Investigating the Effect of Semi-Occluded Vocal Tract Training With a Free-End Tube on Acoustic Characteristics and Glottal Performance in Dysphonic Adults: A Systematic Review.

Objective: Investigating the effect of semi-occluded vocal tract training with a free-end tube on acoustic characteristics and glottal performance in dysphonic adults.

Study design: A systematic review.

Methods: This systematic review adhered to Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines and was guided by the population, intervention, comparison, results and study design framework. Adults with dysphonia were included, while studies with psychiatric, cognitive, or cancer-related conditions were excluded. The intervention involved semi-occluded vocal tract training (SVOT) with a free-end straw, and outcomes included acoustic parameters (eg, jitter, shimmer, HNR, CPP, and F0) and contact quotient. A comprehensive search across multiple databases identified studies, and two independent reviewers screened and assessed them for inclusion. Bias was evaluated using the Cochrane RoB-2 tool, with results visualized via Robvis.

Results: This section outlines the inclusion of three studies with 127 participants from an initial pool of 5752 records. The studies varied in their methodologies, with one utilizing electroglottography evaluation and two employing acoustic assessments, while all reported different durations of vocal training. The Cochrane Risk of Bias-2 tool indicated a high risk of bias across the studies, primarily due to missing outcome data and randomization issues.

Conclusions: This systematic review highlights the beneficial effects of SVOT using a free-end tube in improving acoustic characteristics and glottal performance in dysphonic adults. The technique enhances vocal fold coordination, reduces tension, and promotes efficient phonation. Further research is recommended to explore its long-term effects and efficacy across various dysphonia subtypes.