HFOV Mechanisms of Gas Transport

HFOV Mechanisms of Gas Transport Direct bulk flow Taylor dispersion Pendeluft Asymmetric velocity profiles Cardiogenic mixing Molecular diffusion Krishnan CHEST 2000

Convection (Bulk Flow) Ventilation Even with small tidal volumes, direct alveolar ventilation occurs to short path length units that branch off of the primary airways.

Augmented (Taylor) dispersion Complicated interplay between convective forces and molecular diffusion Addition of convective flow to a diffusive process significantly increased dispersion of molecules

Penduluft At high frequencies, distribution becomes strongly influenced by time constant inequalities. Gas from fast units (short time constants) will empty into the slow (long time constants) units.

Asymmetrical Velocity Profile Inspiration Net Effect Expiration

Cardiogenic Mixing The heart beat adds to the the peripheral gas mixing.

Molecular Diffusion Is felt to be one of the major mechanisms for gas exchange in the alveolar regions. It is responsible for the gas exchange across the AC membrane and also contributes to the transport of O2 and CO2 in the gas phase near the membrane. This may be due to the increased turbulence of molecules.