Gravity-Dependent Atelectasis

Morimoto S, Takeuchi N, Imanaka H, Nishimura M, Takezawa J, Taenaka N, Matsuura N, Tomoda K, Ikezoe J, Arisawa J, Hamada S, Takashima S, Kozuka T. Gravity-dependent atelectasis: radiologic, physiologic and pathologic correlation in rabbits on high-frequency oscillation ventilation. Invest Radiol 1989;24:522–530. The authors identify the radiologic features of progressive atelectasis induced under conditions of reduced lung volume. Control (n=5) and experimental (n=7) animals were placed on highfrequency oscillation (HFO) ventilation (mean airway pressure: 3cm H2O) for 6 hours. In the experimental animals, lung volume was artificially reduced by pneumoperitoneum during HFO ventilation. Computed tomography scans and chest radiographs were obtained every hour, and arterial blood gases analyzed. No changes were detected in the control animals. In the experimental animals, in which hypoxemia developed, homogeneous opacity in the dependent lung was found on CT images, and chest radiographs showed a diffuse homogeneous shadow with loss of lung volume. Study of pathologic sections from the lung showed that the roentgenographic findings represented atelectasis. The lung was divided into three zones, from dependent to nondependent regions: severe atelectasis, mild atelectasis, and normal lung. Hyperinflations eliminated atelectasis seen on the CT images and alleviated hypoxemia; however an undesirable effect that causes barotrauma also was observed.