Intra-airway gas transport during high-frequency chest vibration with tracheal insufflation in dogs.

High-frequency external chest vibration with tracheal insufflation (high-frequency vibration ventilation) has previously been shown to be an effective mode of artificial ventilation in experimental animals. To investigate the intra-airway gas mixing during high-frequency vibration ventilation (frequency 30 Hz, amplitude 0.4 cm), we used an analysis of the single-breath washout curve that gives the vibration-induced mixing coefficient distribution relative to the no-vibration situation. Data from four anesthetized dogs were collected during constant-flow insufflation at six rates (0.05-0.4 l.min-1.kg-1), at three insufflation durations (2, 4, and 7 s), and with the insufflation catheter outlet at three positions (carina, trachea, and a bronchus) while the vibration was on and off. Vibration enhanced intra-airway gas mixing 14.1 +/- 3.9-fold, with the peak of the enhancement distribution located 125 +/- 29 ml from the airway opening and a distribution width of 121 +/- 29 ml. As insufflation flow increased, the position of the peak enhancement shifted toward the alveolar zone and diminished in peak amplitude. Changing the insufflation duration and the catheter position did not affect the intra-airway mixing induced by vibration. External chest vibration causes a substantial increase of intra-airway gas mixing, bringing alveolar gas to central airways. This leads to overall increased pulmonary gas transport when fresh gas is insufflating the tracheal carina area.