Chest: Restoration of Cough Reflex in Lung Transplant Recipients.

Background: Lung transplantation involves vagal nerve interruption resulting in sensory airway denervation and impairment of the cough reflex. Following lung transplantation, it is unclear whether functional recovery of the cough reflex occurs over time. Our objective was to evaluate the afferent limb of the cough reflex in lung transplant recipients. Methods: The assessment of cough reflex involved upper airway anesthesia, conscious sedation, and fiberoptic bronchoscopy; the biopsy forceps and a 5% dextrose solution were applied through the bronchoscope to the airway mucosa at the main carina, proximal and distal to the anastomosis. A cross-sectional group of seven subjects underwent a single assessment, while eight subjects in a longitudinal group underwent assessment at 1.5 and 12 months. Cough frequency was determined by counting the number of audible coughs and abdominal muscle contractions measured with a surface electromyogram recorder. The airway anastomosis from deceased subjects in the longitudinal group was examined for nerves. Results: All seven subjects from the cross-sectional group demonstrated a similar cough frequency after mechanical and chemical irritation of all airway sites. All subjects in the longitudinal group who were evaluated at 1.5 weeks had a cough response at all sites except distal to the anastomosis. Twelve months after transplantation, cough was present at all sites. Immunohistochemical staining for protein gene product 9.5, low-affinity neurotrophin, and vanilloid receptors demonstrated nerves in subepithelial regions proximal and distal to the airway anastomosis. Conclusion: In human lung transplant recipients, recovery of the cough reflex was noted 12 months after lung transplantation.

COMMENTARY

It is a well-known fact that donor lungs and trachea lack innervation in the transplant patient. These patients often lack a protective cough reflex, which can predispose them to pneumonia and aspiration in the postoperative period. However, anecdotal reports suggest that the lack of a cough reflex is not permanent. Duarte et al undertook a very careful analysis of cough response to both saline instillation and mechanical irritation to the airways both above and below the level of the anastamosis at different time points following transplantation. Their finding of cough reflex recovery at 1.5 months postoperatively gives patients and clinicians a timeline for emphasizing specific airway clearance and protection techniques. Further, their autopsy finding of nerve ingrowth at the anastamosis suggests the reason for the restoration of the cough reflex. Further work is needed to pinpoint the time of reinnervation of the donor airways.

2008;134:310316. [c] 2008 American College of Chest Physicians.

Submitted by, Anne Swisher, PT, PhD, CCS

West Virginia University