Address for correspondence : Soo Kweon Koo, MD, PhD, Department of Otolaryngology-Head and Neck Surgery, Busan St. Mary's Hospital, 25-14 Yongho-ro 232beon-gil, Nam-gu, Busan 48575, Korea
Tel : +82-51-933-7214, Fax : +82-51-956-1956, E-mail : koosookweon@naver.com

Introduction

Vocal resonance determines the quality of the voice. Glottal sounds produced by the larynx are filtered as they pass through the pharynx and oral cavity. Glottal sounds are finally "articulated" as they pass through the nose and paranasal sinus.1) The nasal cavity is a dynamic structure incidentally connected to the main vocal tract, and it affects the formation of nasal sound via nasal resonance. Patients with nasal obstruction commonly feel that their voice is changing because of hyponasality due to limitation in nasal resonance. Septoplasty with turbinoplasty is a surgical procedure to relieve nasal obstruction; this procedure has the potential to affect nasal resonance and voice because it alters the resonance characteristics of the vocal tract.2,3,4) Nasal sound is defined as the resonance sound generated within the nasal cavity by some or all of the energy in the sound produced from the vocal cords to the nasal cavity. Nasal sound is heavily influenced by the length and structure of the nasal cavity and the presence or absence of the sinus connected to the nasal cavity.1) The nasal sound is composed of a nasal consonant and a nasalized vowel. Therefore, when measuring the change in the nasal consonant and nasalized vowel, we are able to predict that sound change occurs due to disturbance in the connection between the oral cavity and the nasal cavity. There has been little literature on the effect of septoplasty with turbinoplasty on the voice,5,6) and there have been no studies targeting the Asian population. Language differs according to race and region; hence, our study targeting the Asian population may provide uniquely valuable data. We evaluated the postoperative voice changes in Korean male patients who underwent conventional septoplasty with turbinoplasty and aid in providing subjective and objective data on the effect of surgery.

Subjects and Method

Patient selection
To rule out bias based on sex, only 23 male patients (mean age, 31.3 years) with nasal septal deviation with hypertrophic rhinitis on one side (Guyuron Classification Class II, "C" shaped antreo-posterior direction)7) were enrolled from Jan 2014 to Oct 2014.

Inclusion criteria
The subjects underwent septoplasty with one-sided (concave side) turbinoplasty by the same operator and recovered completely without complications. The mean follow-up period was over 3 months. The diagnosis was based on patient history, nasal endoscopy, allergy test results, and nasal function test results. All patients underwent preoperative computed tomography, and nasal septal deviation and one-sided (concave side) inferior turbinate hypertrophy were confirmed. Subjective satisfaction of the patients with nasal endoscopic examination and nasal function tests confirmed the postoperative improvement.

Exclusion criteria
Patients with known alterations of the voice prior to surgery, any major pathological findings in the larynx, a smoking habit, possible hormonal imbalances, and female sex were excluded.8)

Phonetic definition of the terms the authors use
We have defined the following terms in phonetics. "Twang" is the sound of nasal consonants (/m/, /n/, and /ŋ/) as in the words [^m ma, Korean word "엄마"], [Nu Na, Korean word "누나"], and [sung, Korean word "성"]. "Voice quality" is the most characteristic feature of "You" in speech or is in the most general sense the acoustic signal other than overall pitch, loudness, and phonetic contrast (vowels and consonants). "Nasal," in phonetics, is a speech sound in which the airstream passes through the nose as a result of the lowering of the soft palate (velum) at the back of the mouth.

Outcomes assessment
An analysis of voice changes after surgery (the day before and 3 months after surgery) was carried out through subjective and objective voice analyses. Subjective voice changes associated with surgery were determined by a questionnaire. The questionnaire comprised several questions about voice changes, voice quality, and twang (Table 1). An objective study was carried out on all patients (23 male patients) by voice recordings made before and 3 months after surgery. During each recording session, the subject said [^m ma: the Korean word "엄마"] and [Nu Na: the Korean word "누나"]. We then analyzed the formant frequencies (Hz) and intensity (dB) of the nasal consonant [m] of [^m ma] (the Korean word "엄마"의 /ㅁ/) and the nasalized vowels [a] of [^m ma] (the Korean word "엄마"의 /ㅏ/), [a] of [Nu Na] (the Korean word "누나"의 /ㅏ/). The utterance was repeated three times in one session at a comfortable speaking level to assess the consistency of the data. Data were analyzed by averaging the three. In an audiology booth, an omni-directional microphone placed 15 cm vertically from the subject's lip, and a sampling rate of 44 kHz was used. Praat (ver. 5.2.16 Phonetic Science, Amsterdam, the Netherland) was used for analysis of formant frequencies.

Statistical analysis
All statistical analyses were performed using SPSS software (ver. 18.0; SPSS Inc., Chicago, IL, USA). The paired t-test and Mann-Whitney U-test were used to evaluate differences between preoperative formant frequencies and intensity and postoperative formant frequencies and intensity of nasal sound. The null hypothesis of no difference was rejected if p-values were <0.05. Results are presented as means.
This study was approved by our hospital Institutional Review Board (approval number: BSM 2015-05). Informed consent was obtained from all patients.

Results

Subjective Analysis of Voice Changes by Questionnaire
In total, 73.9% (17/23) and 26.1% (6/23) of patients felt a change and no change in voice, respectively. Among the patients with changed voices, all patients (100%, 17/17) felt that their voice quality had improved and noted "reduced twang." There were a few comments regarding voice changes expressed by the patients; for example, "After surgery, my voice is better and clear," "Vocalization is easier with much reduced twang," and "I can't feel voice change after surgery" (Table 2).

