Speech Organs and Their Physiological Functions
Activator
This refers to the respiratory organs, primarily including the trachea, bronchi, lungs, thoracic cavity, intercostal muscles, diaphragm, and other respiratory muscle groups. The main function is to provide the airflow pressure necessary for the production and maintenance of sound.
Generator
The primary generator is the larynx, with the vocal cords serving as the vibrating body. As exhaled airflow passes through the closed vocal cords, it induces vibrations that produce sound. Sound consists of three main attributes: intensity, pitch, and timbre.
Intensity refers to the loudness of the sound and is determined by the subglottic air pressure. Higher subglottic pressure results in greater vocal cord vibration amplitude and louder sound, while lower pressure produces weaker sound.
Pitch refers to the frequency of the sound, determined by the vibration frequency of the vocal cords. This frequency is influenced by the length, thickness, and tension of the vocal cords. Short, thin, and tense vocal cords vibrate within a limited range and at a higher frequency, producing a higher-pitched sound. Conversely, longer and thicker vocal cords produce lower-pitched sounds.
Timbre refers to the quality or uniqueness of the sound and varies from person to person. It depends on the number and strength of overtones as well as factors such as the vocal cord vibrations, the shape and structure of resonance chambers, and techniques of exhalation and resonance.
Resonator
This refers to organs that participate in resonance during phonation. Resonance chambers are typically divided into upper and lower cavities, separated by the soft palate.
The upper resonance chambers include the nasal cavity, paranasal sinuses, and nasopharynx.
The lower resonance chambers include the oral cavity, oropharynx, hypopharynx, laryngeal cavity, and thoracic cavity. These resonance chambers transform the weak, monotonous, and harsh sounds initially produced by the larynx into harmonious, rich, and full tones with unique characteristics.
Articulator
This refers to the organs involved in articulation, such as the lips, teeth, tongue, and palate. These modify the shape or volume of the oral and pharyngeal cavities to produce vowels and consonants.
Vowels are formed when airflow is not obstructed during phonation, with variations determined by factors such as mouth opening, lip rounding, and tongue position (horizontal and vertical).
Consonants are produced when airflow encounters resistance in the articulatory organs. Depending on where the resistance occurs, consonants are classified into seven types: bilabial, labiodental, dental-alveolar, retroflex, post-alveolar, palatal, and velar sounds.
Pathogenesis
Voice disorders involve abnormalities in sound intensity, pitch, and quality.
Abnormal Intensity
Normal voice intensity typically has a dynamic range of ±20 dB.
Hyperfunction of the Laryngeal Muscles
Excessive tension during phonation, improper techniques, or inappropriate pitch range during singing may lead to excessive contraction of the vocal cords and resonance cavity muscles. This results in excessive vocal cord tension, excessive glottal closure, reduced resonance cavity size, and the production of sharp, weak, and unpleasant sounds.
High-pitched phonation often involves vibration of only the membranous portion of the vocal cords, with maximal vibration amplitude and friction occurring at the anterior-middle third junction of the cords. Chronic mechanical damage caused by excessive laryngeal muscle function often leads to vocal cord thickening, vocal nodules, or polyps.
Hypofunction of the Laryngeal Muscles
Also known as laryngeal muscle weakness, this refers to insufficient tension in the laryngeal muscles due to various causes, such as laryngeal paralysis, improper phonation techniques, or functional disorders. Often secondary to hyperfunction, it may also occur primarily. Early symptoms include difficulty speaking, perceived vocal fatigue, frequent pauses for breath while singing, shorter phonation duration, and noticeable hoarseness. As the condition worsens, incomplete glottal closure and varying degrees of glottal gaps may occur due to inadequate closure of the vocal cords during adduction.
Abnormal Pitch
Normal pitch ranges from approximately 150–350 Hz (average 220 Hz) for females and 80–200 Hz (average 120 Hz) for males. Individual variations in pitch occur; however, pitch exceeding or falling below one musical octave (eight notes) of the normal range is considered abnormal.
High-frequency abnormalities are often observed in males during puberty due to insufficient secretion of sex hormones or psychological factors. In such cases, pitch does not lower during the voice-changing period, resulting in retention of a childlike voice into adulthood. This phenomenon is more common in adolescents who have not yet matured.
Low-frequency abnormalities are less common but may occur in women undergoing treatment with male hormones, leading to excessively low pitch.
Voice variability refers to abnormal pitch after the voice-changing period in both male and female youths.
