Journal of Laryngology and Voice

: 2018  |  Volume : 8  |  Issue : 1  |  Page : 14--18

Effect of vocal loading on throat temperature in young phono-normal adults

Lokheshwar Shanmugasundaram, Rathinaswamy Rajasudhakar 
 Department of Speech-Language Sciences, All India Institute of Speech and Hearing, Mysuru, Karnataka, India

Correspondence Address:
Mr Lokheshwar Shanmugasundaram
Department of Speech-Language Sciences, All India Institute of Speech and Hearing, Manasagangothri, Mysuru - 570 006, Karnataka


Background: Infrared thermography is used to detect heat on the surface and subsurface and online monitoring of process. Vocal loading has been defined as acoustic changes in the voice as a result of prolonged voice use. Vocal loading involves continuous oscillation of vocal folds where the colliding forces between the vocal folds for longer period would generate and dissipate heat. Aims: The primary objective of the study was to determine any difference in temperature (near the neck region) and fundamental frequency (F0) pre- and post-vocal loading task. The secondary objective was to find the influence of gender on these parameters during pre- and post-vocal loading task. Study Design: Pretest-posttest design. Subjects and Methods: The study included two groups: Group I and Group II which included ten phono-normal males and ten phono-normal females, respectively, between the age range of 18 and 24 years. Throat temperature and F0 (phonation sample) were measured before and after vocal loading task (reading a material in English at 70–75 dB for 40 min). The F0 was measured using PRAAT software and temperature using SmartView software. Results: Within-group and between-group comparisons were made using mixed ANOVA for both temperature and F0. There was a significant difference in temperature within groups; however, there was no significant difference between the groups. Comparison of temperature pre- and post-vocal loading revealed significant difference within groups; however, it was not significantly different between the two groups. Pre- and post-vocal loading comparison of F0 revealed significant difference within and between groups. Conclusions: Group II had more temperature and F0 when compared to Group I, that is, higher temperature and higher F0, whereas Group II individuals are vulnerable to get voice problems if they continue to use prolonged loud speech as their vocal behaviors.

How to cite this article:
Shanmugasundaram L, Rajasudhakar R. Effect of vocal loading on throat temperature in young phono-normal adults.J Laryngol Voice 2018;8:14-18

How to cite this URL:
Shanmugasundaram L, Rajasudhakar R. Effect of vocal loading on throat temperature in young phono-normal adults. J Laryngol Voice [serial online] 2018 [cited 2021 Sep 24 ];8:14-18
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Full Text


Infrared thermography

Infrared thermography (IRT) is a noninvasive technique which allows one to measure and visualize IR radiation. IRT is used to detect heat on the surface and subsurface and online monitoring of process.[1] Thermal imaging is a process which is capable of mapping the temperature distribution on the human skin. The distribution of temperature on healthy human skin is highly distributed where the axis is situated in the median plane of the body. It is presumed that the difference in temperature between symmetrical areas should not exceed 0.5°C.[2] The average human body core temperature is approximately 37°C ± 0.5°C, with surface temperature slightly lower and more variable, depending on ambient conditions.[3] IRT has many applications in the medical field and has been extensively used for breast cancer detection,[4] fever scanning,[5],[6] brain imaging (thermoencephaloscopy),[7] and in other domains.

Vocal loading

Vocal loading is defined as acoustic changes in the voice as a result of prolonged voice use.[8] Vocal load can be measured using prolonged voice use and it has been used extensively in the literature as a method to understand how vocal fatigue leads to laryngeal adjustments and the negative consequences.[9] In voice production, the rate of vocal loading is highly dependent on the individual characteristics of each person as the vibratory properties of the vocal folds or the functional state of the laryngeal muscles are distinctive.[10],[11] Krishna and Nataraja[12] found a significant difference in average fundamental frequency (F0) after a 30-min reading task in five normal controls.

Need for the present study

Cooper and Titze[13] used fine-wire thermocouples to measure the generation and dissipation of heat in the vocal fold tissues during mechanical vibration on an excised bovine larynx and stated that an increase in temperature from 0.1°C to 0.8°C was seen. Lokheshwar[14] found increase in throat temperature after 40 min of vocal loading task in seven out of ten males. Existing systems of measuring vocal fatigue are objectively using sophisticated gadgets such as Ambulatory Phonation Monitor and dosimeter where the latter is not available commercially. Moreover, self-rating scale is used to measure vocal fatigue subjectively. In the literature, vocal load was measured using acoustic and aerodynamic measurements, but there are no published studies on using IRT as a measure to infer vocal fatigue after vocal load. Cooper and Titze[13] employed an invasive method to evaluate the heat dissipation in an excised bovine larynx and it was not empirically studied on human larynx. Measurement of temperature is noninvasive, and the results would be viewed instantaneously by focusing the thermal camera toward the target object. Since thermal images act as a screening tool, the present study has attempted to measure the generation and dissipation of heat during, prior to, and postvocal loading task, where the surface temperature is measured by using IR thermal camera and it is a noninvasive procedure.

