Clinical relevance of speaking voice intensity effects on acoustic jitter and shimmer in children between 5;0 and 9;11 years.

Background: Current voice assessment recommendations for dysphonic children comprise instrumental acoustic measurements of the perturbation parameters jitter and shimmer. In healthy adults and children changes in speaking voice sound pressure level (voice SPL) have significant confounding effects on both parameters. In adults these effects were considerably reduced in phonations with controlled voice SPL >80dBA (10cm distance). However, it is unclear if these findings apply to children and if children are able to control for their own voice intensity.

Objective: This cross-sectional single cohort study investigates voice SPL effects on jitter and shimmer in children between 5;0 and 9;11 years phonating at individually "medium" (modeling "comfortable" loudness of the usual clinical protocol), "soft" and "loud" voice and a prescribed intensity level of ">80dBA" (10cm distance, with visual control). Further both their ability to phonate at a prescribed voice intensity level and the effect on SPL related confounding effects were studied.

Subjects And Methods: A total of 68 healthy children (39 f/29m) aged 5;0 to 9;11 years were included. All phonated the vowel/a/for 5s, three times at four defined voice intensity levels (soft/medium/loud/>80dBA) each. Jitter (%), shimmer (%) and voice SPL (dBA) were determined using PRAAT. Voice intensity level effects were assessed by descriptive statistics, Analysis of Variance (ANOVA) and Linear Mixed Models (LMM).

Results: There were significant differences for jitter and shimmer between all voice tasks (p<.01). Jitter and shimmer were lowest and showed the smallest spread in controlled phonations ">80dBA". 19 children below 7;0 years could not perform the voice tasks and were excluded from the study.

Conclusions: This practical study demonstrated a significant effect of voice loudness and task on jitter and shimmer in children. Since the observed confounding effects were large compared to treatment effects, jitter and shimmer may not be meaningful without adequate control of voice SPL. In phonations at ">80dBA" (10cm distance) voice SPL related effects were considerably reduced. However, this assessment protocol was suitable only for children above 7;0 years. Application of this task to future studies of dysphonic children may yield clinically valuable information.