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Altered Upper Airway and Soft Tissue Structures in the New Zealand Obese Mouse

¹ Center for Sleep and Respiratory Neurobiology; ² Division of Sleep Medicine, Department of Medicine, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania; and ³ Department of Radiology, Hospital of the University of Pennsylvania, Philadelphia, Pennsylvania

Correspondence and requests for reprints should be addressed to Michael J. Brennick, Ph.D., Center for Sleep and Respiratory Neurobiology, 3624 Market Street, Suite 205, Philadelphia, PA 19104. E-mail: brennick{at}mail.med.upenn.edu

Rationale: The effect of obesity on upper airway soft tissue structure and size was examined in the New Zealand Obese (NZO) mouse and in a control lean mouse, the New Zealand White (NZW).

Objectives: We hypothesized that the NZO mouse has increased volume of neck fat and upper airway soft tissues and decreased pharyngeal airway caliber.

Methods: Pharyngeal airway size, volume of the upper airway soft tissue structures, and distribution of fat in the neck and body were measured using magnetic resonance imaging (MRI). Dynamic MRI was used to examine the differences in upper airway caliber between inspiration and expiration in NZO versus NZW mice.

Measurements and Main Results: The data support the hypothesis that, in obese NZO versus lean NZW mice, airway caliber was significantly smaller (P < 0.03), with greater parapharyngeal fat pad volumes (P < 0.0001) and a greater volume of other upper airway soft tissue structures (tongue, P = 0.003; lateral pharyngeal walls, P = 0.01; soft palate, P = 0.02). Dynamic MRI showed that the airway of the obese NZO mouse dilated during inspiration, whereas in the lean NZW mouse, the upper airway was reduced in size during inspiration.

Conclusions: In addition to the increased volume of pharyngeal soft tissue structures, direct fat deposits within the tongue may contribute to airway compromise in obesity. Pharyngeal airway dilation during inspiration in NZO mice compared with narrowing in NZW mice suggests that airway compromise in obese mice may lead to muscle activation to defend upper airway patency during inspiration.

Key Words: obstructive sleep apnea • magnetic resonance imaging • body fat distribution • tongue • upper airway

AT A GLANCE COMMENTARY Scientific Knowledge on the Subject Obesity results in upper airway compromise, and the mechanism explaining this relationship remains unclear. What This Study Adds to the Field In addition to the increased volume of pharyngeal soft tissue structures, direct fat deposits within the tongue may contribute to airway compromise in obesity. Airway compromise in obese mice may lead to muscle activation to defend upper airway patency during inspiration.