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Back to Journal »International Journal of General Medicine» Volume 13

Vocal feminization of transgender women: current strategies and patient perspectives

Published on February 12, 2020, Volume 2020: 13 pages, pages 43-52

DOI https://doi.org/10.2147/IJGM.S205102

Single anonymous peer review

Editor approved for publication: Dr. Scott Fraser

Hyung-Tae Kim Yeson Voice Center, Institute of Performing Art Medicine, Seoul, South Korea Mailing address: Hyung-Tae Kim 874 Eonjuro, Gangnamgu, Seoul 06017, South Korea Tel +82 2 3444 0550 Fax +82 2 3443 2621 Email [email protected] Abstract: The feminization of transgender women’s voice is a highly complex and comprehensive transformation process. The feminization of the voice is considered to be equivalent to a pitch increase. Therefore, many surgical procedures only focus on raising the voice to achieve feminization. However, the feminization of voice must not only consider the pitch, but also consider the gender differences in the physiological, neurophysiological and acoustic characteristics of the voice. This is why voice therapy has always been the first choice for voice feminization. Taking into account the gender differences in the vocal system, the method of feminizing voice includes changing the following four key elements: fundamental frequency, resonance frequency related to vocal tract volume and length, formant tuning and vocal mode. The process of voice feminization can generally be divided into non-surgical feminization and surgical feminization. As a non-surgical procedure, feminizing voice therapy includes increasing the fundamental frequency, improving oral and pharynx resonance, and behavioral therapy. The feminization of surgery can usually be achieved through an external approach or an endoscopic approach. According to the three factors of the vocal cords (length, tension and quality), the tone modulation is performed. The surgical procedure can be divided into one-factor, two-factor and three-factor modification of the vocal cord. Recent systematic reviews and meta-analysis studies have reported positive results of voice therapy and voice feminization surgery. The benefits of sound therapy are very satisfying, mainly because it increases the tone and is non-invasive. However, the surgical voice feminization of the three-factor modification of the vocal cords is also very capable and provides the greatest absolute increase in pitch. Voice feminization is a long transitional process of physical, neurophysiological, and psychosomatic changes that transform the male vocal system into a female vocal system. Therefore, the voice feminization strategy should be personalized according to the individual's physical condition, desired tone changes, economic conditions and social roles. Keywords: pitch surgery, voice feminization, vocal cords, voice therapy, formant adjustment, voice pattern retraining

The feminization of voice has appeared in castrates in Italian operas since the 16th century. At that time, women were not allowed to sing in churches. Therefore, the eunuch singer first appeared in the Sistine Chapel in 1562, covering the high range of singing. 1 The voice characteristics of eunuchs are strictly the result of hormonal castration. He uses a component to preserve the child's voice and the child's high-pitched harmonics. This may be the first vocal feminization surgery. 1 Against the background of such facts, vocal feminization surgery has recently been performed for various voice disorders such as androgen therapy for androgen syndrome, ovarian tumor production of male hormones, testicular feminization, and aplastic anemia. Hormones and transgender women.

Kitajima reported in 1979 a preliminary surgical study on experimental tone increase. 2 After solving the understanding of tone modulation in the physiology of the larynx, surgical methods to increase vocal cord tension include cricothyroid approximation (CTA) 3 and anterior commissural advancement (ACA) 4,5. However, the evidence for the effectiveness of this procedure is limited, and most of the peer-reviewed publications are limited to a few case reports. 3-5 Two studies did systematically examine the independent cohort of 14 male-to-female (MTF) transgender individuals who had undergone male voice surgery. Brown et al. reported CTA6 and Wagner et al. assessed ACA, CTA, or both. 7 The quality of the vocal cords can be changed by scratches on the vocal cords, 3 vocal cords injected with steroids, or reduced vocal cords to achieve the quality produced by CO2 laser vaporization. 8,9 The use of CO2 lasers to vaporize discrete parts of the vocal cords can also significantly increase the pitch, as demonstrated by Tanabe et al. on dogs. 8 It seems that the process of scarring leading to a decrease in mass and an increase in stiffness of the vocal cord tissue leads to a significant increase in tone. Donald described a technique for surgically changing the length and quality of the vocal cords by removing the front part of the vocal cords and creating the front net. After 10, various improved procedures have been reported to increase the pitch 11 or reduce the size of the vocal cords and thyroid cartilage by creating a front net. However, when the improvement provided by various programs is insufficient, the postoperative results will show that the sound is unnatural, and the sound quality, loudness and range will be reduced. 13

