CHEST-WALL COMPLIANCE IN INFANTS AND CHILDREN WITH NEUROMUSCULAR DISEASE

Respiratory muscle weakness is the primary cause of respiratory dysfun ction in neuromuscular disease (NMD), but structural abnormalities of the chest wall also play a role. In adults with NMD, restrictive lung disease is in part caused by reduced chest wall compliance (C-W), beli eved to reflect stiffening of connective tissue resulting from chronic ally reduced chest wall motion in the presence of respiratory muscle w eakness. We hypothesized that chronic limitation of chest wall motion in young children with NMD leads to structural underdevelopment of the chest wall, and results in increased, rather than decreased, C-W. In 18 subjects with NMD, ranging from 3 mo to 3.8 yr of age, we compared C-W with values obtained in children without NMD. A modification of th e Mead-Whittenberger technique was used, with respiratory muscle relax ation provided by brief manual ventilation. Respiratory system complia nce (C-rs) and lung compliance (C-L) were calculated from airway openi ng pressure, transpulmonary pressure, and tidal volume. C-W was calcul ated as 1/C-W = 1/C-rs - 1/C-L during manual ventilation. C-W/kg was h igher in subjects with NMD than in controls, at 5.2 +/- 2.8 (mean +/- SD) versus 2.4 +/- 0.8 ml/cm H2O (p < 0.001). In subjects who had norm al lung compliance values during spontaneous breathing (C-Lspont), C-W /C-Lspont was significantly greater in subjects with NMD (5.5 +/- 3.2) than in controls (1.9 +/- 1.0) (p < 0.001). By predisposing to rib ca ge deformation and reduced end-expiratory lung volume, abnormally high C-W in infants and young children with NMD may contribute to respirat ory dysfunction.