Measuring the Heart's Kick

If a man holds his breath and stands perfectly still on a bathroom scale, the needle wobbles slightly but visibly in time with his heartbeat. In theory, it should be easy to use this principle to get medically valuable information about the strength of the heart's thrust and about its subtle subbeats, thus disclosing how healthy the heart is. Inventive minds have been trying for more than half a century to devise an instrument that would yield reliable data. In New York City last week, Astro-Space Laboratories, Inc. demonstrated the latest ballistocardiograph,* which was developed with the aid of missilemen.

The principle of the heart's "kick" is as simple as the thrust of a rocket: with each beat, blood rushes upward and strikes the aortic arch (where the great artery curves downward). The impact is great enough to give the whole body an upthrust. Almost simultaneously, acceleration of the blood directed downward by the aortic arch adds to the upthrust. When the descending blood slows down, there is a rebound effect which gives the body a downthrust, about half as intense as the earlier upthrust.

Streetcar Blur. Ballistocardiographers, led by the University of Pennsylvania's Dr. Isaac Starr, contend that measurements of these and of minor additional thrusts show how well the heart and arteries are working. But the accelerations must be measured in thousandths of a G (the pull of gravity). No building is steady enough to be free of movements that confuse the sensitive machine. In Philadelphia, Dr. Starr got blurs on his ballistocardiograms every time a streetcar rumbled by eight floors below. To cushion out such vibrations, researchers have turned to various systems of floating the body--strapped to a board--in a pool of mercury or (Dr. Starr's choice) on a foot-thick pile of nylon blankets.

The Astro-Spacemen decided that the patient could be floated much more delicately than that. In the first place, the weight of the board must be figured with the patient's, so the less that has to be added the better. The instrument makers hit upon an oversized bedboard made of an aluminum honeycomb, which weighs only 7 Ibs. To float patient and bedboard, they chose an air bearing of a type originally designed for instruments in missiles.

Coronary Warning? The basic model measures head-to-foot and foot-to-head thrusts. A second recording instrument can be added for the sideways thrusts of the blood stream. The recorder has a spare channel, so that if the patient has electrocardiograph leads hooked up the physician can read the ballistocardiogram along with an electrocardiogram.

As countless victims of heart attacks are ruefully aware, the ECG gives no indication of early coronary disease or danger of an imminent attack. The BCG does, its proponents claim: the artery narrowings of atherosclerosis, such as those involving cholesterol deposits, which lead to attacks, show up in measurements the heart's blood output. But the BCG cannot become a standard item in physical checkups until the newer instruments (there are several models by different makers) have been thoroughly tested.

*From the Romans' ballista (which in turn comes from the Greek ballein, to throw), an ancient machine for hurling missiles, plus the Greek for heart and writing.

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