Published ahead of print on January 26, 2006, doi:10.1164/rccm.200505-705OC Am. J. Respir. Crit. Care Med., Volume 173, Number 9, May 2006, 1031-1037 A more recent version of this article appeared on May 1, 2006
Submitted on May 5, 2005 Phasic Respiratory Pharyngeal Mechanics by Magnetic Resonance Imaging in Lean and Obese Zucker RatsMichael J Brennick1*,1 Department of Medicine, University of Pennsylvania, Center for Sleep and Respiratory Neurobiology, Philadelphia, PA, USA, 2 Department of Radiology, University of Pennsylvania, Center for Advanced Magnetic Resonance Imaging and Spectroscopy, Philadelphia, PA, USA, 3 University of Pennsylvania, Biomedical Statistical Consulting, Philadelphia, PA, USA, 4 Department of Medicine and Pulmonary, Critical Care and Sleep Section, University of Pennsylvania, Philadelphia Veterans Administration Medical Center (111P), Philadelphia, PA, USA * To whom correspondence should be addressed. 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 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 non-invasive 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 antero-posterior airway diameters, and tissue strain (stretch, compression and direction of stretch) lateral and ventral pharyngeal walls were compared with ANOVA (significance at p < 0.05). Measurements and Main Results: Compared to 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, rats, Zucker, pharynx
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