High Frequency Oscillatory Ventilation (HFO) is a ventilatory strategy that employs very small tidal volumes (often less than anatomic dead space) combined with very fast rates or frequencies (where 1 Hertz or Hz = 60cycles/min).
The Sensormedics 3100B high frequency oscillator consists of a continuous positive airway pressure circuit with an integrated motor-driven piston/diaphragm for generating the oscillations. There is active inspiration as well as active expiration on the oscillator.
Gas transport during HFO is thought to be as a result of several factors: molecular diffusion, direct alveolar ventilation (bulk gas flow to the proximal alveoli), net convective transport caused by asymmetric gas-velocity profiles, improved gas mixing caused by Taylor dispersion in turbulent flow, pendelluft, and cardiogenic mixing.
In HFO, alveolar ventilation (and thus CO2 elimination) is dependent on frequency and tidal volume, but relatively independent of lung volume. Oxygenation is “uncoupled” from ventilation; that is, it is proportional to mean airway pressure and lung volume.
September 27, 2008