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Trial registered on ANZCTR


Registration number
ACTRN12620000722998
Ethics application status
Approved
Date submitted
16/06/2020
Date registered
7/07/2020
Date last updated
9/05/2024
Date data sharing statement initially provided
7/07/2020
Date results information initially provided
9/05/2024
Type of registration
Prospectively registered

Titles & IDs
Public title
Does hypohydration impact the beneficial effects of electric fan use during a simulated heatwave?
Scientific title
Electric fan use during a hot humid heatwave simulation: impacts of hypohydration on thermal and cardiovascular strain in young healthy adults
Secondary ID [1] 301372 0
None
Universal Trial Number (UTN)
U1111-1252-6171
Trial acronym
Linked study record

Health condition
Health condition(s) or problem(s) studied:
Hypohydration 317620 0
Heat related illness 317621 0
Heat related cardiovascular strain 317622 0
Thermal discomfort 317623 0
Condition category
Condition code
Public Health 315704 315704 0 0
Other public health
Injuries and Accidents 315705 315705 0 0
Other injuries and accidents
Cardiovascular 315706 315706 0 0
Normal development and function of the cardiovascular system

Intervention/exposure
Study type
Interventional
Description of intervention(s) / exposure
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'.
Intervention code [1] 317679 0
Prevention
Comparator / control treatment
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.
Control group
Active

Outcomes
Primary outcome [1] 323938 0
Core temperature change

Prior to each exposure participants will self-insert a single use, thin, flexible thermistor probe ~12 cm into their rectum, where it will remain throughout the subsequent 3-h heatwave simulation. This will facilitate continuous measurement of rectal temperature, an index of deep body core temperature (degrees Celsius). Change in core temperature from baseline (minute 0 of exposure) will indicate thermal strain.
Timepoint [1] 323938 0
The primary time point for this measure will be the end of exposure (minute 180), indicating the total change in core temperature caused by the combination of the heatwave simulation and the intervention. Although recording is continuous, particular emphasis will also be placed on readings taken at the 60-min and 120-min time points to track the development of thermal strain.
Primary outcome [2] 323939 0
Heart rate

Absolute heart rate (beats per minute) will be continuously recorded via chest strap monitor, and subsequently used to calculate change in heart rate from baseline. Both absolute heart rate value and change from baseline will be used to indicate cardiovascular strain throughout the exposure.
Timepoint [2] 323939 0
The primary time point for this measure will be the end of exposure (minute 180), indicating the total change in heart rate caused by the combination of the heatwave simulation and the intervention. Although recording is continuous, particular emphasis will also be placed on readings taken at the 60-min and 120-min time points to track the development of cardiovascular strain.
Secondary outcome [1] 383393 0
Whole body sweat rate/ loss

Nude body mass will be measured on a platform scale, and used in conjunction with fluid intake data to calculate sweating output (g/h).
Timepoint [1] 383393 0
Body mass measurements will take place at the beginning (minute 0) and end (minute 180) of each heatwave simulation, as well as every hour throughout i.e. 60 min and 120 min.
Secondary outcome [2] 383394 0
Resultant/ cumulative hypohydration

Nude body mass, measured on a platform scale, will be used to track the development of hypohydration relative to starting body mass (% total body mass lost).
Timepoint [2] 383394 0
Body mass measurements will take place at the beginning (minute 0) and end (minute 180) of each heatwave simulation, as well as every hour throughout i.e. 60 min and 120 min.
Secondary outcome [3] 383395 0
Blood pressure

Seated, resting blood pressure (mmHg) will be taken in duplicate throughout the exposure via an automated blood pressure cuff.
Timepoint [3] 383395 0
Baseline measurements will be taken in duplicate at the beginning (minute 0) of the exposure, and every 30 min thereafter until the end of exposure (minute 180).
Secondary outcome [4] 383396 0
Rate pressure product

The product of systolic blood pressure (measured via an automated blood pressure cuff) and heart rate (measured via a chest strap monitor) will be calculated and taken as an index of myocardial oxygen consumption, and hence cardiovascular strain (mmHg/bpm).
Timepoint [4] 383396 0
Post hoc calculations will be completed using blood pressure and heart rate data at the beginning (minute 0) and end (minute 180) of each heatwave simulation, as well as every hour throughout i.e. 60 min and 120 min.
Secondary outcome [5] 383397 0
Orthostatic tolerance

The participant will be asked to stand up from their passive, seated position and a blood pressure measurement (measured via an automated blood pressure cuff; mmHg) will be taken 1-min and 3-min after standing. This measurement evaluates the participant's physiological capacity to respond to the gravitational challenge posed to the circulatory system following rapid postural change.
Timepoint [5] 383397 0
Orthostatic tolerance will be measured at the end of each heatwave simulation, immediately following the final resting, seated blood pressure (minute 180).
Secondary outcome [6] 383398 0
Skin blood flow

