Changes in cough motor output during repetitive mechanical stimulation of the tracheobronchial tree in cats

The lack of airway protective responses is highly predictive of pulmonary morbidity and mortality. We investigated changes in motor output of mechanically induced cough during a repeated stimulation protocol, as may occur during aspiration of food / liquid over a meal. The occurrence, magnitude, phase durations, and power spectra characteristics of diaphragm and abdominal muscle electromyograms, and esophageal pressures during coughing were recorded during repeated mechanical stimulation of the trachea in cats. After the initial increase in cough excitability, repeated tracheal stimulation resulted in reduced cough number, electromyograms and esophageal pressure magnitudes, which fit an exponential model. There was little change in cough phase durations. Additionally, a pause in sequential airway stimulation (lasting several minutes) resulted in a further cough reduction, associated with prolongation of cough phase durations, but was resolved after one additional stimulus trial, consistent with long-latency transient depression. Power spectral analysis suggested changes in recruitment of motor units for parasternal muscles and no signs of fatigue although hundreds of coughs were executed. Our results are consistent with the presence of central adaptive mechanisms that can regulate the excitability of repetitive coughing, likely overlapping with transient potentiation and depression. The results have mechanistic implications for predicting airway protective responses in respiratory diseases.