Geschwindigkeitsmessung der Stimmlippenbewegung

Abstract

Introduction: Clinical examinations with short-interval, color-filtered double-flash stroboscopy enable us to estimate the movements of the vocal fold edges during phonation. So-called ‘displacement bands’ show the degree of the vibratory amplitude in these images. Using the two-point light projection method the displacement bands can be measured with very high accuracy. A combination of these two methods was used for velocity measurements of the vocal fold movements within the phonatory cycle. The aim of the study was to explore the influence of change in sound pressure level (SPL) and fundamental frequency (F₀) on the velocity of the horizontal amplitude of the vocal folds during phonation. Material and Methods: 40 healthy volunteers (31 women, 9 men, average age 24.8 years) were examined. During the special videostroboscopy with short-interval, color-filtered double flashes laser spots were projected onto the vocal folds by an endoscopic two-point light projection device. The subjects had to change their SPL and F₀ following a test protocol. During phonation they had to produce tones in low, middle and high chest voice as well as in falsetto register. Each subject was asked to do this in a soft, a modal, a loud and a very loud manner. Images of the phonatory cycle showing the vocal folds immmediately before collision were measured separately at three different positions. About 15,000 single measurements were evaluated. Results: The measured velocity of the horizontal amplitude during the closing phase of the vocal folds in chest voice was 30–160 cm/s. An increase in SPL resulted in an increasing velocity of the displacement bands. A change in F₀ did not lead to statistically relevant changes in the measured velocity. Conclusion: A combination of short-interval, color-filtered double-flash stroboscopy and a two-point light projection method enables measurements of the velocity of vocal fold movements. The SPL is the important factor for the velocity change within the phonatory cycle. F₀ seems not to covary with the velocity of the horizontal amplitude during the closing phase of the phonatory cycle.