Licence: Public Domain Mark
Credit: Heart-beat and pulse-wave / by C.S. Roy and J.G. Adami. Source: Wellcome Collection.
Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.
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![lever (/). Attached to the axis of rotation of this lever is the spiral watch-spring (g), which can be tightened at will, so that the lever can be made to assume a vertical position at any desired hydrostatic pressure within the box. Finally, by means of an appropriate mechanism a piece of blackened glazed paper is made to move in a vertical direction past the end of the re- cording lever. In actual use the box is first fixed firmly over the end of the radius by an appropriate holder, and the tap (c) being opened, the pressure within the box is raised to any desired height, the spring being tightened or slackened until the lever is vertical: then, the tap having been closed, tracings can be obtained without difficulty. The pressure within the box acts in all directions, and is correctly given by the manometer. Let us now see how with an instrument of this kind the height of the pulse-wave is affected by changes in the pressure exerted upon the artery. The diagram, Fig. 35, illustrates this in the case of a healthy male, cet. circa 40. In this diagram the abscissae give the manometric pressures upon the artery, while the ordinates give the heights of the pulse-wave as re- corded by the sphygmometer. It can be seen that with a pressure of 20 mm. of mercury the pulse-wave is low, aDd that its height rises in a rapidly increasing ratio upon the addition of each 20 mm. of pressure, until at a pressure of 100 mm. of mercury it attains its maximum. At pressures above this it falls rapidly, tending to describe a curve which runs asymptotically with the abscissa line. It must be understood that this curve varies with different individuals, and at different ages. As however this subject is being worked out accurately by Mr. L. Rolleston, at our suggestion, we need not here enter further into the subject, except that we must interpret the meaning of this characteristic curve. Why, first of all, is the pulse-curve highest when the extra-arterial pressure is so high as in this case, ] 00 mm. of mercury ? Why, in other words, do the contents of the portion of artery in the box undergo the greatest oscillations in volume when the extra-arterial pressure is in this instance at this particular height ? The explanation, we believe, is not difficult. Let it be clearly understood, in the first place, that the height](https://iiif.wellcomecollection.org/image/b21908515_0087.jp2/full/800%2C/0/default.jpg)