For a long time, people have generally believed that the following three basic principles are essential prerequisites for improving the stadium; increased tension, thinner quality, and shortened vocal cords. 2,3 However, pitch is a functional acoustic result, not only from vocal cord tension, quality and length, but also from subglottic pressure and the resulting changes in pharynx size14 Most importantly, although the vocalization is autonomously controlled , But the extremely complex activities necessary to produce smooth and clear sound are controlled by vocal feedback reflections. 15 The feminization of voice should consider these three basic principles, as well as vocal feedback reflex control and changes in the vocal pattern caused by female resonance. Therefore, considering the neurophysiological complexity of voice feminization, voice therapy is more advantageous than first-line surgical treatment.

The ideal voice feminization process may lead to complete changes in female voice morphology. For voice feminization, the modification process from male vocal organs to female vocal organs that accurately measure the structure and morphology is required. Understanding the morphometric differences of male and female vocal organs is a key process for formulating voice feminization strategies.

Generally speaking, transgender women develop their vocal organs significantly after puberty. This increase affects gender differences in pitch and quality. During adolescence in men, the frame of the larynx, including the vocal cords, grows significantly and is positioned downward. It is related to vocal tract elongation and vocal tract volume expansion. 16,17 Research on human larynx morphometric data in the literature shows that there is no gender dimorphism in the larynx during childhood. 18-20 Although the gender difference in the larynx is not prominent in infancy, due to the testosterone in male puberty, their larynx may undergo significant morphological changes. twenty one

The average vocal cord length measurement data of the four studies, the average vocal cord length of men is 22.79±3.27mm, and the average of women is 18.99±1.82mm. 20,22-24 Membranous vocal cords average 14.97 ± 2.01 mm for males and 11.17 ± 0.68 mm for females. Therefore, the length of the membranous vocal cords of men is about 25% longer than that of women. 20 Other studies have shown differences in the membranous vocal cords in similar proportions. 25 Therefore, the vocal cords should be 25% shorter than their original length, while keeping the female-sized membranous vocal cords to a minimum of 11 mm when considering the feminization of the voice. There are also morphometric differences in voice thickness between men and women. The thickness of the vocal cords is 6.07 ± 1.11 mm for men and 5.03 ± 1.10 mm for women. 20 The width of the vocal cords shows a difference of approximately 20% between genders. Therefore, if transgender women have a male fundamental frequency, in voice feminization surgery, the length of the vocal cords should be shortened by more than 25% in the membrane part, and the thickness should be thinned by more than 20% in width.

In the vocal tract dimension, the length and volume of the oral cavity seem to be increasing. However, the pharyngeal cavity only increases significantly in adolescents. This indicates that males have longer mouth lengths and larger volumes than females. Moreover, the volume of the pharynx, not the length, has considerable gender differences. It can be seen that female resonance is more affected by volume than by pharynx length. 16

Tongue movement affects changes in the length and volume of the mouth. It also affects the height of the hyoid bone. The re-adaptation of tongue movement or pronunciation patterns is one of the key factors in adjusting the vocal tract configuration. 26,27 Therefore, the focus should not only be on raising the throat to reduce the length of the channel, but also on narrowing the channel to reduce the volume of the channel. The range of gender differences. Therefore, in the feminization strategy, the vocal cords (fundamental frequency) and vocal tract (resonance frequency), including the oral cavity, need to be modified at the same time to achieve acoustic changes in gender characteristics.

The vocals of different people are composed of many frequencies and have complex tones. The acoustic signal generated during speech must contain at least two independent variable parameters, one of which provides information about pitch and the other provides information about the content of phonemes characterized by resonance (vocal tract) and pronunciation (oral). 28 The listener's perception of the speaker's pitch mainly depends on the fundamental frequency of the speaker's voice. The fundamental frequency of men is one octave deeper than that of women. The production of female voice requires modification of the synchronization and layered sequence coordination of breathing, vibration, resonance and pronunciation. In addition, in order to obtain clear voice quality, these complex activities should be controlled by appropriate feedback reflection mechanisms. 29 Therefore, the voice feminization strategy to overcome the gender difference in fundamental frequency should simultaneously address the following two phonetic factors: the tone in the utterance and the phoneme in the pronunciation.

