THE ACTION OF COMPRESSION ON THE CONTRACTION OF HEART MUSCLE

Abstract

The isolated ventricle of the heart of the terrapin was arranged so that the tension of isometric contractions was optically recorded from a steel spring lever. With this method the heart muscle, subjected to a compression of about 1000 pounds per square inch, acting upon it through a completely surrounding liquid system, shows when stimulated a response about 42% in excess of the tension developed by the same preparation at atmospheric pressure. A compression force of about 1500 pounds, acting on the ventricle, gave an average augmentation of the tension response of about 68%, and with preparations employing the auricles acting together the same degree of compression gave an increase of about 142% in the power of developing tension. The contraction phase of the ventricle exhibits very little increase in duration associated with a "pressure effect" of 42% on the tension, but with higher grades of compression, giving an increase in tension of 68%, the phase of contraction shows a prolongation of 8%. It is suggested that the higher pressures may produce definite changes in the viscous-elastic properties of the muscle. The phase of relaxation exhibits a definite prolongation by pressure. The average increase in duration amounts to 9.5% at a pressure of about 1000 pounds, and 15.5% at a pressure of about 1500 pounds per square inch.