Abstract
The conventional method of manometric recording of blood pressure in animal experiments with a mercury manometer and a float, which carries a writing point, has been essentially the same since Ludwig described it in the last century. A vertical kymograph and specially treated paper (lamp black, etc.) are necessary, as any substantial friction between the paper surface and the writing point causes the float to submerge. This happens occasionally in spite of all precautions. A comparatively wide manometer tube has to be used in order to support the float, which has to carry the writing point and to overcome the friction on the paper; a wide tube draws several cc of blood from the vessels of the animal, when a rise in blood pressure occurs, and therefore a manometer cannot be used in small animals.
To eliminate these shortcomings of manometric recording an apparatus was designed where the float is substituted by a light beam (Fig. 1)
A slide carries a lamp and a phototube. It has a female thread, which engages a threaded brass rod. This rod is rotated by a reversible electric motor. When the motor runs clockwise, the slide—and with it the lamp and the phototube—are raised, at a speed of 2 cm per second, and it is lowered at the same speed when the motor runs counterclockwise. After amplification† the phototube current operates a relay. The relay contacts are connected with the motor in such a way that the motor runs clockwise when the relay is open, and counterclockwise when it is closed.
When the light beam from the lamp strikes the phototube (the phototube housing has a hole 2 mm in diameter), the relay closes, the motor runs counterclockwise and the slide goes down, until the light beam is cut off by the mercury in the manometer tube.
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