Lead poisoning and lead absorption

by Sir Thomas Morison Legge; Kenneth Weldon Goadby

—The diagnosis of the affected muscle is greatly assisted by careful examination of all the muscles in the affected physiological group by means of the galvanic and faradic currents. The battery for the purpose of testing the electrical reactions must have an available electromotive force of over 40 volts. A battery of thirty-two Leclanché dry cells is ample. For the faradic current, a small induction coil operated by two Leclanché cells is sufficient. One large, flat electrode should be used, and several smaller ones.

The faradic current should be used first, as it stimulates the nerves directly, and the muscles only indirectly, through their nerve-supply. Each nerve trunk should be examined systematically. The motor points correspond for the most part with the points of entry of the motor nerves into the muscles which they supply. A small electrode, either a button or a small disc about the size of a sixpence, should be used for the examining electrode, while the larger electrode should be placed either on the abdomen or between the shoulders. The electrodes should be well soaked in normal saline.

The intensity of the minimum current required to produce a contraction for each point should be noted, and compared with the effect of a similar current on the opposite side of the body.

The reaction of degeneration of the faradic current consists in no contraction at all being elicited, even when a very strong current is employed. If there be unilateral wrist-drop in the left hand, consisting of loss of power of the extensor communis digitorum on that side, no movement of the muscle is produced at all when the electrode is placed across the motor points of the muscle. These are situated to the outer side of the arm when the dorsum of the hand is uppermost, about 1¹⁄₂ to 2 inches below the olecranon. The same quantity of current, when applied to the unaffected muscle on the opposite side, produces a brisk reaction.

Having observed the effect with the faradic current, and the results having been recorded, the continuous current is used, and the electrodes made use of in an exactly similar fashion. When a small electrode is used, the superficial nerves and muscles are more stimulated than those lying deeply. It is necessary, therefore, to begin with a small current and gradually increase it until the individual muscle responds.

The strength of the current employed is registered by means of a milliampèremeter.

With the continuous current quantitative as well as qualitative alterations may be determined, and with the quantitative change of the galvanic current the muscular excitability is increased, contraction following the application of a weaker current than is necessary to produce it in health or in the sound muscle on the other side of the body.

With the qualitative change, the contraction is no longer sharp, but sluggish. The anodal closing contraction is elicited with a weaker current than kathodal closing contraction, so that ACC>KCC.

The quantitative change depends partly on the nutrition of the muscle; the qualitative change depends on the fact that the nerve no longer regulates the character of the contraction, and also to a small extent is the result of changes in the muscle itself.

In a complete reaction of degeneration in an affected muscle, reaction to the faradic current is absent, contraction to the galvanic current is sluggish, and is produced with a smaller current in the anode than the kathode.[A]