Assessment of acoustic characteristics of speech in patients with bilateral abductor vocal cord paralysis following trans oral carbon dioxide LASER posterior cordotomy

Abstract

Aims

The study aimed to assess voice quality in patients with bilateral abductor vocal cord paralysis (BAVCP) following transoral carbon dioxide (CO2) LASER posterior cordotomy with acoustic parameters.

Materials and methods

Twenty-five participants were recruited over a three-year duration. Voice analysis was done twice, pre-operatively and three months post-operatively in decannulated patients, with the help of Praat software (Version 6.1.08) in a soundproof room, and subjective analysis was done using Voice Handicap Index (VHI 10) questionnaire pre-operatively and three months post-operatively.

Results

Of the total sample size of 25, the majority were females (60%). The mean age of participants was 32.16 ± 14.89. Among the 25 patients, 13 (52%) of them decannulated in the first attempt. Acoustic analysis revealed statistically significant decreases in fundamental frequency, intensity, shimmer, and maximum phonation time post-operatively (p = 0.001), while jitter improved. Subjective analysis VHI 10 showed no significant difference between pre- and post-operatively. Thirteen (52%) of the patients were decannulated within two months following the procedure and voice analysis was done at third month following CO2 LASER cordotomy, the remaining 12(48%) of patients were decannulated with repeat procedures.

Conclusion

CO2 LASER posterior transverse cordotomy is a safe option with reasonably good voice quality in patients with BAVCP for an adequate airway with minimal complications and a good success rate of decannulation.

Introduction

Bilateral abductor vocal cord paralysis (BAVCP) is an uncommon, but challenging problem, that can result from various aetiologies, the most common being iatrogenic injuries (44%), mostly related to thyroid surgeries due to injury to the recurrent laryngeal nerve, others include thyroid malignancies (17%), endotracheal intubation (15%), neurological conditions such as Amyotrophic Lateral Sclerosis [1]. The clinical presentation, the most dangerous being stridor due to glottic narrowing [2]. Tracheostomy was considered the initial and sole therapy for patients with BAVCP in the olden times, till the 1920s. Tracheostomy bypasses severe airway obstruction caused by BAVCP by providing immediate access to the airway and preventing potential respiratory failure. Though tracheostomy serves as a temporary solution while waiting for possible recovery of the vocal folds, depending on the underlying cause. If vocal fold function does not recover within two years maximum, further spontaneous recovery is unlikely. In these cases, a more permanent procedures are considered. Various surgical procedures for BAVCP have evolved through time, from ventriculocordectomy, through external approach, eventually replaced by arytenoidectomy through extra laryngeal approach by Woodman in 1946, Thornell introduced the endolaryngeal access in 1948, arytenoidectomy and posterior cordotomy using carbon dioxide (CO2) LASER was developed by Ossoff, and Dennis and Kashima respectively [1, 3]. With the introduction of LASER for the treatment of BAVCP, endoscopic static procedures are being increasingly performed [3]. In LASER-assisted posterior cordotomy, transverse incision is given at the posterior part of the vocal fold, just anterior to the vocal process to include the base of the ventricle till the inner perichondrium of the thyroid cartilage [1, 3]. High success rates of decannulation have been observed with the LASER cordotomy, other advantages include shorter hospital stay and high patient compliance. There are only a few studies that evaluate the acoustic parameters after LASER cordotomy and these studies were carried out in foreign patients with a limited sample size, the present study used the acoustic parameters in the Indian population with BAVCP after LASER cordotomy for voice evaluation.

Materials and methods

This study was conducted in the Department of ENT in a tertiary health institute in South India over three years’ duration, in patients with BAVCP who underwent transoral CO2 LASER posterior cordotomy were included in the study. BAVCP patients due to various causes and had not shown any natural improvement in their condition even after two years underwent transoral CO2 LASER posterior cordotomy were included via consecutive sampling excluding those patients who were less than 10 years old and those who had associated subglottic stenosis, tracheal stenosis. After obtaining approval from the Institute Ethics Committee (JIP/IEC-OS/2022/281), patients were evaluated for their voice after obtaining informed consent from the patients.