So far, sound therapy and surgery have been developed to raise the pitch to increase the fundamental frequency and feminization of the voice. The surgical principle of raising the pitch must meet the requirements of the following three basic principles: increased tension, thinning of the mass, and shortened vocal cord length. 2,10,11,30 Morphologically speaking, the vocal cords should be changed to be shorter, thinner, and tighter to increase the pitch. Under this concept, voice feminization surgery is introduced to change the direction of the larynx frame through vocal cord modification. Elevation surgery can be divided into three basic categories physiologically; basic principles of one-factor, two-factor and three-factor modification.

Bei Dao and his colleagues conducted the first experimental study of pitch programs in 1979. 2 They analyzed the relationship between the pitch and the distance of the cricoid, and reported an experimental surgical approximation of the distance of the anterior cricoid. They found that the pitch has a linear relationship with the distance of the ring armor. After solving the understanding of pitch modulation, surgical methods to increase vocal cord tension have been described, including cricotal approximation (CTA). 3 CTA is the most popular pitch raising surgery in the past few decades. This procedure approximates the anterior parts of cricoid cartilage and thyroid cartilage with a permanent thread. Therefore, the cricothyroid distance decreases and the tension of the vocal cords increases, thereby increasing the pitch. However, CTA may not show satisfactory long-term results. 31,32

A report stated that only 50% of patients were satisfied, and only 31% had a decent voice after surgery. 32 Since ossification has not yet occurred, the thyroid cartilage of young patients has not yet formed a strong concrete frame to prevent postoperative deformities. Therefore, surgery is not recommended for young people under 30 years of age. Another factor that has been criticized is the CT muscle, which is the most important muscle that controls voice recording. CTA can impair this muscle activity and significantly reduce the pitch range, resulting in unnatural falsetto.

In addition to CTA, another tension correction surgery is anterior commissural advancement (ACA). 4,5 This kind of tension correction surgery is introduced to adjust the tension of the vocal cords and is not suitable for transgender women. It is only designed to tighten loose vocal cords, such as senile throat. The part of the thyroid cartilage connected to the anterior commissure is wedged in and pushed forward. It is held in place with a tantalum splint. However, the post-surgery pitch is not enough to apply it to transgender women. To enhance the increase in pitch, Wagner and colleagues tried a combined CTA plus ACA operation. However, the increase in pitch after this combined surgery is also limited. 7

Donald (1982) first tried to change the length of the vocal cords to increase the fundamental frequency. He introduced a new surgical technique that uses an external approach to create the front web through the opening in the larynx. 10 In 1989, Wendler introduced Donald's endoscopic surgical technique in an unpublished lecture. Wendler's method is performed under rigid laryngoscope and general anesthesia. It includes the deepithelization of the anterior third of the vocal cords, sutured with thread and glue at the level of the deepithelized area to form the anterior glottis network. 33

Gross (1999) reported a similar modification, using muscle sutures to access the anterior glottis, instead of using glue. 11 After establishing the main form of endoscopic surgery for the formation of the anterior glottis, a similar modification was reported. Some authors use a CO2 laser to evaporate the anterior part of the vocal cords and suture the muscles with absorbable Vicryl suture, 34 or use no suture in combination with Radiesse voice gel. 35 Radiesse is injected into the front third of the vocal cords to make close contact with the vocal cords. 35 The weakness of this surgery is that the formation of the anterior glottal network cannot change the thickness, although it can change the length of the vocal cords. Suture the vocal cords with absorbable sutures or strengthened attachment through Radiesse is not enough to keep the vocal cord muscles tightly shortened. It can only reduce the length of mucosal vibration of the vocal cords. It cannot shorten the muscle length of the vocal cords. Generally speaking, the muscle repair mechanism requires a remodeling phase of 3 to 6 months. 36,37 In addition, the wound healing process of the covered part of the vocal cords requires 8 weeks to rearrange and organize the epithelial and basement membrane areas. 38 Therefore, considering muscle remodeling in the process of wound healing, use absorbable sutures to suture the vocal cord muscles and absorb them within 3 or 4 weeks, which will not cause muscle shortening, but will aggravate scar formation. If the attachment point of the anterior vocal cords cannot fit tightly before it is fully healed, severe scar tissue will be formed, because this contact area is a very fast moving part and is an area of ​​concentrated tension. Incomplete glottal closure will be inevitable. Therefore, some patients who fail to follow the instructions or use the voice early after the operation may have difficulty breathing and voice weakness after the operation.

