Effect of pleural effusion on respiratory mechanics, and the influence of deep inflation, in dogs.

We wished to study how pleural effusion affects dynamic mechanics of the lung and the chest wall. We also determined if these changes could be reversed by deep lung inflations. Pleural effusion was produced by saline infusion into the pleural space. During the infusion and over the following 2 hours, dynamic elastance and resistance of the lungs, the chest wall and the whole respiratory system were recorded. Dynamic elastance and resistance of the lung increased significantly during fluid loading and were partially, and only transiently, reversed by deep inflations. Dynamic elastance and resistance of the chest wall were little affected by these procedures. Thus, pleural effusion can have significant effects on dynamic elastance and resistance of the respiratory system (ERS, RRS). The transient nature of the change in lung parameters after deep inflation suggests that therapies based on periodic lung inflations may be of little benefit to patients with this condition.