A laser doppler flowmetry (LDF) unit will be secured to the upper back of the participant and used to monitor cutaneous blood flow. As this is monitored in arbitrary units, the final 45 min of exposure will include local heating of the area via a heat pad (fixed to the LDF unit) to 42 degrees Celsius to achieve a maximum skin blood flow reading. Skin blood flow will be reported as percentage of maximum.
Timepoint [6] 383398 0
The LDF unit records continuously at a rate of 1 Hz, primary timepoints for analysis will be minutes 0, 60 and 120; local heating will commence at minute 135.
Secondary outcome [7] 383399 0
Forearm blood flow

Venous occlusion plethysmography will be employed to determine the rate of blood flow into the forearm (ml/100 ml/min).
Timepoint [7] 383399 0
Forearm blood flow measurements will take place at the beginning (minute 0) and end (minute 180) of each heatwave simulation, as well as every hour throughout i.e. 60 min and 120 min.
Secondary outcome [8] 383400 0
Local sweat rate

Technical absorbent pads (highly absorbent patches which will capture any secreted sweat) will be fixed to the upper back and forearm intermittently throughout the exposure for 4 min periods. Using the known covered surface area as well as the application time, local sweat rate at these areas will be calculated (g/cm^2/min).
Timepoint [8] 383400 0
Technical absorbent pads will be in place for 4 min periods at the beginning (minutes 0-4) and end (minutes 176-180) of the heatwave simulation, as well as the period leading up to every hour mark i.e. minutes 56-60 and 116 to 120.
Secondary outcome [9] 383401 0
Activated sweat gland density

Iodine soaked cotton paper (9 cm^2) will be applied to the skin surface next to measurement sites for local sweat rate (upper back and forearm) for a period of 3-5 seconds intermittently throughout the exposure. This will reveal each individual sweat gland that is active in the area of application allowing the subsequent estimation of active sweat glands (glands/cm^2).
Timepoint [9] 383401 0
Sweat gland density will be measured during local sweat rate measurement i.e. minutes 2, 58, 118 and 178.
Secondary outcome [10] 383402 0
Thirst perception

Participants will be asked to rate their thirst, mouth dryness and how pleasant a drink of water would be on three separate visual analogue scales. These scales are each 100 mm long and the participant may mark anywhere on the line, with a score between 0-100 being determined for each. These three scores will be taken as an indication of the participants level of thirst throughout the exposure.
Timepoint [10] 383402 0
Baseline thirst measurements will be taken at the beginning of each heatwave simulation (minute 0) and every 30 min throughout i.e. minutes 30, 60, 90, 120, 150 and 180.
Secondary outcome [11] 383403 0
Thermal discomfort

Thermal discomfort will be monitored via a four-point visual analogue scale which ranges from not uncomfortable (1) to very uncomfortable (4). This outcome will indicate the thermal acceptability of the environment/ intervention combination.
Timepoint [11] 383403 0
Baseline thermal discomfort measurements will be taken at the beginning of each heatwave simulation (minute 0) and every 30 min throughout i.e. minutes 30, 60, 90, 120, 150 and 180.
Secondary outcome [12] 383404 0
Whole body thermal sensation

Using a 100 mm visual analogue scale participants will rate their whole body thermal sensation from neutral (0 mm) to very hot (100 mm) providing inside into their perception of their thermal environment as well as the influence of the intervention on this perception.
Timepoint [12] 383404 0
Baseline whole body thermal sensation measurements will be taken at the beginning of each heatwave simulation (minute 0) and every 30 min throughout i.e. minutes 30, 60, 90, 120, 150 and 180.
Secondary outcome [13] 383681 0
Plasma osmolality

A small (300 microliters) capillary blood sample will be centrifuged, and the plasma's osmolality determined via freezing point depression. Plasma osmolality (mOsm/kg) will provide a high quality indication of hydration status, and allow precise tracking of the development of hypohydration.
Timepoint [13] 383681 0
Plasma osmolality will be measured at baseline (minute 0) and every 60 min throughout the heatwave simulation i.e. minutes 60, 120 and 180.
Secondary outcome [14] 383683 0
Urine specific gravity

A first pass urine sample will be collected prior to each heatwave simulation and used in conjunction with body mass and plasma osmolality to confirm either euhydration (specific gravity <1.020) or hypohydration (specific gravity >1.020) via specific gravity analysis using a refractometer.
Timepoint [14] 383683 0
The urine sample used for analysis of specific gravity will be collected by the participant on the morning of each heatwave simulation during their first micturition.

Eligibility
Key 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.
Minimum age
18 Years
Maximum age
40 Years
Sex
Both males and females
Can healthy volunteers participate?
Yes
Key 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)

Study design
Purpose of the study
Prevention
Allocation to intervention
Randomised controlled trial
Procedure for enrolling a subject and allocating the treatment (allocation concealment procedures)
Allocation is not concealed.
Methods used to generate the sequence in which subjects will be randomised (sequence generation)
A balanced latin square sequence was generated using a randomisation table created by computer software.
Masking / blinding
Open (masking not used)
Who is / are masked / blinded?



