Does Stridor HAVE to be Present for Diagnosis of Vocal Cord Dysfunction?

Laryngospasm, the most severe form of vocal cord dysfunction, does include stridor as a symptom. However, a patient can still suffer from vocal cord dysfunction and even laryngospasm without an obvious stridor present.

In order to understand stridor's relationship to vocal cord dysfunction (VCD), one must first understand what exactly is happening anatomically... or skip to the bottom of the article if you already understand the basics.

When a person breathes, the vocal cords move apart allowing air to pass easily through and into the windpipe. When a person talks, the vocal cords come together and vibrate allowing for voice production. [watch video]

Vocal cord dysfunction is when the vocal cords come together (instead of apart) when a person is trying to inhale air. Given the physically smaller airway created by the approximated vocal cords, the patient would typically experience shortness of breath and some wheezing.

Laryngospasm is when the vocal cords come completely together when a patient is trying to breath and stridor is typically produced with attempted strong inhalation against closed vocal cords.

Watch a video showing both types here.

As such, in order for stridor to be produced, TWO things must be present:

1) The vocal cords need to be nearly or completely closed together.
2) There must be strong breathing attempts

If any two elements are absent, stridor will not occur.

For example, if a patient is in a full-fledged laryngospasm attack, but is either breath-holding or making weak attempts at breathing, no stridor will occur.

Conversely, if a patient is suffering from a severe case of vocal cord dysfunction and is breathing hard enough, due to venturi effect against vocal cords that are almost closed (but still open), stridor like sounds may occur.

Venturi effect???

What's that?

In essence, it is a physics concept whereby there is a reduction in pressure when a fluid (or air) flows through a constricted section of a pipe (or airway) in this case.

In essence, the venturi effect as it applies to the voicebox, is a highly localized area of negative pressure created between the vocal cords when a person is breathing fast causing the vocal cords to come together even more... leading to more "sound" with breathing even if the vocal cords are not completely together.

It is perhaps one reason why athletes who suffer from vocal cord dysfunction may sound like they are suffering from laryngospasm during a VCD attack while exercising. Technically, it may not be laryngospasm because the vocal cords are still apart, but due to the venturi effect, causes a functional vocal cord closure leading to aggressive vocal cord vibration and a stridor-like sound production.