R427 – Mechanism Producing Subglottic Air Pressure While Swallowing

Abstract

Problem The importance of positive subglottic air pressure during swallowing has been recognized, yet no experiment has sought to determine the mechanism that generates this pressure. We hypothesized that transpulmonary recoil forces are responsible for this pressure. Objective: To compare direct subglottic air pressure measurements obtained while swallowing at different lung volumes with airway pressures obtained by total respiratory system recoil measurements. Methods Direct measurement of subglottic air pressure during swallowing was obtained via a percutaneous puncture of the cricothyroid membrane. Tidal volumes were measured via a heated pneumotachometer as the subjects breathed through a nasal mask. Next, to model swallowing, airway pressures were measured at the mouth by occluding the airflow for a duration consistent with true vocal fold closure during swallowing. Passive exhalation was used to mimic the central inhibition of respiratory muscles that occurs during the swallow. Results Regression analyses on the combined data showed strong linear relationships between lung volumes (X) and airway pressures (Y) with overall goodness of fit which were highly significant (p values less than 0.00001). R Square values ranged from 0.78 to 0.91. Conclusion The subglottic air pressure during a swallow is likely generated by transpulmonary recoil forces that dominate when respiratory muscles are inhibited. The degree of subglottic pressure produced is directly related to lung volume. Significance The influence of the respiratory phase, lung volume, and available transpulmonary recoil pressure may alter the effects of therapeutic interventions intended to increase subglottic pressure such as tracheostomy tube occlusion and decannulation. Support UPMC Competitive Medical Research Fund, Greater Pittsburgh Chapter, National Parkinson's Foundation.