Effect of tracheal and tongue displacement on upper airway airflow dynamics

TLDR

Caudal tracheal displacement alters upper airway airflow dynamics. This study examined how tongue and tracheal displacement affect upper airway airflow dynamics. Using isolated upper airway of paralyzed cats, we measured maximal inspiratory airflow (VImax), pharyngeal critical pressure (Pcrit), and nasal resistance (Rn) while systematically varying tongue and tracheal displacement. Tongue displacement alone had no effect on VImax, Pcrit, or Rn, whereas 2 cm tracheal displacement increased VImax with decreased Pcrit and increased Rn; combined displacement interacted on VImax and Pcrit but not Rn, and tongue displacement > 2.5 cm with no tracheal shift produced a large VImax increase, large Pcrit decrease, and large Rn increase.

Abstract

We have previously shown that caudal tracheal displacement alters the airflow dynamics of the upper airway. In the present study, we specifically examined the effects of tongue and tracheal displacement on upper airway airflow dynamics. To determine how tongue and tracheal displacement modulate maximal inspiratory airflow (VImax), we analyzed the pressure-flow relationships obtained in the isolated upper airway of paralyzed cats. VImax and its determinants, the pharyngeal critical pressure (Pcrit) and the nasal resistance (Rn) upstream to the flow-limiting site, were measured as tongue displacement and tracheal displacement were systematically varied. Four results were obtained: 1) there was no independent effect of tongue displacement on VImax, Pcrit, or Rn; 2) there was an increase in VImax with 2 cm of tracheal displacement, which was associated with a decrease in Pcrit and an increase in Rn; 3) there was an interactive effect of tongue and tracheal displacement on VImax and Pcrit but not on Rn; and 4) there was a large increase in VImax with tongue displacement > 2.5 cm with the trachea nondisplaced, which was associated with a large decrease in Pcrit and a large increase in Rn. We conclude that tongue and tracheal displacement exert differing influences on airflow dynamics and present a mechanical model of the upper airway that explains these results.