The confusing and complex interplay of factors leading to "cor pulmonale" may be somewhat clarified if the effects of excessive pulmonary hypertension causing right heart overloading ("pulmonary hypertensive heart disease") are separated from the ventilatory defects that result in arterial desaturation, erythrocytosis, and moderate pulmonary hypertension ("emphysema heart"). In the former group, heart failure dominates the clinical picture; in the latter, it is assumed that heart failure occurs on the basis of a "myocardial factor"—presumably arteriosclerotic heart disease—whose manifestations are colored and modified by the coexisting and contributing respiratory dysfunction. Overlapping of these two distinct forms occurs frequently, and pulmonary hypertension may be severe enough to be the chief precipitating cause of failure in emphysema, particularly in young subjects and in patients with kyphoscoliosis. Respiratory disturbances, fibrosis, and loss of pulmonary elasticity may accompany heart failure secondary to right ventricular overloading which may ultimately lead to significant arterial desaturation at rest and the development of polycythemia, even in this group. It is typical, however, that the disturbances leading to cor pulmonale rarely, if ever, involve the actual pulmonary function of alveolar-capillary gas exchange; they are confined to the abnormalities of the precapillary pulmonary vasculature and to the mechanical apparatus of the chest cage and of the pulmonary parenchyma concerned with breathing mechanisms.
Pulmonary hypertensive heart disease, whatever its cause, has a monotonous symptomatology that is dominated by the signs of heart failure. In cor pulmonale due to emphysema and its allied types, the clinical picture is varied, and oxygen deficiency with arterial desaturation is of central significance. It raises pulmonary artery pressure by a mechanism not fully understood, and it stimulates erythropoiesis. When erythrocytosis has occurred, heart failure from cor pulmonale will soon make its appearance. Unless the arterial oxygen content falls sharply on exercise, resting oxygen saturation values in excess of 80 per cent do not cause this type of polycythemia; nor does polycythemia as such, as in erythremia ("vera"), result in significant arterial desaturation, pulmonary hypertension, or heart failure. However, little is known concerning the hemodynamic load imposed by an increase in blood viscosity.
The management of cor pulmonale must recognize the multiplicity of factors that are concerned and should weigh their relative significance in any given subject. The kaleidoscopic appearance of cor pulmonale requires flexibility of therapy based on a grasp of the individual pathophysiologic interrelations, which may differ from patient to patient.
- © 1956 American Heart Association, Inc.