We produced a localized right lower lobe (RLL) contusion in 14 anesthetized ventilated dogs, 7 of which were treated with positive end-expiratory pressure (PEEP group). We measured gas exchange, pulmonary mechanics, and regional function before and 5 h after the contusion. Arterial PO2 decreased by 20 Torr and venous admixture doubled in both groups during air breathing. The shunt fraction (Qs/Qt) was minimally increased, despite a large lobar Qs/Qt (0.43) in the contused RLL. These results were explained by reduced ventilation per unit volume (VA/V), and ventilation-to-perfusion ratios of the contused RLL measured with 133Xe technique. We conclude that pulmonary contusion causes a leak of blood and plasma, flooding 25% of the air spaces of the RLL at FRC, reducing the compliance of adjacent air spaces, and resulting in a reduced VA/V and a large RLL Qs/Qt. These results are consistent with the observed reduction in regional volume and perfusion in the contused RLL, and suggest that Qs/Qt was not increased because blood flow was markedly reduced to flooded air spaces. PEEP reduced the hypoxemia, but increased the contusion.

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Localized pulmonary contusions were produced in the right lower lobes (RLL) of 12 anesthetized ventilated dogs, 6 of which had a flail segment in the chest wall over the RLL. Pulmonary oxygen exchange during ventilation with air and oxygen, and the lobar distribution of pulmonary perfusion by radioactive microsphere techniques were measured before and 3 h after contusion, and again after thoracotomy. These were compared to 12 noncontused dogs, 6 of which had a flail segment. Contusion produced an average decrease of 20 Torr in Pao2 during air breathing and an average increase in Qs/Qt of less than 5%, surprisingly small given the doubled weight and average 44% shunt calculated in the contused lobe after thoracotomy. No significant effect of flail or thoracotomy was found, indicating that the presence of an intact chest wall and lung-chest wall interdependence was not a major factor preventing a larger increase in intact whole-animal shunt of contused dogs. Rather, the small effect of this severe lobar injury on whole-animal shunt was due to a 30% decrease in RLL relative perfusion. This reduction was demonstrated to be localized to a smaller hemorrhagic subsection of the contused lobe.

Using flat balloon techniques to minimize distortion and artifacts, we studied the effect of positive end-expiratory pressure (PEEP) on local surface pressures between the lung and pericardium overlying the right (R) and left (L) ventricles of ventilated closed-chest anesthetized dogs in right lateral decubitus position. To test the hypothesis that local extrapericardial [Pep(L) and Pep(R)] and average pleural pressures change equally with PEEP, we also measured esophageal pressure (Pes). When 10-cmH2O PEEP was applied, mean increases in Pes, Pep(L), and Pep(R) were 6.2, 5.6, and 5.3 cmH2O, respectively. When PEEP was raised to 20 cmH2O, further average increases in Pes, Pep(L), and Pep(R) were 5.8, 5.0, and 5.4 cmH2O. At each level of PEEP, volume infusion was used to increase stroke volume. Volume infusion at 20-cmH2O PEEP was associated with small 1.0- and 1.5-cmH2O increases in Pep but no change in Pes. Analysis of confidence limits showed that application of up to 20-cmH2O PEEP, with or without volume infusion to restore stroke volume, is associated with nearly equal changes in esophageal and local extrapericardial pressures.

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