High frequency ventilation and gas diffusion.

The efficiency of CO2 removal was studied using a simple lung model with a high frequency positive pressure device (up to 100 b.p.m.) with and without an anatomical deadspace. At a constant minute ventilation without an anatomical dead space, the efficiency of CO2 elimination increased with increasing frequency. However, when a dead space was introduced, the efficiency of CO2 elimination decreased with increasing frequency. Using a high frequency oscillation technique (360 to 900 b.p.m.), it was not possible to maintain a reasonable CO2 elimination with tidal volumes less than the anatomical dead space. In this model there was no evidence that accelerated diffusion was a factor in CO2 removal during high frequency ventilation or oscillation.