Abnormal Quality
Vocal quality abnormalities caused by laryngeal lesions manifest as hoarseness, roughness, or loss of voice.
Resonance cavity abnormalities produce variances in vocal quality, such as hypernasality or hyponasality.
Etiology
Voice disorders are often associated with vocal overuse and improper vocal techniques, making them common among professionals who frequently use their voice, such as teachers, actors, and salespeople. Poor general health can act as a contributing factor. Functional voice disorders are frequently linked to personality type, psychological state, and emotional factors. Organic voice disorders may arise from inflammation, trauma, tumors, neuromuscular system abnormalities, or congenital developmental anomalies.
Clinical Manifestations
The primary symptom is varying degrees of hoarseness. In mild cases, symptoms may not be apparent during normal speech but may manifest as a rough, intermittent voice or double pitch when attempting high notes. In severe cases, there may be a complete loss of voice.
Congenital Voice Disorders
Conditions such as laryngomalacia, laryngeal webs, cleft palate, congenital laryngeal-tracheal clefts, vocal cord dysplasia (vocal cord sulcus), and congenital laryngeal cysts can cause hoarseness. These symptoms often appear at birth and are frequently accompanied by congenital laryngeal stridor or respiratory distress.
Voice Disorders Due to Improper Use
This is the most common cause. It often results from incorrect techniques during speaking or singing, leading to excessive contraction of the laryngeal and resonance cavity muscles, excessive vocal cord tension, overly tight glottal closure, and reduced resonance cavity size. Excessive vibration at the anterior-middle third junction of the vocal cord leads to chronic mechanical injury, commonly resulting in vocal nodules. Overuse of the voice may also damage vocal cord mucosa, causing benign proliferative lesions such as vocal cord polyps and Reinke's edema. The degree of hoarseness depends on the location and size of the lesion.
Inflammatory Voice Disorders
Acute inflammation has a rapid onset. Mild cases are characterized by rough voice and vocal strain, while severe cases involve hoarseness or aphonia due to thick and viscous laryngeal secretions affecting vocal cord elasticity and poor glottal closure. Systemic symptoms such as general malaise may be present. Chronic inflammation develops slowly, beginning with intermittent symptoms that worsen with vocal overuse, eventually becoming persistent. Reflux laryngitis-related voice disorders present with hoarseness and may include symptoms such as a foreign body sensation in the throat, frequent throat clearing, bothersome coughing, excessive phlegm, difficulty breathing, chest pain, and heartburn. Laryngoscopy often reveals mucosal erythema, disappearance of the laryngeal ventricle, thickening of the arytenoid mucosa, vocal cord edema, pseudocord sulci, or contact granulomas at the vocal process.
Vocal process contact ulcers are chronic ulcers of the mucosa at the vocal processes, usually accompanied by granulation tissue formation (contact granulomas). They are believed to be associated with factors such as intubation trauma, mucosal injury, excessive vocal strain, or acid reflux to the larynx. Clinical symptoms include varying degrees of hoarseness, low-pitched voice, coughing, involuntary throat clearing, and difficulty maintaining pitch in higher registers. Laryngoscopy reveals ulceration or granulation tissue formation on the medial or superior edge of the vocal process.
Benign Hyperplastic Laryngeal Lesions
These are non-neoplastic, benign proliferative or space-occupying lesions that develop slowly with prolonged disease courses. The primary symptom is hoarseness, with a smooth surface observed on the lesion. Different conditions present unique clinical manifestations:
- Vocal cord polyps appear as pale, smooth protuberances on the vocal cord surface and may present as generalized swelling (Reinke's edema).
- Vocal cord cysts appear as smooth, yellowish-white, elevated lesions along the edge or surface of the vocal cords.
- Laryngeal leukoplakia is characterized by white, raised mucosal lesions, predominantly on the vocal cords, and is considered a precancerous condition, with pathology ranging from inflammation to high-grade dysplasia or carcinoma in situ.
- Laryngeal amyloidosis, related to metabolic disorders and tissue degeneration, may cause diffuse, smooth, reddish or dark-reddish lesions in the vocal cords, laryngeal ventricle, or subglottic area, potentially leading to breathing difficulties.
- Laryngeal granulomas are often associated with trauma to the larynx, where tissue proliferation leads to granuloma formation.