Initially, changes in vocal cord quality or density were achieved by vocal cord scratches, vocal cord injection with steroids, or CO2 laser vaporization to reduce vocal cord quality. 3,8,9 Tanabe reported the first surgical experiment in 1985.8. It is deeply cut longitudinally. In addition, triamcinolone was injected into the vocal cord muscles. The result of this method is not satisfactory, and the voice quality is pathological. 11

Orloff described a clinical report of changing vocal cord density in 2006. This method is called Laser Assisted Voice Adjustment (LAVA). 9 In LAVA, CO2 laser is used to vaporize the vocal cord membrane excluding the vocal cord muscles to increase the stiffness of the diaphragm and increase the fundamental frequency. The average increase in pitch of 26 Hz is not enough to obtain the pitch range of a female voice. On the basis of LAVA, improvements to LAVA technology were introduced in 2009. It is called Laser Reduction Glotoplasty (LRG). 39 In LRG, the epithelium and vocal cord muscles are evaporated using CO2 laser, and the ablation of the vocal cord muscles extends to the anterior point of the vocal cord muscles. This type of surgery was first performed for cases of failed CTA, and it has been developed into an elevation surgery performed at the same time as CTA, as a two-factor (tension and density) revision surgery.

In the short-term and long-term results, univariate correction surgery did not show attractive results because it would only lead to a limited increase in pitch. Therefore, some doctors have been performing combined surgery and can modify the two factors of the basic principle to achieve a higher distance increase. Koçak and colleagues performed laser reduction glottoplasty (LRG) to treat cases with unsatisfactory results after CTA surgery. 39 They changed the two factors of tension and density, and reported that the average pitch increased by 45 Hz after the operation. 39

Clinically, some doctors performed CTA and Wendler glottoplasty at the same time. This combined surgery method is sometimes referred to as "double surgery" or "triple surgery" and includes the patient's thyroid cartilage reduction (Adam's apple shaving). The results of the operation have not been confirmed because the results have not yet been announced. However, physiologically, this combined operation may be an unnecessary operation to raise the pitch, because the operation may damage the known cricothyroid (CT) muscle function to regulate and control the voice register, and at the same time Interference with the feedback control system of the thyroid prickle (TA) muscle. In the later stage, the tone becomes low, the CT and TA muscle feedback adjustment is interrupted, and the important function of controlling the sound clarity is lost, and the voice may be hoarse and rough.

In theory, Wendler glottoplasty plus LAVA or LRG can simultaneously perform two-factor modification surgery under an endoscopic field of view. The pitch improvement of this type of two-factor correction surgery is limited to an increase of about 32 Hz in the fundamental frequency. 40

The ideal surgical method needs to meet all three basic principles, not just one or two. Kunachak (2000) reported an external method to modify three factors, including the larynx frame. It can reduce the size of the vocal cords and thyroid cartilage. In this approach, the anterior column of the thyroid cartilage and the anterior vocal cords are removed through an external approach, thereby reducing the larynx and shortening and tightening the vocal cords to increase the pitch. 12 This program can improve the external shape of the vocal cords. Throat and pitch. Although this surgical procedure is ideal, it is very aggressive. In addition, it causes an abnormally high postoperative tone to increase to 320 Hz. Due to the cutting of the vocal cord muscles, this surgical procedure can damage the throat feedback reflex system of the vocal cords. It also increases the chance of differences in muscle tone and asymmetry of the vocal cords, which can lead to polyphony and difficulty in vocalization.

Thomas and colleagues reported a modified procedure called feminization laryngoplasty to reduce thyroid cartilage and vocal cords, including thyroid hyoid bone approximation. 41 They tried to change the length of the pharynx by approximating the thyroid hyoid bone to change the resonance frequency. 41 However, it is difficult to assume that the thyroid hyoid bone approximation can increase the resonance frequency because the volume of the oral cavity and pharyngeal cavity, which is mainly affected by the movement of the tongue and hyoid bone, has a greater influence on the resonance frequency. 42 On the contrary, it may have some hyperfunctioning effects on the extralaryngeal muscles seen in patients with muscle tension and difficulty in vocalization.

