title: A meta-analysis of outcomes of hydration intervention on phonation threshold pressure.
abstract: OBJECTIVE
  Vocal fold hydration is purported to promote optimal biomechanical characteristics of vocal fold mucosa, increase efficiency of vocal fold oscillation, and enhance voice quality. The purpose of this work was to determine the magnitude and consistency of the effect of vocal fold hydration on vocal fold function across published clinical studies.
  
  
  METHODS
  We completed a comprehensive meta-analysis of the effects of superficial and systemic vocal fold hydration on phonation threshold pressure (PTP), a measure of efficiency of voice production.
  
  
  RESULTS
  We identified 34 studies that examined the effects of hydration on vocal function. Of these studies, 14 examined the effects of hydration on PTP. Nine of these articles met the criteria for inclusion in this analysis. We observed an average effect size of 0.33, indicating that, overall, hydration treatment demonstrated a tendency to reduce PTP. However, this decrease in phonatory effort did not reach significance at the 95% confidence level. The effects of hydration intervention varied considerably across studies (-0.19 to 3.96). We considered that two factors, pitch level of the task and vocal health of participants, may have contributed to this variability in findings. However, our analysis found that these factors could not account for differences in effect size.
  
  
  CONCLUSIONS
  To understand the variability in outcomes across studies, the role of factors that may impact the effects of hydration, such as the amount, type, and duration of intervention, must be determined. Only then can we obtain data to guide best clinical practice for protecting and rehabilitating vocal function.
authors.affiliation: Department of Speech Communication Arts and Sciences, Brooklyn College Brooklyn, New York, USA. cleydon@brooklyn.cuny.edu
authors.forename: Ciara
authors.initials: C
authors.lastname: Leydon
authors.forename: Marcin
authors.initials: M
authors.lastname: Wroblewski
authors.forename: Naomi
authors.initials: N
authors.lastname: Eichorn
authors.forename: Mahalakshmi
authors.initials: M
authors.lastname: Sivasankar
mesh_terms: D000280:Administration, Inhalation; D000336:Aerosols; D000399:Air Pressure; D001696:Biomechanical Phenomena; D004326:Drinking; D005100:Expectorants / Q000008:administration & dosage; D006801:Humans; D006813:Humidity; D009330:Nebulizers and Vaporizers; D010699:Phonation / Q000187:drug effects; D015656:Respiratory Mechanics; D014783:Viscosity; D014827:Vocal Cords / Q000187:drug effects / Q000378:metabolism*; D014833:Voice Quality; D014867:Water / Q000378:metabolism*
chemical_list: D000336:Aerosols; D005100:Expectorants; D014867:Water