Table 3.

Investigations of systemic hydration induced voice changes in vivo with altered fluid intake

Ref	Patients	Hydration Inducement	Hydration Measures	Hydration Status	Vocal Function Measures	Main Results	Conclusions
Solomon et al. (2003) (43)	4 M 19–29 yr healthy	Method Typical hydration Usual amount non-caffeinated fluids Low hydration 25% typical amount non-caffeinated fluids + repeated dry swallows High hydration 75% more than typical amount non-caffeinated fluids + repeated ingestion of 30ml water Timing 2 days prior to Ax patient altered fluid intake Every 5 min during reading tasks - fluid intake (high) or dry swallow (low)	Method Self-report nutrition & hydration log Timing Prior to initial Ax & during	Pre Not measured Post Not measured	Measures PTP 10, 50, 80 PPE VAS-PTP Lx imaging closure, supraglottic activity, mucus, color, mucosal wave, symmetry & amplitude Timing Pre ✓ Post✓	PTP ↓ (>2SDs) high cf low hydration 2/4 patient at selected pitches only PTP↑(>2SDs) from typical for 88% of trials (both low & high hydration conditions) PPE correlated with PTP across all pitches, patient & sessions Lx imaging - characteristics varied inconsistently across hydration & fatigue conditions 2/6 patients displayed sustained changes in 50% parameters in low-hydration	Drinking water should not be expected to lower PTP Findings did not support the prediction that drinking water would attenuate detrimental effects of strenuous phonation task Ability to match PPE with PTP varies amongst individuals PTP & PPE increase after prolonged loud phonation
Solomon et al. (2000) (42)	4 F 22–29 yr healthy	Method 24–32% humidity, no liquid prior Typical Low Hydration 16oz water/day High hydration ≥ 5×16oz water/day Timing 2 days prior to baseline & experimental sessions - monitor intake & abstain from caffeine, alcohol, high-sodium foods, dehydrating substances, strenuous voice use	Method Self-report nutrition & hydration log Timing Prior to initial Ax	Pre Not measured Post Not measured	Measures PTP 10, 50, 80, conv PPE VAS-speaking Lx imaging Vibratory closure pattern Timing Pre ✓ Post ✓	PTP ↑PPE with loud reading in each hydration condition 1/4 patients ↓PTP in high hydration condition prior to loud reading PTP generally returned to pre-loud reading levels after 15 min rest Laryngeal imaging No diff. between hydration conditions	PTP can be used as a repeatable measure & is seen to vary with prolonged loud phonation Drinking water appeared to attenuate or delay increased PTP in prolonged reading
Hamdan et al. (2007) (44)	28 F 21–45 yr healthy	Method Fasting Abstain from all food & drink Non-fasting Usual intake Timing Testing occurred 1–2 hrs prior to sunset to ensure at least 14hrs fast	Method Not measured Timing Not measured	Pre Not measured Post Not measured	Measures PPE -4-point scale Acoustics Fo, RAP, NHR, shimmer, turbulence index, habitual pitch, MPT Lx imaging Symmetry & amplitude mucosal wave periodicity closure Timing Pre ✓ Post ✓	Patient perception post fast-vocal fatigue (53.6%) deepening of voice (21.4%) harshness (10.2%) PPE sig. ↑ during fasting Acoustic sig. ↓ max phonation time (~2.7sec) Lx imaging - no changes	Fasting has an effect on voice, most perceived by the individual as an ↑ in phonatory effort Acoustic analysis is not revealing, nor is laryngeal videostroboscopy ↑phonatory effort likely secondary to dehydration & an element of muscular fatigue at respiratory & phonatory levels
Hamdan et al. (2011) (45)	26 M 22–50 yr healthy	As per (44)	As per (44)	As per (44)	As per (44)	Patient perception post fast - vocal fatigue not sig. different Sig ↑ PPE during fasting Acoustic - Sig. diff habitual pitch, voice turbulence index, NHR Lx imaging - no changes	Fasting results in increased effort in males which may be due to dehydration or decreased museular endurance
Fluid intake + rest
Yiu & Chan (2003) (46)	10 M 10 F 20–25 yr healthy Amateur singers previous fatigue post karaoke singing	Method Hydration & voice rest (HVR) rest + 100ml water Non-hydration & (non HVR) no rest & no fluids Timing Ingestion of fluid following each song	Method Not measured Timing Not measured	Pre Not measured Post Not measured	Measures Acoustics Fo, jitter, shimmer, NHR Perceptual roughness & breathiness (VAS) Phonetogram Timing Pre ✓ Post ✓	Significant difference ↑ time till fatigue HVR group ↑jitter in speech non HVR male patients after 10 songs (returned to normal) ↓highest Hz for female non HVR patients after 10 songs (returned to normal)	Some evidence that hydration & vocal rest reduces vocal fatigue Hydration & vocal rest should be recommended for singers as preventative measure to reduce vocal fatigue & negative effects of prolonged voice use