Real-Time EGG Analysis, Model 5138

Electroglottography (EGG) is a simple, non-invasive technique for analyzing the vibratory characteristics of the vocal folds. Used in the assessment and treatment of voice disorders, EGG provides an intuitive representation of vocal fold dynamics and relative contact patterns during phonation. Additionally, visual feedback can be presented to patients for behavioral guidance during therapy.

Real-time processing of the EGG waveform in its proper aspect ratio is not typically provided in general-purpose data-acquisition systems. These systems display the compressed EGG waveform during acquisition. The user then redisplays short segments of data, post-acquisition, in order to observe the configuration of individual glottal cycles, as represented by the EGG waveform. To see the EGG waveform properly displayed during phonation requires a triggered display of very short time durations (e.g., 40 msec or less).

Kay’s Real-Time EGG Analysis program not only provides a triggered display with proper aspect ratio as the patient phonates, but also calculates and displays user-defined quantitative EGG measures which have proved useful in clinical settings. This powerful software option can be used in conjunction with Kay’s CSL, Visi-Pitch, and Multi-Speech platforms. 

EGG Technique

Real-Time EGG Analysis requires a commercially available electroglottograph for signal acquisition (e.g., Kay’s Electroglottograph, Model 6103). The hardware consists of an external module for signal conditioning and output; the EGG transducers consist of two surface electrodes which are placed on the patient’s neck at the level of the thyroid cartilage. Velcro straps are provided so patients do not need to hold the electrodes and can produce voice naturally.

As the patient phonates, EGG detects impedance changes across the larynx which are produced by the changing contact pattern of the vibrating vocal folds; the EGG output signal reflects vocal fold movement and relative contact patterns. Because of the transducers’ location (i.e., at the thyroid cartilage), the EGG waveform is virtually unaffected by supraglottal activity (vocal resonance) or environmental noise. Also, phonatory and articulatory processes are unimpeded by the technique.

As a means of non-invasive exploration of vocal fold dynamics, EGG is an easy procedure to administer, does not require the user to select filters to properly display a reliable waveform, and provides an intuitive waveform that can be observed in conjunction with stroboscopic evaluation (see Kay’s Digital Strobe brochure) or acoustic analysis (see Kay’s Computerized Speech Lab (CSL), Model 4500 brochure). EGG complements imaging, acoustic, and aerodynamic analysis of the patient’s voice.

Software Display and Analysis

Used in conjunction with the Electroglottograph, the Real-Time EGG Analysis program works in multiple Kay hardware environments (CSL, Visi-Pitch, and Multi-Speech), but CSL, with its DC-coupled channels for EGG display, is the preferred hardware platform. 

The program processes the EGG signal and displays it in real time while eliminating any DC float and broadband noise without distorting the phase of the signal. After data has been acquired, the clinician can review any portion of the acquired signal by scrolling through the data buffer.

Additionally, Real-Time EGG Analysis provides more in-depth analysis of the patient’s voice by calculating user-defined EGG quotients (only one quotient can be displayed in real time, but any quotient can be calculated post-processing). For example, the Open Quotient displays the ratio of the opened-phase duration and the glottal-cycle duration. The program’s flexibility allows the user to define the demarcations of the various phases used in quotient calculations. The demarcations are defined as a percentage of the height of the EGG waveform. 

Visual Feedback Applications

In addition to voice assessment, Real-Time EGG Analysis can be used for visual feedback to the patient. This requires the clinician to instruct the patient on “desirable” vocal behavior (e.g., less pressed phonation) with regard to the EGG waveform configuration or the quotient display, and then allowing the patient to “experiment.” Patients can then be sensitized to proper phonatory behavior with the aid of the EGG display.

EGG waveforms of breathy phonation (left) and pressed phonation (right). Note the differences in the opened phase as a percentage of the glottal cycle. The Open Quotient values (upper screen) reflect these differences quantitatively.

Researchers can access the raw quantitative quotient
data and can export values as a text file for more in-depth analysis.

Current CSL, Model 4500 and 4150, software and database options include:

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