BALLISTOCARDIOGRAM. II. NORMAL STANDARDS, ABNORMALITIES COMMONLY FOUND IN DISEASES OF THE HEART AND CIRCULATION, AND THEIR SIGNIFICANCE 1

Abstract

The Ballistocardiograph (1), a modern adaptation of an old idea, consists of a table suspended from the ceiling on wires and braced to prevent motion in any but the longitudinal direction. Motion in this direction, opposed by a strong steel spring, is magnified about 8,000 times and photographed. When a subject lies on the table he is not conscious of its motion but the records obtained are characteristic and reproducible. Figures 1, 3, and 4 give typical examples. The chief forces producing this motion have been identified as the recoil from the ejection of blood from the heart, the impact of the blood striking the arch of the aorta and the curve of the pulmonary artery and, of less importance, the recoil from the systemic blood accelerated feetward when the aortic arch has been passed. The resultant of these forces is not perfectly reproduced in the record, the chief difficulty being due to the physical properties of body tissues which vibrate for a brief instant after receiving a single blow. These after-vibrations warp the descending part of the record but they have a much smaller effect on the ascending part, and from this part reliable data can be secured. Evidence has been presented (1) that the size of the initial waves, I and J, is related to the cardiac output and that the form of the ballistic curve is determined by the shape of the curve of blood velocity in the great vessels. These conceptions lead one to expect that, when the circulation is feeble, the ballistocardiogram will be of low amplitude and, when the heart is weak, the form of the ballistic record will be altered. Therefore, we believe that this simple method will permit the easy identification of patients with 1 The completion of this work was assisted by a grant from the Penrose Fund of the American Philosophical Society. abnormal circulations and will also provide evidence of cardiac health or disease of a type which has no counterpart in the ordinary clinical tests. To realize this expectation it was first necessary to determine the normal standards. To this end over 200 healthy persons from 20 to 84 years of age were examined and standards of normality have been obtained from the results. Ballisto-cardiograms have also been secured on over 400 patients and this experience has permitted description and analysis of the more common variations from the normal. TECHNIQUE At first all tests were performed with the subject under conditions of basal metabolic rate, but we soon abandoned this in favor of a test made after 15 or 30 minutes' rest and not less than 2 hours after a meal. The chief reason for this change was convenience but we justified it by several arguments. It is true that the basal ballisto-cardiogram is of somewhat lower amplitude than that obtained in the resting condition described, but the differences found in pathological conditions are so much larger that confusion seems most unlikely. One can point to an analogy with the blood pressure. The basal blood pressure is considerably lower than the value obtained at other times but the differences found in disease are so large that to restrict one's attention to basal values is unnecessary for most purposes. In another respect our technique changed early in the investigation. We started with the belief that the results would be more comparable if the weight on the table was kept constant and, accordingly, added iron bars until the combined weight of subject and bars was 200 lbs. After working 3 months with this plan it was abandoned because of the discovery that the additional dead weight diminished the damping and so increased the error due to the secondary vibrations. For the heavier men this error was negligible, but for the lightest women the extra weight increased the sum of the altitudes of waves I and J by almost 20 per cent. For the following 6 months all subjects were tested both with and without the extra weight and from this experience .a correction was established. In this report the values obtained on normal subjects during the first 3 months have been corrected to 437