Published ahead of print on January 26, 2006, doi:10.1164/rccm.200505-705OC
© 2006 American Thoracic Society doi: 10.1164/rccm.200505-705OC
Phasic Respiratory Pharyngeal Mechanics by Magnetic Resonance Imaging in Lean and Obese Zucker RatsCenter for Sleep and Respiratory Neurobiology; Center for Advanced Magnetic Resonance Imaging and Spectroscopy, Department of Radiology; Biomedical Statistical Consulting; Department of Medicine, University of Pennsylvania; and Pulmonary, Critical Care, and Sleep Section, Philadelphia Veterans Administration Medical Center, Philadelphia, Pennsylvania Correspondence and requests for reprints should be addressed to Michael J. Brennick, Ph.D., Center for Sleep and Respiratory Neurobiology, University of Pennsylvania, Maloney Building, 3600 Spruce Street, Philadelphia, PA 19104.E-mail: brennick{at}mail.med.upenn.edu Rationale: Although obstructive sleep apnea is strongly associated with obesity, we have little understanding of how obesity may alter the mechanical properties of the pharynx and the role of obesity in the pathogenesis of sleep apnea. Objectives: The overall objective of this study was to determine the effect of obesity on pharyngeal airway size and pharyngeal wall tissue strain in lean and obese Zucker rats. Methods: Respiratory-gated magnetic resonance imaging with noninvasive tissue tagging was performed in anesthetized, spontaneously breathing lean (n = 9) and obese (n = 9) Zucker rats. Images acquired during expiration and inspiration of the rostral, mid-, and caudal pharynx were analyzed for airway size and pharyngeal wall tissue strain, using planimetry, optical flow, and finite element analyses. Differences in cross-sectional airway area, lateral and anteroposterior airway diameters, and tissue strain (stretch, compression, and direction of stretch) in the lateral and ventral pharyngeal walls were compared by analysis of variance (significance at p < 0.05). Measurements and Main Results: Compared with their lean littermates, obese rats had the following significant findings: reduced pharyngeal airway cross-sectional area during inspiration and expiration, smaller increases in airway area during inspiration, and decreased lateral airway dilation during inspiration. Tissue strain in the pharyngeal walls showed no significant differences between obese and lean rats. Conclusions: These findings suggest that obesity results in a mechanical abnormality that decreases pharyngeal airway size and prevents a normal airway response to a given change in pharyngeal wall tissue strain.
Key Words: magnetic resonance imaging • obstructive sleep apnea • pharynx • rats, Zucker This article has been cited by other articles:
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