Lung Volumes and Their Significance for Pharyngeal and Esophageal Swallowing Function

Subglottic airway pressure is generated during each swallow and this supports the probability that subglottic mechanoreceptors function as part of the overall afferent collage of signals that guide motor output. Lung volume at swallow onset, lung recoil forces, and chest wall compliance are all important factors that combine for the generation of sufficiently positive subglottic air pressure during the pharyngeal swallow. Higher lung volumes at swallow onset may also be advantageous to the esophageal pressure gradient during esophageal bolus transit. Patients with impaired lung-thoracic unit recoil and disordered breathing/swallowing patterns may not only benefit from learning to swallow during early exhalation, but may also need to start at a higher lung volume in order to compensate for reduced recoil effects on swallowing function.

Subglottic Air Pressure and Swallowing

The existence of positive subglottic air pressure at the time of the swallow was first demonstrated in patients with indwelling tracheostomy tubes. Deglutitive subglottic air pressure has also been measured in non-tracheostomized persons. Several investigations that compared the occlusion status of tracheostomy tubes (open vs. closed) have found relationships between swallowing physiology and tube status. Similar findings were reported when healthy individuals swallowed at various lung volumes. As such, there is emerging evidence for the role of subglottic air pressure in swallowing motor control. Clinically, subglottic pressures in relation to breathing and swallowing coordination, pulmonary function, and lung-thoracic unit recoil forces may need to be considered when working with both tracheostomized and non-tracheostomized patients.

R427 – Mechanism Producing Subglottic Air Pressure While Swallowing

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.

Physiologic Effects of Open and Closed Tracheostomy Tubes on the Pharyngeal Swallow

Studies linking aspiration and dysphagia to an open tracheostomy tube exemplify the possibility that the larynx may have an influence on oropharyngeal swallow function. Experiments addressing the effects of tracheostomy tube occlusion during the swallow have looked at the presence and severity of aspiration, but few have included measurements that capture the changes in swallowing physiology. Also, hypotheses for the importance of near-normal subglottic air pressure during the swallow have not been offered to date. As such, the aim of this study was to compare the depth of laryngeal penetration, bolus speed, and duration of pharyngeal muscle contraction during the swallow in individuals with tracheostomy tubes while their tubes were open and closed. The results of this series of experiments indicate that within the same tracheostomized patient, pharyngeal swallowing physiology is measurably different in the absence of subglottic air pressure (open tube) as compared to the closed tube condition.

Subglottic Air Pressure: A Key Component of Swallowing Efficiency

The relationship between tracheostomy and swallowing dysfunction has been long recognized. Often this dysfunction is manifested by aspiration, for which a number of etiologic factors may be responsible. Disruption of glottic closure has been previously demonstrated in association with the presence of an indwelling tracheostomy tube. The plugging or removal of the tracheostomy tube, or the use of an expiratory air valve, has been demonstrated to decrease aspiration and improve swallowing function. Measurement of subglottic pressure through an indwelling tracheostomy tube during swallowing demonstrated pressure peaks occurring concomitant with swallowing and laryngeal elevation. This presentation will review the evidence supporting the role of subglottic pressure rise in swallowing efficiency. Current investigational activity will be reviewed, and new areas for study will be suggested.