RECENT ADVANCE IN LARYNGEAL ELECTROMYOGRAPHY IN HUMAN

Abstract

Electromyography is a useful technic both in diagnosing neuromuscular diseases and in investigating function of muscles. It has been utilized extensively with large skeletal muscles. For the intrinsic laryngeal muscles, however, electromyography has not been a popular clinical test or a popular technic in laboratory experiments. This lack of popularity may be attributed to difficulties met in inserting electrodes into such small muscles and holding them in place. Since Weddell, Feinstein and Pattle (1944) first studied seven cases of laryngeal paralysis, many investigators have attempted to utilize the electromyography in studying human laryngeal muscles clinically and experimentally, with successful results to a certain extent. In almost all of these studies, a needle electrode was inserted into the laryngeal muscles through the mouth except for the cricothyroid muscle, in which an electrode was always inserted through the skin of the neck. The muscular activity was evaluated on raw tracings on a oscillograph. There are some disadvantages inherent to this traditional technic: 1. The pain and discomfort caused by the needle and the presence of the electrode leads in the mouth and the pharynx interfere with executing normal laryngeal activities, such as phonation, speech, cough, and deglutition. 2. It is difficult to keep the electrode from shifting throughout the test. The muscular activity among different conditions can be reasonably compared only when the electrode is located in the same place in a given muscle. 3. Evaluation of the muscular activity on oscillographic tracings not infrequently causes misleading, especially when studying the muscular function related to speech. In such a complicated behavior as speech, the muscles involved are often activated not only when necessary for a given gesture (obligatory excitation) but also when not necessarily required (associated or accidental excitation). Furthermore, the muscular activity pattern for a given speech material is usually not exactly the same among repeated utterances. It is often difficult to differentiate the substantial activity from the physiological noise on oscillographic recordings. To improve the situation, several technical devices have been employed recently.