[S/z ratio in glottic closure defects]

The quotient between the maximum phonation time (MPT) of the sound /s/ and a vowel sound, measures the relation of resistances to the expiratory air flow. When the sound /s/ is emitted, resistance is located at the teeth, and when a vowel is phonated, the site of resistance is the glottis. Estimating the quotient instead of measuring only the MPT, we avoid the influence of respiratory alterations in the results. We evaluated the utility of the s/z ratio as a clinical indicator of laryngeal pathology in 72 patients with organic vocal cord pathology. We compared the results of the s/z ratio to the degree of glottic closure defect, measured by videolaryngostroboscopy. S/z ratio in 22 normal-speaking subjects was also measured. S/z ratio in normal-speaking subjects was nearly 1.0. When a glottic closure defect was present, the ratio was over 1.4. Organic lesions that difficult glottic closure, produce a decrease of air flow resistance and, therefore, a shortening of the MPT of the vowel sounds.