Gas transport during high-frequency ventilation

Abstract

During high-frequency small-volume ventilation (HFV), the transport rate of gas from the mouth to a lung region is a function of 2 conductances (conductance is the transfer rate of a gas divided by its partial pressure difference): regional longitudinal gas conductance along the airways (Grlongi) and gas conductance between lung regions (Ginter). Grlongi per unit regional lung (gas) volume (GRlongi/[Vr.beta.g]) was determined during HFV in 11 anesthetized paralyzed dogs lying supine. Distribution of Grlongi/(Vr.beta.g) was nearly uniform during HFV when stroke volumes were < .apprx. 2/3 of the Fowler dead-space volume. The distribution of Grlongi/(Vr.beta.g) was nonuniform when the stroke volume exceeded .apprx. 2/3 of the Fowler dead-space volume and the oscillation frequency was 5 Hz. Gas conductance along the airways per unit gas volume (average Glongi/[V.beta.g]), for the entire lung, increased with stroke volume at all frequencies, but for a given product of oscillation frequency and stroke volume, the average Glongi/(V.beta.g) was greater when stroke volume was large and oscillation frequency was low. The average Glongi/(V.beta.g) increased with frequency up to a maximal value; the frequency at which the maximum occurred depended on the kinematic viscosity of the inspired gas mixture.