INTRA-AIRWAY GAS-TRANSPORT DURING HIGH-FREQUENCY CHEST VIBRATION WITHTRACHEAL INSUFFLATION IN DOGS

High-frequency external chest vibration with tracheal insufflation (hi gh-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 vibratio n ventilation (frequency 30 Hz, amplitude 0.4 cm), we used an analysis of the single-breath washout curve that gives the vibration-induced m ixing coefficient distribution relative to the no-vibration situation. Data from four anesthetized dogs were collected during constant-flow insufflation at six rates (0.05-0.41 . min(-1) kg(-1)), at three insuf flation 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 1 4.1 +/- 3.9-fold, with the peak of the enhancement distribution locate d 125 +/- 29 ml from the airway opening and a distribution width of 12 1 +/- 29 ml. As insufflation flow increased, the position of the peak enhancement shifted toward the alveolar zone and diminished in peak am plitude. 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 mixi ng, bringing alveolar gas to central airways. This leads to overall in creased pulmonary gas transport when fresh gas is insufflating the tra cheal carina area.