When the vocal cords fail to close during phonation. A phonatory gap may be seen in patients who have muscle tension dysphonia, vocal cord paresis or paralysis, loss of tissue, or vocal cord flaccidity.
In addition, however, a phonatory gap occasionally occurs in patients who have none of the above conditions. In this type of case, the patient will struggle with onset delays, but delays that “pop” followed by relatively clear voice rather than the scratchier or hoarser-sounding onset delays associated with vocal cord mucosal swelling. Also, if asked to perform our vocal cord swelling checks, such a patient will tend to struggle more with the “Happy birthday” task than the descending staccato task (the opposite is true for patients with mucosal swelling).
Phonatory gap (1 of 4)
At the prephonatory instant, D4 (~294 Hz), standard light. Notice how separated the vocal cords are.
Phonatory gap (2 of 4)
Phonation, a moment later, with vibratory blur. The cords remain separated. The question is whether this gap is due to: 1) a posturing problem, such as muscular tension dysphonia (MTD); 2) flaccidity-induced bowing; 3) some other cause.
Phonatory gap (3 of 4)
The most “closed” phase of vibration, as seen under strobe light, at the relatively low pitch of F4 (~349 Hz); again, the cords are not actually closed. This is not the picture of MTD, however; with MTD, there would be a greater gap between the vocal processes of the arytenoid cartilages (at arrows).
Phonatory gap (4 of 4)
Open phase of vibration, at the same pitch as photo 3. The lateral amplitude of each cord's vibration is equal, and relatively small (midline shown by a dotted line), which would not be seen with vocal cord flaccidity. Hence, neither MTD nor flaccidity is the explanation for this patient's gap. Also, this patient's voice manifests "popping" onset delays that are similar to other phonatory gap patients who have neither MTD nor flaccidity.
Closed phase at a high pitch (1 of 4)
A mezzo soprano is singing at A5 (880 Hz). This is the “closed” (or rather “more closed,” since a slight gap remains) phase of vibration as seen under strobe light.
Open phase at a high pitch (2 of 4)
Here the voice is at the same pitch, but at the open phase of vibration. The amplitude of vibration (distance moved from the midline) is small.
Closed phase at a low pitch (3 of 4)
Now singing 2 octaves lower at A3 (220 Hz). This is the closed phase of vibration. The vocal cords are short and “fat.” In contrast to stringed instruments and the piano where high pitches are made with short and thin strings, the voice produces high pitches with long and thin. For an analogy, twang a rubber band stretched to different lengths and hear the change in pitch.