Task Instructions Significantly Affect Maximum Phonation Time

Maximum phonation time (MPT) is a widely used clinical measure for assessing the effects of voice disorder on vocal function as well as pre-/post-treatment effects. Although its cost-effective nature makes MPT an appealing tool for clinicians, previous works have raised concerns regarding its intra- and inter-subject reliability and comparability. Furthermore, little work has been done to assess whether task instructions affect MPT performance.

21 healthy volunteers were asked to perform MPT tasks with systematically varying instructions. The Phonatory Aerodynamic System was used to measure phonation time, inspiratory and expiratory air volumes, inspiratory and expiratory airflow, and inspiratory duration. Friedman's χ² was used to assess differences between task instructions, and bivariate correlations were assessed using Spearman's rho.

A significant instruction effect was observed for MPT in seconds (χ² = 97.81, P < 0.0001, W = 0.78). Inspiratory duration, inspiratory volume, and the difference between inspiratory and expiratory volume were significantly different between task instructions. Airflow did not significantly change between instructions. A near-perfect linear relationship was seen between MPT and the ratio between expiratory volume and airflow.

If the effects of instruction on inspiratory behaviors and effort are not accounted for, accurate interpretation of MPT as a measure of vocal efficiency will be hindered. By instructing clients to inhale maximally and then phonate until they completely run out of air, some of these effects may be mitigated. Further research is needed to standardize voice assessment procedures and instructions for MPT in both clinical and research contexts.