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.