Action of the diaphragm during cough in tetraplegic subjects

Subjects with traumatic tetraplegia use the pectoralis major to compress the upper rib cage and increase intrathoracic pressure during cough. It is not known, however, whether they also contact the diaphragm during the expiratory phase of cough, as normal subjects do. We have investigated the action of the diaphragm during single voluntary coughing efforts in subjects with complete transection of the lower cervical (n = 5) or midthoracic (n = 2) cord. All subjects showed at least one peak of transdiaphragmatic pressure during the expiratory phase of the effort, and simultaneous bursts of electrical activity were recorded from the diaphragm. Coughing also resulted in an outward (paradoxical) motion of the abdomen during the compressive phase. We conclude that antagonistic contraction of the diaphragm is present during the expiratory phase of cough in spinal cord-injured subjects with paralysis of the abdominal muscles; this contraction, therefore, does not occur in response to activation of these muscles. The present results also indicate that the cough-induced paradoxical expansion of the abdomen is due to contraction of the pectoralis major and not of the diaphragm.