Effects of Short-Term Dehydration and Rehydration on Acoustic Measures of Voice

The purpose of this study was to determine whether short-term dehydration (i.e., no fluid or food intake for a 10-hour period) and subsequent rehydration (i.e., 4-ounce fluid intake every 17 minutes over a period of 2 hours and 15 minutes) resulted in significant changes in acoustic measures of voice. Employing a within-subject, quasi-time series design, a total of 25 healthy subjects (3 males and 22 females) between the ages of 20 and 30 years participated in the study. Baseline data were established through speech samples obtained on four successive evenings and mornings. Speech samples consisted of phonating the randomly ordered vowels /a/, I'll, IvJ, and lol within the carrier phrase "Say /hAb_b/ again." During experimental procedures, speech samples were obtained at 17-minute intervals following intake of 4 ounces of water. It was hypothesized that the morning pretest samples would exhibit decreased fundamental frequency and greater values for jitter, shimmer, and harmonic-to-noise ratio across vowels due to decreased hydration levels. During post-tests, it was hypothesized that fundamental frequency values would increase and jitter, shimmer, and harmonic-to-noise ratio measures would decrease for all vowels over time as a function of increased hydration. Results indicated a significant (p < 0.01) main effect for vowel type across all acoustic measures; however, a significant (p < 0.01) main effect for time was only noted for fundamental frequency, jitter, and shimmer. Descriptive statistics revealed trends which supported the hypotheses for all vowels and acoustic measures with the exception of harmonic-to-noise ratio. Results of this study contribute to normative data and have implications for voice therapy and care of the professional voice.