Quantification of videostrobolaryngoscopic findings--measurements of the normal glottal cycle.

Videostrobolaryngoscopic (VSL) images of vocal fold behavior in 32 male and 33 female normal speakers were analyzed by computer. Image analysis software enhanced the glottal image, allowing extraction of the glottal area. Frame-by-frame analysis produced 20 glottal area values for each glottal cycle. The glottal area waveform (GAW) plots these values. From the GAW, features such as peak glottal area, duration of opening and closing, and rates of vocal fold opening and closing were measured. Acoustic measures of sound pressure level (SPL) and fundamental frequency were used to compare changes in GAW with changes in loudness and pitch. Analysis of the data showed significant differences between the sexes in GAW, peak glottal area, closed period, closing slope, and size and incidence of the posterior glottal gap. Intensity and frequency changes significantly affected GAW. Intensity variations affected the steepness of the closing phase and the duration of the closed period. Frequency changes affected the open period and the relative duration of opening vs. closing. This study provides quantitative measures of the VSL image that supplement and corroborate perceptual observations. These measures provide normative data against which similar measures of dysphonic larynges can be compared.