The apnea-hypopnea index (AHI) is a widely accepted measure for the severity of obstructive sleep apnea (OSA). Current methods to determine AHI fail to provide anatomic information for treatment decisions. In this report, we studied three-dimensional models of upper airways acquired by computed tomographic scanning with geometric measurements and computational fluid dynamics (CFD) analysis and evaluated the correlations with AHI.
Participants had CT scans of their upper airways after standard polysomnography studies. Three-dimensional surface models of upper airways were generated for cross-sectional area measurements of the choanae (A CH) and the smallest cross-sectional area (A min). Computational fluid dynamic analysis was then performed by using this three-dimensional model. Pressure differences required to set tidal volume during inspiration (ΔP min-INSP) and expiration (ΔP max-EXP) and minimum negative pressure produced in the level of A CH (Pmin-INSP at A CH) and A min (P min-INSP at A min) were calculated. Correlations of these parameters and the body mass index with AHI were analyzed. Statistical differences between groups of different AHI ranges were also compared.
The pressure distribution simulated by CFD demonstrated abrupt pressure drops in A min level, and this phenomenon was more significant in severe OSA. All parameters except A CH and P min-INSP at A min significantly correlated with the AHI, and there were significant statistical differences between the OSA groups and the normal group. The results indicate that, in our study group, the geometry of pharyngeal airway and its CFD simulation correlate well with AHI. This model may be further applied for clinical evaluation.
From the *Craniofacial Center, Department of Plastic and Reconstructive Surgery, Chang Gung Memorial Hospital, Chang Gung University, Taoyuan; †Computational Application Division, National Center for High-Performance Computing, Hsinchu City; ‡Sleep Center, Department of Chest Medicine, and §Department of Radiology, Chang Gung Memorial Hospital, Chang Gung University, Taoyuan, Taiwan.
Received April 22, 2011.
Accepted for publication July 11, 2011.
Address correspondence and reprint requests to Yu-Ray Chen, MD, Craniofacial Center, Department of Plastic and Reconstructive Surgery, Chang Gung Memorial Hospital, Chang Gung University, No. 5, Fu-Hsin St, Gueishan, Taoyuan, Taiwan; E-mail: firstname.lastname@example.org
This report is part of the projects NSC 96-2314-B-182-018 and NSC-98-2314-B-182-016-MY2, supported by grants from the National Science Council of Taiwan.
The authors report no conflicts of interest.