The Relationships between Dyspnea, Pulmonary Function and Intracardiac Pressures in Adults with Left Heart Valve Lesions

¹ Cardio-Respiratory Laboratory, Toronto General Hospital and the Department of Medicine, University of Toronto

Sixty-nine patients with left heart valve lesions have been studied in order to define a sequence of events relating raised intracardiac pressure to abnormalities of pulmonary function and dyspnea.

Mitral valve disease was present in 50, aortic valve disease in 12 and both valves were abnormal in seven patients.

Evidence is presented that the raised left atrial pressure causes a generalized thickening of the alveolar capillary membrane which usually shows its effect by a decreased pulmonary elasticity (low compliance) and abnormal gas exchange (low fractional carbon monoxide uptake). In some patients the raised pulmonary artery pressure is transmitted, by anastomoses, to the bronchial capillaries and this results in exudation of fluid or edema of the mucous membrane of the smallest air passage causing an obstruction to air flow (high nonelastic resistance). These pulmonary abnormalities may result in difficulty in obtaining the oxygen required for exercise. In some patients the hyperventilation during exercise is an attempt to compensate for this abnormality of gas exchange. In other patients abnormal hyperventilation during exercise is related to nervous causes. Where there is not an abnormally high minute ventilation during exercise, this may be due to gas exchange being normal or due to ventilation being limited by the very high work of breathing.

Dyspnea is best related to the amount of respiratory work related to the uptake of oxygen and appears to be associated with this increased respiratory work in the presence of difficulty in gas exchange.