1 1 Department of Anesthesiology, Chiba University School of Medicine, Chiba, 260 Japan; and 2 Department of Medicine, Faculty of Medicine, University of Calgary, Calgary, Alberta, Canada T2N 4N1 Received 15 July 1996; accepted in final form 4 December 1996. Isono, Shiroh, John E Remmers, Atsuko Tanaka, Yasuhide Sho, Jiro Sato, and Takashi Nishino. Anatomy of pharynx in patients with obstructive sleep apnea and in normal subjects. J. Appl. Physiol. 82(4): 1319-1326, 1997. Anatomic abnormalities of the pharynx are thought to play a role in the pathogenesis of obstructive sleep apnea (OSA), but their contribution has never been conclusively proven. The present study tested this anatomic hypothesis by comparing the mechanics of the paralyzed pharynx in OSA patients and in normal subjects. According to evaluation of sleep-disordered breathing (SDB) by nocturnal oximetry, subjects were divided into three groups: normal group ( n = 17), SDB-1 ( n = 18), and SDB-2 ( n = 22). The static pressure-area relationship of the passive pharynx was quantified under general anesthesia with complete paralysis. Age and body mass index were matched among the three groups. The site of the primary closure was the velopharynx in 49 subjects and the oropharynx in only 8 subjects. Distribution of the location of the primary closure did not differ among the groups. Closing pressure (P C ) of the velopharynx for SDB-1 and SDB-2 groups (0.90 ± 1.34 and 2.78 ± 2.78 cmH 2 O, respectively) was significantly higher than that for the normal group ( 3.77 ± 3.44 cmH 2 O; P < 0.01). Maximal velopharyngeal area for the normal group (2.10 ± 0.85 cm 2 ) was significantly greater than for SDB-1 and SDB-2 groups (1.15 ± 0.46 and 1.06 ± 0.75 cm 2 , respectively). The shape of the pressure-area curve for the velopharynx differed between normal subjects and patients with SDB, being steeper in slope near P C in patients with SDB. Multivariate analysis of mechanical parameters and oxygen desaturation index (ODI) revealed that velopharyngeal P C was the only variable highly correlated with ODI. Velopharyngeal P C was associated with oropharyngeal P C , suggesting mechanical interdependence of these segments. We conclude that the passive pharynx is more narrow and collapsible in sleep-apneic patients than in matched controls and that velopharyngeal P C is the principal correlate of the frequenc