The effects of frequency and intensity level on glottal closure in normal subjects.

The degree of glottal closure during phonation has an influence on voice quality and it is related to the robustness of the voice source. To quantify glottal closure a frame of reference was created by investigating 47 healthy men and 92 healthy women with no vocal complaints using videolaryngostroboscopy. Observing recorded images the degree of glottal closure was rated with a percentage. Results indicate that men have better glottal closure than women (P < 0.001). An increase in vocal intensity is related to improved glottal closure (P < 0.001), and in women a negative relationship was established between pitch and glottal closure (P < 0.001). Normal glottal closure in men is a complete closure, whereas in women a closure of at least 90% should be attained. If these percentages cannot be established during loud phonation, it suggests the presence of a less robust larynx. To evaluate and quantify the function of the voice source, in clinical practice the larynx should not be observed at only one intensity level, but at a variety of intensity and frequency levels.