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Functional decline, remodeling, and compensation in the respiratory system of a canine model of Duchenne muscular dystrophy

Patients with Duchenne muscular dystrophy (DMD) experience a progressive loss of pulmonary performance and eventual insufficiency. The clinical course is well known, but the inability of the DMD patient to raise his metabolic rate has prevented respiratory reserve from being measured directly. The golden retriever muscular dystrophy (GRMD) dog model of DMD exhibits many of the hallmarks of the human disease, including respiratory muscle dysfunction. We used the respiratory stimulant doxapram in anesthetized dogs to simulate the effects of increased metabolic demand on respiratory drive while measuring multiple respiratory parameters. We found indicators of reduced reserve – reduced maximum tidal volume and ventilatory rate – and altered chest wall kinematics. GRMD diaphragms were severely hypertrophic and foreshortened. The abdominal contribution to inspired volume, an indicator of diaphragm involvement, was severely reduced in GRMD dogs. We propose that this remodeling of the diaphragm is adaptive, and allows the GRMD dog to employ accessory respiratory muscles to store elastic energy during expiration, aiding inspiratory pressure and flow and delaying the onset of respiratory insufficiency.