Intervention assignment
Crossover
Other design features
Phase
Not Applicable
Type of endpoint/s
Efficacy
Statistical methods / analysis
The number of participants required to complete this study (16) was determined via a power calculation using an alpha of 0.05, beta of 0.1 and effect size of 0.78 calculated based on previously reported differences in rectal temperature change between hypohydrated and euhydrated individuals, across a 3-h heatwave simulation.

Data for change in rectal temperature, heart rate, whole body sweat rate, cumulative dehydration, rate pressure product, skin blood flow, forearm blood flow, local sweat rate, activated sweat gland density, thirst, thermal discomfort, whole body thermal sensation and plasma osmolality will be analysed via a 2-way repeated measures ANOVA with the repeated factors of time (4 levels: 0, 60, 120 and 180 minutes) and condition (4 levels: EUH-NF, EUH-F, HYP-NF and HYP-F). Additionally, a 1-way ANOVA will be employed to compare hydration indices (urine specific gravity, plasma osmolality and nude body mass change over the 24 h fluid restriction/ euhydration protocol) prior to each heatwave simulation. A 1-way ANOVA will also be used to compare whole body sweat losses and resultant dehydration levels across the full exposure for each intervention.

If significant main effects or interactions are found, independent differences will be assessed using a two-tailed paired Student’s t-tests while maintaining a fixed probability (5%) of making a type I error using a Sidak correction.

Recruitment
Recruitment status
Completed
Date of first participant enrolment
Anticipated
24/07/2020
Actual
27/07/2020
Date of last participant enrolment
Anticipated
31/05/2023
Actual
31/03/2023
Date of last data collection
Anticipated
30/06/2023
Actual
2/05/2023
Sample size
Target
16
Accrual to date
Final
16
Recruitment in Australia
Recruitment state(s)
NSW

Funding & Sponsors
Funding source category [1] 305813 0
University
Name [1] 305813 0
Discretionary research account held at the University of Sydney by Dr. Ollie Jay
Country [1] 305813 0
Australia
Funding source category [2] 316470 0
Government body
Name [2] 316470 0
National Health and Medical Research Council (NHMRC) Investigator Grant
Country [2] 316470 0
Australia
Primary sponsor type
University
Name
The University of Sydney
Address
The University of Sydney
Camperdown
NSW
2006
Country
Australia
Secondary sponsor category [1] 306372 0
None
Name [1] 306372 0
Address [1] 306372 0
Country [1] 306372 0

Ethics approval
Ethics application status
Approved
Ethics committee name [1] 306082 0
The University of Sydney Human Research Ethics Committee
Ethics committee address [1] 306082 0
Research Integrity & Ethics Administration
Research Portfolio
Level 3, F23 Administration Building
The University of Sydney, NSW, 2006
Ethics committee country [1] 306082 0
Australia
Date submitted for ethics approval [1] 306082 0
20/09/2019
Approval date [1] 306082 0
28/10/2019
Ethics approval number [1] 306082 0
2019/798

Summary
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.
Trial website
Trial related presentations / publications
Public notes

Contacts
Principal investigator
Name 102638 0
Prof Ollie Jay
Address 102638 0
Susan Wakil Health Building, University of Sydney, Western Ave, Camperdown NSW 2050
Country 102638 0
Australia
Phone 102638 0
+61 449116760
Fax 102638 0
Email 102638 0
[email protected]
Contact person for public queries
Name 102639 0
Ollie Jay
Address 102639 0
Susan Wakil Health Building, University of Sydney, Western Ave, Camperdown NSW 2050
Country 102639 0
Australia
Phone 102639 0
+61 449116760
Fax 102639 0
Email 102639 0
[email protected]
Contact person for scientific queries
Name 102640 0
A/Prof Ollie Jay
Address 102640 0
Susan Wakil Health Building, University of Sydney, Western Ave, Camperdown NSW 2050
Country 102640 0
Australia
Phone 102640 0
+61 449116760
Fax 102640 0
Email 102640 0
[email protected]

Data sharing statement
Will individual participant data (IPD) for this trial be available (including data dictionaries)?
Yes
What data in particular will be shared?
De-identified individual participant data underlying published results only.
When will data be available (start and end dates)?
Immediately following publication, no end date.
Available to whom?
Case-by-case basis at the discretion of the primary investigator.
Available for what types of analyses?
Meta-analysis.
How or where can data be obtained?
Access subject to approvals by the primary investigator with a requirement to sign a data access agreement. The primary investigator may be contacted via email at: [email protected].


What supporting documents are/will be available?

Doc. No.TypeCitationLinkEmailOther DetailsAttachment
8196Informed consent form    379895-(Uploaded-10-06-2020-13-12-04)-Study-related document.pdf
8197Ethical approval    379895-(Uploaded-10-06-2020-13-12-18)-Study-related document.pdf



Results publications and other study-related documents

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No documents have been uploaded by study researchers.

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