None listed
Conditions
Brief summary
It is as yet unknown whether fluctuations in hydration status, such as those which may occur in a realistic heatwave scenario, may impact the efficacy of electric fan usage during heatwaves, and hence should be accounted for in future publicly disseminated advice surrounding fan use during extreme heat events. Therefore, the proposed study aims to examine the combined effect of hypohydration (reduced body water) and fan use during heatwave conditions. To achieve this, participants (n=16) will undergo four separate passive heatwave simulations within a climatic chamber (39 degrees Celsius, 50% relative humidity, 3-h duration). Both hydration status and the presence of an electric fan will be varied resulting in four scenarios: 1. Well hydrated, no electric fan used (EUH-NF) 2. Well hydrated, electric fan used (EUH-F) 3. Hypohydrated, no electric fan used (HYP-NF) 4. Hypohydrated, electric fan used (HYP-F) Throughout these four heatwave simulations we will monitor markers of thermal and cardiovascular strain as well as indices of hydration status and different heat transfer pathways such as sweating output. Manipulation of hydration status prior to the each exposure will be achieved via either 24 h of adhering to a fluid consumption plan (EUH-NF and EUH-F) or 24 h of fluid restriction (HYP-NF and HYP-F). We hypothesise that, the use of an electric fan will be beneficial (i.e. lower thermal and cardiovascular strain) during the 'well hydrated condition'; EUH-F compared to EUH-NF. However, in the 'hypohydrated' conditions (HYP-F and HYP-NF) this relation will be reversed, as hypohydration will cause a reduction in sweating output and therefore the mechanism by which electric fans augment heat loss will be compromised.
Interventions
Each participant will undergo four experimental trials in a counterbalanced order, separated from each other by a minimum of 72 hours. Each of these four experimental sessions will involve 3 hours of passive exposure (seated) to a heatwave simulation (39°C ambient temperature, 50% relative humidity) in a climatic chamber. On each occasion one of the following four interventions will be implemented:
1. Euhydration-Fan (EUH-F): Participants will be euhydrated leading up to and throughout the expo
Each participant will undergo four experimental trials in a counterbalanced order, separated from each other by a minimum of 72 hours. Each of these four experimental sessions will involve 3 hours of passive exposure (seated) to a heatwave simulation (39°C ambient temperature, 50% relative humidity) in a climatic chamber. On each occasion one of the following four interventions will be implemented: 1. Euhydration-Fan (EUH-F): Participants will be euhydrated leading up to and throughout the exposure and will have an electric fan blowing a constant air flow (~3 m/s) across them. Throughout the exposure, participants will be given intermittent bolus’ of 37°C water to match sweat losses, ensuring euhydration is maintained. 2. Hypohydration-Fan (HYP-F): Participants will commence the trial in a mildly hypohydrated state and will have an electric fan blowing a constant air flow (~3 m/s) across them. Participants will remain fluid restricted throughout the exposure. 3. Euhydration-No Fan (EUH-NF): Participants will be euhydrated leading up to and throughout the exposure. Throughout the exposure, participants will be given intermittent bolus’ of 37°C water to match sweat losses, ensuring euhydration is maintained. 4. Hypohydration-No Fan (HYP-NF): Participants will commence the trial in a mildly hypohydrated state. Participants will remain fluid restricted throughout the exposure. To better contextualise the magnitude of changes in body mass caused by the hydration manipulation interventions preceding each trial (described below) a 5-day 'hydration baseline' will take place in the lead up to their first trial. This will involve the assessment of morning nude body mass and first pass urine specific gravity on each of these 5 days. Hypohydration prior to trial commencement in the HYP-F and HYP-NF trials will be achieved via fluid restriction in the 24 hours preceding these trials. Prior to the EUH-F and EUH-NF trials participants will adhere to a tailored fluid consumption plan in the 24 hours preceding these trials. This consumption plan will be designed to endure euhydration at the start of both the EUH-F and EUH-NF trials, confirmed via both urine specific gravity measurements, and comparison of morning body mass measurements compared to the 5-day 'hydration baseline'.
Sponsors
The University of Sydney
Study design
Allocation
Randomised controlled trial
Intervention model
Crossover
Primary purpose
Prevention
Masking
Open (masking not used)
Eligibility
Sex/Gender
All
Age
18 Years to 40 Years
Healthy volunteers
Yes
Inclusion criteria
Participants must be within our age bracket (18-40 years) and apparently healthy at both the time of enrolment, and throughout their participation. Apparently healthy for the purposes of this study is defined as free from renal, cardiovascular, respiratory and metabolic diseases/disorders, and not currently taking medications which may influence either thermoregulation or fluid balance.
Exclusion criteria
1. Younger than 18 years or older than 40 years 2. Currently taking medications that may impact thermoregulation/ fluid balance 3. Current respiratory, renal, cardiovascular or metabolic disease/ disorder 4. Current smoker 5. Iodine allergy 6. Pregnant 7. Trypanophobia (fear of needles)
Outcome results
None listed