Evidence of dynamic airway compression during cough in tetraplegic patients

Although all the well-recognized muscles of expiration are paralyzed after traumatic transection of the lower cervical cord, tetraplegic subjects can still empty their lungs actively by contracting the clavicular portion of the pectoralis major. It is not known, however, whether contraction of this muscle bundle may raise pleural pressure enough to cause dynamic compression of the intrathoracic airways, which is critical for the production of an effective cough. To investigate this question, we measured expiratory flow rate and esophageal pressure during a series of forced expiratory vital capacity (VC) maneuvers in twelve subjects with C5-8 traumatic tetraplegia and constructed isovolume-pressure flow (IVPF) curves. The curves were interpretable with certainty in nine patients. Three of them did not show any plateau of flow. On the other hand, six patients had clearcut plateaus of flow on all IVPF curves between 80-60 and 20% VC, suggesting they had dynamic airway compression. Videoendoscopic recordings in two patients confirmed trachea and main bronchi collapse during forced expiration and cough. We conclude, therefore, that contraction of the pectoralis major causes dynamic airway compression during expiratory efforts in a substantial proportion of tetraplegic subjects. Increasing the pressure-generating capacity of this muscle might thus improve the effectiveness of cough and reduce the prevalence of bronchopulmonary infections.