Thermography Analysis of Low-Level Laser Therapy Effect on the Swine Larynx

The vocal folds are intrinsically associated with the thyroarytenoid muscle. During phonation, microlesions and inflammations can occur due to excessive voice use, which can hinder the correct vibration of the mucosa and alter the voice quality. In addition to vocal hygiene and exercises to reduce phonatory effort, resources such as low-level laser therapy (LLLT) are being used in clinical settings. LLLT has been reported to have a biomodulatory action that can reduce pain and edema in the larynx by accelerating the inflammatory process through temperature variation. This study aimed to evaluate the temperature before and after the application of single or multiple doses of red (RL) and infrared (IRL) in the laryngeal tissues of swine.

This descriptive and comparative study was conducted at NuPMIA-FM/UnB and at Granja Miunça, located in the rural region of Brasília. The animals were randomly divided into 13 groups (n = 5) to evaluate the temperature of the larynx before and after LLLT treatment using photothermographic analysis.

The study showed the thermoregulatory effect of the laser as an acute response to 1 and 8 doses of LLLT in the swine larynx. One dose of RL increased the temperature of the young animals (P = 0.0318); multiple doses of IRL increased the laryngeal temperature of the adult group by 2.1%, with differences between the applications (paired t test, P = 0.0208). In the combination of lasers (RL + IRL), the laryngeal temperature in the group of adult animals increased by 0.9%, between the minimum and maximum temperature before application, and between the minimum and maximum temperature after LLLT. There was a difference between the mean temperatures before (P = 0.0010) and after the combined (RL + IRL) (P = 0.0025). Also, the results showed that young animals with no LLLT treatment had 12% higher temperature (35.7 ± 1.7 ºC) than adult animals with no treatment (31.2 ± 1.9).

The results demonstrated that there is an increase and decrease in laryngeal temperature after different low-level laser therapy application protocols and at different doses. These findings could provide a clinical guide for the use of LLLT in humans.