What is the impact of dousing water on the skin on the rate of dehydration during a simulated heatwave?
Water dousing on the skin surface during a very-hot-and-dry heatwave: impacts on fluid balance, and thermal and cardiovascular strain in young, middle aged and older adults
The University of Sydney
108 participants
May 20, 2019
Interventional
Conditions
Summary
In an extreme heat context, dehydration has been demonstrated to increase cardiovascular strain and exacerbate core temperature rises. Naturally then, when heatwaves strike in areas where access to clean drinking water is limited, human health suffers. Although clean drinking water is often in short supply in these areas, there may be plentiful access to water that is not safe to consume, but can be doused on the skin, taking the place of sweat. We therefore wish to investigate whether dousing of water on the skin may slow an individual’s rate of dehydration, thereby reducing the amount of fluid they must consume to offset any hydration related exacerbations of physiological strain. To achieve this, we will compare resultant dehydration, as well as thermal and cardiovascular outcomes during a four hour passive heatwave exposure (45°C/ 15% relative humidity) during three different interventions: 1. Full fluid replacement, sham dousing (FFR-S) (comparator) 2. Quarter fluid replacement, sham dousing (QFR-S) 3. Quarter fluid replacement, optimal dousing (QFR-F) Participants will complete only one exposure each, and will fit into one of three age brackets: 1. 18-40 years 2. 45-55 years 3. 65 + years The research hypotheses going into this study are: 1. Resultant dehydration will be less in QFR-F than in QFR-S. 2. Heat related thermal and cardiovascular strain will be least inn FFR-S, followed by QFR-F and greatest in QFR-S. 3. During FFR-S and QFR-S the 65+ years age group will have a greater change in core temperature than the 45-55 years age group who will have a greater change in core temperature than the 18-40 years age group. During QFR-F all age groups will have similar changes in core temperature.
Eligibility
Inclusion Criteria1
- Participants must fall into one of our three potential age categories; 18-40, 45-55 or 65+ years old.
Exclusion Criteria6
- Not within a specified age bracket
- Currently taking medication that may impact thermoregulatory outcomes
- Current respiratory, renal or metabolic disease/ disorder(s)
- Current smoker
- Recent (<12 months) stomach surgery
- Pregnant
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Interventions
Each participant will undergo one four-hour simulated heatwave exposure in a climate chamber, undertaking one of three possible interventions: 1. Full fluid replacement, sham dousing (FFR-S) (comparator) 2. Quarter fluid replacement, sham dousing (QFR-S) 3. Quarter fluid replacement, frequent dousing (QFR-F) They will be asked to sit in a thermally regulated environmental chamber at a temperature of 45°C and 15% relative humidity, with an electric fan stack on a low setting simulating a light breeze (~0.6 m/s). Prior to exposure, predicted water loss due to sweat and respiration across the four hours will be calculated and used to determine the amount of fluid given to the participant to consume throughout. Briefly, this will be achieved using known thermoregulatory constants, the environmental conditions, and an assumed resting metabolic rate equal to one MET. The sweat loss required to achieve heat balance will be subsequently calculated, as will the respiratory water loss, and this will inform fluid consumption. In the FFR-S trial, participants will be given 100% of their predicted fluid losses, broken into four water drinks (~20°C). In the QFR-S and QFR-F trials the participant will receive only 25% of their predicted water losses, also broken into four drinks. These drinks will be of equal volume and delivered at the 35, 95, 155 and 215 minute time points. In the two sham dousing trials (FFR-S and QFR-S) participants forearms will be doused with water once every five minutes using a spray bottle. This will be administered by the researcher. Each spray dispense 1.2ml of ~20 degrees Celsius water, for a total dousing in these two trials of 2.4ml per five minutes. In the optimal dousing trial (QFRO) participants will spray themselves a pre-determined number of times every two minutes. This number will also be based upon calculated fluid losses; 75% of the expected fluid losses across four hours will be calculated prior to exposure, and then broken down into two minute increments, then an allotted number of 1.2ml sprays will be determined. For a typical participant (75kg, 175cm) this will be equal to ~6 sprays (7.2ml) every two minutes. The participant will spray their forearms, legs, chest, abdomen and face. Adherence to the spraying routine throughout the QFR-F trial will be monitored by the researcher, who will offer reminders at each two minute time point.
Locations(1)
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ACTRN12619000722190