ORIGINAL ARTICLE |
https://doi.org/10.5005/jp-journals-10023-1255 |
A Prospective Observational Study of Effect of Tonsillectomy on Voice
1Department of Otorhinolaryngology, Dr Somervell Memorial CSI Medical College, Thiruvananthapuram, Kerala, India
2Department of Laryngology, Dr Jayakumar’s Institute of Laryngology, Thiruvananthapuram, Kerala, India
Corresponding Author: Jayakumar Menon, Department of Laryngology, Dr Jayakumar’s Institute of Laryngology, Thiruvananthapuram, Kerala, India, Phone: +91 9846011740, e-mail: jkrmenon@rediffmail.com
Received: 11 January 2024; Accepted: 04 June 2024; Published on: 17 July 2024
ABSTRACT
Introduction: Tonsillectomy, or excision of palatine tonsils situated in the oropharynx, is a surgical procedure executed on modulation structures of the vocal tract and may produce substantial changes in voice quality. Potential changes in the voice may be of great importance if the patient is a singer or a performing artist, and also in the present setting where global voice biometrics is gaining momentum as a person’s voice is as unique as a fingerprint. Therefore, it seems purposeful to determine objectively the changes in voice characteristics resulting from tonsillectomy.
Aim: To determine if vocal resonance changes after tonsillectomy.
Materials and methods: A prospective descriptive study of postoperative voice change in 31 tonsillectomy cases was done over a period of 1 year. Preoperative and postoperative voice was recorded, and formant frequencies were obtained and compared.
Results: The first and second formants increased postoperatively, but only the change in the second formant was found to be statistically significant.
Conclusion: As expected, the voice changed after tonsillectomy but was barely perceptible to the patients, except in the case of voice professionals, where it can have a significant impact because of the change in signature voice.
Keywords: Formant, PRAAT, Tonsillectomy, Velum, Voice
How to cite this article: Murali S, Menon J. A Prospective Observational Study of Effect of Tonsillectomy on Voice. Int J Phonosurg Laryngol 2024;14(1):5–9.
Source of support: Nil
Conflict of interest: None
INTRODUCTION
The human vocal apparatus is an efficient resonator that imparts quality to the voice that passes through it. The voice passing through the vocal tract resonator has multiple overtones. The fundamental frequency is the one with the lowest frequency and highest intensity, and it is heard without any amplification. The overtones with frequencies closest to the natural vibrating frequency of air in the resonating chambers get amplified, and these amplified overtones are called formants. This phenomenon of selective amplification of overtones in their corresponding resonating chambers is called resonance. Hence the voice is shaped acoustically depending on the vocal tract configuration1 as depicted in Figure 1. Depending on the number of resonating chambers, the number of formants also varies. In the case of the human voice, there are four significant formant frequencies, and the important resonating chambers are the nasal cavity, mouth, and throat. The shape of these resonance chambers is adjusted by the movement of the mandible, lips, tongue, and palate. A change in the position of the palate changes the volume of the nasal and oral cavities, hence changing resonance. Similarly, a change in tongue position and lip rounding affects the shape of the oral resonance chamber, thereby changing oral resonance. The movement of the mandible, and hence the mouth opening, raises the frequency of the first formant by constricting the vocal tract in its laryngeal region. The second formant is mainly affected by oral resonance, which in turn is affected by the shape of the tongue.2 The third formant is sensitive, especially to the position of the tip of the tongue and lip rounding.
