CO2 elimination as a function of frequency and tidal volume in rabbits during HFO.

CO2 elimination (VCO2) was monitored during high-frequency oscillation (HFO) over a frequency (f) range of 2-30 Hz in anesthetized and paralyzed rabbits to determine whether effective gas exchange could be achieved in this species, to determine the f and tidal volume (VT) dependence of gas exchange in this species, and to compare these results with those from dog and human studies. We were able to produce VCO2 levels during HFO that exceeded normal steady-state levels of CO2 production with VT's less than the total dead space volume. VCO2 was related to f in a curvilinear fashion, whereas in some rabbits VCO2 became independent of f at higher frequencies. This curvilinear relationship between f and VCO2 is similar to data from humans but contrasts with the linear relationship found in dogs. Evidence is presented indicating frequency-dependent behavior of gas exchange is correlated with a frequency-dependent decrease in respiratory system resistance. We propose that the frequency-dependent mechanical properties of the rabbit lung may also account for the species differences in HFO gas exchange.