Voice Disorders Caused by Tumors
Benign tumors progress slowly, causing gradual hoarseness. Malignant tumors, on the other hand, result in rapidly worsening hoarseness over a short period, eventually leading to complete voice loss. Additional symptoms may include breathing difficulties, swallowing difficulties, and signs of involvement of adjacent structures.
Traumatic Voice Disorders
Various injuries, foreign bodies, surgeries, or other factors can cause damage or dislocation of laryngeal cartilage, soft tissues, the cricoarytenoid joint, or the cricothyroid joint, leading to hoarseness. Most cases involve a clear history of trauma or surgical procedures.
Neurogenic Voice Disorders Due to Laryngeal Motor Nerve Injury
Voice disorders caused by central or peripheral nervous system damage or muscle diseases can result in vocal cord paralysis and varying degrees of hoarseness. The severity of symptoms is often determined by the position of the paralyzed vocal cord and the extent of compensatory laryngeal function.
Spasmodic Dysphonia
Spasmodic dysphonia is a chronic neurological disorder caused by central motor information processing abnormalities, resulting in impaired laryngeal muscle tone and disrupted phonation. It can manifest as a standalone condition or coexist with dystonia affecting other parts of the body. The clinical hallmark is motor-induced symptoms characterized by involuntary spasmodic muscle movements of the vocal cords, which worsen with tension. This condition can be classified into three subtypes:
Adductor Type
This subtype involves the thyroarytenoid muscle and is the most common, accounting for over 80% of cases, with a higher prevalence in females. It is characterized by involuntary and irregular excessive adduction or overly tight closure of the vocal cords and ventricular folds during phonation. Symptoms include vocal tension, rough and interrupted voice, frequent tremors, dissonance, and often distended neck veins during phonation.
Abductor Type
This subtype involves the posterior cricoarytenoid muscle and is less common. It is characterized by intermittent and involuntary abduction of the vocal cords during phonation. Manifestations include inadequate vocal loudness, intermittent breathy voice, or aphonia, often resembling bilateral vocal cord paralysis, leading to potential misdiagnosis.
Mixed Type
Rarely, some patients may exhibit features of both adductor and abductor subtypes simultaneously. Laryngeal electromyography can reveal abnormal laryngeal muscle electrical activity.
Functional Voice Disorders
This disorder occurs with normal laryngeal structure and is more common in females. The presentation includes sudden onset of hoarseness, ranging from whispered speech to complete loss of voice, while coughing and crying or laughing sounds remain unaffected. Recovery is often rapid, but recurrence may occur, typically triggered by psychological trauma or emotional excitement. Laryngoscopic examination reveals vocal cords in a slightly abducted position, which becomes more pronounced during deep inhalation, though the cords retain the ability to adduct during coughing or laughing. When attempting to produce an "ee" sound, the vocal cords fail to fully adduct to the midline.
Other Causes
Ventricular fold hypertrophy or hyperfunction of the ventricular folds is another potential cause of voice disorders. This condition results from the involvement of ventricular fold adduction during phonation, producing vocal abnormalities. The most common underlying cause is compensatory adduction of the ventricular folds. Certain vocal cord pathologies, such as vocal cord motion impairment, partial vocal cord removal due to surgery, or chronic laryngitis, may lead to compensatory ventricular fold adduction or hypertrophy. Symptoms include muffled, hoarse, rough speech with low pitch, vocal strain, and fatigue. Laryngoscopic findings show adduction of the ventricular folds toward the midline during phonation, partially or completely obscuring the vocal cords.
A vocal cord sulcus refers to a longitudinal groove-like depression along the medial edge of the vocal cord, parallel to the free edge, affecting one or both sides. It is commonly caused by trauma or inflammation, resulting in submucosal scarring. Clinical features include a long-standing history of hoarseness, rough and breathy voice, low vocal intensity, vocal strain, and fatigue. Laryngoscopic examination reveals a groove-like depression on the free edge or superior surface of the vocal cords. During phonation, the affected vocal cord may exhibit a bowing deformity, and bilateral involvement results in incomplete spindle-shaped glottal closure. Dynamic laryngoscopy shows reduced or absent mucosal wave activity.
Examinations
General Examination
Laryngeal Examination
Laryngoscopy, including fiberoptic laryngoscopy, electronic laryngoscopy, and rigid laryngoscopy, is conducted to assess the color, morphology, movements of the vocal cords, and glottal closure. Observations are made both during respiration and phonation.
Examination of Resonance Organs
This includes the examination of the nasal cavity, paranasal sinuses, oral cavity, and pharyngeal cavity.