Fig. 1: Modulation of voice in the vocal tract
Normal resonance is highly dependent on the velopharyngeal mechanism, comprising the coordinated action of the velum, the lateral pharyngeal walls, and the posterior pharyngeal wall, which brings about the velopharyngeal closure as a sphincter.3
The palatopharyngeal and palatoglossal muscles depress the palate or velum. The position of these muscle arches can vary based on the size and shape of the tonsils, which are located between them, and thus, the forces exerted on the palate, and hence palate closure, may be affected.4
Tonsils have also been noted to alter articulation by affecting tongue positioning.5 In the case of very large tonsils, the voice is blocked from entering the oral cavity, resulting in a muffled speech described as ”potato-in-the-mouth” speech, which is referred to as cul-de-sac resonance.6
Removal of tonsils might change the voice as the volume and shape of the vocal tract change. Moreover, wound healing after tonsillectomy occurs via secondary intention. As a result of healing by fibrosis, pillars undergo contracture and are drawn toward each other. The anterior tonsillar pillar helps in restoring a neutral palatal position.7 It plays a good role in drawing the soft palate anteriorly and preventing its collapse.8-10 When these pillars are compromised during tonsillectomy, scarring and a loss of elasticity ensue. This prevents the palate from adequately drawing forward, leading to the collapse of the soft palate. Rarely, posttonsillectomy healing by scarring and fibrosis may impair palatal functioning, resulting in velopharyngeal insufficiency leading to hypernasality.
MATERIALS AND METHODS
A prospective descriptive study of 31 tonsillectomy cases, aged 18–50 years, was carried out over 1 year from July 2018 to June 2019. Patients undergoing tonsillectomy as part of another surgery and cases suspecting malignancy of the tonsils were excluded. Patients’ voices were recorded in a properly insulated room using the PRAAT application, which is software for estimation of acoustic parameters.
Voice recordings were conducted before and after surgery. The first recording took place 1–2 days before the surgery, and the second recording was performed approximately 6 weeks after the surgery. Tonsillectomy was performed using the cold knife dissection technique.
For each recording, patients were asked to read a selected passage. The same passage was given to all patients for voice recording. The recorded samples were then analyzed using the PRAAT application (Figs 2 and 3),11 and F1 and F2 formants were obtained.12
Fig. 2: Analyzing formants in PRAAT
Fig. 3: Brodsky grading of tonsillar hypertrophy
The pre- and postoperative values of each formant were then compared to look for any postoperative changes in values and statistically analyzed. Patients were also asked whether they perceived any change, negative or positive, in their voices postoperatively. Data collected were tabulated using Microsoft Excel and analyzed using Statistical Package for the Social Sciences version 16.0. Categorical variables were represented using frequencies and percentages. Continuous variables were reported using mean and standard deviation (SD). Nonnormal data were analyzed using nonparametric tests (Mann–Whitney U test and Wilcoxon signed-rank test). A p-value < 0.05 was considered statistically significant.
RESULTS AND OBSERVATION
Change in Formants: Statistical Analysis
Table 1 shows the mean and SD of pre- and postoperative F1 and F2, along with the corresponding p-values. Both the first formant and second formant showed an increase postoperatively, but only the change in the second formant was found to be statistically significant, with a p-value of 0.001.
| Formant | N | Mean | SD | p-value |
|---|---|---|---|---|
| Preoperative F1 | 31 | 723.19 | 136.890 | 0.505 |
| Postoperative F1 | 31 | 729.58 | 117.124 | |
| Preoperative F2 | 31 | 1572.10 | 345.476 | 0.0001 |
| Postoperative F2 | 31 | 1654.68 | 400.529 |
Subgroup Analysis based on Sex of the Patient
As shown in Table 2 the mean change in F1 is greater in males compared to females, but the change in F2 was noted to be much greater in females. The p-values were 0.528 for the change in F1 and 0.258 for the change in F2, indicating no significant difference between males and females when comparing changes in formants.
| Gender | Change in F1 | Change in F2 | ||
|---|---|---|---|---|
| Mean | SD | Mean | SD | |
| Male | 9.09 | 104.676 | 57.82 | 112.962 |
| Female | −0.22 | 52.352 | 143.11 | 190.180 |
| p-value | 0.528 | 0.258 | ||
Subgroup Analysis Based on Tonsillar Hypertrophy Grade
Grade IV tonsils showed a decrease in both formants postoperatively, as shown in Table 3. In this analysis, the p-values were 0.995 and 0.117 for the change in F1 and F2, respectively, indicating no significant difference.
