Mediastinal and chest wall limitations to asymmetry of lung inflation.

The extent to which inflation of one lung increases pleural pressure around the contralateral lung could affect ventilatory function, e.g., after pneumonectomy or lung transplantation. The rise in contralateral pleural pressure is limited by mediastinal stiffness and other chest wall properties. To estimate these properties, we determined an elastance of asymmetric expansion (E(Asym)) in 20 supine adults undergoing thoracic surgery requiring endobronchial intubation. Esophageal pressure, measured with a balloon catheter, was used as an estimate of pleural pressure for determining chest wall elastance during symmetric inflation. Pressures measured in the left and right lung airways during sequential asymmetric inflations with known volumes were used to calculate E(Asym) and elastances of left and right lungs by using a four-element mathematical model. Elastances (means +/- SD) were 13.0 +/- 8.7 (E(Asym)), 14.0 +/- 7.0 (left lung), 12.2 +/- 6.1 (right lung), and 6.7 +/- 2.1 cmH(2)O/l (chest wall). E(Asym) was high in three patients with prior cardiac surgery or mediastinal radiation therapy, suggesting that mediastinal stiffening due to scarring and fibrosis reduced pressure transmission between hemithoraxes. Simulations with a previously published model showed that changes in E(Asym) in the range of values observed could substantially affect lung ventilation after single-lung transplantation for emphysema.