These patients were counseled regarding the use of LASER for posterior transverse cordotomy for improving the airway and the possibility of decannulation following the procedure, the patients were also made to interact with the patients who underwent the procedure for better understanding and anxiety alleviation. Patients were counseled regarding the possibility of a decline in voice quality postoperatively. Pre-operatively, patients were given the Voice Handicap Index (VHI-10) questionnaire. After all the pre-operative investigations and analysis, patients underwent LASER cordotomy as a definitive procedure. Unilateral CO2 LASER transverse cordotomy was made in the posterior portion of the membranous vocal fold, extending laterally to the inner perichondrium of the thyroid cartilage and inferiorly to the subglottis.

During the first follow-up visit one month post-operatively, a video laryngoscopic examination was done, and if the glottic chink was deemed adequate, patients were corked and observed for 48 h. This allowed sufficient time for evaluating the tolerance and whether they could be subjected to decannulation. Patients were assessed after 48 h and those tolerating corking were decannulated. Patients who had postoperative edema were followed up with video laryngoscopic evaluation monthly. Patients whose airways were inadequate even after 3 months of post-operative follow-up, were subjected to a revision procedure. Postoperatively speech therapy was offered to the patients and a support group was made with patients who underwent the procedure that formed a platform for them to help each other [4]. Relaxation exercises like regular breathing, regulated breathing, and modified breathing all to establish diaphragmatic breathing, lip trills first voiceless and then voiced, tongue trills- voiceless and voiced, then neck stretches, progressive muscle relaxation, deep breathing exercises and gentle massage to the muscles of the neck and shoulders were given aiming to reduce tension in the muscles of the neck, shoulders, and chin, which could interfere with voice production. Resonance voice therapy, like humming, forward focus was given to improve voice quality by maximizing the vibration and resonance within the larynx. Semi-occluded vocal tract exercises to regulate airflow, pressure and reduce vocal strain were taught to patients. Neck stretch exercises like head tilts and head rotations were taught to release tension. Ventricular phonations were taught, which involved using the ventricular folds to produce voice.

The voice analysis was done with the help of a computer software package, Praat software (Version 6.1.08) which was done in a soundproof room in the audiology department. Patients were asked to utter syllables ‘aaa’, and ‘eee’, clearly into the microphone with the mouthpiece held at a distance of 10–15 cms, and the voice was recorded and processed with a default application in the Praat software. The patients were asked to inhale as deeply as possible and then utter the syllable ‘aaa’ for as long as possible, maximum phonation time was recorded in seconds. Jitter and shimmer are acoustic measures used to assess voice quality. Increased jitter (pitch variation) and shimmer (amplitude variation) often indicate vocal fold dysfunction or impairment.

Results

Of the total sample size of 25, the majority were females (60%). The mean age of the participants was 32.16 ± 14.89, range (10–59 years). Among the 25 patients, 13 (52%) of them were decannulated following the first surgery, remaining 12 patients (48%) needed revision procedures for decannulation. Among the 13 patients who were decannulated, 84.6% (11 patients) were decannulated one month post-operatively, remaining 15.4% (2 patients) were decannulated two months postoperatively. Decannulation was carried out as per the protocol stated earlier. The mean pre-operative VHI was 10.23 and the mean post-operative VHI was 13.2 following LASER cordotomy but was not statistically significant [5]. Other preoperative and post operative voice parameters after LASER cordotomy are depicted in Table 1. Statistical significance of changes in voice parameters before and after LASER Cordotomy are depicted in Table 2.

Table 1.