| Grade of tonsillar hypertrophy | Change in F1 | Change in F2 | ||
|---|---|---|---|---|
| Mean | SD | Mean | SD | |
| Grade II | 6.24 | 68.192 | 91.96 | 133.192 |
| Grade III | 31.33 | 252.310 | 158.67 | 157.106 |
| Grade IV | −17.33 | 71.066 | −71.67 | 137.318 |
| p-value | 0.995 | 0.117 | ||
Subgroup Analysis Based on Indication for Tonsillectomy
Table 4 shows that the mean increase in F1 after surgery is much higher in obstructive sleep apnea (OSA) patients, but the change in F2 was found to be lesser in them compared to patients with recurrent tonsillitis. The p-values were 0.376 for the change in F1 and 0.346 for the change in F2. Thus, the change in formants when compared among these subgroups did not show any statistically significant difference (Table 5).
| Indication of tonsillectomy | Change in F1 | Change in F2 | ||
|---|---|---|---|---|
| Mean | SD | Mean | SD | |
| OSA | 62.25 | 169.413 | 26 | 225.224 |
| Recurrent tonsillitis | −1.89 | 76.497 | 90.96 | 129.630 |
| p-value | 0.376 | 0.346 | ||
| Grade | Description |
|---|---|
| 0 | Tonsils within the tonsillar fossa |
| I | Tonsils just outside the tonsillar fossa and occupy ≤25% of the oropharyngeal width |
| II | Tonsils occupy 26–50% of oropharyngeal width |
| III | Tonsils occupy 51–75% of oropharyngeal width |
| IV | Tonsils occupy >75% of oropharyngeal width |
DISCUSSION
This study assesses changes in voice after tonsillectomy. Any surgery in the vocal tract invariably carries the risk of altering the shape of the vocal tract, thereby changing vocal resonance, which may be hardly recognizable unless an acoustic analysis is made using voice analysis software. Similarly, tonsillectomy is a surgery in the oropharynx that changes the shape of the oropharynx by removing tonsils. It also causes scarring of the palatal arches, leading to impairment in velopharyngeal closure. These mechanisms explain the change in resonance following tonsillectomy.
We studied the voices of 31 patients who underwent tonsillectomy during the study period. This prospective observational study recorded voice preoperatively and postoperatively for comparison.
Several studies have evaluated changes in acoustic parameters and formant frequencies after tonsillectomy, with or without adenoidectomy. Chuma et al.10 reported that tonsillectomy had only minor quantitative and qualitative effects on various acoustic parameters. Saida et al.13 also reported similar observations in their Studies. Saida et al.13 examined changes in pharyngeal size and acoustic features of voice after tonsillectomy. They found that the distance between both anterior pillars became wider 2 weeks postoperatively and tended to become narrower thereafter. The distance between both posterior pillars also became wider even after 4 weeks postoperatively, thereby changing the shape of the vocal tract.
In a retrospective study among the performing artists done by Jarboe et al.,14 it was stated that patients’ voices were not impaired after tonsillectomy. Zagolski et al.15,16 found that hypernasality was greatest in patients with large tonsils and a low soft palate position in relation to the tongue base. Lin et al.17 in their study of 15 cases, found that there is a consistent increase of the fourth formant frequency in all vowels after the subject has had a tonsillectomy.
In our study, the postoperative recording was done after 6 weeks, as this allowed enough time for complete healing to take place and for normal mucosa to cover the tonsillar fossa. The difference between the mean preoperative F1 (723) and mean postoperative F1 (729) was statistically insignificant. However, the difference between the mean preoperative F2 (1572) and mean postoperative F2 (1654) was significant (p-value = 0.001; p < 0.05 is considered significant).11,12
The change in F1 is statistically insignificant, possibly due to the small sample size, although it may be clinically significant. Significant changes were noted in F2, which is in accordance with the fact that the height of the tongue and its movement in the mid-oral cavity primarily affect the second formant.
