While previous studies have demonstrated that perfluorocarbon is distributed predominantly to the atelectatic, dependent part of the injured lung, the distribution of gas and perfluorocarbon during the ventilatory cycle has not been well characterized. Method: We evaluated this in five normal, male pigs 16.0-22.6kg who underwent PLV with perfluorocarbon RM101(Mercantile Development, Inc., Bridgeport, CT) filling their lungs to FRC. Pressure-volume curves were constructed using a sustained inflation maneuver to define the deflation limb of the curve. This describes the PV envelope of the whole lung. With the animals maintained in the supine position, CT scans were then performed of the thorax with the lung sequentially inflated to predetermined plateau pressures first without and then with a sustained inflation to simulate the ventilatory cycle. These CT scans were then analyzed using lung densitometry. Results: The lung displayed marked hysteresis (fig 1) with the presence of an inflection point. Analysis of the CT scans demonstrated preferential gas ventilation to the non-dependent part of the lung at low mean airway pressures. Only at significant airway pressures was the distribution of gas and liquid uniform. Plotting lung density in Hounsfield units against pressure for each region of the lung studied again revealed significant hysteresis (fig 2). Conclusion: During PLV there is marked regional variation in the distribution of gas and liquid.

figure 1

Figure 1

figure 2

Figure 2