Emphysema and Mitral Valve Disease

¹ Director, Pulmonary Division, and Senior Associate in Medicine, Peter Bent Brigham Hospital; and Assistant Professor in Medicine, Harvard Medical School

Preoperative pulmonary evluation in 88 patients with class III or IV mitral valve disease revealed emphysema to be present in 17. Total operative mortality was 17 percent, 7 percent in patients without emphysema, 65 percent in patients with emphysema (37 percent when generalized throughout both lungs and 89 percent when upper lobe). In patients with mitral valve disease an increase in left atrial pressure is associated with redistribution of blood from the bottom to the top of the lung without a concomitant redistribution of ventilation, producing a ventilation/perfusion imbalance and a low steady state diffusing capacity. Pulmonary emphysema causes a loss of alveolar surface for gas transfer and a low steady state diffusing capacity. An increase in left atrial pressure and the resultant ventilation/perfusion imbalance will cause patients with generalized emphysema to have further reduction in an already low diffusing capacity. Patients with upper lobe emphysema cannot redistribute blood to the top of their lungs in response to an increase in left atrial pressure, do not develop a ventilation/perfusion imbalance and have an increase in diffusing capacity due to overperfusion of well-ventilated airways. In the postoperative state, patients with upper lobe emphysema do not gain lung units for gas exchange when left atrial pressure decreases, and when they lose additional lung units secondary to fluid transudation caused by operative trauma, there may be limited oxygen transport at a time of increased oxygen demand. The presence of a normal or very low steady state diffusing capacity in the preoperative state in a patient with increased left atrial pressure secondary to mitral valve disease should alert the physician to the possibility of increased surgical risk.