Pre-operative and post-operative acoustic parameters after LASER cordotomy

S.No	Acoustic parameters	Pre-operative value	Post-operative value	p-value
1.	Frequency (Hz)	190.61 ± 19.39	182.71 ± 19.54	0.001
2.	Intensity(dB)	68.58 ± 3.44	60.33 ± 5.90	0.001
3.	Jitter (%)	2.3 ± 0.46	1.54 ± 0.62	0.001
4.	Shimmer(dB)	0.90 ± 0.21	1.75 ± 0.65	0.001
5.	Maximum Phonation Time(sec)	9.20 ± 1.44	6.40 ± 1.40	0.001

The mean ± SD, fundamental Frequency (Hz), Intensity (dB), jitter (%), Shimmer(dB), and Maximum phonation time(sec) among patients decannulated using paired sample t-test showing a significant p-value in comparison of pre-operative and post-operative values

Table 2.

Statistical significance of changes in voice parameters after LASER cordotomy

S.No		Parameters	Paired Differences				t value	Sig. (2- tailed)
			Mean difference between preoperative and postoperative parameters	Standard Deviation	95% Confidence Interval of the Difference
					Lower	Upper
1.	Frequency(Hz)		7.90000	2.21848	6.55938	9.24062	12.839	0.000
2.	Intensity(dB)		8.24692	5.66733	4.82219	11.67166	5.247	0.000
3.	Jitter(%)		0.75077	0.27828	0.58260	0.91893	9.727	0.000
4.	Shimmer(dB)		-0.85385	0.61862	-1.22768	-0.48002	-4.977	0.000
5.	Maximum Phonation Time(sec)		2.80000	1.98242	1.60203	3.99797	5.093	0.000

Statistical analysis of voice parameters revealed significant changes in fundamental frequency, sound intensity, and other vocal measures after LASER cordotomy, indicating a decline in voice quality. While the perceived voice handicap as measured by the VHI did not show a statistically significant change after LASER cordotomy.

The rate of decannulation in the present study after the first attempt with LASER cordotomy was 13(52%). The rest of the patients 12 (48%) required revision surgeries for decannulation.

The patients who were unable to get decannulated after the first procedure had superimposing aetiologies like peristomal and infrastomal granulations due to the use of metallic tracheostomy tube in the Indian population. These patients were treated conservatively and monitored regularly. One patient (4%) developed an arytenoid prolapse after surgery, which prevented decannulation for which the patient underwent CO2 LASER vaporization of redundant mucosa over arytenoid and was subsequently decannulated. Patients who could not be decannulated following the first procedure despite all measures underwent a repeat procedure using trans oral CO2 LASER posterior cordotomy in the same side and eight of the 12 patients (48%) were eventually decannulated following second procedure. The remaining four patients (16%) who could not be decannulated underwent a third procedure with CO2 LASER in the same side with ipsilateral partial arytenoidectomy and were eventually decannulated. Because the patients requiring revision procedures were a diverse group with varied surgical procedures and in small numbers, their acoustic outcomes were also varied. This made it impossible to compare their results with those who underwent single staged CO2 LASER cordotomy alone.

Discussion

LASER posterior cordotomy is widely practiced for the management of BAVCP with high success rates of decannulation ranging from 63% success rates in the study by Jackowska et al. to 100% success of decannulation by Mohammed et al., and minimal post-operative complications [2, 3]. The present study was performed on 25 patients with BAVCP who underwent transoral CO2 LASER posterior transverse cordotomy. Of the 25 patients recruited for the study, 15 were female and 10 male patients. This distribution might be attributed to the fact that thyroid aetiologies are common in the female population and one of the most common causes for BAVCP is following total thyroidectomy [6, 7]. In this current study, 14 patients (56%) of the patients who presented with BAVCP underwent total thyroidectomy in outside hospitals and were referred to our hospital for further management. The patients recruited in this study were from ages 10 to 59 years, although many of the patients were in their second to third decade, and this might also be due to the prevalence of thyroid aetiologies in this age group. We also had two pediatric patients (12 years, 14 years) with an idiopathic etiology.

The fundamental frequency (Hz), which is defined as the first harmonic, physiologically determined by the number of cycles of vocal fold vibration in one second, is commonly used to define voice [8]. Fundamental frequency(Hz) of the present study in comparison with the study by Asik et al. is depicted in Tabls 3 [9].

Table 3.

