Esthesiometers

ESTHESIOMETERS (from Greek aisthesis - feeling and metron - measure), instruments for determining tactile sensitivity. A number of instruments of various designs have been proposed depending on which particular type of tactile sensitivity they are intended to investigate. For investigating the sense of touch (tactile sensitivity), the most commonly used instrument is the Ziveking esthesiometer or Weber's caliper. The Ziveking esthesiometer consists of a longitudinal metal plate (Fig. 1), to which two short, bone-made legs ending in blunt points at the bottom are attached. One of these legs, located at the end of the plate, is fixed immovably, while the other can move freely along the plate, sometimes approaching the fixed leg, sometimes moving away from it. The plate has a scale with divisions marked on it, by means of which the distance at which both legs are from each other is determined. The investigation using the Ziveking esthesiometer is carried out by touching both legs, spread at a certain distance, to a particular area of skin. It is necessary to carefully ensure that both legs touch simultaneously. One should also avoid strong pressure on the skin so as not to cause painful irritation. If the subject initially feels two touches, then by repeated applications of the legs with gradually decreasing distance between them, one reaches a point at which the touch of the legs ceases to be perceived separately and is felt as one. If, however, the touch of both legs was initially perceived as single, then one proceeds in the reverse order, constantly spreading the legs apart until reaching the limit at which the single sensation changes to separate. The smallest distance obtained in this way, marked by the corresponding number on the scale, will be an indicator of the state of tactile sensitivity in the investigated area of skin. The data obtained are then compared with a table compiled by Weber for various places on the surface of the body and mucous membranes, on the basis of which a judgment is made about the absence or presence of deviations from normal. For investigating tactile sensitivity, Mochutkovsky proposed the so-called taktiometer. This instrument consists of a solid rubber quadrangular bar 17 cm long and 1.72 cm thick, divided in the middle into two halves by a deep groove (Fig. 2). Each of the four surfaces of the bar in each half is numbered with corresponding numbers, of which there are eight in total. The surface under No. 1 is polished perfectly smooth, the surface under No. 2 appears rough due to being covered with very fine notches. The other surfaces of the bar are covered with progressively deeper notches, due to which the roughness of the surface becomes progressively coarser, ending with the surface under No. 8, which is covered with large four-sided pyramids. Each of the numbered surfaces in normal conditions can be very distinctly distinguished by the degree of its roughness from any other side. With a decrease in tactile sensitivity, roughness begins to be distinguished not from No. 2, as in normal conditions, but from higher numbers, and the higher the number of the surface that first begins to be distinguished as rough, the more severe the disorder of tactile sensitivity.

Figure 2. Mochutkovsky's taktiometer.

The sense of pressure is investigated by means of lead weights of various weights having a flat shape, the upper part of which is made somewhat recessed so that a smaller weight can be placed on it. The bottom of the weights is lined with a thin layer of cloth to avoid temperature irritations. For investigation, a set of six weights weighing 500, 200, 100, 50, 20 and 10 z is sufficient. The investigation is carried out by successively placing two different loads on the investigated area, and in case of a sensation of difference between their weights, the weights are changed in such a way that the difference between their weights becomes smaller and smaller until reaching a threshold at which it ceases to be definitely perceived. Then it is determined what part of the original weight constitutes this smallest perceivable difference, and the data obtained are compared with Eilenburger's table. For investigating the sense of pressure, specially constructed instruments called baresthesiometers are also used, of which the most common are the Eilenburger and Bekhterev baresthesiometers. These instruments are also based on the principle of determining the smallest difference between pressures of different strength. An essential part is a spiral spring that presses on a rod ending in a button-like expansion. The pressure is applied by the hand of the investigator and is indicated by a pointer on the dial connected to the apparatus. The position of the pointer shows in grams the force of pressure. For investigating hair sensitivity, so-called trichesthesiometers are used. Mochutkovsky's trichesthesiometer consists of a pincer and a set of clock springs of various thinness. Bekhterev's electrical trichesthesiometer consists of a metal plate actuated by means of electromagnets. Instruments for investigating pain and temperature sensitivity - see Algesimeter and Thermoesthesiometers.