Cough reflex sensitivity in subjects with cervical spinal cord injury

An effective cough requires an intact cough reflex as well as adequate respiratory muscle function to generate elevated intrathoracic pressures. Since the major muscles of expiration are innervated by the first thoracic segment and below, transection of the cervical spinal cord results in severely compromised expiratory function and cough. To investigate the effects of cervical spinal cord injury (C-SCI) on cough reflex sensitivity, we measured responsiveness to inhaled capsaicin in 12 male subjects with chronic C-SCI and compared findings to those from a control group of 50 able- bodied men. The concentrations (μM) of capsaicin inducing two or more (C₂) and five or more coughs (C₅) did not significantly differ between the two groups. Mean (± SEM) values for log C₂ in subjects with C-SCI and control subjects were 0.65 ± 0.15 and 0.87 ± 0.07, respectively (p = 0.15). Mean values for log Cs in subjects with C-SCI and control subjects were 1.43 ± 0.23 and 1.41 ± 0.08, respectively (p = 0.94). We conclude that cough reflex sensitivity is preserved after C-SCI, and that ineffective cough in this population results primarily from the loss of innervation of respiratory muscles.