title: Tracheal traction effects on upper airway patency in rabbits: the role of tissue pressure.
abstract: OBJECTIVE
  To investigate the mechanisms via which lung volume related caudal tracheal traction decreases upper airway collapsibility.
  
  
  METHODS
  Acute physiological study.
  
  
  METHODS
  20 male, supine, anesthetised, tracheostomised, spontaneously breathing, NZ white rabbits fitted with a sealed face mask.
  
  
  METHODS
  N/A.
  
  
  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.
authors.affiliation: Ludwig Engel Centre for Respiratory Research, Department of Respiratory Medicine, Westmead Hospital, Hawkesbury Rd, Westmead, NSW, Australia. kristinak@westgate.wh.usyd.edu.au
authors.forename: Kristina
authors.initials: K
authors.lastname: Kairaitis
authors.forename: Karen
authors.initials: K
authors.lastname: Byth
authors.forename: Radha
authors.initials: R
authors.lastname: Parikh
authors.forename: Rosie
authors.initials: R
authors.lastname: Stavrinou
authors.forename: John R
authors.initials: JR
authors.lastname: Wheatley
authors.forename: Terence C
authors.initials: TC
authors.lastname: Amis
mesh_terms: D000402:Airway Obstruction / Q000517:prevention & control*; D000403:Airway Resistance / Q000502:physiology; D000818:Animals; D045853:Exhalation / Q000502:physiology; D008176:Lung Volume Measurements; D008297:Male; D010614:Pharynx / Q000503:physiopathology*; D011312:Pressure; D011817:Rabbits; D012132:Respiratory Muscles / Q000503:physiopathology; D016683:Supine Position; D013997:Time Factors; D014132:Trachea / Q000502:physiology*; D014143:Traction / Q000379:methods*