Effect of dehydration on phonation threshold flow in excised canine larynges

Objectives: The minimum airflow necessary to initiate stable vocal fold vibration - phonation threshold flow (PTF) - may increase as exposure to dry air increases. A critical period of dehydration may exist after which phonation can no longer be initiated. Methods: We collected PTF data for 11 excised canine larynges mounted on a bench apparatus. Trials consisted of cycles of 10 seconds of phonation followed by 3 seconds of rest. During the experimental trials, subglottal flow of comparatively dry air was increased until phonation was initiated, and phonation was sustained for the remainder of the 10-second period. The subglottal flow was then decreased until phonation ceased. No saline solution was applied during the dehydration trials. During the control trials, subglottal airflow was humidified and saline solution was applied frequently to the vocal folds. Results: The PTF increased as exposure to dry air increased during the experimental trials (p = 0.010); this relationship was not statistically significant in control trials. A point existed after which phonation could not be initiated. Conclusions: Knowledge of the effect of exposure to dry air on PTF could be useful in the clinical assessment and prevention of dehydration. Further exploration of this relationship in vivo could be used to evaluate the effectiveness of current hydration therapies and provide theoretical support for the development of new ones.