As another three-factor revision surgery using an endoscopic method, Kim introduced vocal cord shortening and anterior commissural movement (VFSRAC). 29 The procedure appears to be similar to anterior glottic network creation or Wendler glottoplasty. However, compared with other single-factor modified endoscopic surgery, VFSRAC has produced significantly different physiological changes. It can change all three factors (tension, length, and quality) of the vocal cords by using permanent suture material and suture the thyroid peritoneum muscle to the inner perichondrium of the subglottic part of the thyroid cartilage. The vocal cords can be made shorter, thinner, and firmer with a single operation (Figures 1 and 2). 29 In the field of endoscopic surgery, VFSRAC can complete the three-factor modification of the vocal cords. Although it provides normal physiological changes, the increase in pitch is limited to 50.8 Hz for those older than 50 years, resulting in an increase in pitch of the entire TG group that is lower than the average value of 76.6 Hz. Figure 1 Postoperative findings of Wendler's glottoplasty. The arrow indicates the glottis network. Figure 2 The postoperative discovery of VFSRAC was a revision of the Wendler glottoplasty in the same patient. The arrow indicates the new front commissure.

Figure 1 Postoperative findings of Wendler's glottoplasty. The arrow indicates the glottis network.

Figure 2 The postoperative discovery of VFSRAC was a revision of the Wendler glottoplasty in the same patient. The arrow indicates the new front commissure.

Generally speaking, with the annual increase of 1.5% and 4% from birth to 50 years old, thyroid cartilage calcification. 43 In addition, with age, the thyroid gland muscles will undergo significant myopathy changes. They may cause impaired vocal function. 44,45 Based on the physiological conditions of aging, the external thyroid approach and the reduction of vocal cords may be more beneficial than the endoscopic approach for the improvement of pitch in patients over 50 years of age. However, for patients under the age of 40, choosing less destructive and conservative surgery may help feminize the voice.

From the surgeon's point of view, we speculate that the postoperative outcome depends on the accuracy of the postoperative vocal cord symmetry balance and the way in which normal and regular vibrations are generated. Technical problems may cause difficulty in vocalization or insufficient pitch increase after surgery, which may be related to asymmetry of vocal cord level, inappropriate scar membranous vocal cords, excessive scar formation, differences in vocal cord muscle tension, and deformation of the larynx frame. From the patient's point of view, hyperactive voices or possible focal laryngeal dystonia can cause increased dysphonia, reduced pitch and pitch instability, and no response to voice therapy for a long time after surgery. 46

According to our experience, many patients with dysphonia and unsatisfactory pitch elevation after surgery are related to the phonation symptoms or functional dysphonia of the larynx before surgery. Comprehensive preoperative sound analysis and preoperative sound processing are the keys to obtain reasonable and satisfactory postoperative results. It is worth noting that patients with symptoms of voice dystonia in the larynx are not considered to be clearly spastic dysphonia. They present regular speech patterns. All of these patients who had functional dysphonia during the preoperative speech assessment described that the dysphonia after surgery could not be controlled by speech therapy and were dissatisfied with the minimum pitch increase. However, these unpredictable symptoms can be treated with botulinum injections. 29 Kim described the following criteria for Botox injection: 1) Patients who have a tense voice, strangulation, frequent glottis during general conversation, and tremor or staccato when long vowels or long voiceless consonants; 2) Yuan Patients with intermittent sounds, one or more times in every three sentences; 3) Patients with more than three tonal interruptions and irregular vertical stripes on the speech analysis spectrogram; 4) Nasopharyngoscopy shows that vowels are on the top Intermittent excessive adduction of the true vocal cords is accompanied by compensatory supraglottic contracture. 46,47 If the patient’s subjective and acoustic findings meet all of the above criteria, postoperative injection of botulinum to two thyroid peritoneum muscles (each 0.4 U) can help prevent the development of unpredictable postoperative dysphonia. 29

