Validation of ultrasonography for non-invasive assessment of diaphragm function in muscular dystrophy

Abstract Duchennemuscular dystrophy (DMD) is a severe, degenerativemuscle disease caused by dystrophin mutations. The mdx mouse is a widely used animal model of DMD. The mdx diaphragmmuscle most closely recapitulates key features ofDMDmuscles, including progressive fibrosis and considerable force loss. Diaphragmfunction in mdx mice is commonly evaluated by specific force measurements ex vivo.While useful, this method only measures force from a small muscle sample at one time point. Therefore, accurate assessment of diaphragm function in vivo would provide an important advance to study the time course of functional decline and treatment benefits.Here,we evaluatedanultrasonography techniqueformeasuring time-dependentchanges of diaphragm function in mdx mice. Diaphragm movement amplitude values for mdx mice were considerably lower than those for wild-type, decreased from 8 to 18 months of age, and correlated strongly with ex vivo specific force.We then investigated the time course of diaphragm amplitude changes following administration of an adeno-associated viral vector expressing Flag-micro-dystrophin (AAV-µDys) to young adult mdx mice. Diaphragm amplitude peaked 4weeks afterAAV-µDys administration, and was 26% greater than control mdx mice at this time. This value decreased slightly to 21% above mdx controls after 12 weeks of treatment. Importantly, diaphragm amplitude again correlated strongly with ex vivo specific force. Also, diaphragm amplitude and specific force negatively. Together, our results validate diaphragm ultrasonography as a reliable technique for assessing time-dependent changes in dystrophic diaphragm function in vivo, and for evaluating potential therapies for DMD.