An interventional study of Humidity-ramp protocol and Above-inflection fixed-condition exposure in Heat Stress, Heat Exposure and Temperature Change, Body, sponsored by University of Ottawa. Completed at 1 site in Canada. Open to participants aged 18 Years to 85 Years, including healthy volunteers. Per ClinicalTrials.gov, last updated 2023-11-29.
Sponsored by University of Ottawa · Not applicable, Interventional, and Basic science
The global populace is at growing risk of heat-related illness due to climate change and accompanying increases in the intensity and regularity of extremely hot temperatures. In heat-exposed persons, heat gain from the environment and metabolism initially exceeds the rate of heat dissipation from the skin. Heat is stored in the body, causing core and skin temperatures to rise, which in turn triggers autonomically mediated elevations in cutaneous blood flow and sweating to facilitate heat loss. If conditions are compensable, heat loss increases until it balances total heat gain. At this point, the rate of heat storage falls to zero (i.e., heat balance is achieved) and body temperature stabilizes, albeit at a level elevated from thermoneutral conditions. If, however, the maximal achievable rate of heat dissipation is insufficient to offset heat gain, conditions are uncompensable, and prolonged exposure will cause a continual rise in core temperature that can compromise health if left unchecked. The environmental limits of compensability (i.e., the temperatures/humidities above which heat balance can not be maintained) are therefore an important determinant of survival during prolonged heat exposure. Evaluating this limit and how it can be modified (e.g., by behavior or individual factors like age or sex) is an increasingly important and active field of study.
Contemporary evaluations of the environmental limits of compensability utilize "ramping protocols" in which participants are exposed to increasing levels of temperature or humidity (in 5-10 min stages) while core temperature is monitored. It is generally observed that core temperature is relatively stable (or rises slightly) in the early stages of exposure but undergoes an abrupt and rapid increase as heat stress becomes more severe. The conditions (e.g., wet-bulb temperature or wet-bulb globe temperature) at this "inflection point" are taken as the limits of compensability. That is, it is assumed that inflection corresponds to the demarcation point, below which core temperature would remain stable for prolonged periods (theoretically indefinitely if hydration is maintained) but above which heat loss is insufficient to offset heat gain, causing core temperature to rise continuously. Despite the increasing use of these protocols, no study has clearly demonstrated their validity for identifying the environmental limits of compensability. The goal of this project is therefore to assess the validity of ramping protocols for determining the ambient conditions above which thermal compensation is not possible.
Enrolled participants will complete four experimental trials in a climate-controlled chamber: one ramping protocol followed by three randomized fixed-condition exposures. In the ramping protocol, participants will rest in 42°C with 28% relative humidity (RH) for 70 min, after which RH will be increased 3% every 10 min until 70% RH is achieved. The core (esophageal) temperature inflection point will be determined. For the fixed-condition exposures, participants will rest in i) 42°C with RH \~5% below their individual inflection point (below-inflection condition), ii) 42°C with RH \~5% above their individual inflection point (above-inflection condition), and iii) 26°C with 45% RH (control condition). Comparing the rate of change in esophageal temperature between each fixed-condition exposure will provide important insight into the validity of ramping protocols for identifying the limits of compensability.
118 studies on the registry are indexed under Heat Stress Disorders; 45 are open to participants now.
This study's enrollment of 12 is below the median of 24 across 104 interventional studies indexed under Heat Stress Disorders.
Browse Heat Stress Disorders studies →University of Ottawa is the lead sponsor of 125 studies on the registry; 34 are open to participants now.
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Exclusion Criteria:
Underlined terms in the criteria open these too. Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Before you join, the study team explains what taking part involves — its purpose, what happens, the risks and possible benefits — and answers your questions, so you can decide freely. Consent is usually recorded on a form (the informed consent form, ICF) signed by you or, where the law allows, by someone legally authorised to decide for you.
You can keep asking questions during the study, you are told of new information that matters, and you can choose to leave at any time.
Informed consent
Before you join, the study team explains what taking part involves — its purpose, what happens, the risks and possible benefits — and answers your questions, so you can decide freely. Consent is usually recorded on a form (the informed consent form, ICF) signed by you or, where the law allows, by someone legally authorised to decide for you.
You can keep asking questions during the study, you are told of new information that matters, and you can choose to leave at any time.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Healthy male and female volunteers. Participants will complete all exposures. The humidity-ramp protocol will necessarily be performed first. The order of the fixed-condition exposures will be randomized.
Other: Humidity-ramp protocol
Healthy male and female volunteers. Participants will complete all exposures. The humidity-ramp protocol will necessarily be performed first. The order of the fixed-condition exposures will be randomized.
Other: Above-inflection fixed-condition exposure
Healthy male and female volunteers. Participants will complete all exposures. The humidity-ramp protocol will necessarily be performed first. The order of the fixed-condition exposures will be randomized.
