Effects of dehydration on phonation in excised canine larynges

The effects of exposure to dry air on phonation were measured in an ex vivo model of vocal fold vibration. Excised canine larynges were mounted on an apparatus and made to phonate at a constant subglottal pressure by means of unhumidified airflow. The phonation threshold pressure (PTP), glottal airflow, sound intensity of the acoustic output, and effects on vocal efficiency were also assessed. Student's t-test was performed on the results. In 17 larynges, the average PTP increased from 10.0 cm H20 to 15.0 cm H2O after exposure to dry airflow (p < .001). In addition, the average flow increased from 585 mL/s to 801 mL/s at a constant suprathreshold subglottal pressure (p < .001), and from 323 mL/s to 610 mL/s at the PTP (p < .001). The average acoustic output levels, measured during stable phonation segments, markedly decreased with exposure to the dry airflow, from 91.5 dB to 88.5 dB (p < .001). The average vocal efficiency decreased from 3.63 x 10^-4 to 7.00 x 10^-5 (p < .001). No such changes were seen in control larynges phonated with 100% humidified air used for driving the airflow. The results support previously reported modeling and experimental findings that dehydration of the vocal fold generally degrades laryngeal performance.