Ignite Creation Date:
2024-05-06 @ 7:19 PM
Last Modification Date:
2024-10-26 @ 3:04 PM
Study NCT ID:
NCT05963529
Status:
COMPLETED
Last Update Posted:
2023-11-29
First Post:
2023-07-13
Brief Title:
Validity of Humidity Ramp Protocols for Identifying Limits of Survivability in Heat-exposed Persons
Sponsor:
University of Ottawa
Organization:
University of Ottawa
Study Overview
Official Title:
Evaluating the Validity of a Rapid Humidity Ramp Protocol for Identifying the Upper Environmental Limits of Thermal Compensation in Humans
Status:
COMPLETED
Status Verified Date:
2023-11
Last Known Status:
None
Delayed Posting:
No
If Stopped, Why?:
Not Stopped
Has Expanded Access:
False
If Expanded Access, NCT#:
N/A
Has Expanded Access, NCT# Status:
N/A
Acronym:
None
Brief Summary:
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 ie 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 ie the temperatureshumidities 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 eg 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 eg 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 42C 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 42C with RH 5 below their individual inflection point below-inflection condition ii 42C with RH 5 above their individual inflection point above-inflection condition and iii 26C 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
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 eg 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 42C 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 42C with RH 5 below their individual inflection point below-inflection condition ii 42C with RH 5 above their individual inflection point above-inflection condition and iii 26C 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
Detailed Description:
None
Study Oversight
Has Oversight DMC:
None
Is a FDA Regulated Drug?:
False
Is a FDA Regulated Device?:
False
Is an Unapproved Device?:
None
Is a PPSD?:
None
Is a US Export?:
None
Is an FDA AA801 Violation?:
None