The Archives of Internal Medicine, 1913, Vol. 12 (Classic Reprint)

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Excerpt from The Archives of Internal Medicine, 1913, Vol. 12 Inspection of the above formula shows that in order to lessen the time of a single vibration in the apparatus the length of the connecting tube, the weight and movement of the recording device and the volume of air in the plethysmograph should be as small as possible, while the cross section of the tube should be as large as possible. In shortening the tube we have endeavored to leave a length which will be sufficient to allow manipulations about the plethysmograph and to allow the individual to move his arm in the suspended plethysmograph Without putting traction on the rigidly fixed recorder. For this purpose a length of about 60 cm. Is necessary. The connecting tube used had a diameter of cm. Between and cc. Of air usually occupied the portion of plethysmograph about the arm. By far the most important part of the apparatus, however, is the recording device. Two types of sensitive recorders were experimented with. In one of these a soap bubble was placed over the end of the tube leading from the plethysmograph, and the oscillations of its summit occasioned by the volume changes in the arm were photographed on a moving sensitized surface. Garten has published plethysmograph tracings taken by this method and we have attempted to use it for recording the pulse ¿ow in the brachial. After a rather extended trial of the method, however, we became convinced that the oscillation time of the apparatus was inadequate. When connected with a tube sufficiently long to permit fixation of the carrier of the soap bubble the oscillation time was usually between 9 and 13 per second, which was slow for our purposes. Garten's tracings also suggest that the oscillation time in his apparatus was slow, as has been pointed out by 0. Frank. The reason for this slow time even when the recorder itself is of neglible weight, becomes evident on inspection of the above formula. In the soap bubble which is essentially a volume recorder the rise of pressure when one unit of air is added to the recorder is practically nil. E, therefore, approaches zero, and since the fraction l/v is also very small, the period of oscillation is relatively long. We were able to get very satisfactory plethysmograph tracings of the finger by this method, for in this case the volume of air surrounding the finger is small and consequently the fraction l/v is relatively large. A trial soon con vinced us, however, that our method for determining the blood-¿ow could not be applied satisfactorily to the finger. About the Publisher Forgotten Books publishes hundreds of thousands of rare and classic books. Find more at www.forgottenbooks.com This book is a reproduction of an important historical work. Forgotten Books uses state-of-the-art technology to digitally reconstruct the work, preserving the original format whilst repairing imperfections present in the aged copy. In rare cases, an imperfection in the original, such as a blemish or missing page, may be replicated in our edition. We do, however, repair the vast majority of imperfections successfully, any imperfections that remain are intentionally left to preserve the state of such historical works.