Aim of the study

The primary objective of the study was to determine difference in temperature (near the neck region) and F0 at two conditions, namely pre loud reading (condition 1) and post (condition 2) loud reading. The secondary objective of the study was to document gender difference on throat temperature and F0 at pre- and post-reading.

Study design

Pretest-posttest design.

 Subjects and Methods

Two groups of phono-normal individuals participated in the study. Group I included ten males and Group II included ten age-matched females. All the participants were between the age range of 18 and 24 years. Phono-normal here represents a perceptually normal voice in terms of pitch, loudness, and quality. Further, participants who had a history of smoking, laryngeal pathology, intubation, neurological disorders, and surgery/accidents/trauma, and a history of sustained or prolonged use of medications for any medical conditions were excluded from the study.

Material and instrumentation

Participants were asked to read a material (newspaper/novel/magazines) in English. Thermal imaging camera model Ti32, (Fluke, Everett, WA, USA), sound recorder model LS-100 (Olympus, Tokyo, Japan), and software such as SmartView Version 4 (Fluke, Everett, WA, USA) and PRAAT[15] (Institute of Phonetic Sciences, University of Amsterdam, Amsterdam, Netherlands) were used. Sound level meter (SLM) model DSL-331 (TECPEL, New Taipei, Taiwan) was used to monitor the intensity of reading.


Participants were briefed about the aim and procedure of the study and informed written consent was obtained from them. The study was conducted in three phases: (i) Preexperimental phase involved placing the participants in a sound-treated air-conditioned room of 25°C and were instructed to remain silent (voice rest) until vocal loading task. Participants were asked to look up for better visualization of the larynx (throat) and multiple baseline measurements of temperature at the throat region were carried out at 3-min interval until it stabilized (temperature remaining constant at two consecutive measures). Once the temperature stabilized, the images were captured (front and side views) which served as a final baseline for the upcoming task and also participants were asked to phonate/a/vowel for 6–7 s thrice and was recorded using Olympus (LS-100) sound recorder which was placed at 10 cm away from the mouth of the participant; (ii) experimental phase involved prolonged loud reading, where participants were asked to read the material of their interest in English (novels, newspapers, etc.) at 70–75 dB for 40 min using SLM placed at a distance of 2 ft. Participants were provided with nonverbal/gestural feedback or indication by the examiner (by monitoring the visual screen on the SLM) to increase/match the intensity of reading at 70–75 dB level, if they reduce intensity level while reading; and (iii) postexperimental phase, in which the postreading temperature was measured after oral reading and phonation sample of/a/vowel for 6–7 s thrice was recorded using a sound recorder.


The F0 was measured from phonation samples using PRAAT v. 5.2.23 software. Among the three samples taken, only the steady medial portion was selected for analysis and averaged. The throat/neck temperature was measured by thermal imaging camera and these thermal images were analyzed using SmartView software (Version 4.0) software. Emissivity was set to 0.98 (for human skin) and the palate was set to high contrast (rainbow palate which represents wide temperature distribution). The obtained IS2 images were analyzed where the visible larynx was marked using a polygon tool, and the average temperature of the selected region was jotted down followed by averaging the averages from the three images captured using thermal camera at different positions, i.e., from front and both the sides which are represented in [Figure 1], [Figure 2], [Figure 3], respectively.{Figure 1}{Figure 2}{Figure 3}

Statistical analysis

Statistical Package for the Social Sciences software version 21 (IBM, Chicogo, Illinos, U.S.A) was used for statistical analysis. Test of normality revealed normal distribution of data (both temperature and F0) in Group I and Group II (after removal of one participant). Descriptive statistics were done followed by mixed ANOVA to compare within groups for pre- and post-reading F0 measures and throat temperature and to compare between groups for F0 and throat temperature.


