THE ROLE OF THE NERVOUS SYSTEM IN THE MAINTENANCE OF PULMONARY ARTERIAL HYPERTENSION IN HEART FAILURE

Elevation of pressure in the pulmonary veins, with a consequent elevation of pressure in the pulmonary capillaries and pulmonary artery has for many years been invoked to explain pulmonary hypertension in both mitral stenosis and left ventricular failure. Ignoring the possibility of pul-monary vasoconstriction, this hypothesis was in complete accordance with the " mechanistic " concept of the regulation of pulmonary pressure, emphasized recently by Cournand (1947, 1950) and Hamilton (1951). It was based mainly on the relative refractoriness of the pulmonary circula-tion towards substances affecting the systemic circulation. It was soon established, however, that elevation of the pulmonary venous pressure is only partly responsible for the high pressure in the pulmonary artery that is observed in heart failure. Elevation of pulmonary " capillary " pressure beyond the colloid osmotic pressure of plasma causes an increase in the pulmonary pressure gradient (Dexter et al., 1950), as a result of an increase of the pulmonary arteriolar resistance. Lewis et al. (1952), emphasize that in mitral stenosis this increased arteriolar resistance is a physiological counterpart to the anatomical changes observed in the small pulmonary arteries by Parker and Weiss (1936) and Larrabee et al. (1949). In face of this " static " theory of increased pulmonary arteriolar resistance it seems hard to understand wh