Interregional gas mixing and gas transport during high frequency oscillations

We investigated gas mixing between lung regions and its relationship to gas transport out of the lungs during high frequency oscillation (HFO) in eight, healthy male volunteers. Gas mixing within the lung during HFO was assessed by measuring changes in the regional concentration of 133Xenon with scintillation detectors positioned over the posterior chest, 5, 15 and 25 cm below each lung apex. Gas transport out of the lungs was assessed by measuring changes in 133Xenon concentration at the mouth during HFO. Mixing between topographic lung regions from the apex to base was increased by both the stroke volume (P less than 0.05) and the frequency (P less than 0.05) of HFO. This mixing correlated best with the product of f X SV1.5 (r = 0.99 P less than 0.001). Changes in regional gradient with HFO showed a strong positive correlation with changes in mouth concentration (r = 0.94, P less than 0.025). We conclude that gas mixing between lung regions in man is increased more by stroke volume than frequency during HFO. This mixing is closely related to gas transport out of the lungs.