Galvanopallpation

ГАЛЬВАНОПАЛЬПАЦИЯ, a method for investigating the excitability of cutaneous sensory and vasomotor nerves by means of galvanic current, proposed by M. Kagan (M. Kahane) in 1912. The diagnostic value of G. consists in establishing a certain regular relationship between certain diseases of internal organs and changes in the excitability of cutaneous sensory and vasomotor nerves; this change in excitability manifests as a change in the intensity of cutaneous pain sensitivity and an increase in the excitability of cutaneous vasodilators during investigation with direct current. After a certain duration of application of direct current on the skin, a fairly persistent redness remains at the places of application of the electrodes, connected with the widening of the lumen of the skin capillaries, due to the effect on the vegetative innervation of the vessels. Under normal conditions, a short-term effect of direct current on the skin does not change the lumen of the vessels. In the presence of mild general cutaneous vasomotor excitability, direct current can be applied as a diagnostic procedure to determine the predominance of the tone of cutaneous capillary vasoconstrictors or vasodilators; in the presence of greater excitability of vasodilators, local short-term application of direct current on any part of the body (with a small surface of the anode of 2 sq. cm) leaves a slight redness of the skin due to the dilation of the capillaries; in the case of more excitable vasoconstrictors (in the presence of white dermographism), the same effect of galvanic current gives a local pallor of the skin due to the narrowing of the lumen of the capillaries. G. is applied not for the investigation of general universal cutaneous vasomotor excitability, but for revealing the reaction of the sensory and vasomotor nerves, localized only on that part of the skin which corresponds to the diseased organ; thus, this reaction is strictly localized. For G. a button electrode with a small spherical head covered with a hydrophilic tissue is used (see figure). The electrode must not be pointed, so that its touch itself does not give painful sensations. The indifferent electrode, with a surface of 60--80 sq. cm, is connected to the negative pole, the button electrode to the anode. The active electrode is the anode, since the cathode irritates the sensory and vasomotor nerves more strongly. In a state of hyperexcitability of these cutaneous nerves, the application of the cathode as an active electrode may obscure the true picture, further intensifying the vascular reaction to irritation. For G. it is necessary to apply currents of weak strength (strong currents always cause a vascular reaction even under normal innervation) with high density, since only with high density (which is achieved by a small surface of the active electrode's head) does a weak current act irritatively on the cutaneous vessels. One should begin G. by moving the rheostat knob a little in advance, i.e., not introducing the current gradually, but giving a certain small load immediately. For investigation one must use the palpation method, i.e., touching the active electrode slightly to the investigated area of skin several times at very short intervals. The electrode is moistened with warm, but not hot, water; before the start of the investigation, which must be carried out in a room with an air temperature of 18-19°, the naked body must be allowed to acclimatize to the surrounding temperature. For the investigation of the skin of the head and neck, a current strength of 0.3-0.5-1 mA is used, for the chest 1-1.5 mA, and for the abdomen 2-3 mA. During G. there is a very weak effect on the endings of the sensory nerves (animal nervous system), which gives a sensation of throbbing, burning, and itching. This reaction, being purely subjective, has considerably less value compared with the vascular reaction in the form of a change in the lumen of the vessels, due to the action on the vasomotor nerves (vegetative nervous system). A very characteristic feature of a positive reaction is its rapid appearance. The intensity of the reaction is judged by the intensity, spread, rapidity of appearance, and duration of the local redness of the skin. Often, during G., redness of the skin occurs in certain areas of the body when the same current gives no vascular reaction on the corresponding areas on the other side of the body. Kagan considers this state of increased excitability of cutaneous vasomotor fibers to galvanic current to be an undeniable proof of the presence of some inflammatory focus of tissue lying directly (at varying depths) under the skin, in the area of the intensified redness of the skin. The inflamed organ, through a reflex via the spinal cord, causes increased excitability of the skin on a strictly defined area of it. Acute inflammatory processes give a positive reaction during G. more often than subacute processes. In chronic processes, investigation gives no definite answer. G. can have significance for differential diagnosis—in inflammatory processes in the apices of the lungs, in diseases of the frontal sinuses, the maxillary sinus, inflammation of the gallbladder, liver, large intestine, ovaries, appendix, and others.