Other: Below-inflection fixed-condition exposure
Healthy male and female volunteers. Participants will complete all exposures. The humidity-ramp protocol will necessarily be performed first. The order of the fixed-condition exposures will be randomized.
Other: Control fixed-condition exposure
Participants are exposed to 42°C and 28% relative humidity for 70 minutes. Thereafter, humidity is increased 3% until an ambient humidity of 70% is achieved. The humidity at which esophageal temperature (and rectal temperature and heart rate) inflect is subsequently determined.
After a 1 hour equilibrium at 42°C and 28% relative humidity, humidity will be increased 3% every 10 min until it is \~5% higher than the participants' individual esophageal temperature inflection point identified in the humidity ramp protocol. These conditions will be held constant for the remainder of the 9-hour exposure period (starting from the beginning of equilibrium). Tap water will be provided at regular intervals to limit dehydration.
After a 1 hour equilibrium at 42°C and 28% relative humidity, humidity will be increased 3% every 10 min until it is \~5% lower than the participants' individual esophageal temperature inflection point identified in the humidity ramp protocol. These conditions will be held constant for the remainder of the 9-hour exposure period (starting from the beginning of equilibrium). Tap water will be provided at regular intervals to limit dehydration.
Participants are exposed for 9-hours to 28°C with 35% relative humidity. Participant will be allowed to drink tap water ad libitum.
Esophageal temperature rate of change
Rate of change of esophageal temperature measured over the final 2-hours of heat exposure
Time frame: End of fixed-condition heat exposure (hour 9 or termination)
Predicted time until 40.2°C esophageal temperature
Estimated time for esophageal temperature to reach 40.2°C, a commonly-cited criteria for severe heat-illness (e.g., heat stroke), calculated from the end-exposure esophageal temperature and its rate of change (assuming this rate of change is sustained)
Time frame: End of fixed-condition heat exposure (hour 9 or termination)
Rectal temperature rate of change
Rate of change of rectal temperature measured over the final 2-hours of heat exposure
Time frame: End of fixed-condition heat exposure (hour 9 or termination)
Predicted time until 40.2°C rectal temperature
Estimated time for rectal temperature to reach 40.2°C, a commonly-cited criteria for
Time frame: End of fixed-condition heat exposure (hour 9 or termination)
Number of participants unable to finish fixed-condition heat exposure
Number of participants who could not complete each fixed-condition heat exposure due to participant withdrawal or achieving a core temperature of 39.5°C
Time frame: End of fixed-condition heat exposure (hour 9 or termination)
Mean skin temperature rate of change
Rate of change of skin temperature measured over the final 2-hours of heat exposure
Time frame: End of fixed-condition heat exposure (hour 9 or termination)
Heart rate rate of change
Rate of change of heart rate measured over the final 2-hours of heat exposure
Time frame: End of fixed-condition heat exposure (hour 9 or termination)
Esophageal temperature
Esophageal temperature at the end of the fixed-condition exposures
Time frame: End of fixed-condition heat exposure (hour 9 or termination)
Rectal temperature
Rectal temperature at the end of the fixed-condition exposures
Time frame: End of fixed-condition heat exposure (hour 9 or termination)
Mean skin temperature
Mean skin temperature at the end of the fixed-condition exposures
Time frame: End of fixed-condition heat exposure (hour 9 or termination)
Heart rate
Heart rate at the end of the fixed-condition exposures
Time frame: End of fixed-condition heat exposure (hour 9 or termination)
Thermal sensation
Self-reported thermal sensation at the end of the fixed-condition exposures using and 8-point scale ranging from neutral (0) to extremely hot (8).
Time frame: End of fixed-condition heat exposure (hour 9 or termination)
Sweat rate
Sweat rate at the end of the fixed-condition exposures (calculated via change in body weight)
Time frame: End of fixed-condition heat exposure (hour 9 or termination)
Net fluid loss
Net fluid loss estimated as the percentage change in body mass over the fixed-condition exposures.
Time frame: End of fixed-condition heat exposure (hour 9 or termination)
Esophageal temperature inflection point
Inflection point for esophageal temperature during the humidity-ramp protocol
Time frame: During the ramp protocol (up to 2.5 hours)
Rectal temperature inflection point
Inflection point for rectal temperature during the humidity-ramp protocol
Time frame: During the ramp protocol (up to 2.5 hours)
Heart rate inflection point
Inflection point for heart rate during the humidity-ramp protocol
Time frame: During the ramp protocol (up to 2.5 hours)
Plan to share: Yes — De-identified participant data will be made available upon reasonable request and signed access agreement.
Supporting information: Study protocol, Statistical analysis plan, Analytic code
Time frame: Data will be made available following publication of the primary study report.
Access criteria: Reasonable request and signed access agreement
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This study is completed, as verified in Nov 2023. You cannot join it, but the record below documents what was studied.
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