The change in formants in patients with recurrent tonsillitis was compared with that in OSA patients. The mean change in F1 in patients of the former group showed a reverse trend compared to the mean change in F1 overall, which could be attributed to OSA patients contributing to the greater part of the overall change. The mean increase in F1 after surgery is much higher in OSA patients. Due to the constant inward suctioning effect in accordance with Bernoulli’s phenomenon in OSA patients, the soft palate level is lowered. Therefore, the pull-up effect of the tongue due to wound contracture at the junction of the faucial pillars and tongue is also less, leading to an increase in the first formant. The mean increase in F2 was lesser in cases of OSA, likely due to a remnant at the tonsillolingual sulcus impairing the pull on the tongue. The chances of a remnant at the tonsillolingual sulcus are higher in cases of very large tonsils.
Comparing the male and female groups, it was found that the mean change in F2 is greater in females compared to males. This can be explained by the fact that females generally have less bulk of the tongue, allowing for better upward movement of the tongue. This results in a greater increase in F2, as F2 is primarily influenced by the height of the tongue. In females, the mean change in F1 is very insignificant, which could be due to the small sample size of females.
We also studied the change in formant frequencies with respect to the grade of tonsillar hypertrophy. Contrary to expectations, postoperative formants decreased in grade IV tonsillar hypertrophy. This can be explained by the fact that in cases of larger tonsils, there is a higher risk of a tonsillar remnant at the lower pole. The remnant decreases fibrosis at the tonsillolingual sulcus, impairing tongue positioning in the mid-oral cavity and thus decreasing the second formant.
CONCLUSION
An understanding of the change in conformation of the resonating chamber after this surgery, which enlarges the space in the oropharynx, has led to various research that emphasize changes in resonance after tonsillectomy, with or without adenoidectomy. In our study, the primary objective was to identify formant frequencies significantly affected after tonsillectomy. F1 and F2 were studied, as changes in jaw advancement and anterior tongue positioning maximally affect these formants, respectively. The results of the study can be concluded as follows:
-
Statistically significant changes were noted in F2, which could be attributed to fibrosis and the upward pull of the tongue, increasing the height of the tongue and thus leading to an increase in formant frequency.
-
No significant change was noted in F1. This could be attributed to the smaller sample size.
-
Subgroup analysis between males and females showed that the mean change in F2 in females is greater compared to males, assumed to be due to the lesser tongue bulk in females. Greater tongue mass in males may counteract the upward pull on the tongue.
-
Regarding F1, the mean change is very insignificant in females, which could be due to the small sample size of females.
-
A comparative study between OSA patients and those with recurrent tonsillitis showed that the mean increase in F1 is much higher in OSA patients, likely due to the lowered soft palate in relation to the tongue base.
-
In the case of the second formant, the mean change was much higher in recurrent tonsillitis than in OSA. This is assumed to be due to reduced fibrosis secondary to a small remnant in the tonsillolingual sulcus in cases of OSA.
-
With respect to the size of tonsils, grades II and III showed increasing formants postoperatively, but surprisingly, grade IV showed a decreasing trend in both formants. This finding can be explained by a small remnant in the tonsillolingual sulcus, as previously stated.
Further studies with a larger sample size conducted over a longer follow-up period are required for more valid and accurate results. As expected, the voice changed after tonsillectomy, but patients did not perceive much change in their own voice except in the immediate postoperative period for about 1 week or 2 due to the pain following surgery. Over time, patients gradually became accustomed to their new voice, and it became difficult to perceive any gross change in their own voice. Based on the above study, we can also draw conclusions regarding tonsillectomy in performers. It is evident that there are subtle changes in voice, as evidenced by statistically significant changes in the second formant in our study. While this may not be a major concern for nonprofessionals, it can have a significant impact on voice professionals due to changes in their signature voice. Therefore, regarding tonsillectomy in performers, a decision should be made after explaining the potential impact on the voice and considering the pros and cons of living with the morbidity of chronic tonsillitis. Preservation of normal mucosa as much as possible should be the aim in this group to minimize wound contracture. Based on the limited evidence we have, it may be advisable to leave a small remnant at the tonsillolingual sulcus to minimize upward pull on the tongue base and thereby reduce changes in the second formant. Further studies comparing mucosa-preserving tonsillectomy versus conventional tonsillectomy will help validate the effects of tonsillectomy on voice.
ORCID
Seetha Murali https://orcid.org/0000-0001-7562-4668
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