Assessment of Vocal Function
Subjective Evaluation of Voice
This includes subjective perceptual evaluation of voice quality by the physician as well as self-assessment by the patient. Perceptual evaluation often uses the GRBAS scale, which includes:
- G (Grade): Overall severity of abnormal voice.
- R (Roughness): Degree of roughness, often observed when vocal cords are swollen and vibrate irregularly, such as in vocal cord polyps.
- B (Breathiness): Degree of breathiness, which occurs when incomplete glottal closure leads to increased airflow during phonation, commonly seen in vocal cord paralysis.
- A (Asthenia): Degree of weakness, characterized by thinning of the vocal cords, reduced mass, and decreased tension, frequently associated with vocal cord paralysis.
- S (Strain): Degree of strain, reflecting abnormal stiffness and heaviness of the vocal cords, often found in advanced cases of vocal cord carcinoma.
These five factors are graded on a 4-point scale (0: normal; 1: mild; 2: moderate; 3: severe). Patient self-assessment is often conducted using a questionnaire, with the Voice Handicap Index (VHI) as a common tool for measurement.
Objective Voice Analysis
Assessment of Vocal Cord Vibration
This includes techniques such as videostroboscopy and electroglottography. Dynamic laryngoscopy utilizes stroboscopic light sources to assess vocal cord vibration characteristics, including vibratory frequency, symmetry, periodicity, amplitude, mucosal wave activity, and glottal closure patterns. Normally, low-pitched phonation involves slow vibration with larger amplitude, while high-pitched phonation involves faster vibration with smaller amplitude. Healthy vocal cords exhibit symmetrical vibrations, normal mucosal waves, and uniform amplitude. In cases of vocal cord pathology, the degree of abnormality may vary, manifesting as decreased vibration rate, reduced amplitude, weakened or absent mucosal waves, and asymmetry between the two sides.
Voice Acoustics Testing
Sound spectrographs, sound spectrometers, and computerized acoustic analysis systems are used to record voice signals through physical acoustic methods. The frequency, intensity, and timbre of the voice are then analyzed, providing objective, quantitative data on voice quality. This is helpful for diagnosing laryngeal diseases and evaluating treatment outcomes.
Aerodynamic Testing
Measurement of Average Airflow Rate
This involves determining the airflow rate passing through the glottis during phonation. In cases of vocal cord pathology, the phonation time is shortened, leading to a higher airflow rate compared to normal individuals. This allows for indirect assessment of glottal closure, vocal cord tension, and changes in vocal cord mass, providing value for evaluating clinical treatment outcomes
Maximum Phonation Time
Referring to the maximum duration of sustained phonation following a deep inhalation, phonation time evaluates the ability of the larynx to regulate and sustain phonation. Normal maximum phonation time ranges from 20–30 seconds in males (abnormal if less than 14 seconds), 15–20 seconds in females (abnormal if less than 9 seconds), and approximately 10 seconds in children. Phonation time tends to decrease with aging and increases in children as they grow. Health status, age, physical build, lung capacity, and breathing techniques are among the factors influencing phonation time. Phonation time is typically reduced in cases of vocal cord pathology, making it a useful reference for evaluating treatment efficacy over time.
Laryngeal Electromyography (EMG)
Laryngeal EMG evaluates the neuromuscular function of the laryngeal muscles by recording their bioelectrical activity during various physiological activities (such as phonation, respiration, and swallowing) and measuring the evoked potential amplitudes of laryngeal muscles in response to electrical stimulation of the laryngeal nerves. This examination can differentiate vocal cord motion impairment caused by nerve paralysis, functional disorders, or arytenoid cartilage fixation, and it also provides information about the extent of nerve damage.
Imaging Studies
Imaging studies of the larynx during quiet respiration and phonation can aid in the study of vocal disorders. X-ray imaging of the lateral larynx, chest radiographs (anteroposterior and lateral views), esophageal barium swallow studies, as well as laryngeal CT and MRI scans, are valuable for identifying and differentiating the causes of voice disorders.
Other Examinations
Dynamic 24-hour dual-probe pH monitoring can be used to evaluate acid reflux in the proximal esophagus, pharynx, and even the upper airway. This is particularly useful for investigating laryngopharyngeal reflux disease.
Treatment
The causes of voice disorders are complex. In addition to addressing the underlying causes, the following treatment methods are commonly used:
Vocal Rest
For vocal cord inflammation or postoperative reactive congestion and edema, vocal rest, such as refraining from speaking or speaking less, helps reduce inflammation.
