Interpretation of the HJ interval of the normal ballistocardiogram based on the principle of conservation of momentum and aortic ultrasonic Doppler velocity measurements during left ventricular ejection.

The principle of conservation of momentum and the observation that blood acceleration in the ascending aorta is approximately constant during ventricular ejection was applied to develop a new interpretation of the HI and IJ intervals of the normal ballistocardiogram. The results indicate that the acceleration (A), velocity (V), and displacement (D) of the ballistocardiogram in the HI and IJ phases may be expressed by a set of equations which, when evaluated numerically, give theoretical acceleration, velocity, and displacement curves. The theoretical A, V, and D curves corresponded closely to those observed on the normal ballistocardiogram record during the HJ interval.