Studies of the Action of Calcium on the Vertebrate Heart.

Abstract

These studies are based upon a series of experiments upon the hearts of 52 animals perfused with oxygenated Locke's solution by a modified Langendorff technique. The essential features in the modification of this method were: (1) Complete water bath circulation about the perfusion fluid, maintained at a constant rate of flow by means of a pump and regulated at a constant temperature by means of a thermostat. (2) Control of the pressure head of the perfusing fluid by graduation of the pressure of flow against a mercury manometer. (3) Introduction of a warm air chamber about the beating heart. (4) The recording simultaneously of auricular and ventricular contractions by means of pins, attached through the auricles and ventricular apices. The series of animals was composed of one turtle, 2 cats, 3 dogs and 46 rabbits. Calcium was introduced into the perfusing fluid, in varying quantities of a 0.25% solution of the chloride. Observations upon the beating heart were made by direct inspection and notation at the time of experiment and by means of kymographic tracings. The commonest effects of the pharmacological administration of calcium upon the perfused heart are noted in the accompanying table.

As a normal amount of calcium ions is necessary for the ordinary strength of the heart's contraction so the addition of more calcium results in a greater force of both auricular and ventricular systole, often but not invariably associated with an increase of myocardial tonus. Just as Brull 1 found in the perfused hearts of dogs and rabbits, and as Bowler and Walters 2 learned by electrocardiogram studies in dogs injected intravenously with calcium chloride, large doses resulted in the production of varying types of cardiac arhthymias. Anatomically, the site of the different actions of varying amounts of calcium on the vertebrate heart has not been certain. In the excised heart it cannot be responsible to changes centrally effected in the vagus and sympathetic innervation. That these effects are probably not upon the intrinsic conducting system of the heart has been demonstrated in these experiments by section of the auriculo-ventricular bundle in the beating heart. During the course of resulting complete auricular-ventricular dissociation, the addition of calcium to the perfusing fluid has resulted, as in the intact heart, in the recorded effects of increased strength of systole, bradycardia, and with smaller amounts tachycardia in the ventricular muscle.