Objective analysis of the voice changes
In the objective study, there was a tendency for increased formant frequencies in the nasal consonant, and F₁ of [m] in [^m ma] (the Korean word "엄마"의 /ㅁ/) was increased significantly (p=0.003) (Table 3). Also, there was a tendency for decreased formant frequencies in the nasalized vowel, F2 of [a] in [^m ma] (the Korean word "엄마"의 /ㅏ/), and F1 of [a] in [Nu Na] (the Korean word "누나"의 /ㅏ/) were decreased significantly (p<0.001) (Table 3), and there was an increase in the intensity of nasal sound [^m ma; the Korean word "엄마"] from 56.8 to 58.7 dB (p=0.009) and [Nu Na: the Korean word "누나"] from 55.9 to 57.6 dB after surgery (p=0.013) (Table 4, Fig. 1).

Discussion

Nasal septal deviation with hypertrophic rhinitis prevents sound delivery into the nasal cavity.9,10) Therefore, patients with adenoid hypertrophy or nasal septal deviation will experience changes in the nasal sound because of disturbance in the connection between the oral and nasal cavities. Change in the nasal sound is categorized into hyponasality and hypernasality. Hyponasality occurs in nasal septal deviation, hypertrophic rhinitis, and adenoid hypertrophy because of disturbance in the connection between the nasal cavity and oral cavity. Hypernasality occurs in cleft palate because of excessive connection between the nasal cavity and oral cavity.1)
Mora, et al.5) evaluated 20 Italian males, and Ozbal Koc, et al.6) evaluated 15 Turkish males and 5 Turkish females. The female voice is under the influence of sex hormones and menstruation.8,11) To avoid the possibility of sex bias, only male patients were enrolled in our study.
For voice analysis after surgery, the measurement time point is important. This is because of the recovery time for surgical wounds. Mora, et al.5) performed voice analysis 1 month after surgery, and Ozbal Koc, et al.6) performed voice analysis 3 months after surgery. Although the recovery time for septoplasty with turbinoplasty has not been fully researched, we performed voice analysis after 3 months postoperatively, when the clots had disappeared and the surgical wound had stabilized.
Analysis of the subjective feeling about the voice is very important for determining the effectiveness of therapy, and it also allows a more meaningful analysis, especially in relation to the quality of life.12,13) There are various ways of performing subjective analysis; we performed a survey using a questionnaire. In our study, most patients experienced improvement in the voice and reduced twang after surgery. More studies examining tonsillectomy reported no change than change.14) However, among studies investigating septoplasty, certain studies reported subjective improvement in the quality of voice,5) and this result was in partial agreement with the result of our subjective questionnaire.
In an objective study, Mora, et al.5) performed vowel analysis using the Multi-Dimensional Voice Program (MDVP). Ozbal Koc, et al.6) performed vowel analysis using MDVP and analyzed formant frequencies in the nasal consonant and nasalized vowel. In vowel analysis using MDVP, Mora, et al.5) reported that all acoustic parameters such as fundamental frequency (F0), jitter, and shimmer improved after surgery, but Ozbal Koc, et al.6) did not detect significant differences in acoustic parameters after surgery. The nasal sound is composed of a nasal consonant and a nasalized vowel. The nasal consonants are [m], [n], and [ŋ], and the nasalized vowel is followed by resonance on the nasal consonant, such as [a] in [^m ma] (the Korean word "엄마"의 /ㅏ/) and [a] in [Nu Na] (the Korean word "누나"의 /ㅏ/) or created when coming back. Therefore, when measuring the change in the nasal consonant and nasalized vowel, we are able to predict that sound change occurs due to disturbance in the connection between the oral cavity and the nasal cavity. Based on this evidence, after asking the patients to phonate [^m ma: the Korean word "엄마"] and [Nu Na: the Korean word "누나"], we analyzed the formant frequencies (Hz) of the nasal consonant [m] in [^m ma] (the Korean word "엄마"의 /ㅁ/) and the nasalized vowel [a] in [^m ma] (the Korean word "엄마"의 /ㅏ/) and [a] in [Nu Na] (the Korean word "누나"의 /ㅏ/).4) In cases of nasal obstruction, the energy and intensity of the nasal consonant and the nasalized vowel are significantly weak. The widened nasal passages after surgery would be expected to result in a general decrease in acoustic damping and an increase in acoustic coupling with paranasal sinuses, thereby increasing the amplitude, or energy, of the voice.4) Hence, we compared the intensity of nasal sound before and after surgery. In our objective study, F1 of [m] in [^m ma] (the Korean word "엄마"의 /ㅁ/) increased significantly after surgery; this means that change occurred at the supralaryngeal vocal tract, and the excess energy absorption caused by nasal obstruction was improved. Typically, formant frequency varies depending on the length of the vocal tract; it increases when the vocal tract length becomes shorter and decreases when the vocal tract length becomes longer.1.5,6) Mora, et al.5) reported that formant frequencies of the nasal consonant and nasalized vowel did not change after surgery, but in our objective study, there was a tendency for decreased formant frequencies in the nasal vowel, and some data were statistically significant. This suggests that the vocal tract length was increased due to relief of nasal obstruction after surgery.
In our analysis of the intensity of nasal sound, a statistically significant increase was observed. This means that the nasal sound became relatively stronger and clearer due to surgery, and this result was in partial agreement with that of the subjective questionnaire.
Our study has some limitation. The nasal cavity is a very complicated structure, and the resonance of the nasal cavity is influenced by length, size, the paranasal sinus, the septum, etc. However, there are few studies about resonance according to various morphological changes. Our study was not targeted to specific morphological changes of the internal nasal cavity and relative small scale study. This will be a future research direction.

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