Soft phonation index - a sensitive parameter?

Abstract

The diagnosis of voice disorders is based on perceptual and acoustic paradigms. Modern acoustic analysis systems are relatively inexpensive and user friendly. One aspect of laryngeal function that is of great interest is the extent of vocal fold closure. Soft phonation index (SPI) is the parameter in Multi Dimensional Voice Program, which reflects the approximation of vocal folds. High values of SPI are stated to correlate with incomplete vocal fold adduction and are a better indicator of breathiness than EGG. This study aims to determine the sensitivity of this acoustic parameter of SPI, as a reflective indicator of incomplete vocal fold adduction in male patients diagnosed with unilateral vocal nodules. 60 participants were included in the study; 30 with normal vocal fold functioning in the control group and 30 with unilateral vocal nodules in the experimental group. The phonation sample of vowel /a/ was recorded into CSL 4150 of Kay Elemetrics, in a sound treated room. The readings of SPI on the MDVP analysis was extracted and subjected to statistical analysis using independent samples 't-test' using SPSS Version 11. The results of the study reveal that there was a statistically significant difference between the means of the SPI values between the control and the experimental groups. It can be understood that SPI is a sensitive parameter to detect abnormalities in vocal fold approximation in the considered population of individuals with vocal nodules. This is in coherence with a study done on patients with vocal fold palsy and cordectomy, wherein SPI was found to be a good indicator of breathiness. The SPI mean obtained for participants in the control group was higher than the Western normative mean specified in MDVP, which highlights the importance of establishing normative values for Indian population. It can be concluded that SPI was sensitive to detect changes affecting vocal fold closure in unilateral vocal nodules. But this conclusion has to be generalized with caution keeping in mind that only one population with vocal pathology was studied. The factors of vocal fold physiology and mechanical properties of vocal tract, which may contribute to individual variations in SPI values, have to be considered for further research.