Electroglottography

Electroglottography (EGG) is a noninvasive technique for assessing vocal fold contact during phonation. It measures changes in electrical impedance between two surface electrodes placed on either side of the larynx as the glottis opens and closes. By passing a small high-frequency alternating current through the neck region, the device detects variations in contact area between the vocal folds; when folds adduct, contact area increases and impedance decreases, and when they separate, impedance rises. The resulting electroglottogram (EGG) is a waveform whose features correspond to contact events, and the first derivative of the signal (dEGG) is often used to identify precise opening and closing instants. A commonly reported parameter is the contact quotient (CQ), the proportion of a glottal cycle during which contact occurs.

Procedure and interpretation typically involve placing the electrodes laterally on the neck at the level of the vocal folds, and applying a small high-frequency current while the subject phonates at various pitches and loudness levels. The recorded EGG signal is analyzed graphically or with software to derive CQ and other timing measures such as the speed quotient (SQ). EGG is commonly used in speech science and clinical voice assessment to study glottal closure patterns, monitor therapy progress, and complement acoustic and aerodynamic measures.

Limitations include that EGG estimates contact area rather than force, and results can be affected by electrode placement, skin impedance, neck anatomy, and hydration. It provides no direct anatomical imaging and must be interpreted alongside other assessments, such as laryngoscopy or stroboscopy, for comprehensive evaluation.