Catheter-tip instrument for measuring left ventricular diameter in closed-chest dogs.

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Abstract
A new catheter-tip instrument has been designed for the continuous recording of left ventricular diameter in closed-chest anesthetized dogs. The measuring tip of this instrument, which is attached to a no. 7 cardiac catheter, is inserted into a carotid artery and placed into the left ventricle. The tip consists of a small center tube which contains a linear differential transformer. Arranged circularly around this center tube and spaced 120[degree] apart are 3 braces which are hinged to the center tube. These braces are spring loaded and are collapsed during insertion of the instrument. Once in the left ventricle, the braces spread apart until they touch the ventricular wall. The braces are mechanically linked to a ferromagnetic sleeve which slides along the center tube as the braces open and close. The position of this sleeve determines the coupling of the differential transformer and results in a signal proportional to the degree of spread of the braces and thus to the left ventricular diameter. Tests have shown that the instrument accurately records the instantaneous inside diameter of the left ventricle.

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