Hydraulic Heart

When a San Diego physician asked a technician at General Dynamics' Convair Division to sharpen a big and costly type of hypodermic needle, he had no idea that the trail would lead into the human heart. But more Convair design specialists and engineers got interested in medical gadgeteering; *last week a notable result was announced. They had developed a new and sophisticated heart-lung machine.

Machines to bypass the heart and lungs during operations inside the heart vary widely because surgeons have pet preferences about details. Biggest difference is in how the blood is oxygenated: some machines bubble the oxygen through the blood, others spread the blood in a thin film over screens in an oxygen-filled chamber. Virtually all the machines are now driven by an electric motor pump, and many need a squad of physicians and technicians to keep an eye on them.

The San Diego pump is radically different in many ways. Instead of being plugged into an electric outlet (an explosion hazard in the operating room), it gets its power from the pressure of tap water. This is converted by the reciprocating-engine principle into a pump action, giving pulsatile pressure in four Plexiglas chambers. In each of these is a rubber bladder corresponding to one of the heart's own chambers. The bladders are paired (like the auricles and ventricles) and they contract and expand in a rhythm like the heart's. In an additional chamber, corresponding to the lungs, the blood is oxygenated by the conventional film-on-screen method.

Chief advantages claimed for the Convair heart: its gentle hydraulic action is less damaging to the blood; its flowmeter is in the water system, not in the bloodstream itself, further reducing damage; by ingenious servomechanisms it provides automatic control of oxygenation and acidity; it can handle up to two gallons of blood a minute, against five quarts for present models. It needs only two men to tend it. If the power fails, it keeps running. If water pressure fails, it can be cranked by hand.

This week a woman of 44, first patient operated on with the machine's aid, was making a good recovery after an operation to close an opening between her heart's chambers.

*An old tradition among air-faring folk. Aviator Charles A. Lindbergh spent years (1930-35) helping Dr. Alexis Carrel to perfect a "robot heart," a germ-free pumping device in which entire organs were kept alive outside the body.

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