Upper Airway and Translaryngeal Resistance During Mechanical Insufflation-Exsufflation

Mechanical insufflation-exsufflation (MI-E) uses positive and negative pressures to assist weak cough and to help clear airway secretions. Laryngeal visualization during MI-E has revealed that inappropriate upper airway responses can impede its efficacy. However, the dynamics of pressure transmission in the upper airways during MI-E are unclear, as are the relationships among anatomic structure, pressure, and airflow.

Can airflow resistance through the upper airway and the larynx feasibly be calculated during MI-E, and if so, how are the pressures transmitted to the trachea?

Cross-sectional study of 10 healthy adults, where MI-E was provided with and without active cough using pressure settings +20/-40 cm H₂O and ± 40 cm H₂O. Airflow and pressure at the level of the facemask were measured using a pneumotachograph, whereas pressure transducers (positioned via transnasal fiber-optic laryngoscopy) recorded pressures above the larynx and within the trachea. Upper airway resistance (R_uaw) and translaryngeal resistance (R_tl) were calculated (in centimeters of water per liter per second) and were compared with direct observations via laryngoscopy.

Positive pressures reached the trachea effectively, whereas negative tracheal pressures during exsufflation were approximately one-half of the intended settings. Insufflation pressure increased slightly when passing through the larynx. Participant effort influenced tracheal pressures and the resistances, with findings consistent with laryngoscopic observations. During MI-E, resistance seems to be dynamic, with R_uaw exceeding R_tl. Inappropriate laryngeal closure increased R_tl during both positive and negative pressures.

We found that R_uaw and R_tl can be calculated feasibly during MI-E. The findings indicate different transmission dynamics for positive and negative pressures and that resistances are influenced by participant effort. The findings support using lower insufflation pressures and higher negative pressures in clinical practice.