Hoarseness from asymmetric vocal cord tension

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Continuing our introductory story

Returning to Faith, whom we met earlier, we may recall that she lost her voice suddenly for no apparent reason. When she went to her primary physician, he predicted that she would improve with time. Indeed she did. After a few weeks, some voice returned. Her voice was higher pitched and softer than before, but seemingly her physician was correct, she would get better on her own.

Still, after several more weeks, Faith was unsatisfied with her merely marginal improvement. At a follow up visit with her primary physician, she was referred to an otolaryngologist. Still she failed to improve with various treatments. Several months later she appeared in my office still hoarse. 

As she tells me her story, I listen to her voice. Next, I asked her to start at a high note and gradually descend to the lower pitched notes. At the highest notes, her voice is fairly clear and fairly robust. At a lower pitch, approaching the typical speaking pitch for a female, she loses volume and below that pitch, her voice becomes very rough. We repeat the task several times. Her voice fading in volume and quality at low pitch is very consistent. 

When I observe her vocal cords as she descends toward the lowest pitches where her voice becomes rough, I can see one vocal cord become loose, bow, buckle and ultimately flutter in an irregular pattern.

The vocal cords oscillate in a wild pattern at a low pitch because the right side is much looser than the left. The right cord has two separate wave segments compared to the left cord’s single wave. Yellow arrows point to an anterior segment. Pink arrows point to a posterior segment.

Faith’s vocal cords oscillating in a wild pattern at a low pitch because the right side is much looser than the left. The right cord has two separate wave segments compared to the left cord’s single wave (arrows). On the right, the yellow arrows point to one physical wave generating a sound. The purple arrows point to a second segment generating a different pitch. The left vocal cord, oscillating as a single segment generates a third pitch.

Faith’s rough vocal quality is due to an uneven tension between the vocal cords. The uneven tension is partially compensated at high pitch, remaining subtle and hidden. Her comfortable speaking pitch is automatically higher than it used to be as she unconsciously tries to compensate for her voice problem by tightening the vocal cords to avoid the flutter. In her lower range, however, the difference in tension is pronounced and at some point each vocal cord vibrates at a separate pitch or multiple pitches.

To describe two separate pitches occurring simultaneously – diplophonia (or in this case triplophonia), I could use terms such as roughness or gravelliness to describe the character of her low voice, while she might say, “I am hoarse” or “My voice is rough.” Pitches produced simultaneously and sonically competing with each other are irregular vibrations. Faith’s roughness is due to uneven tension.

We really only need one sound source to generate a harmonic sound such as a single string on a guitar, but we have two vocal cords. Like a piano that has two or three strings at some pitches to increase volume (as long as they are tuned together), we have two vocal cords and two sources of sound. They are typically tuned to the same pitch. In hoarseness, they may not be tuned the same.

Summary

Asymmetric tension leads to hoarseness

  • Two vocal cords should have the same tension to produce the same pitch.
  • With differening tensions the left and right vocal cords will tend to vibrate at separate pitches.
  • With insufficient tension, a very loose vocal cord can break up into multiple vibratory segments.