Vocal cord paralysis (VCP) is a medical condition where nerve impulses to the voice box, or larynx, are disrupted. This disruption causes the muscles of one or both vocal folds (the two small bands of tissue responsible for controlling airflow and creating sound) to lose the ability to move correctly. The inability of the folds to operate normally results in distinct changes to a person’s voice, ranging from a slight change in tone to a complete loss of audible speech. VCP affects not only the voice but also other functions that rely on the proper movement of the vocal folds.
How Vocal Cord Movement Creates Sound
The production of voice, known as phonation, depends on the highly coordinated movement of the two vocal folds housed within the larynx. To speak, the folds must adduct (move together), creating a seal across the airway (the glottis). Air expelled from the lungs builds up pressure underneath this closed glottis, forcing the folds to vibrate rapidly and release sound waves. For breathing, the folds must abduct (move apart) to create an open passage for air.
Vocal cord paralysis disrupts this cycle by preventing the paralyzed fold from moving fully to meet the healthy fold. When nerve signals are interrupted, the muscle becomes immobile, often leaving a gap between the folds during attempted speech. This gap allows air to leak out continuously, preventing the necessary pressure buildup for a strong, clear voice. The resulting voice quality reflects this physical disruption, as the healthy fold struggles to compensate. The paralyzed fold’s position—too far open or too close to the center—determines the severity of air leakage or airway obstruction.
Auditory Characteristics of Unilateral Paralysis
Unilateral vocal cord paralysis, affecting only one fold, is the most common presentation. The resulting sound is typically characterized by profound breathiness because the paralyzed fold cannot fully adduct to meet the functioning fold. This persistent opening allows air to escape before it can be fully converted into sound, resulting in a voice that sounds airy and weak.
The voice also has a rough or hoarse quality, caused by the uneven and turbulent vibration of the folds. Since only one fold vibrates normally, the surfaces do not strike each other evenly, leading to an irregular sound wave. This turbulent airflow significantly reduces volume, making it difficult to project the voice above a whisper. Patients frequently report a loss of vocal pitch control and a reduced dynamic range, often speaking in a lower pitch or monotone. The inability to sustain strong airflow also shortens the maximum phonation time (the longest a person can hold a vowel sound).
Non-Vocal Symptoms Accompanying Paralysis
While voice change is the most recognizable symptom, the failure of the vocal folds to close properly compromises their protective functions, leading to several non-vocal issues. Difficulty swallowing (dysphagia) is common because the folds cannot seal the airway completely to prevent food or liquids from passing into the trachea. This inability to close the glottis raises the risk of aspiration, where material enters the lungs, potentially leading to pneumonia.
A weak or ineffective cough is another symptom, as a cough requires the vocal folds to snap shut tightly to build up pressure. The persistent gap prevents this pressure from being generated, making it difficult to clear the throat or expel foreign matter. People with paralysis often need to take frequent breaths while speaking, as constant air leakage rapidly depletes breath support. This results in vocal fatigue, meaning the voice may worsen noticeably over the course of a conversation or during the day.
The Sound of Bilateral Vocal Cord Paralysis
Bilateral vocal cord paralysis, where both folds are immobile, presents a more serious set of auditory characteristics than the unilateral form. The primary threat shifts from voice quality to severe airway obstruction, reflected in a distinct breathing sound called stridor. Stridor is a harsh, high-pitched sound audible during breathing, occurring when air is forced through a severely narrowed or partially blocked airway.
If both vocal folds are paralyzed close to the midline, they obstruct the passage of air, causing the turbulent flow responsible for stridor. This noisy breathing is often biphasic, heard during both inhalation and exhalation, indicating a fixed obstruction at the glottis. The effort required to move air results in labored breathing and shortness of breath, even at rest. While the voice itself may be nearly normal or a weak whisper, the loud, raspy stridor dominates the auditory presentation, signaling a dangerously restricted flow of oxygen.