Upper airway extraluminal tissue pressure fluctuations during breathing in rabbits

Transmural pressure at any level in the upper airway is dependent on the difference between intraluminal airway and extraluminal tissue pressure (ETP). We hypothesized that ETP would be influenced by topography, head and neck position, resistive loading, and stimulated breathing. Twenty-eight male, New Zealand White, anesthetized, spontaneously breathing rabbits breathed via a face mask with attached pneumotachograph to measure airflow and pressure transducer to monitor mask pressure. Tidal volume was measured via integration of the airflow signal. ETP was measured with a pressure transducer-tipped catheter inserted in the tissues of the lateral (ETPlat, n = 28) and anterior (ETPant, n = 21) pharyngeal wall. Head position was controlled at 30, 50, or 70°, and the effect of addition of an external resistor, brief occlusion, or stimulated breathing was examined. Mean ETPlat was ∼0.7 cmH₂O greater than mean ETPant when adjusted for degree of head and neck flexion (P < 0.05). Mean, maximum, and minimum ETP values increased significantly by 0.7-0.8 cmH₂O/20° of head and neck flexion when adjusted for site of measurement (P < 0.0001). The main effect of resistive loading and occlusion was an increase in the change in ETPlat (maximum - minimum ETPlat) and change in ETPant at all head and neck positions (P < 0.05). Mean ETPlat and ETPant increased with increasing tidal volume at head and neck position of 30° (all P < 0.05). In conclusion, ETP was nonhomogeneously distributed around the upper airway and increased with both increasing head and neck flexion and increasing tidal volume. Brief airway occlusion increased the size of respiratory-related ETP fluctuations in upper airway ETP.