COMPARATIVE-STUDY OF INTRA-AIRWAY GAS-TRANSPORT BY ALTERNATIVE MODES OF VENTILATION

The effectiveness of three alternative modes of ventilation [high-freq uency ventilation (HFV), constant-flow ventilation (CFV), and high-fre quency external vibration ventilation (HFVV)] was compared. Local intr a-airway gas transport was measured with catheters placed in the dista l trachea and in bronchi located 5.5, 9, and 11 cm from the carina. A new bolus dispersion method was devised to measure the local effective diffusivities (D-eff) induced by these modes of ventilation and by ca rdiogenic oscillations relative to molecular diffusivity (D-mol). Mixi ng induced by cardiogenic oscillations was 7 +/- 2- to 26 +/- 4-fold g reater than by molecular diffusion alone. Intra-airway transport by CF V, applied at three flow rates (0.3, 1.0, and 3.0 1 . min(-1) kg(-1)), was most effective in the trachea but fell sharply in the more periph eral airways. Local transport by HFVV, at a frequency of 22 Hz and a v ertical amplitude of 0.4 cm, was most effective in the periphery (D-ef f = 793 . D-mol), whereas the effectiveness of transport by HFV, appli ed with 10 and 20 mi at 22 Hz, was evenly distributed. Doubling the HF V oscillatory volume caused a 4.5 +/- 2.7-fold increase in D-eff/D-mol . Combining HFVV with CFV at 0.3 1 . min(-1). kg(-1) induced transport rates that were 187- to 2,034-fold greater than by molecular diffusio n alone in the bronchi and a higher relative transport (due to convect ion) in the trachea. We conclude that the combination of HFVV with low -flow CFV provides a high rate of intra-airway transport with minimal mechanical perturbations to the pulmonary system.