Are electric fans effective for keeping people cool in both very-hot-and-dry and hot-and-humid heatwaves?

INTERVENTION: Two target heatwave conditions will be tested: 46degC with 10% relative humidity and 40degC with 50% relative humidity. All participants will be exposed to both conditions two times: once with an electric fan for cooling and once without (control trial). All participants will complete four experimental trials in total. For each of the four experimental trials, participants will arrive at the laboratory, be instrumented in temperate ( 22degC) conditions outside of the climatic chamber, have their pre‐exposure body weight measured, then will enter the climatic chamber set to one of the two environmental conditions, where they will sit passively for 2 hours before re‐measuring their body mass, then exiting the climatic chamber to be de‐instrumented. In all four trials, participants will be given 250 ml of cool ( 22degC) tap water, at 30, 60 and 90 min of exposure (750 ml total water consumption throughout the entire two‐hour exposure). In the conditions using an electric fan, a common 44.5 cm diameter standing floor fan will be placed 1.25 meters in front of the participants and placed on the “highâ€? setting, eliciting an air speed of approximately 2.0 meters per second. The fan will be turned on immediately following the participants assuming their seated position within the climatic chamber and will remain on throughout the 2‐hour exposure. For safety purposes, as well as to ensure the participant remains seated throughout the 2 hour exposure and the exact experimental protocol is followed, one member of the research team will remain inside the climatic chamber with the participant at all times, while a second research team member will remain outside of the climate chamber, in order to provide assistance, in case it is needed. At least 24 hours will separate all experimental trials and all four experimental trials will be completed within a one‐month period, in order to minimize seasonal variations in physiological responses. Only data from participant CONDITION: Cardiovascular ‐ Other cardiovascular diseases Heat‐related illness;Hyperthermia;Heat‐related cardiovascular strain;Thermal discomfort;Dehydration; ; Heat‐related illness ; Hyperthermia ; Heat‐related cardiovascular strain ; Thermal discomfort ; Dehydration Injuries and Accidents ‐ Other injuries and accidents Metabolic and Endocrine ‐ Normal metabolism and endocrine development and function Public Health ‐ Other public health SECONDARY OUTCOME: Heart rate ‐ will be measured using 3‐lead electrocardiography (Vrije Universiteit Ambulatory Monitoring System, Amsterdam, Netherlands).[Changes from baseline following two hours of passive heat exposure.] Systolic blood pressure ‐ will be measured using an automatic blood pressure cuff (Tango M2, SunTech Medical, Morrisville, USA).[Changes from baseline following two hours of passive heat exposure.] Whole‐body thermal discomfort ‐ will be recorded on a hand‐scored 120 mm visual analogue scale with anchor points every 30 mm which consisted of: not uncomfortable, slightly uncomfortable and very uncomfortable.[Changes from baseline following two hours of passive heat exposure.] INCLUSION CRITERIA: Healthy young adult males who are healthy (no self‐reported history of respiratory, metabolic, cardiovascular, blood pressure disease, or of diabetes and not currently on any medication related to these conditions). Non‐smokers. PRIMARY OUTCOME: Rate pressure product ‐ will be calculated by multiplying systolic blood pressure (measured using an automatic blood pressure cuff; Tango M2, SunTech Medical, Morrisville, USA) by heart rate (measured using 3‐lead electrocardiography; Vrije Universiteit Ambulatory Monitoring System, Amsterdam, Netherlands) in order to best characterise cardiovascular strain.[Change from baseline following two hours of passive heat exposure.] Rectal temperature ‐ will be measured using a paediatric thermistor probe (Mon‐a‐therm General Purpose Temperature Probe 400TM, Covidien, Mansfield, USA) inserted to a minimum of 12 cm past the anal sphincter. Data will be recorded every five seconds and displayed in real‐time on a personal computer. ; ; Potential risks: Elevations in core temperature are much smaller with passive heating (i.e. sitting in a hot environment) compared to active heating (i.e. exercise) as core temperature will not increase until the body’s heat loss mechanisms can no longer offset the heat gain from the environment. Indeed in a similar study in hot and humid conditions, the highest core temperature observed in any participant was 37.62°C and the largest change in core temperature was 1.08°C. As such, risks of hyperthermia related injuries in the present investigation are minimal. Nevertheless, there is always some risk that accompanies an elevation in core temperature and dehydration due to sweat loss. Worst‐case scenario risks include: headache, weakness, dizziness, nausea, hyperventilation, hypotension, confusion, diarrhoea, vomiting and loss of consciousness. These symptoms however, are unlikely under the present experimental conditions. In order to minimize these risks, the participant will be under close examination by the investigators during all protocols, additionally core body temperatures will be monitored continuously during the experimental trials, and the trials will be ended if a rectal temperature of 39.0°C is reached. If the participant becomes light‐headed or dizzy, the protocol will be stopped. A bathtub filled with cool water will be present in the climate chamber throughout testing and if at any time a participant becomes hyperthermic and/or display symptoms of hyperthermic illness, they will be quickly de‐instrumented and helped into the bathtub to be cooled down. After initial cooling, the participant will be moved to an examination bed in an adjacent room maintained at a comfortable ambient temperature where the participant will be laid in the supine position, cooled with cold towels, and given a commercially available sports drink in order to rehydrate and maintain blood sugar.[Change from baseline following two hours of passive heat exposure.] Whole‐body sweat losses ‐ will be calculated from the difference in pre and post exposure body mass measurements taken on a platform scale (Id1 multirange, Mettler‐Toledo; accurate to 2 grams), corrected for weight gain through fluid ingestion and sweat trapped in clothing. [Total sweat loss following two hours of heat exposure.]