Study objective: To determine the role of the clavicular portion of the pectoralis major during cough in tetraplegic subjects.
Patients: Eight patients with longstanding traumatic transection of the lower cervical cord.
Methods: The electromyographic activity of the pectoralis major and abdominal external oblique muscles and the changes in the anteroposterior diameter of the lower rib cage, the upper rib cage, and the abdomen were measured during voluntary coughing efforts in the seated posture.
Results: When coughing, all subjects showed a large amount of electrical activity in the pectoralis major with no activity in the external oblique. Simultaneously, they had a clear-cut decrease in the anteroposterior diameter of the upper rib cage together with an increase in the anteroposterior diameter of the abdomen. In five subjects, the anteroposterior diameter of the lower rib cage also showed an initial increase. These changes were seen when cough was initiated at functional residual capacity or at a higher lung volume; they were also seen during a fit of coughing.
Conclusions: In tetraplegic subjects the clavicular portion of the pectoralis major plays a major role during coughing. Its contraction causes a reduction in the size of the upper part of the rib cage and a rise in intrathoracic pressure; this pressure rise results secondarily in an outward (paradoxical) motion of the abdomen and the lower rib cage. Cough in tetraplegic subjects is thus an active, rather than a passive, process, and its effectiveness might be improved by a combination of specific muscle training and abdominal binding.