On the premise that there is no problem with the surgical perspective, the reasons for dissatisfaction with the long-term consequences of the postoperative results can be found from the perspective of the patient. We speculate that the reason for the unsatisfactory limited increase in pitch is related to problems with the larynx and neuronal vocalization patterns. Reasonable causes are: 1) During the healing process, due to improper postoperative care, the operation site was damaged or severe scars were formed; 2) Vocal cord swelling, edema, granuloma or polyps caused by smoking, drinking or abusing voice Benign diseases of the larynx; 3) Reverse adaptation to the resonance frequency caused by deliberately lowering the tone to overcome the instability or hoarseness of the tone caused by the mismatch between the increased fundamental frequency and the resonance frequency after the operation; 4) Poor adaptation of the vocal cords rather than generating new vocal patterns. The problem is to maintain a person's original abnormal vocalization pattern, which is usually used to generate high subglottic pressure and force hyperactive vocalization to increase the pitch before surgery. Throat problems (first to second) will be treated with medications, reoperations, botulinum injections, or sound therapy. However, the problem of neuronal vocalization mode (third and fourth) requires retraining in combination with medical treatment and vocalization mode. According to our experience, some cases have unexpectedly compensated high-functioning voices with limited pitch increase, although part of the vocal cords healed well without abnormalities. This phenomenon is believed to be caused by an abnormal adaptation to underlying functional laryngeal diseases, and can be compensated by releasing cricothyroid muscle tension and lowering the pitch. However, these patients showed normal laryngeal EMG on the cricothyroid muscle and superior laryngeal nerve. After treating potential functional laryngeal diseases and intensive retraining of speech patterns, they can obtain a reasonable increase in pitch and feminine voice.

Pitch is the most important feature of voice femininity. According to reports, the minimum F0 value required for a voice to be considered femininity is 180 Hz. 48 However, Coleman reports that the increase in pitch is insufficient to obtain a relationship between femininity and vowel formant frequency values ​​and gender perception. 49 Resonance is another sound feature that contributes to gender perception, and may be the second most important acoustic clue. 50 In resonance, the second increasing formant frequency (F2) leads to the perception of female voices. Another meaningful female voice perception is related to increased breathing. 51 Focusing on changes in F0 and the frequency of the second formant is the most effective treatment for changing gender perception. 52,53 Sound therapy is not different from the process of raising the fundamental frequency and raising the formant frequency to resonate, but raising the second formant frequency to change the vocal tract resonance process, which can spontaneously obtain the effect of raising the fundamental frequency and increasing the feminization of the voice. 26 Hancock reported 5 years of cases of voice feminization treatment techniques and results. They pointed out that every transgender woman should address at least one of the following treatment goals: increase forward resonance, increase speaking intonation, relaxation techniques, increase intonation, reduce acoustic trauma behavior, improve respiratory control, female nonverbal communication, female pragmatics Learn to improve sound hygiene. 54 The treatment goals of these trans women are consistent with the most commonly recommended goals in the research literature on trans women’s voice and communication therapy.

Generally speaking, due to the easy availability and implementation of voice therapy, the rate of transgender women receiving voice therapy is much higher than that of voice surgery. 14% of transgender women received speech therapy, while only 1% received speech surgery. 55 However, a recent systematic review and meta-analysis study found that only a few studies provide standardized data for feminizing speech therapy. A large amount of literature on feminizing voice therapy is usually non-standardized and the analysis is unreliable. 56 Moreover, there have been many changes in the techniques and strategies of feminizing voices. An article pointed out that these differences are partly due to the complexity of personal baseline and speech goals and the lack of standardized treatment by speech pathologists. 57 Of the papers published to date, only two studies have investigated long-term results58,59 In addition, long-term treatment results remain in the high male voice range of 145-155 Hz. In addition, the initial result was that approximately 50.8% of the subjects were identified as female, but the long-term result was reduced to 33.1%. 59 Therefore, with the significant increase in the number of long-term data on voice therapy, after the establishment, the standard treatment plan for voice therapy will improve the evidence-based treatment strategy for transgender women’s voice feminization.

In the literature, the focus of speech therapy is to improve the tone, rhythm, intonation, resonance, speed of speech, wording patterns, speech quality, and nonverbal communication patterns of speech. 56 Based on the gender difference of the vocal organs, voice therapy to successfully feminize the voice should make more biomechanical changes than the physiological movement of the vocal cords to raise the pitch to a level higher than the range of your own voice. Sound therapy should also change the size of the vocal tract to change the resonance of the oral cavity and pharynx. In other words, sound therapy refers to the process of changing male vocal organs into female vocal organs. However, if the patient’s larynx and vocal tract have a wide range of morphological features, voice therapy may not be able to achieve a feminine voice. If the patient is in the opposite situation, voice therapy may be sufficient to feminize the voice. According to our experience, for patients with a relatively high fundamental frequency above 140Hz, a wide range, a small membranous vocal cord, a length less than 12mm, and a strong conversion motivation, the voice therapy alone can achieve satisfactory results. The voice is feminine.

