THE RELATIONSHIP BETWEEN THE CARDIAC EJECTION CURVE AND THE BALLISTOCARDIOGRAPHIC FORCES

Abstract

The theoretical cardiovascular forces which would cause body displacement in the head-foot axis were calculated for both the human and the dog from the contour of a cardiac ejection curve and the dimensions of the aorta as determined from stretch curves for isolated aortic rings. Such forces were compared with actual ballistocardiograms as recorded by high and low frequency instruments. Calculated and actual curves show serious discrepancies in onset and in amplitude. The actual ballistocardiogram seems to be a distorted recording of a viscous, highly damped system. The period of the body is such that the relatively frequent oscillations of cardiovascular forces cannot be quantitatively registered. These oscillations have origin not only in the acceleration of blood leaving the heart, but also in the pressure pulse transmissions to and from the arterioles of the periphery. The nature of these several forces is discussed. Since cardiac ejection curves and pulse wave velocities are variables between subjects, or from time to time, the quantitation of the ballistocardiogram by a single set of formulae seems an over-simplification, and cardiac values so derived should be looked at as comparative rather than absolute.