Abstract
With the usual apparatus used in clinical study, such as the blood pressure manometer or the Erlanger capsule recording on a smoked drum, the pressure changes in the cardio-vascular system can not be followed accurately. The inertia of the apparatus and the variation in the elasticity and responsiveness of the different instruments give inaccurate or asynchronous data. 1
The application of the Frank capsule method to the study of pressure has been to record pressure curves or pressure gradients by means of an optical system consisting of a mirror on the rubber capsule, reflecting a beam of light. 2 Its immediate responsiveness and accuracy are extremely efficient.
By a simple means of adaptation, it can be made to record with extreme sensitiveness the amount of blood pressure over a continuous period of time. The rubber dam stretched over the end of a piece of metal or glass tubing is made so tight as to resist pressure up to 300 mm. of mercury. The band of light reflected from the mirror on the capsule is so arranged, directed over the slit of a camera, that its excursion from 0 to 300 mm. of mercury pressure should range from one end to the other end of the slit in the camera. The position of the band of light at any point across the moving film represents a known, previously standardized, amount of pressure (Figure I).
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