As mentioned earlier, in many studies, speech therapy is applied to patients with various treatment goals and techniques. 26,54,56,58-61 However, given the morphological differences between male and female vocal organs, speech therapy should focus on changes in the resonance frequency related to the volume and length of the oral cavity and the volume of the pharynx. The volume and length of the oral cavity are mainly controlled by the movement of the tongue, which also affects the movement of the hyoid bone and changes the movement of the larynx. Tongue movement is essential for muscle movements that change the resonance frequency of the mouth and pharynx. 26,62 Generally speaking, oral resonance therapy is considered to be very beneficial to increase the forward resonance of the sound and femininity. 26 In terms of the physiology of vocal organ resonance, sound should be treated to improve oral resonance and reduce the pharyngeal volume of pharyngeal resonance.

Although the height adjustment operation can change the size of the vocal cords, it cannot change the vocal tract volume. After performing an ascension operation, the fundamental frequency suddenly increases to a higher level. However, the increased F0 may not match the resonance frequency in the old sounding mode. In order to properly resonate the elevated glottal sound, the resonant peak of the resonant frequency should match F0. In addition, a small space must be made in the oral cavity to increase the frequency of the second resonant peak. The frequency of the formant changes due to changes in the spatial shape of the vocal tract, including the position of the main tongue contraction, the opening or closing of the jaw, the rounding or opening of the lips, and the raising or lowering of the throat. 63,64

The formant frequency of vocal tract resonance may be the second most important acoustic clue to feminine sound. 26,65 As the basic knowledge of vocal tract resonance, the first formant (R1) is the most sensitive to changes in mouth opening. The second resonance peak (R2) is most sensitive to changes in oral cavity size. Moving the tongue forward or opening the lips may increase the frequency of this formant. The third formant (R3) changes due to the anteroposterior contraction of the hypopharyngeal area. 42 The femininity of the voice is highly correlated with the high F0 and elevated formant frequencies of all four vowels. 62 Therefore, based on the source filter theory, the formant adjustment used to improve the feminization of the voice after the operation and the re-adjustment of the vocal pattern to achieve the vocal tract resonance are essential for the feminization of the voice after the operation. Postoperative sound therapy techniques that cause this resonance change include tongue and lips relaxation, oral and pharynx resonance movements, larynx relaxation, and vowel modification. 54 Finally, postoperative voice therapy may increase F0, stabilize the pitch, and increase the femininity of the voice. 56

Another importance of postoperative speech therapy is to prevent the reverse adaptation of the resonance frequency. The old vocal pattern before surgery has a lower male fundamental frequency and adjusted resonance frequency. After the operation, the fundamental frequency increases, but the resonant vocal pattern remains unchanged, causing a mismatch between the increased fundamental frequency after the operation and the old formant frequency. In order to solve the problem of this mismatch, some patients who have undergone surgery have a more relaxed and convenient compensatory response, by lowering the larynx to intentionally reduce the resonance frequency, rather than adjusting the two frequencies to increase F0 through training.

This reverse adaptation phenomenon is considered to be an unfavorable compensation mechanism that can overcome tone instability or hoarseness caused by the mismatch between the fundamental frequency and the resonance frequency that occurs early after surgery. Sometimes, this may be misdiagnosed due to imperfect surgery or lack of surgical results. Therefore, long-term postoperative speech therapy is necessary to maintain proper pronunciation patterns, suppress the generation of inappropriate patterns, and improve the acoustics of the sound.

After all, voice feminization is the process of transforming male vocal organs into female vocal organs through speech therapy or surgical treatment, and internalizing a new vocal pattern in long-term memory. Practice facilitates the transfer of patterns from primary memories to longer-lasting secondary memories. 66 This can be done with postoperative speech therapy.

The feminization of voice is not just an increase in pitch, it is a very complex and complicated modulation process. This is a comprehensive medical process, and all speech science knowledge including laryngology, speech language pathology and acoustics must be applied. The feminization of voice is a long transitional process, which transforms the male vocal system, including the vocal organs and patterns, into the female vocal system. From the perspective of the patient, we should consider the sequence, economic aspects and social role of the transformation process to choose the treatment method and direction. From the perspective of the medical provider, the treatment process should be determined as a method that maximizes the safety of the patient’s voice and minimizes side effects while feminizing the voice.

The author has no funds, financial relationships, or conflicts of interest to disclose.

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