Sphygmograph

SPHYGMOGRAPH (from Greek sphygmos—movement, oscillation, and grapho—I write), an apparatus for the graphic registration of the pulse (sphygmography), which gained wide distribution in practical medicine; it was first constructed by Vierordt. Due to significant shortcomings, it soon gave way to more perfect designs, of which the sphygmograph of Marey (Marey) enjoyed the greatest fame for a long time. The requirements imposed on such apparatuses boil down to the most accurate possible reproduction of those oscillations of the arterial wall which are the result of the rhythmic pumping activity of the heart. Most designs are adapted for recording the pulse of the radial artery; these apparatuses are properly called sphygmographs; other types, more universal and suitable for registering the pulse of other arteries, are known by the name of pansphygmographs. An essential part of every sphygmograph is a lever that registers the pulse oscillations on a moving plate. These oscillations are transmitted to the lever through a special button-pelotte,

Figure 1.

which is placed on the pulsating artery and thus serves as a connection between the lever and the artery. In view of the fact that a significant layer of tissue (skin, subcutaneous fat layer) is included between the pelotte and the artery, the resistance of which must be overcome, the pressure of the pelotte in the proposed systems is regulated in different ways. In the Marey sphygmograph (Fig. 1), a screw II serves this purpose, which presses on an elastic plate with a pelotte attached to it, whereby the required pressure of the latter on the artery is achieved. The pelotte carries in its center a pin S with a screw thread, which, during its excursions up and down, engages a toothed wheel m, mounted on a common axis with the lever p. The apparatus is equipped with a clockwork mechanism that moves a strip of smoked paper, on which the sphygmogram is drawn. With the help of splints N, the sphygmograph is firmly fixed on the forearm. Ludwig proposed a special holder (Armhalter), on which the forearm rests while the hand grips a specially adapted wooden handle fixed to the stand of the holder. This position firmly fixes the arm and protects the apparatus from accidental tremors. The Marey sphygmograph, however, leaves something to be desired in terms of more accurate recordings, and its further improvements, while retaining the same principle of general construction, boiled down to details which, however, provided many significant advantages compared to their prototype. Thus, in the Dudgeon sphygmograph, to reduce the moment of inertia, the long lever is replaced by a system of two short levers, which represents a significant benefit both in terms of the amplitude of the curve and a significant reduction in the inertia of the lever. The Dudgeon sphygmograph is still the most common in the clinic, although in terms of the accuracy of the sphygmogram, it must yield to the very popular Frank-Petter sphygmograph (Frank, Petter). The authors prefaced their design with a whole series of purely theoretical works and, on the basis of rigorous mathematical analysis, provided a number of propositions that formed the basis of their system. The external appearance of the Frank-Petter sphygmograph (Fig. 2), while resembling the Dudgeon sphygmograph, differs favorably from the latter in some details of construction. Firstly, the lever a (Fig. 3), carrying the pelotte P at one end, rotates on a free axis, which achieves its extreme mobility. The small arm is pulled by a spring F₁, the tension of which is regulated by a screw S. At the end of the long arm, there is a hook on top, connected by a free ring to the lever b, which is held in equilibrium on one side by a spring F₂, and on the other by the rod of the short arm of the lever c, suspended on an axis with a spring F₃. The writing pen slides along the smoked paper at an acute angle, and in order to ensure uniform pressure of the pen on the paper, the latter has a curvature in the plane of the pen's oscillation with a radius equal to the lever c. In this apparatus, all the conditions are implemented as far as possible,

required by theory for the best registration. The moment of inertia of the moving parts is reduced to a minimum; the double-lever system (as in Dudgeon's) allows increasing the amplitudes of the pelotte's oscillations from 5 to 80 times without losing the advantageous properties of the short lever; free axes, as well as the sliding of the pen at an acute angle, significantly reduce the friction of these moving parts. A time marker with a small lever is mounted on the wall of the clockwork mechanism, marking fractions of a second parallel to the sphygmogram. In addition to those just mentioned, a whole series of other systems were proposed: v. Frey, Jaquet, Hackett, and others, which, however, differ little from those of Marey and Dudgeon. Among pansphygmographs, the Brondgeest pansphygmograph is distinguished by the simplicity of its construction and sufficient versatility.

Figure 4.

(Fig. 4). A metal capsule K is covered with an elastic membrane, to the center of which a wooden button-pelotte P is attached. The outlet tube r is movable in the holder of the horseshoe-shaped stand b and can be fixed with a screw S at any height. After the horseshoe is fixed with a bandage on one limb or another, the capsule is moved down until the pelotte presses with sufficient force on the pulsating area, and is secured with a screw. The outlet tube is connected to the Marey recording capsule (see Graphic method, Air transmission) by a rubber tube, and registration is carried out via air transmission. Polygraphs and cardiosphygmographs are built on the same principle. Of the latter, the Jaquet cardiosphygmograph is served by two receiving capsules, which transmit oscillations to two Marey drums placed side by side on the apparatus. With the help of their levers, two recordings of the examined areas (e.g., atrium and ventricle) are obtained simultaneously. The third lever is intended for recording the pulse of the radial artery using a Jaquet sphygmograph, mounted on a common stand and thus constituting a part of the cardiosphygmograph. The apparatus is portable and is fastened to the arm like a sphygmograph. Sphygmogram, see Pulse.