The obtained data were subjected to statistical analysis. The mean values and standard deviation for temperature and F0 are mentioned in [Table 1]. Postvocal loading has increased mean temperature of 1.94°C and 2.81°C in males and females, respectively, compared to prevocal loading. Similarly, postvocal loading has increased mean F0 of 7.43 and 19.25 Hz in males and females, respectively, compared to prevocal loading. Mean temperature and mean F0 were more in Group II than Group I. Mixed ANOVA was administered for comparison of F0 and temperature with group as an independent factor. Further, it was employed to check the significant difference between F0 and temperature for within-group and between group comparisons. Also to see the interaction between F0 and the group, and temperature and the group. [Table 2] shows the results of mixed ANOVA which revealed significant main effect, and interaction effect between condition and group for temperature and F0.{Table 1}{Table 2}


The results of the study are discussed under two subheadings: (i) Throat temperature and (ii) F0 measure.

Throat temperature

Scientifically, the amount of vibration determines the internal energy and temperature of a body and is expressed in the form of heat known as IR radiation.[16] Frequencies are associated with the vibration of vocal cords,[17] and increase in temperature is higher in females which can be attributed to higher F0 in females compared to males even during pre- and post-vocal loading task. The increase in temperature at the neck region after loud reading in both the groups indicates that the temperature on the vocal fold is the result of continued prolong oscillations of the vocal folds. If this oscillation exceeds the limit, the risk of developing some organic lesions on vocal folds might happen due to colloidal forces between the vocal folds. Owing to the fact that vibration leads to generation of heat, Group II had greater difference with temperature as their F0 was relatively higher than Group I.

F0 measure

The mean values of average F0 were found to be increased in both males and females after loud reading. As observed from [Table 1], there is an increase in both the groups following prolonged reading. The increased F0 can be attributed to increased length and decreased thickness of vocal folds as a result of increased stiffness[18] and also increased muscular and structural tension of the vocal folds.[9] The results of the present study are in consonance with the findings of Vilkman et al.[19] who found increased F0 after vocal loading in both males and females after 45 min of vocal loading task for three times morning till noon. Findings of Remacle et al.[20] reported increased F0 at two intensity levels which varied between 60–65 dB(A) and 70–75 dB(A), each session lasting for 2 h with an interval of 22 days in normophonic females. On the other hand, Stemple et al.[21] stated that the weakness of thyroarytenoid (TA) muscle leads to increase in F0 after reading a novel 2 h at 75–80 dB (sound pressure level). When the muscular layer of TA slackens, the cover and the transition layers of the vocal folds stiffen, thereby increasing the rate of vibration in the vocal folds leading to increased F0. From various studies,[12],[18],[19] it can be observed that the increase in F0 after prolonged loud reading is the resultant of vocal fatigue or tiredness. Hence, the present study supports the view of vocal fatigue after prolonged loud reading as a function of the increment of F0 parameter.


The present study aimed to use IRT and F0 to measure vocal load in phono-normal individuals. The results of the present study showed that there is an increase in temperature near the throat region and F0 in both the groups after prolonged loud reading. The increase in temperature at the vocal region after prolonged loud reading was around 3°C among the participants. Group II (females) had 1.45 times higher mean temperature values and 2.59 times higher mean F0 values at postreading phase than Group I (males). This shows that after prolonged loud reading, F0 increases relatively more in females compared to males. The increase in F0 or throat temperature reflects the presence of vocal fatigue and is temporary. Considering higher temperature and higher F0 in Group II (females), they are vulnerable to get voice problems if they continue to use loud prolonged voice use as their vocal behaviors. The obtained results could be used during counseling sessions regarding voice care.


The study is limited to less number of participants, with no barrier for reading material (newspaper and novel), and is also restricted to the laboratory condition.

Future directions

As this is the first study of this kind, it opens many avenues for further research by employing temperature as one of the methods to document vocal fatigue. The temperature based on the present study may need to correlate with the videostroboscopic results. Similarly, the study can be replicated in clinical population (voice disorder patients).


The authors extend their gratitude to Dr. S.R. Savithri, Director AIISH, Mysuru, for granting permission to carry out the research study and also to Dr. Vasanthalakshmi, Associate Professor in Biostatistics, for guidance in statistical analysis. The authors appreciate A2Z NDT Services, Bengaluru, for lending their infrared thermal camera, and are grateful to the individuals who participated in the experiment.

Financial support and sponsorship

This study was financially supported by AIISH Research Fund.

Conflicts of interest

There are no conflicts of interest.


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