Compensation by laryngeal muscles
Surprisingly, when someone with hoarseness comes in seeking a diagnosis, they try to avoid sounding hoarse during the examination. Naturally and fairly immediately they try to compensate for any hoarseness. As soon as their voice breaks or cracks, they stop the vocal task and apologize. Then they try the vocal task again, trying not to sound “bad.” Internally they compensate and produce the sound again.
It is fortunate that there is redundancy in the vocal system so compensation is usually available to maintain sound production even when there is a problem. However, for the examiner, compensation tends to hide a voice disorder, both audibly as well as visually. Some common instances hidden by compensation include mucosal disorders on the edge of the vocal cord or weakness from neurologic and muscular disorders. Yet the astute examiner attempts to eliminate compensation, exposing a problem.
For example, the TA muscle and the CT muscle both have the effect of raising pitch. The TA muscle is within the vocal cord and isometrically tightens the vocal cord to raise pitch, while the CT muscle is located on the external surface of the laryngeal cartilages and lengthens the vocal cords to raise the pitch. If there is decreased neurologic input to one of these muscles, the other muscle compensates at least partially. In the case where the TA muscle is not working on one side, a patient automatically compensates by pulling the CT muscle tighter. This has a net effect of raising the comfortable speaking pitch when the patient tries to speak with the same volume as before the injury.
When I perform an endoscopic exam on a patient speaking at an unnaturally high pitch, I really want to hear the patient produce a lower and lower pitch. At each lower note, compensatory tightness from the CT muscle is progressively removed. As the CT muscle’s contraction is removed, if there is a weak TA muscle, the vocal cord would begin to bow and then flutter in the wind while a healthy TA muscle on the other side would remain tight. Removing compensation amplifies this difference between each side of the larynx and allows improved visualization of this neurologic impairment.
Mucosal disorders – problems with a swelling on the edge of the vocal cord – also involve natural compensation. At higher pitches, the vocal cord is pulled tighter. A mucosal swelling on the edge of a vocal cord would stand out farther and farther with the increasing tension of higher pitch. The further the swelling sticks out, the more likely the swelling is to touch the other vocal cord and stop vibrations. The patient compensates for this “stopping effect” in some instances by increasing the airflow from below to blow the touching swellings apart. In effect, the patient increases their volume to compensate for effects from the vocal swelling sticking out along the edge of the vocal cord. A singer with a swelling will sing louder and louder as she goes up in pitch to prevent the vocal stoppages. As an examiner, I remove this compensation by asking the patient to make only soft sounds as she goes up in pitch. At low lung pressure, the slightest touch of a swelling on one vocal cord stops or alters the vibrations on both. I remove the volume compensation in order to better hear, visualize and discover the pathology.
There are other forms of compensation, which will be discussed in some of the case studies in later chapters. Key concepts for the examiner:
- Patients automatically try to compensate and maintain smooth vibration as much as possible,
- When an examiner removes compensation, – typically by initiating a change in pitch or volume – asymmetries and gaps become more audible and more visible.
- Compensation may involve a trade off, one impairment is less bothersome than another impairment.