Volumetric xenon-CT imaging of conventional and high-frequency oscillatory ventilation.
OBJECTIVE
For mechanical ventilation of patients with pulmonary injuries, it has been proposed that high-frequency oscillatory ventilation (HFOV) offers advantages over conventional ventilation (CV); however, these advantages have been difficult to quantify. We used volumetric, dynamic imaging of Xenon (Xe) washout of the canine lung during both HFOV and CV to compare regional ventilation in the two modalities.


METHODS
Three anesthetized, mechanically ventilated animals were studied, each at three different ventilator settings. Imaging was performed on an experimental Toshiba 256-slice scanner at 80 kV, 250 mAs, and 0.5-second scans, yielding 12.8 cm of Z-axis coverage. Repeated images were acquired at increasing intervals between 1 and 10 seconds for 90 seconds during HFOV and using retrospective respiratory gating to end-expiration for 60 seconds during CV. Image series were analyzed to quantify regional specific ventilation (sV ) from the regional density washout time constants.


RESULTS
High-quality, high-resolution regional ventilation maps were obtained during both CV and HFOV. Overall ventilation decreased at smaller tidal volume, as expected. Regional sV was more uniform during HFOV compared to CV, but the underlying distribution of lung aeration was similar.


CONCLUSIONS
High-resolution volumetric ventilation maps of the lung may be obtained with the 256-slice multidetector computed tomographic scanner. There is a marked difference in the distribution of regional ventilation between CV and HFOV, with a significant gravitational ventilation gradient in CV that was not present during HFOV. This technique may be useful in exploring the mechanisms by which HFOV improves gas exchange.
Mulreany
Daniel G
DG
Departments of Anesthesiology and Critical Care Medicine, The Johns Hopkins University, Baltimore, MD 21287-8711, USA.
Simon
Brett A
BA
Murphy
Kieran J
KJ
Easley
R Blaine
RB
D000818:Animals; D035641:Chest Wall Oscillation / Q000379:methods*; D004285:Dogs; D008168:Lung / Q000000981:diagnostic imaging* / Q000502:physiology*; D012123:Pulmonary Ventilation / Q000502:physiology*; D014057:Tomography, X-Ray Computed / Q000379:methods*; D014978:Xenon
D014978:Xenon