The S/Z Ratio as an Indicator of Laryngeal Pathology

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Abstract
The use of the s/z ratio as a clinical indicator of laryngeal pathology was investigated with 28 dysphonic subjects with laryngeal pathology (nodules or polyps), 36 dysphonic subjects without laryngeal pathology, and 86 normal-speaking subjects. While no statistical difference was found between the three groups in their ability to sustain /s/, the subjects with laryngeal pathology had significantly lower duration times for /z/ than subjects in the other two groups. The computed s/z ratios were significantly higher for the dysphonic subjects with laryngeal pathology; subjects with functional dysphonia free of laryngeal pathology demonstrated the same s/z ratios (approximately 1.0) as the normal-speaking control subjects. The dysphonic subjects with laryngeal pathology produced s/z ratios in excess of 1.4 ninety-five percent of the time. It appeared from these data that when an additive mass developed along the glottal margin, vocal fold approximation was less efficient. This decrement in efficiency appears to result in a decrease in glottal resistance, increasing air flow, and a shortened phonatory duration time. The clinical usefulness of the s/z ratio as a duration measure for identifying voice clients who may have laryngeal lesions is considered.

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