Analysis of the gas exchange system dynamics during high-frequency ventilation

High-frequency ventilation (HFV) as a form of artificial respiration has attracted interest in recent years as a means of reducing the risk of barotrauma in clinical applications. This paper explores the high-frequency dynamics of the gas exchange system in order to obtain mathematical models that allow optimization studies aimed at answering the question: What is the optimum ventilatory waveform that secures a certain level of gas exchange while minimizing the resulting fluctuations in pleural or alveolar pressure? Two classes of input are considered: sinusoids and band-limited white noise. A model for the dynamic relation between tracheal flow and CO2 tension is obtained from experimental data which, in combination with existing models relating tracheal flow to pleural or alveolar pressure, allows optimization of the input flow waveform for a given level of CO2 elimination rate. The developed relation between CO2 elimination rate and input was verified by experimentally measured arterial CO2 tension.