54 Pulmonary dynamics during high frequency ventilation, evaluated by digital pulmonary fluorography

Abstract

We ventilated 6 NZ white rabbits (wt 3.0-3.8 kg) using high frequency ventilation (HFV) at combinations of frequencies (f) 1 to 8 Hz and mean airway pressures (Paw) 4 to 12 cm H2O. The changes in thoracic gas volume (TGV) during ventilation were evaluated by digital subtraction fluorography. Fluoroscopic video images of thorax in ap-projection were captured at 40 ms intervals during HFV trials, digitized and stored in computer's memory. Special software allowed analysis of intra-breath changes (at 40 ms intervals) in TGV over regions of interest covering the whole lung or projectional areas of the lungs. Using consecutive intra-breath digital subtractions, tidal volume (Vt)-related changes as well as expiration and inspiration dynamics could be evaluated. Changes in TGV at end-expiration (-FRC) were both f and Paw dependent (ANOVA), showing f related air trapping especially at higher Paw:s. Vt:s were f dependent at constant Paw:s. Ventilation at applied f:s and Paw:s was mainly synchronous over the lungs. Digital pulmonary fluoroscopy is a novel technique to monitor pulmonary dynamics during mechanical ventilation. Air leak in ventilator-lung interface does not effect the results. The low radiation dose makes the technique applicable also in newborns.