Cardiac asthma may be defined as the clinical syndrome induced by acute passive congestion and edema of the lungs. It occurs when the left side of the heart suffers from a sudden disproportion between work load and work capacity. It may result, therefore: (1) from disorders which cause rapid impairment of the myocardium, the load being constant (for example, myocardial infarction); (2) from disorders which suddenly increase the resistance or pressure load (such as paroxysmal hypertension consequent to an adrenal medullary tumor); (3) from disorders which markedly elevate the inflow or venous load without impairing the myocardium (such as strenuous exertion in a person with mitral stenosis); or (4) from a combination of these factors. The most common cause is increased venous return in a recumbent subject with left ventricular strain consequent to hypertension. Of the numerous conditions which may produce increased venous return, nocturnal reabsorption of extracellular fluid from dependent parts is probably the most common. The therapeutic implications are obvious.
Cardiac asthma must be differentiated from the various primary diseases of the lungs which cause paroxysms of wheezing or panting. The differentiation is usually readily made by simple clinical measures; in doubtful instances measurements of circulation time may be of crucial value.
The management of cardiac asthma involves chiefly three therapeutic principles: (1) Control of precipitating factors (and especially treatment of latent edema and control of nocturnal cough); (2) measures aimed at reducing the inflow load (sitting position, morphine, venesection, tourniquets on extremities, positive pressure breathing); (3) attempts to reduce the amount of residual blood in the left ventricle (rapid digitalization, use of oxygen, and aminophyllin).
A severe attack of cardiac asthma associated with rapidly developing pulmonary edema constitutes one of the commonest and gravest of all medical emergencies. There are few conditions in the broad domain of internal medicine in which prompt and energetic therapy, based on an understanding of the mechanism of the disorder, can produce such immediate and gratifying benefit.
- © 1951 American Heart Association, Inc.