REGIONAL VENTILATION IN STATICALLY AND DYNAMICALLY HYPERINFLATED DOGS

Using the parenchymal marker technique in normal anesthetized dogs, we compared the dynamics of regional lung expansion between two ventilat ion strategies designed to increase mean thoracic volume. Dynamic hype rinflation (DH) was produced by ventilating the lungs at a rate of 50 breaths/min and with a duty cycle of 0.5. Static hyperinflation (SH) w as produced through the application of extrinsic positive end-expirato ry pressure while the lungs were ventilated at a rate of 15 breaths/mi n and with a duty cycle of 0.15. Regional tidal volume (VT,r), regiona l functional residual volume, and the time delay between regional expa nsion and the flow signal at the common airway were computed for up to 100 regions/lobe in 5 animals. Ventilation strategy had no effect on the overall variance of VT,r within lobes. Although the VT,r measured during SH correlated with VT,r measured during DH, the average correla tion coefficient was only 0.69. Ventilation rate-related differences i n VT,r and regional functional residual capacity varied with the regio nal time delay in ways qualitatively consistent with parallel inhomoge neity of unit time constants. However, a large component of frequency- dependent behavior remains unexplained by established mechanisms. We c onclude that DH and SH should not be considered equivalent lung unit r ecruitment strategies.