Difference of pharyngeal morphology and mechanical property between OSAHS patients and normal subjects

The intrinsic properties such as baseline caliber and compliance of upper airway are thought to be important in the pathogenesis of obstructive sleep apnea hypopnea syndrome (OSAHS). Our study was designed to detect the difference of baseline caliber (morphological property) of pharynx during both wakefulness and sleep, and difference of pharyngeal compliance (mechanical property) between OSAHS patients and normal subjects.

CT scan was performed on 7 normal subjects and 13 OSAHS patients when they are awake, during drug-induced sleep with minimally effective therapeutic pressure (P(eff)), 0 cmH2O, and critical pressure (P(crit)) being given via a nose mask system, respectively. 3D images of pharyngeal airway were reconstructed, and volume of each subdivision of pharynx was measured. Volume, average area and compliance of each subdivision and in total were compared between the two groups.

The OSAHS group was shown to have a smaller average area at upper (1.20+/-0.26 cm2 versus 1.57+/-0.17 cm2, p<0.05) and middle part of pharynx (1.89+/-0.52 cm2 versus 2.58+/-0.27 cm2, p<0.05) during wakefulness. During sleep, this difference was shown to be even more obvious at upper part (0.77+/-0.30 cm2 versus 1.45+/-0.18 cm2, p<0.01); and middle part, (1.15+/-0.47 cm2 versus 2.44+/-0.26 cm2, p<0.01). The average area during wakefulness and sleep was also shown to be highly correlated. OSAHS group had a higher compliance at middle part (0.28+/-0.15 cmH2O(-1) versus 0.13+/-0.07 cmH2O(-1), p<0.05) of pharynx.

We conclude that OSAHS patients have a narrower and more collapsible upper airway than normal subjects do, the caliber data obtained during wakefulness could reflect the baseline caliber during sleep, and our method is valid to evaluate both morphology and function of upper airway.