Residual lung volume in mitral disease.

The degree of lung distension during quiet respiration, the so-called respiratory position or resting expiratory level, is essentially determined by a balance between the passive forces produced by the thoracic wall and the active forces due to the elastic properties of the lung. Therefore the interplay of these forces has a direct role in determining the extent of the functional residual capacity and, consequently, of the residual lung volume. Previous work (Heyer et al., 1948; and Mack et al., 1947) has demonstrated that pulmonary vascular congestion does induce a certain degree of lung stiffness, and in addition pulmonary congestion is a constant finding in mitral valve disease. In view of the relationships between functional residual capacity on the one hand, and lung stiffness and pulmonary congestion on the other, this investigation was carried out with the purpose of studying the functional residual capacity in a large series of patients with pulmonary engorgement due to mitral disease.