Abstract
An optically recording flow meter has been devised which accurately registers the phasic blood flow in the various vessels of the heart.
The rate of flow is measured by directing the blood through a thin orifice plate (or Pitot tube arrangement). The momentary acceleration of the blood so produced causes a lowering of the lateral pressure (for a short distance downstream) which is proportional to the square of the acceleration. The moment to moment differences between the lateral pressures above and below the orifice, recorded by a differential manometer, give the phasic changes in the rate of blood flow.
The upstream lateral pressure is led to a manometer tip with a 4 mm opening covered with a special rubber membrane 0.003 to 0.006 inch thick stretched 3 to 5 times. A waterproofed piano mirror (chip from a Bureau of Standards certified counting chamber cover slip) is mounted on the membrane by a peg or splint with special cement (to prevent hysteresis). The downstream lateral pressure is led directly to a water tight chamber (made of transparent Lucite) which surrounds the membrane. The light beam enters this chamber through a low diopter plano-convex lens (0.5 to 0.7). This lens should be at least 1.5 mm thick to prevent distortion under pressure. A small angle prism, capable of rotation through 360 degrees, mounted in front of the lens, corrects the prismatic effect of the Locke's solution with which the chamber and unit are filled. The whole assembly is mounted in the carriage of a Gregg manometer.
When filled with Locke's solution by means of a flexible tube the meter, as used in small vessels such as the coronary arteries, has a frequency of 80 to 120 double vibrations per second and for a differential pressure of 10 mm Hg gives a deflection of 40 to 60 mm at 4 meters camera projection distance.
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