The Effect of Phonation into a Glass Tube Immersed in Water Compared to Other Interventions on General Degree of Vocal Deviation, Fundamental Frequency, Sound Pressure Level, and Vocal Self-assessment in Vocally Healthy Individuals: A Systematic Review and Meta-analysis.

Objective: To analyze the effect of phonation in a glass tube immersed in water compared to other interventions on general degree of vocal deviation, fundamental frequency, sound pressure level, and vocal self-assessment in vocally healthy individuals.

Methods: This is a systematic review and meta-analysis developed from the research question: "In vocally healthy individuals, what is the effect of phonation into a glass tube immersed in water versus other vocal interventions, other activities, or no intervention on general degree of vocal deviation, fundamental frequency, sound pressure level, and vocal self-assessment?" An electronic search was performed using Medline, LILACS, Cochrane Library, Embase, Web of Science, and SCOPUS databases, and a manual search was performed in the gray literature (Brazilian Digital Library of Theses and Dissertations and OpenGrey), the Journal of Voice, and the citations of the studies. Studies with (P) population of adults with healthy voices, (I) intervention with phonation into a glass tube immersed in water, (C) comparison with other vocal interventions, other activities, or no intervention, (O) outcomes of the general degree of vocal deviation, fundamental frequency, sound pressure level, and vocal self-assessment, and an (S) study with the experimental or quasi-experimental design were included. Risk of bias assessment and meta-analysis of the outcomes were performed.

Results: A total of 457 studies were found in the search; four were selected for the systematic review and meta-analysis. In the risk of bias assessment, there was an uncertain risk of selection and performance bias in 100% of the studies and uncertain risk of detection bias of 75%. All studies had an experimental design, and most of them were conducted on women. In the fundamental frequency analysis, there was no difference between the effect sizes of the interventions (z = 0.471, P = 0.638). In the vocal self-assessment, the estimated odds ratio was 1.31, showing a greater chance of improvement in the intervention group than with the comparison group (z = 3.45, P < 0.001). There were not enough studies to analyze the general degree of vocal deviation and sound pressure level outcomes.

Conclusion: Phonation into a glass tube immersed in water has a greater positive effect on vocal self-assessment than other interventions in vocally healthy individuals.