Study objectives: To investigate the mechanisms via which lung volume related caudal tracheal traction decreases upper airway collapsibility.
Design: Acute physiological study.
Participants: 20 male, supine, anesthetised, tracheostomised, spontaneously breathing, NZ white rabbits fitted with a sealed face mask.
Setting: N/A.
Measurements and results: Upper airway extraluminal tissue pressure (ETP) was measured in the lateral (ETPlat) and anterior (ETPant) pharyngeal walls (pressure transducer tipped catheters). Graded traction was applied to the isolated upper airway (n = 17, 0-140 g). Subsequently, inflation and deflation was performed (with and without traction, 48 g, n = 13) with measurement of intraluminal pressure. Upper airway transmural pressure (PTM) was calculated (at closure and reopening) for both ETP sites (PTMlat and PTMant, respectively). A traction force of 144 g decreased ETPlat from 2.6 +/- 0.7 cm H2O (mean +/- SEM) to 2.1 +/- 0.7 cm H2O and ETPant from 1.1 +/- 0.4 cm H2O to 0.8 +/- 0.4 cm H2O (both P < 0.001). Increasing traction decreased closing and reopening pressures by 1.4 +/- 0.2 cm H2O for 48 g of traction (n = 13, P < 0.0001). In addition, 48 g of traction decreased ETPlat (at closure and reopening) by 0.2 +/- 0.05 cm H2O (P < 0.0001), and decreased ETPant by 0.5 +/- 0.1 cm H2O at closing pressure and 0.8 +/- 0.1 cm H2O at reopening (both p < 0.0001). Thus, for 48 g of traction, PTMlat (at closure and reopening) fell by 1.1 +/- 0.2 cm H2O and PTMant (reopening only) fell by 0.9 +/- 0.3 cm H2O (all P < 0.0001).
Conclusions: Since tracheal traction decreased PTMlat and PTMant by a greater amount than ETPlat and ETPant, we conclude that the decrease in upper airway collapsibility mediated by lung volume related caudal tracheal traction is partially explained by reductions in ETP.