Inspiratory flow reserve in boys with Duchenne muscular dystrophy

Patients with advanced muscular dystrophy frequently develop ventilatory failure. Currently respiratory impairment usually is assessed by measuring vital capacity and the mouth pressure generated during a maximal inspiratory maneuver (PI,max), neither of which directly measures ventilatory capacity. We assessed inspiratory flow reserve in 26 boys [mean (SD) age 12.8 (3.8) years] with Duchenne muscular dystrophy (DMD) without ventilatory failure and in 28 normal boys [mean (SD) age 12.6 (1.9) years] by analyzing the ratio between the largest inspiratory flow during tidal breathing (V′I,max(t)) and during a forced vital capacity maneuver (V′I,max(FVC)), (V′I,max(t)/V′I,max(FVC)). We have compared this ratio with the forced vital capacity (FVC) and PI,max measured at functional residual capacity. Mean PI,max was −90(30)cmH2O, average 112% (range 57–179%) of predicted values in control boys and −31(11)cmH2O, average 40% predicted values in DMD boys (control vs DMD, P