Respiratory abdominal muscle recruitment and chest wall motion in myotonicmuscular dystrophy

Abdominal muscles are selectively active in normal subjects during stress a nd may increase the potential energy for inspiration by reducing the end-ex piratory lung volume (EELV). We hypothesized that a similar process would o ccur in subjects with myotonic muscular dystrophy (MMD), but would be less effective, because of to their weakness and altered chest wall mechanics. F ine-wire electromyography (EMG) of the transversus abdominis (TA), internal oblique (IO), external oblique, and rectus abdominis was recorded in 10 MM D and 10 control subjects. EMG activity, respiratory inductive plethysmogra phy, and gastric pressure were recorded during static pressure measurement and at increasing levels of inspiratory resistance breathing. EELV was redu ced and chest wall motion was synchronous only in controls. Although the TA and IO were selectively recruited in both groups, EMG activity of the MMD group was twice that of controls at the same inspiratory pressure. In MMD s ubjects with mildly reduced forced vital capacity, significant differences can be seen in abdominal muscle recruitment, wall motion, work of breathing , and ventilatory parameters.