Background/objective: The aim of this study is to estimate the effect of voice therapy intervention in adults with vocal fold nodules, on three acoustic voice parameters (fundamental frequency, jitter and shimmer). The purpose of this meta-analysis is to present evidence based on literature regarding objective acoustic voice parameters changes, after voice therapy, in patients with bilateral VFNs. A pooled statistical analysis comparing pre- and post-therapy measurements of three acoustic voice parameters (average F0, % jitter and % shimmer) were performed.
Methods: A literature review was performed by searching studies in adults, with bilateral vocal fold nodules who received voice therapy, and where voice quality was evaluated quantitatively using acoustic analysis, before and after treatment. Meta-analysis was performed using random-effects model. PubMed, CINAHL, CENTRAL and Web of Science were searched for retrospective and prospective cohort, cross-sectional and case-control with comparative studies in adults published between January/1995 and March/2019 and English written. Search terms used were: intervention, therapy, vocal, voice, nodules, bilateral, multidimensional assessment, acoustic and analysis.
Results: Overall 1950 articles were identified. After removing repeated articles and conducting screening stages using inclusion and exclusion criteria, a total of four studies were selected with 147 participants for the meta-analysis. The pooled results analysis showed a statistically significant effect in two acoustic parameters after voice therapy: (1) F0 [increased mean difference post-therapy was 33.00 Hz (95% CI 20.26-45.74, p < 0.001)] and (2) jitter (%) [decreased mean difference post-therapy was 0.59% (95% CI 0.23-0.94%, p = 0.001)]. In addition, a non-statistically significant effect in shimmer (%) [decreased mean difference post-therapy was 2.98% (95% CI - 0.03-6.00, p = 0.052)].
Conclusion: Acoustic analysis has a clinical role in patients with vocal fold nodules, by objectively assessing and providing data on the effect of voice therapy in voice acoustic parameters. This meta-analysis has shown that patients with vocal fold nodules improved their acoustic voice parameters after receiving voice therapy.
Keywords: Acoustic; Speech-language pathology; Vocal fold nodules; Voice outcome; Voice therapy.