Comparison of fundamental frequency of the present study with the study by Asik et al

S.No	Fundamental frequency (Hz)	Asik et al(n = 11)	Current study decannulated patients after the first procedure (n = 13)
1.	Pre-op (Mean+/-SD)	191+/-31	190.61+/-19.39
2.	Post op (Mean+/-SD)	187.9+/-36.9	182.71+/-18.57
3.	Statistical significance	1.000	0.001

Jitter measures perturbation in the pitch/frequency of the voice, while shimmer measures perturbation in the loudness/amplitude, also showed a statistically significant difference pre- and post-operatively [7]. The current study demonstrated improved jitter values post-operatively following decannulation whereas shimmer values show worsening postoperatively. Jitter values, while crucial in predicting outcomes in many studies, can be less effective for voices with high roughness and low pitch [10]. This is because jitter is highly influenced by changes in fundamental frequency and present study, observed a post-operative decrease in fundamental frequency, which could explain the lower (better) jitter values measured in the present study [11].

In studies by Hans et al., the jitter and shimmer values showed worsening postoperatively, and also in the study by Dursun et al., the post-operative values of jitter and shimmer showed worsening postoperatively [1, 12]. Vocal cord damage by surgery, causes direct trauma to the vocal folds, leading to inflammation, scarring, and changes in muscle function, and the healing process could temporarily affect vocal fold function, resulting in increased jitter and shimmer.

The decreased maximum phonation time postoperatively might be due to the increased air leak caused by the procedure that affects the physiological process of phonation and the LASER cordotomy being a cord-destructive procedure would have contributed to its decline postoperatively. Although the maximum phonation time estimated after one year of the procedure showed a 65.6% return to the pre-operative value [1]. Comparison of statistical significance of acoustic parameters between the study conducted by Asik et al. and the current study with decannulated patients after the first LASER cordotomy procedure is shown in Table 4.

Table 4.

Comparing acoustic parameter significance: Asik et al. and current study post-cordotomy

S.No	Other Acoustic Parameters	Asik et al(n = 11)	Current study decannulated patients after the first procedure (n = 13)
1.	Fundamental frequency	1.000	0.001
2.	Jitter	0.247	0.001
3.	Shimmer	0.083	0.001
4.	Maximum Phonation Time	0.027	0.001

This table showed a significant difference in acoustic parameters between the study by Asik et al. and the current study of decannulated patients after their first CO2 LASER cordotomy. In the study by Asik et al., the voice analysis was performed post operatively during the second month following surgery. They used A Shure^® dynamic cardioid microphone (model C606N)) using the multidimensional voice program, while in the present study acoustic assessment was done after three months post operatively using Praat software (Version 6.1.08).

Multidimensional voice program and Praat software are two commonly used applications for voice analysis. The data comparing both the applications showed fundamental frequency was comparable whereas other variables such as shimmer and jitter vary considerably between the two [13].

Another reason that could have altered the results between the studies might be the sex ratio. The male and female fundamental frequencies vary. In the study by Asik et al., nine were females and rest two males, in our study six were males and seven females. In Asik et al. primarily patients underwent CO2 LASER cordotomy without tracheostomy. These might be some of the reasons for the variations in the statistical analysis between Asik et al. study and the present study.

Subjective analysis using the VHI-10 showed no significant difference in pre and post-operatively and showed no significant impact on their personal life, which is comparable with the results of some of the previous studies conducted in this area [1]. But objective voice parameters showed decline. These findings revealed a noteworthy discrepancy between patient perception and objective acoustic measurements of voice quality following LASER cordotomy. While patients did not report a significant change in their perceived VHI, the acoustic analysis demonstrated a clear decline in voice quality. This suggested that patients might not fully perceive the subtle changes in their voice that are detectable through objective acoustic measurements. Subjective nature of voice perception, the potential for adaptation to the altered voice quality, and the limitations of the VHI in capturing all aspects of vocal impairment could be the factors for the discrepancy. Despite the lack of statistical significance in the VHI scores, the significant changes in acoustic parameters highlighted the importance of incorporating objective voice measures in the assessment of post-operative outcomes following LASER cordotomy.

