THE NATURE OF THE ELECTRICAL FIELD AROUND THE HEART

Abstract

In a series of expts. on tortoise hearts, the rate of fall of potential due to the R wave at increasing distances from the heart was obtained, with the heart in situ, isolated in a plane conducting medium and in a volume conductor the shape of the body of the animal or in a sphere. On plotting potential against distance from the heart, the curves obtained from the plane conductor ap-proached more closely the heart in situ than the heart immersed in a volume conductor. The conducting field around the tortoise heart in situ thus approximates that of a plane rather than that of a homogeneous volume conductor, presumably due to different degrees of electrical conductivity in different tissues. The probability that the same situation exists in the mammal led to the investigation in a second series of expts., carried out on dogs and rabbits, of the conductance over different paths between the anterior and posterior extremities. The paths of greatest conductance were found to be the dorsal muscle of the trunk and spinal cord. These two paths together constitute approximately 80% of the total conductance of the trunk. The abdominal viscera were found to represent a poor conducting path, particularly when their large total volume was taken into consideration. The blood in the blood vascular system accounted for approximately 25% of the total conductance of the body. The approximation to a plane distribution of the principal paths of electrical conduction in the organism is believed to account for the approximation of the electrical field surrounding the heart in situ to the electrical field in a plane.