Vocal Training
Correction of Excessive Laryngeal Muscle Tension and Abnormal Pitch
Training typically involves actions such as lowering the jaw, flattening the tongue, and promoting the expansion of the pharyngeal cavity. Among the most effective techniques is the chewing voice method, which is conducted in four steps:
- Chewing food while phonating.
- Chewing movements with lips open while phonating.
- Practicing phonating words and sentences once successful in combining chewing and phonation, to gradually establish a new voice.
- Gradual reduction of chewing activities during phonation.
Correction of Insufficient Laryngeal Muscle Activity
Repeatedly practicing breath-holding maneuvers enhances glottal closure, with stabilization of the thoracic cavity during phonation.
Correction of Abnormal Voice Quality
For individuals with suboptimal voice due to improper breathing techniques, the focus is on establishing a thoraco-abdominal mixed breathing method and practicing control of exhalation. This helps produce slower and more even breaths, extending the duration of exhalation.
Medication
Nebulization and Physical Therapy
Inhaled medications often include antibiotics, glucocorticoids, expectorants, and mucolytic agents. Physical therapies such as ultrashortwave or direct current treatments are also commonly used. For hypertrophic and early stage vocal nodules, iontophoresis with iodine or soundwave therapy may promote blood circulation, reduce swelling, and soften and dissolve hypertrophy. For cases of inadequate laryngeal muscle function, low-frequency or high-frequency electrical stimulation therapies may be beneficial.
Use of Antacids
For conditions caused by acid reflux, antacid medications such as proton pump inhibitors or H2 receptor antagonists help control reflux of acidic substances in the pharyngeal and laryngeal areas and improve vocal function.
Surgical Treatments
Benign Hyperplastic Lesions of the Vocal Cords and Ventricular Phonation Disorders
For cases unresponsive to medication or vocal training, microsurgical excision of the lesions can be performed. Care is taken to avoid damaging the vocal ligament during surgery.
Precancerous Lesions and Early Glottic Carcinoma
Microsurgical removal with CO2 lasers can be employed, with the extent of vocal cord resection depending on the location and severity of the cancer. Options range from mucosal layer removal to extensive excision of the vocal cord.
Advanced Laryngeal Cancer
Partial laryngectomy or functional preservation surgeries may be considered. Total laryngectomy may require alternative voice techniques, such as esophageal speech, artificial larynx, or various methods of laryngeal voice reconstruction, to restore vocal function.
Abnormal Vocal Cord Adduction and Sulcus Vocalis
Procedures such as vocal cord injection, vocal cord medialization, or type I thyroplasty may be used to reduce the glottal gap and improve voice quality.
Pitch Modification Surgeries
For male-to-female pitch adjustments, type III thyroplasty can reduce vocal cord tension to lower the pitch. Female-to-male pitch adjustments can involve type IV thyroplasty (cricothyroid approximation), which increases tension in the vocal cords to raise the pitch.
Spasmodic Dysphonia
For cases unresponsive to vocal training, botulinum toxin A injections may be administered into the thyroarytenoid muscle. This reduces acetylcholine release at the motor endplate, inducing neuromuscular blockade and lowering laryngeal muscle tension. Selective denervation of the recurrent laryngeal nerve and anastomosis with the cervical ansa, or endoscopic CO2 laser resection of the thyroarytenoid muscle, may also be considered.
Unilateral Vocal Cord Paralysis and Incomplete Glottal Closure
Suitable options include vocal cord injection and medialization augmentation, thyroplasty, or exploration and repair of the recurrent laryngeal nerve to improve or restore phonation. For bilateral vocal cord paralysis, arytenoidectomy or combined techniques involving hypoglossal nerve reconstruction of both abductory and adductory functions may be performed, preserving vocal function while ensuring airway patency.
Voice Care
Enhanced physical fitness and prevention of upper respiratory tract infections are critical for protecting the voice. Individuals who use their voice extensively in their work should understand proper vocal techniques and avoid voice misuse or overuse. During male puberty, reducing practice time is advisable, while during menstruation, females should note that vocal cords may become congested or swollen, warranting vocal rest. Avoidance of smoking, alcohol, spicy foods, harmful gases, and dust is necessary to protect the vocal apparatus.
Psychological Counseling
For functional voice disorders, the combination of speech and voice therapy with psychological counseling often leads to favorable outcomes.