The rate of decannulation in the present study after the first attempt with CO2 LASER cordotomy was 13(52%). The rest of the patients required revision surgeries for decannulation. Table 5 depicts the number of patients with BAVCP who underwent repeat procedures for decannulation.

Table 5.

Decannulation in BAVCP patients: A comparison of repeat procedure rates

	Ozdemir et al(n = 58)	Jackowska et al(n = 41)	Current Study(n = 25)
No of patients who required repeat surgeries for decannulation	12(18%)	27(46%)	12(48%)

The need for repeat surgeries to achieve decannulation varied significantly among the studies, ranging from 18% in Ozdemir et al. to 46% in Jackowska et al. [2, 14]. In the present study, some patients required additional interventions to achieve decannulation after the initial CO2 LASER cordotomy. The present study (48%) indicated the highest percentage of BAVCP patients requiring repeat procedures for successful decannulation suggesting potential differences in patient characteristics, surgical techniques including use of adjunctive procedures and post-operative management/infection compared to the other studies.

The present study evaluated the voice quality separately in patients who underwent decannulation and compared it to the pre-operative values to have uniformity and avoid flaws. The voice evaluation was performed after three months to give adequate time for healing after the procedure, since cordotomy is a cord-destroying procedure, the result was expected to be poor quality of voice in patients who underwent the procedure which was shown in our study to be statistically significant [15].

This study was carried out with a good sample size of 25 patients in the Indian population, with acoustic analysis. Another factor that contributed to strength and avoiding bias is that the surgeries were done by the same surgeon experienced in doing CO2 LASER posterior cordotomies. While CO2 laser cordotomy is effective for achieving decannulation in BAVCP, it permanently alters the vocal fold structure. This can lead to limitations in acoustic parameters. In contrast to ablative procedures, laryngeal reinnervation procedures aimed at restoring lost neural connections to the larynx. These techniques involve connecting a donor nerve to the larynx, either through direct end-to-end anastomosis, implantation into a muscle, or utilizing nerve-muscle pedicle techniques. Advantages of laryngeal reinnervation include the potential for near-normal voice quality without the need for synthetic implants, restoration of muscle bulk, and improved vocal fold positioning. However, disadvantages include the requirement for an intact donor nerve and identifiable recurrent laryngeal nerve stump, a delay of several months for reinnervation to take effect. Despite these drawbacks, laryngeal reinnervation offers a promising approach to restoring vocal function and improving quality of life for individuals with laryngeal paralysis [16].

However, this study is not without limitations. Two pediatric patients who were not able to fully follow the instructions during voice evaluation might have led to differences in the values of voice parameters. Another limiting factor in this study is that underlying comorbidities of the patient that could have interfered with the process of decannulation were not taken into account and extremes of age in the study population might be a contributory factor [17].

Conclusion

This study investigated the impact of CO2 LASER posterior transverse cordotomy on voice quality in patients with BAVCP. While statistically significant changes in acoustic parameters were observed postoperatively, including a decline in fundamental frequency, intensity, shimmer, and maximum phonation time, these changes did not translate to significant subjective dissatisfaction. This suggests that while LASER cordotomy does influence vocal quality, the impact is clinically acceptable and does not substantially impair quality of life. Hence CO2 LASER posterior transverse cordotomy is a safe option in patients with BAVCP for an adequate airway and a good success rate of decannulation.

Authors contribution

All the authors have equally contributed to the original article. HG and RK are the major contributors in writing the manuscript. Others participated in writing, editing and data interpretation. All authors have equally participated in writing the manuscript.

Funding

There was no funding required to take up the study.

Data availability

The datasets during and/or analyzed during the current study are available from the corresponding author upon reasonable request.

Declarations

Ethics approval and consent to participate

Ethics approval is not required for publication of case reports and case series as per institutional policies.

Consent for publication

Written informed consent for publication of their clinical details and/or clinical images was obtained from the patient. A copy of the consent form is available for review by the Editor of this journal.

Competing interests

The authors declare that they have no competing interests.