As thyroid disorders increase, there is a rising interest in vocal assessment and management after a thyroidectomy. Since vocal changes after a thyroidectomy are transient and minor, it is not easy to get precise information about the pathological characteristics of the voice and care for it.
The purpose of this study was to evaluate characteristics of vocal changes after a thyroidectomy using periodic and multi-parameter analysis, as well as, feasibility and features of ‘cepstral analysis’ by Multi-speech program.
Acoustic analysis was conducted on speech samples (sustained vowel /a/,/e/,/i/,/o/,/u/ and one sentence) provided by 35 patients at three time points (prior to thyroidectomy, 3 days, and 1 month after surgery). Acoustic data was recorded by Multi-speech and MDVP (Kay Pentax). Laryngeal aerodynamic measures (glottal input power, glottal efficiency, MPT) were obtained for 21 patients using the AerophoneⅡ (F-J Electronics) three times as well. Repeated measure ANOVA, One-way ANOVA, and the paired t-test were used to find out the statistical significance.
According to the assessment times, there was no meaningful difference in any whole vowel samples through Cepstral analysis. However, in case samples of sustained vowels divided into 3 fragments (onset, mid, offset), the results of cepstral analysis showed a significant difference (p<.05) depending on the evaluation time in the on-set segment of the vowel /i/. Aerodynamic analysis revealed that glottal input power increased significantly (p<.05) right after surgery and decreased one month later; whereas, glottal efficiency and MPT were reduced after the thyroidectomy and then grew. When MDVP parameters (jitter, shimmer, and NHR) were compared with cepstrum, jitter values revealed a significant negative correlation(p<.05).
These results of vocal changes after a thyroidectomy supported advanced researches. The on-set fragment of the vowel /i/ should be effective data for understanding pathological characteristics of voice disorders through acoustic analysis. Cepstrum is closely related to the parameters of fundamental frequency, and cepatral analysis can be used to analyze voice disorders.
All these results should be useful data for vocal management in individuals who have had a thyroidectomy and for the assessments of voice disorders in clinical settings.