Fig. 1. Various mechanisms of gas transport and pressure damping during high-frequency ventilation (HFV).

In the trachea and main bronchi, HFV facilitates gas transport by convection, direct ventilation of close alveoli (bulk convection), and asymmetric inspiratory and expiratory velocity profiles. In the smaller bronchi and alveoli pendelluft, cardiogenic mixing, Taylor dispersion with laminar flow, and molecular diffusion are the primary mechanisms. The oscillatory pressure waveform is damped by the inertia of the respiratory system. Atelectatic alveoli are less compliant and are exposed to higher oscillatory pressures compared to normally aerated alveoli. For a detailed review, we recommend “High-frequency oscillatory ventilation: mechanisms of gas exchange and lung mechanics” by JJ Pillow.¹⁵ Figure 1 was first published by Slutsky A.S. & Drazen J.M. in 2002¹⁷ and adapted by Pillow J.J.¹⁵.