Assessment of Cough Reflex in Lung Transplant Recipients

Bronchoscopy Stable, lung transplant recipients undergoing surveillance bronchoscopy will be enrolled. We will exclude subjects with new or persistent cough, hypoxemia, new radiographic infiltrates, or hemodynamic instability.

Before bronchoscopy, patients will receive diazepam while codeine and atropine will be withheld. Upper airway anesthesia was performed using cotton swabs soaked with 4 % lidocaine applied on the oropharyngeal mucosa and gradually placed posteriorly with the aid of curved foreceps to anesthetize the supraglottic region. A trained individual will perform topical upper airway anesthesia over 15 minutes and adequate anesthesia will be determined once subjects fail to cough during foreceps application to the supraglottic region. Conscious sedation will be administered using intravenous midazolam while vital signs are monitored. Once adequate sedation is achieved, the bronchoscope will be introduced through the mouth beyond the vocal chords to the main carina and slowly advanced to the airway anastomosis. Coughing that occurs with advancement of the bronchoscope from the chords to the anastomosis will be addressed by maintaining the bronchoscope in an immobile neutral position for 60-180 seconds until coughing stops and the cough provocation will be performed.

Cough provocation Airway irritants will be applied in the following sequence: 1) one cm distal to anastomosis, 2) one cm proximal to anastomosis and 3) at the main carina. Chemical irritation will consist of 3 mL aliquots of 5 % dextrose water (D5W) instilled through the bronchoscope channel on the bronchial mucosa (21). Aliquots of D5W will be administered at each site on three separate occasions with a 60 second interval between administrations. Mechanical irritation will involve placement of the biopsy foreceps on the bronchial mucosa at each site. The sequence of airway irritation sites will always begin with the distal anastomosis followed by the proximal anastomosis and main carina.

Airway lidocaine administration Patients demonstrating a cough reflex at the distal anastomotic site will be recorded. After measurements are obtained at all airway sites, the bronchoscope will be reintroduced to the distal anastomosis and 3 mL of 4 % lidocaine instilled on the bronchial mucosa. Sixty seconds later, mechanical and chemical irritation of the proximal and distal anastomosis will be performed as previously outlined.

Cough assessment Cough frequency will be determined by counting audible coughs and abdominal muscle contractions measured with a surface electromyograph (EMG) recorder. Surface electrodes placed on the skin, 2 cm below each costal margin along the midclavicular line will be connected to an EMG recorder (Biopac Systems Inc, Santa Barbara, CA) linked to a dedicated computer. Continuous EMG recordings will be obtained 15 seconds before administration of the airway irritant to ensure absence of cough before airway irritant administration (Figure 1). Twenty seconds or more of recording will be obtained after airway irritant application. Cough will be defined as abdominal muscle contraction and audible expiratory sound.