Temporal pulmonary function changes in cervical cord injury.

Temporal changes in pulmonary function (PF) in subjects with complete cervical cord transection occur in two stages. The first, extending from the acute to post-acute periods, is characterized by relatively rapid increases in the following: vital, inspiratory, and total lung capacities (VC, IC, and TLC, respectively), and inspiratory and expiratory airflows coupled with decreases in functional residual capacity (FRC). Second stage changes--from the post-acute period on--are more gradual, with both VC increase and FRC decrease continuing while TLC and ventilatory indices remain unchanged. The initial stage appears to be caused in part by functional respiratory muscle return coincident with resolution of inflammation and edema above the injury level. Altered respiratory mechanics also contribute to these early changes and the continuing later changes. Mechanical changes in the lung are probably both decreased compliance (which decreases FRC) and increased airway resistance (which diminishes airflow). Chest wall changes, resulting from returning spinal cord reflexes, affect PF via: (1) increased rib cage stability, leading to a more effective transduction of diaphragmatic displacement into lung volume, and (2) abdominal and expiratory intercostal spasticity, which could limit maximum inspiration. The net effect of these changes, however, may eventually lead to chronic hypoventilation.