Sustained phonation is a part of the vocal capability battery in which the patient is asked to sustain a sung tone as steadily as possible, so as to detect tremor, or other kinds of vocal instability.

Adductory Spasmodic Dysphonia

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AD-SD (1 of 2)

Sustained, clear phonation, standard light. Note vibratory blur of the vocal cord margins. The false vocal cords (lines) are in normal relation to the true vocal cords.

AD-SD (2 of 2)

Involuntary adductory spasm. Note that the false vocal cords suddenly over-close (arrows) as a result of the adductory spasm, and voice momentarily stops (along with vibratory blur).