HFOV Mechanisms of Gas Transport

1
HFOV Mechanisms of Gas Transport
2
HFOV Mechanisms of Gas Transport

• Direct bulk flow
• Taylor dispersion
• Pendeluft
• Asymmetric velocity profiles
• Cardiogenic mixing
• Molecular diffusion

Krishnan CHEST 2000
3
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.

4
Augmented (Taylor) dispersion

• Complicated interplay between convective forces
  and molecular diffusion
• Addition of convective flow to a diffusive
  process significantly increased dispersion of
  molecules

5
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.

6
Asymmetrical Velocity Profile
7
Cardiogenic Mixing

• The heart beat adds to the the peripheral gas
  
  mixing.

8
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.