Asymmetric Mass

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A story of a polyp

Norm is an unabashed sports fan, with season tickets to several professional leagues in town. He is a vocally enthusiastic supporter at his kids’ games also. His voice has been rough for several months. He never had any trouble with it until last autumn. In retrospect, he recalls going to a Friday night football game, where he was yelling quite a bit and by the end of the game he had lost his voice. His voice came back to a usable level by Monday and he was able to go to work, but it never regained a normal quality since that event. 

His story suggests that yelling and hence vocal trauma might be the likely cause of his voice loss and subsequent hoarseness. When I listen to his voice, he can make the low notes reasonably well, though he says that as he talks more, his voice becomes rougher. Indeed, during the course of our conversation, his voice sounds progressively rougher. When I ask him to glide up in pitch, his voice cracks and squeaks.

Looking at his vocal cords with an endoscope, a large red polyp hangs on one edge of one vocal cord. The polyp adds mass to this vocal cord. This is a hemorrhagic polyp and has blood coursing through it. As he vibrates his vocal cords, the vibrations create a whipping of the polyp back and forth and the polyp fills with more blood as he continues talking, making this vocal cord heavier and heavier. When the mass between the two vocal cords is different enough, they begin to vibrate separately at different pitches. Hoarseness due to an asymmetric mass is most evident at his low pitches. 

Hemorrhagic polyp on left vocal cord adds mass to the left side. It breaks the wave up into two segments of different lengths by touching the right vocal cord.

He really has more than one type of dysphonia created by the polyp depending on the pitch he is trying to make, so he provides some insight into the complexities of hoarseness. In the middle of his range, his pitch tends to jump around and he cannot seem to control it. All of us tighten our vocal cords as we move up in pitch. At some specific pitch in the middle of Norm’s vocal range, with progressive tightening of his vocal cords, the polyp just barely begins to rub the opposite vocal cord. As it touches the opposite cord, vibrations are thrown off, his voice quits, squeaks (the pitch jumps up) or breaks up into roughness as they are thrown completely out of synchrony.

A further increase in pitch and the polyp compresses against the other vocal cord stopping the vibration in the middle, leaving either end to vibrate separately. If the polyp is precisely in the middle, the segments may be the same length (and less than half the length of his vocal cord). They will each vibrate at the same, very high pitch (typically the jump is about one octave). If the segments are different lengths because the polyp is based slightly off the middle of the cord, we will distinctly hear two different high pitches simultaneously. Effectively he doesn’t have a functional middle range. He can make either low or very high pitches.

In Norm, at various pitches, we have three types of asymmetries as well as a husky hoarseness:

  • asymmetric mass at low pitches (in the left photo, the left vocal cord is heavier than the right because of the blood in the polyp),
  • asymmetric stiffness (the blood filling the polyp reduces the left vocal cord flexibility),
  • asymmetric segment length at high pitches (in the right photo the front segment is a different length than the rear segment – arrows) and
  • huskiness - air leak on either side of the polyp since the cords cannot come together (the black gaps in the right photo at the arrows).

In his mid-range, we hear a pitch break, something we normally associate with puberty. The pitch break occurs as the vocal cords are stretched to the point where the polyp just begins to touch the opposite cord. If the sound produced by vibrations of the full cord are suddenly shifted to half the cord, the pitch jumps up. Alternatively, the touching may be followed by a diplophonia if the touching is light enough to just throw the cords out of sync with each other.

Many people quickly adapt to avoid these pitch breaks. By holding the vocal cords farther and farther apart the swelling doesn’t touch and disrupt the vibrations. Of course, more air leaks and a greater huskiness is created by this compensation to avoid the pitch breaks.

Summary

Asymmetric mass

  • Increased mass on one vocal cord will lead to asymmetic vibrations — mostly at low pitch
  • Increased mass on one vocal cord introduces sonic complexities because;
    • it may also alter tension
    • split the vocal cords into multiple vibratory segments and,
    • the indivdiual may introduce compensation by adjusting closure.