Regional lung volume changes during high-frequency oscillatory ventilation.
OBJECTIVE
To investigate regional lung volume changes occurring during an inflation-deflation maneuver using high-frequency oscillatory ventilation.


METHODS
Prospective animal trial.


METHODS
Animal research laboratory.


METHODS
Six Yorkshire swine.


METHODS
Electrical impedance tomography was used to quantify regional ventilation during high-frequency oscillatory ventilation. The electrical impedance tomography-derived center of ventilation was used to describe the distribution of regional ventilation, whereas spectral analysis was used to describe regional ventilation-induced impedance changes. Lung injury was induced using surfactant lavage. Animals were transitioned to high-frequency oscillatory ventilation and a slow inflation-deflation maneuver was performed by changing mean airway pressure by 5 cm H2O every 15 mins to a maximum mean airway pressure of 40 cm H2O.


RESULTS
The induction of lung injury was associated with a significant shift of the center of ventilation toward nondependent areas and an increase in shunt fraction (p < .001). During the following inflation-deflation maneuver using high-frequency oscillatory ventilation, inflation was associated with a shift of the center of ventilation from nondependent to dependent areas. Center of ventilation was significantly correlated with the shunt fraction (p < .001). Analyzing different lung layers along the gravitational axis separately, nondependent lung areas showed significantly decreased regional ventilation-induced impedance changes at higher pressures, suggesting overdistension, whereas dependent lung areas showed increased impedance changes, suggesting recruitment. The reverse was observed during deflation (all p < .05).


CONCLUSIONS
The center of ventilation during high-frequency oscillatory ventilation correlated with oxygenating efficiency as measured by the shunt fraction. Lung recruitment during high-frequency oscillatory ventilation produced a significant shift of regional ventilation toward dependent areas of the lung and led to overdistension of nondependent areas.
Wolf
Gerhard K
GK
Division of Critical Care Medicine, Children's Hospital Boston, Harvard Medical School, Boston, MA, USA. gerhard.wolf@childrens.harvard.edu
Grychtol
Bartłomiej
B
Frerichs
Inez
I
Zurakowski
David
D
Arnold
John H
JH
D000818:Animals; D004195:Disease Models, Animal; D017097:Electric Impedance; D006612:High-Frequency Ventilation; D008176:Lung Volume Measurements; D013552:Swine; D014054:Tomography; D055397:Ventilator-Induced Lung Injury / Q000503:physiopathology*