Effect of tracheal and tongue displacement on upper airway airflow dynamics

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 (Vover dotI(max)), we analyzed the pressure-flow relationships obtained in the isolated upper airway of paralyzed cats. Vover dotI(max) and its determinants, the pharyngeal critical pressure (P-crit) 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 Vover dotI(max) P-crit, or Rn; 2) there was an increase in Vover dotI(max) with 2 cm of tracheal displacement, which was associated with a decrease in P-crit and an increase in Rn; 3) there was an interactive effect of tongue and tracheal displacement on Vover dotI(max) and P-crit but not on Rn; and 4) there was a large increase in Vover dotI(max) with tongue displacement >2.5 cm with the trachea nondisplaced, which was associated with a large decrease in P-crit 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.