Respiratory mechanics in quadriplegia. The respiratory function of the intercostal muscles.

Pulmonary mechanics and inspiratory muscle pressures were studied in relation to electromyograms (EMG) of the respiratory muscles in 10 chronic quadriplegic patients . Transdiaphragmatic pressures at maximal inflation were normal, but minimal pleural pressures at functional residual capacity (FRC) were reduced to about one half the normal values. On the basis of the parasternal intercostal EMG results, 2 groups were defined. In 8 patients (Group I), no electromyographic activity was found in the intercostal muscles, even during large inspiratory maneuvers. In 2 patients (Group II), both intercostal and diaphragmatic activities were recorded during inspiration, and intercostal EMG activity increased with increasing inspiratory volume. Group 1 patients had reduced FRC, transpulmonary pressure at FRC, and static expiratory compliance; therefore, the pressure-volume curves of the lungs resembled those obtained in patients with generalized weakness of the respiratory muscles. Specific compliance was normal in each patient, suggesting that the low compliance resulted in large part from the collapse of air spaces. Group 2 patients had FRC, transpulmonary pressure at FRC, and lung compliance values within normal limits. We concluded that longstanding paralysis of intercostal muscles causes marked alterations in the elastic properties of the lungs and reduces the passive (outward) recoil of the chest wall. These findings suggested that the intercostal muscles normally stabilize the chest wall and prevent lung collapse. Moreover, intercostal surface EMG recordings may help to identify tetraplegic patients who may be at risk of developing respiratory failure during rather minor insults to the respiratory system.