A Comparison of the s/z Ratio to Instrumental Aerodynamic Measures of Phonation

Objective: The purpose of this study was to examine how the s/z ratio and instrumental measures of laryngeal valving and voicing efficiency. Study Design: Prospective, cohort design. Methods: Fifteen adult males (mean age 28.3 years) and 15 adult females (mean age 29.2 years) with normal voice quality were recruited and compared on productions of the s/z ratio and instrumental aerodynamic measures. The aerodynamic measures included vital capacity, maximum phonation time, airflow rate during sustained and sentence production, subglottal pressure, and laryngeal airway resistance. These measures were obtained on the Phonatory Aerodynamic System Model 6600. Statistical analyses included a univariate analysis of variance to examine for differences between sexes for all the variables, and between the s/z ratios for each of the three trials. Pearson's Product Moment Correlations were performed to identify the strength and nature of any significant relationships between the s/z ratio and instrumental aerodynamics. Results: There were significant differences in the mean values between males and females only for the measures of vital capacity and maximum phonation time. There were no significant differences between the three trials for the s/z ratio. There was a significant moderate negative correlation between the s/z ratio and laryngeal airway resistance in females and between the s/z ratio and sentence airflow rate in males. Conclusions: The s/z ratio demonstrated only a moderate correlation with limited instrumental measures of laryngeal valving. In the absence of clear evidence of its ability to accurately assess laryngeal valving, the s/z ratio should be used in combination with other instrumental measures of laryngeal aerodynamics for a better representation of aerodynamic functioning.