Intrapulmonary gas transport and perfusion during high-frequency oscillation.

The effects of high-frequency oscillation (HFO) on 1) regional pulmonary 133Xe clearance after equilibration, 2) regional distribution and subsequent clearance of 133Xe after right atrial bolus injection, and 3) pulmonary gas exchange were examined in anesthetized supine dogs. After equilibration 133Xe cleared similarly from all lung regions with HFO at 16 and 30 Hz and a stroke volume of 2.6 ml/kg. Pulmonary gas exchange was adequate. 133Xe, injected as a bolus into the right atrium, was preferentially distributed to dependent lung regions during both HFO and apnea, indicating vertical gradients in pulmonary perfusion. During the subsequent pulmonary clearance of 133Xe, regional 133Xe concentrations (CrXe) increased initially in nondependent regions. By contrast, CrXe decreased immediately in the dependent lung region; after CrXe's became similar in dependent and nondependent regions, all lung regions started to clear at similar rates. The initial increases of CrXe in nondependent regions were attributed to interregional mixing, which may contribute to the uniformity in regional pulmonary 133Xe clearance after equilibration.