Electroglottography is a noninvasive laryngeal vocal fold diagnostic procedure used especially to monitor treatment success in laryngeal vocal fold therapy. The two electrodes attached superficially to the thyroid cartilage wings determine the altered electroimpedances in the case of vibrating vocal folds and graphically represent the use of the voice in a so-called electroglottogram. In evaluating this electroglottogram, the recorded Lx waveform of vocal fold vibration is checked for abnormalities, such as incomplete vibrations, which enables the physician to further classify dysphonia and voice production disorders.
What is electroglottography?
The ENT physician uses electroglottography to diagnose the laryngeal vocal folds. For this purpose, after an examination, the patient is given two electrodes placed on the thyroid cartilage lobes and thus the use of the voice can be graphically displayed. Electroglottography depicts the vibration cycle of the vocal folds and larynx during normal and impaired speech and singing using a laryngograph. The procedure is a non-invasive measurement method that works primarily through two superficially attached electrodes. It can therefore also be referred to as EGG and, in particular, registers altered electrical impedances of the vibrating vocal folds. The laryngographer’s recordings are called electroglottograms and provide information about the quality and quantity of vocal fold vibration. This ultimately illustrates the linguistic use of the voice. Originally, electroglottography was designed for hearing disorders. However, the procedure is now also clinically instrumental for visual feedback therapy. Fabre had already described the basics of the measurement procedure in 1957. After this initial idea, electroglottography was modified and refined until it corresponded to what is commonly used today.
Function, effect and goals
Applied electroglottography is mainly used to control laryngeal vocal fold treatments or voice therapies. In particular, the success of therapy for organic disorders of the voice can be evaluated almost ideally with the procedure. Sometimes electroglottography is also used in laryngeal-voice-lip diagnostics. For example, the EEG procedure can be used for dysphonia diagnostics. Two electrodes are placed symmetrically on the wings of the thyroid cartilage in preparation for the measurement. During speech, singing or phonation, the laryngograph finally takes a measurement of the alternating current resistance between these two electrodes. The device records its measurements in the form of an Lx waveform, where Lx stands for the recorded laryngogram. The waveform moves in a positive range as the vocal folds close. Each peak of the wave marks a maximum contact of the two vocal folds. The main edge of the wave provides information about the beginning of each closing phase. In contrast, the electroglottogram does not provide definitive information about the opening width of the glottis. Horizontal opening and closing movements of the laryngeal vocal folds from and to the midline, on the other hand, can be readily observed and are therefore the main component in the laryngograph waveform. The vertical components of the vibration cycle, however, can hardly be described. The recorded waveform is medically evaluated after measurement. Abnormal waveforms occur with physical abnormalities and thus lead the physician to suspect a medically caused voice disorder. Such a disorder can manifest itself, for example, in consistently irregular or even partially incomplete vibrations. Even shorter sections of such disturbed vibrations can be an indication of voice disorders. Irregular vibrations as an indication of voice disorders can be most clearly traced in main pitch changes and in the articulation of velar consonants. However, abnormal phenomena can also be expressed on the electroglottogram via airflow aerodynamic disturbances in addition to dissymmetric vocal fold vibrations.
Risks, side effects, and hazards
Because electroglottography is a noninvasive procedure, its use is not associated with any side effects or risks for the patient. An inpatient stay is not required to perform it. There are also procedures besides electroglottography for laryngeal vocal fold diagnosis.Whether electroglottography or an alternative procedure is indicated is therefore decided by the treating physician for the individual case. One of the best-known alternative procedures is classic indirect laryngoscopy. In this visual procedure, the physician inserts a mirror or a magnifying endoscope into the throat. If the gag reflex is strong, local anesthesia of the pharyngeal wall may be indicated. Compared to this procedure, electroglottography is much more comfortable and easier for the patient, as well as the physician. In the alternative procedure of direct laryngoscopy, the physician again inserts a support laryngoscope and an endoscope, which is also usually connected to a microscope. This allows the mucous membrane of the larynx to be viewed. Changes and deposits can also be made visible in this way. When diagnosing paralysis as well as carcinomas or other changes of this kind, this procedure may make more sense than pure electroglottography. A third alternative procedure is the so-called laryngostroboscopy, in which short flashes of light are generated and synchronized with the vibrations of the vocal folds by a laryngeal microphone. The physician then changes the frequency of the flashes, possibly visualizing a slowed vibration. Like electroglottography, this procedure does not visualize the vertical component of the vibrations, but focuses on the vocal fold surface. Electroglottography has something in advance of all the aforementioned methods because the non-invasive procedure does not require complex evaluations of acoustic signals during speech, nor does it force the physician to intervene in the process of speech itself. For these reasons, electroglottography is particularly popular in laryngeal-vocal fold diagnosis, despite the potential alternative procedures. However, in cases of tumorous changes, the procedure may be combined with direct laryngoscopy.
Typical and common laryngeal diseases
- Laryngitis
- Laryngeal cancer
- Laryngeal paralysis
- Epiglottitis (inflammation of the epiglottis)
