Submitted on September 15, 2008
Revised on December 18, 2008
Accepted on December 21, 2008
Mass loading of the upper airway extraluminal tissue space in rabbits: effects on tissue pressure and pharyngeal airway lumen geometry
Kristina Kairaitis1*, Lauren Howitt2, John R Wheatley3, and Terence Charles Amis3
1 Ludwig Engel Centre for Respiratory Research, Westmead Millennium Institute and University of Sydney
2 Ludwig Engel Centre for Respiratory Research, Westmead Millennium Institute
3 Ludwig Engel Centre for Respiratory Research, Westmead Millennium Institute and the University of Sydney
* To whom correspondence should be addressed. E-mail: kristina_kairaitis{at}wmi.usyd.edu.au.
Lateral pharyngeal fat pad compression of the upper airway (UA) wall is thought to influence UA size in patients with obstructive sleep apnoea. We examined interactions between acute mass/volume loading of the UA extra-luminal tissue space and UA patency. We studied 12 supine, anaesthetised, spontaneously breathing, head position controlled (50° NZ white rabbits. Sub-mucosal extra-luminal tissue pressures (ETP) in the antero-lateral (ETPlat) and anterior (ETPant) pharyngeal wall were monitored with surgically inserted pressure transducer tipped catheters (Millar). Tracheal pressure (PT) and airflow (V) were measured via a pneumotachograph and pressure transducer inserted in series into the intact trachea, with hypopharyngeal cross sectional area (CSA) measured via computed tomography, whilst graded saline inflation (0-1.5ml) of a compliant tissue expander balloon in the antero-lateral subcutaneous tissue was performed. Inspiratory UA resistance (RUA) at 20ml/s was calculated from a power function fitted to PT versus V data. Graded expansion of the antero-lateral balloon increased ETPlat from 2.3±0.5cmH20 (n=11, mean±SEM) to 5.0±1.1cm H2O at 1.5ml inflation (p<0.05,ANOVA). However, ETPant was unchanged from 0.5±0.5 cmH2O (n=9,p=0.17). Concurrently, RUA increased to 119±4.2 % of baseline value (n=12,p<0.001) associated with a significant reduction in CSA between 10-70% of airway length to a minimum of 82.2±4.4% of baseline CSA at 40% of airway length (p<0.05). We conclude that antero-lateral loading of the upper airway extra-luminal tissue space decreases upper airway patency via an increase in ETPlat, but not ETPant. Lateral pharyngeal fat pad size may influence UA patency via increased tissue volume and pressure causing UA wall compression.
