The Predictive Value of Maximum Phonation Time for Vietnamese Adults.

OBJECTIVES: Maximum phonation time (MPT) is a critical aerodynamic metric for assessing glottal efficiency and respiratory control. However, clinical implementation in Vietnam is hindered by a reliance on Caucasian normative data, which may not account for the physiological and linguistic characteristics of Asian populations. This study aimed to establish reference normative data for MPT in healthy Vietnamese adults and to determine the optimal number of repetitions required for accurate clinical assessment. METHODS: We conducted a cross-sectional study in which participants performed 10 repetitions of the sustained vowel /a/ following maximum inhalation. The difference in MPT between gender and age groups was analyzed using two-way Analysis of Variance (ANOVA). A stepwise multiple linear regression was used to develop predictive models based on age, gender, and physical characteristics. A descriptive analysis was performed to identify the frequency of optimal performance across trials. RESULTS: There were 340 participants in this study. Males exhibited significantly higher MPT values than females (mean difference = 6.1 s). MPT showed a moderate negative correlation with age (r = -0.44) and a weak positive correlation with height (r = 0.17). Predictive models incorporating age, height, and gender explained 27% of the variance, with a calculated lower limit of normal of 13 s. Optimal performance occurred most frequently on the 4th, 5th, 6th, and 10th trials. CONCLUSIONS: This study establishes the first maximum phonation time norms for Vietnamese adults. Results show lower values compared to Caucasian counterparts and a steady decline with age. To ensure clinical reliability, this study recommends at least six repetitions, with adequate rest between trials, to capture MPT accurately.