Objective: To investigate the effects of the PBM with the Low-level-laser (LLL) on the self-perception of vocal effort, acoustic measures and voice quality in a group of women without self-reported voice complaints.
Methods: Randomized clinical trial. Participants were randomly divided in four groups: PG (Placebo Group – light off); G1 (Group 1 – LLL 9J per infrared wavelength point at three equidistant points, starting from the laryngeal prominence); G2 (Group 2 – tongue trill technique for 3 minutes in habitual tone); G3 (Group 3 – LLL in the same conditions as G1 followed by tongue trill technique in the same conditions as G2). The Vocal Fatigue Index Protocol was applied before interventions in all groups; voice samples (sustained vowel /a/, connected speech and CAPE-V sentences) and responses to the BORG CR10-BR scale adapted for vocal effort were collected before and after the interventions. The AVQI, ABI, CPP and CPPS acoustic measures were extracted and an auditory-perceptual evaluation (APE) of the overall severity of voice quality was performed (CAPE-V) by a voice specialist through its visual analogue scale (VAS) and also by a comparative analysis (Voice ‘’A’’ better, worse or equal to Voice ‘’B’’). The judge was blinded to the group and the moment (pre or post) that the sample belonged to. Fisher's Exact Test was used in the analysis of inter-groups comparison between nominal variables with post hoc analysis for comparison of pairs of groups through the Z Test. The General Linear Model was also adopted in which the significance of fixed effects was assessed with F tests and the Linear Mixed Model with post hoc analyses conducted using the t Test. All analyses performed adopted a significance level of 0.05.
Results: Fifty-seven women (18-45 years old) participated (PG=14, G1=14, G2=14 and G3=15). There was a significant reduction in self-perceived vocal effort after the intervention (p=0.046) only for G1; there was no worsening in self-perceived vocal effort in any of the other groups. The comparison between the groups did not indicate significant differences regarding in both APE (VAS and comparative), however, the comparative one showed a difference with a relevant magnitude of average effect (r=0.410) comparing G1 with the other groups in relation to the occurrence of “Better” classifications. Only the CPPS showed significant difference (p=0.048) in the comparison between moment (pre or post) x group.
Conclusion: The PBM reduced self-perceived vocal effort in G1. The dosimetric parameters used in this study suggest safe clinical use for this group and contribute to understanding its effects in future research. Changings in the acoustic parameters were isolated and insufficient to indicate immediate effect after the PBM.