Paroxysmal pulmonary edema consequent to stimulation of cardiovascular receptors: II. Mechanical and neurogenic elements

Abstract

The part played by mechanical and neurogenic factors in pulmonary edema experimentally produced in dogs by the use of a standard technique has been investigated. The basis of this standard technique is the rapid, interrupted infusion of saline solution into the carotid arteries toward the brain. 1. 1. The quantity of injected fluid may be considered as submaximal, in the sense that, while the fluid favors the development of edema by distending the pulmonary vessels, the amount of fluid administered is insufficient of itself to produce edema. 2. 2. The importance of specific receptors of the cardiovascular apparatus has been demonstrated. Their stimulation causes a reflex leading to increased permeability of the pulmonary capillaries, and favors the development of edema if these vessels are already distended. The problem of whether the reflex causes first a dilatation of the vessels, or whether its effect is the result of a direct increase of permeability needs further study. The most important among these reflexes is the carotido-pulmonary reflex whose afferent pathway to the central nervous system is through the glossopharyngeal nerve, and whose efferent pathway to the lungs is through fibers which are anatomically part of the sympathetic system. Another important reflex is that elicited by distention of the heart chambers. A third reflex, whose importance cannot yet be measured, is the pulmonary artery-pulmonary vessels reflex. All these reflexes are able to cause pulmonary edema when a submaximal quantity of fluid, in itself insufficient to produce edema, is injected into the circulation. 3. 3. Deeper understanding of the mechanism can be obtained only by using drugs either to enhance or to inhibit the edema, and by studying by means of biologic assay the properties of both the blood and the edema fluid. 4. 4. Electrical stimulation of either the cardiac end of the cut vagi or the intact nerves favors pulmonary edema by causing extreme bradycardia. This factor, however, does not play any role in the experiments of infusion with standard technique.