High-frequency ventilation

Recent experiments have demonstrated that normal pulmonary gas exchange rates can be achieved in humans and test animals using high frequency (1 to 30 Hz), low volume (comparable to, or less than the dead space volume) oscillations imposed at the mouth or through an endotracheal tube. This review examines the different methods of High Frequency Ventilation (HFV) and the mechanisms thought to be responsible for gas transport, which are intrinsically different than in normal tidal breathing. Several potentially important transport mechanisms are discussed, including augmented dispersion, bidirectional streaming due to asymmetric velocity profiles, direct ventilation of near alveoli, and intercompartmental mixing or pendelluft. Models used to predict the rate of gas exchange in HFV are described in terms of their theoretical and experimental bases. The model predictions are compared to results of physiologic experiments.