Table 4.

Investigations of systemic hydration Induced voice changes in vivo employing rapid reversal of dehydrated state

Ref	Patient	Hydration Inducement	Hydration Measures	Hydration Status	Vocal Function Measures	Main Results	Conclusions
Franca & Simpson (2009) (47)	19 F 18–35 yr healthy	Method Abstain from water & food intake prior to testing Ingest 1l water Timing 14 hr fast prior to testing 1l water in 20 min Test 90mins post ingestion	Method Patient report intake of tobacco, caffeine, alcohol & medications Timing Initial recruitment	Pre Not measured Post Not measured	Measures Acoustics jitter & shimmer Timing Pre ✘ Post ✓ Initial Ax in dehydrated state post fast	Improved jitter & shimmer in rehydrated condition, but not for all participants	Hydration has a positive impact on voice Results may be applied in prevention, counseling & treatment of voice disorders for individuals & employers
Selby & Wilson (n.d.) (56)	8 M 18–31 yr healthy	Method All patients abstain from alcohol & caffeinated drinks. Testing at 20°C no air conditioning Dehydration Abstain from all fluids & food prior to testing Rehydration Ingest 2l electrolytic fluid Timing 1 day prior abstinence from alcohol & caffeine Dehydration - abstain fluid from 4pm & food from 6pm day prior to testing (~18hrs) Rehydration -ingest 20min period, testing 1hr post	Method Patient report intake of alcohol, caffeine, & water Bioelectric impedance Timing Initial recruitment Day of testing	Pre Patient water intake .25–2l/day 50% often thirsty Impedance data not reported inconsistent& unable to track small changes in TBW Post Not measured	Measures Laryngograph Lx imaging Acoustics jitter, Fo mode, range, irregularity Timing Pre ✘ Post ✓ Initial Ax in dehydrated state post abstinence	Lx imaging 1/8 patients excluded due to sulcus vocalis No diff. between smokers & non-smokers Acoustics Sig. ↑ modal Fo in conversation post rehydration	Hydration status does not have a marked influence on Fo mode, range & regularity
Fujita et al. (2004) (3)	6 M 28–36 yr healthy PVU Working in low humidity	Method Remain in workplace environment (except transit) & abstain from systemic medications, coffee, alcoholic drinks & diet products Dehydration Abstain all liquids Rehydration Ingest 200ml room temperature aqueous solution with electrolytes + inhalation 0.9% saline Timing Unknown general abstinence period, no fluid 4hrs prior to testing Fluid ingestion immediately following initial Ax Saline inhalation 10mins	Method Not measured Timing Not measured	Pre Not measured Post Not measured	Measures Lx imaging Videokymography quotient open phase time/closed phase time dB & Hz Timing Pre ✘ Post ✓ Initial Ax in dehydrated state post abstinence	No statistical analysis completed on results ↓ open phase time/closed phase time post hydration in 80% of patient, but ↑ in remaining 20% patient 5/6 patient presented with affections of the VF mucosa After hydration ↓ appearance of viscosity of mucus & bright VFs ↑ amplitude of VF mucosa wave vibration	Videokymography is an objective method of Ax to determine abnormalities of VF mucosa pre- & post- hydration Reduced quotient open phase time/closed phase time following hydration