Simplified Vocal Efficiency Metrics Normalize Following Voice Therapy in Subgroups of Patients With Nonphonotraumatic Vocal Hyperfunction

Abstract

Purpose: The purpose of this study is to determine whether simplified vocal efficiency (VE) metrics could accurately identify changes after voice therapy in individuals with nonphonotraumatic vocal hyperfunction (NPVH). This study analyzes treatment-related changes for traditional VE-vocal intensity (square of sound pressure) over aerodynamic power-and three simplified VE ratios: (a) sound pressure level over aerodynamic power (SPL/AP), (b) SPL over subglottal pressure (SPL/Ps), and (c) SPL over airflow (SPL/AFLOW).

Method: Retrospective data from 108 adults (80 females, 28 males) diagnosed with primary muscle tension dysphonia (associated with NPVH) and 208 vocally healthy adults (181 females, 27 males). Study participants produced repeated consonant-vowel utterances in comfortable and loud conditions before and after voice therapy, with acoustic SPL and aerodynamic measurements (Ps and AFLOW) derived. Pre- to posttherapy VE changes were analyzed using mixed-design analysis of variance models. In an exploratory analysis, patients were divided into three subgroups based on their pretherapy VE measures to investigate treatment effects within NPVH subgroups.

Results: Pre- to posttherapy VE changes were not observed for the NPVH group as a whole. A subsequent subgroup analysis revealed treatment effects within female patients with NPVH exhibiting lower and higher than typical pretherapy VE metrics. SPL/Ps exhibited a treatment effect in both loudness conditions and migration toward normative ranges following therapy. Posttherapy changes were observed to varying degrees in both loudness conditions for traditional VE and simplified VE metrics of SPL/AP and SPL/AFLOW.

Conclusions: VE ratios, especially SPL/Ps, demonstrate potential as metrics for evaluating the outcome of voice therapy in individuals with NPVH and aid in stratifying individuals with NPVH into subgroups compared to vocally healthy values. Further investigations are warranted to investigate the role of VE metrics in the assessment, treatment, and prevention of NPVH.