AGE-RELATED CHANGES IN DIAPHRAGM MECHANICS IN OBESE ZUCKER RATS 529

Abstract

This study evaluated aging on the functional and fatigue characteristics of the costal diaphragm (DPM) in lean litter-mates and morbidly obese male Zucker rats at 6-8 weeks (YOUNG), 10-12 months (MATURE), and 17-18 months (OLD). Body weights were significantly higher at all ages in the obese animals as compared to lean. Respiratory system compliance was significantly reduced in MATURE(53% of lean) and OLD (46% of lean) obese animals, but not YOUNG obese, as compared to lean aged-matched group. In-vitro (37°C) mechanical characteristics, expressed as percent aged-matched lean, of DPM bundles were as follows: (* sign. different at 0.05 level or less between lean and obese of same age) Table Fatigabiltity, assessed as a drop in force to fixed (35 Hz train for 350 ms), repeated (120s) stimulation revealed that DPM from MATURE and OLD, but not YOUNG, obese rats was reduced compared to age-matched lean animals. We conclude that differences observed in DPM mechanics between lean and obese rats are not genetic but related to age, and mirror the restriction placed on the respiratory system by mass loading of the thorax.