Temperature Control for Heat Stress

Overseen By Glen P Kenny, PhD

Age: 65+

Sex: Any

Trial Phase: Academic

Sponsor: University of Ottawa

Disqualifiers: Severe hypoglycemia, Uncontrolled hypertension, Serious diabetes complications, Cardiac abnormalities, others

No Placebo Group All trial participants will receive the active study treatment (no placebo)

Compensation: Varies

Number of Visits: 3

Duration: 3 days

18 Participants Needed

What You Need to Know Before You Apply

What is the purpose of this trial?

A recent report showed that maintaining indoor temperature at or below 26°C safeguards older, heat vulnerable adults against potentially dangerous increases in thermal and cardiovascular strain during an extreme heat event (PMID: 38329752). However, this proposed limit does not consider the potential cumulative effect of successive days of heat exposure, which could lead to a progressive deterioration in thermoregulatory and cardiovascular function and necessitate adjustments to upper indoor temperature limits. Further, thermal comfort and quality of sleep may be negatively impacted when bedroom temperatures exceed 24°C (PMID: 3090680). On this basis, some health agencies have recommended that bedroom temperatures at night should not exceed 26°C unless ceiling fans are available (PMID: 3090680). Currently, however, it is unknown whether indoor overheating impairs sleep quality and physiological strain on a subsequent day in older adults and, if so, whether maintaining indoor temperature at 26°C is sufficient to prevent these adverse health impacts. With rising global temperatures and more extreme heat events, energy management strategies to limit the strain on the power grid during the daytime are now increasingly commonplace. Thus, understanding the benefits of maintaining indoor temperature at the recommend upper limits of 26°C during the nighttime only on surrogate physiological indicators of health is an important step in understanding how to optimize protection for heat-vulnerable older adults when power outages occur. The investigators will assess the efficacy of proposed indoor temperature limits (i.e., 26°C) in mitigating increases in core temperature and cardiovascular strain over three consecutive days (3 days, 2 nights) in older adults (60-85 years) with (indoor temperatures maintained at the recommend 26°C at all times throughout the three days) and without (daytime temperature fixed at 34°C (temperature experienced in homes without air-conditioning during an extreme heat event) with nighttime temperature at 26°C) access to daytime cooling. By quantifying the effect of daylong indoor overheating on surrogate physiological outcomes linked with heat-related mortality and morbidity in older adults, the investigators can determine if refinements in the recommended upper temperature threshold is required, including best practices when power outages may occur during an extreme heat event.

Will I have to stop taking my current medications?

The trial protocol does not specify if you need to stop taking your current medications. However, if you or the investigators believe that your medication use or any changes in it make participation inadvisable, it may affect your eligibility.

Is temperature control for heat stress generally safe for humans?

The research highlights that exposure to high temperatures can lead to heat stress illnesses, such as heat stroke and heat exhaustion, especially in physically active individuals like military personnel and outdoor workers. While the studies focus on the risks associated with heat exposure, they emphasize the importance of monitoring and controlling heat exposure to prevent these illnesses, suggesting that temperature control measures are important for safety. ^{1 2 3 4 5}

How does the treatment 'Simulated multi-day heatwave exposure' differ from other treatments for heat stress?

This treatment is unique because it involves simulating a multi-day heatwave to study the effects of consecutive days of heat exposure, which is different from standard treatments that typically focus on immediate relief or prevention of heat stress. It aims to understand the cumulative physiological strain and recovery patterns, which is not commonly addressed in existing treatments. ^{1 6 7 8 9}

What data supports the effectiveness of the treatment Simulated multi-day heatwave exposure for Temperature Control for Heat Stress?

The research suggests that monitoring temperature and heat indices, like the wet bulb globe temperature (WBGT), can help in assessing and managing heat stress, which is relevant for understanding and controlling heat stress during simulated heatwave exposures. Additionally, wearable technology for predicting core body temperature can aid in early intervention to prevent heat-related illnesses, which may support the effectiveness of treatments involving heat exposure. ^{1 9 10 11 12}

Are You a Good Fit for This Trial?

This trial is for older adults aged 60-85 who can safely undergo simulated heatwave conditions. The study aims to understand how indoor temperatures affect their body's response to heat and sleep quality over three days. Specific eligibility criteria are not provided, but typically participants must be in stable health without conditions that could interfere with the trial.

Inclusion Criteria

Non-smoking

Ability to provide informed consent

I have had high blood pressure or type 2 diabetes for over 5 years.

Exclusion Criteria

Use of or changes in medication judged by the patient or investigators to make participation in this study inadvisable

Uncontrolled hypertension - BP >150 mmHg systolic or >95 mmHg diastolic in a sitting position

Cardiac abnormalities identified during screening

Timeline for a Trial Participant

Screening

Participants are screened for eligibility to participate in the trial

1-2 weeks

Treatment

Participants are exposed to indoor temperature limits over three consecutive days (3 days, 2 nights) to assess the efficacy of proposed indoor temperature limits in mitigating increases in core temperature and cardiovascular strain.

3 days

Continuous monitoring during the 3-day exposure

Follow-up

Participants are monitored for any delayed effects of the heat exposure and to assess recovery.

1 week

What Are the Treatments Tested in This Trial?

Interventions

• Simulated multi-day heatwave exposure

Trial Overview The study tests whether keeping indoor temperatures at or below 26°C during a simulated three-day heatwave helps reduce physical strain and improve sleep for older adults. Participants experience both constant recommended temperatures and higher daytime temperatures without cooling.

How Is the Trial Designed?

Group I: Exposure to indoor temperature limits nighttime only Experimental Treatment 1 Intervention

Participants exposed to three consecutive days (3 days, 2 nights) to indoor overheating during the daytime (34°C, temperatures experienced in homes without air-conditioning) (9:00 to 19:00) with nighttime (19:00 to 9:00) indoor temperatures reduced to the recommended limit of 26°C.

Group II: Exposure to indoor temperature limits daylong Experimental Treatment 1 Intervention

Participants exposed to three consecutive days (3 days, 2 nights) in an indoor environment maintained at either 26°C at all times (condition A, recommended upper indoor temperature limits during an extreme heat event).

Who Is Running the Clinical Trial?

University of Ottawa

Lead Sponsor

Trials

231

Recruited

267,000+

Published Research Related to This Trial

A study of 31,642 heat stress illness cases among active duty servicemembers from 1998 to 2019 found that higher daily heat indices, particularly maximum wet bulb globe temperature (WBGT) and heat index, significantly increase the risk of heat-related illnesses, with risks nearly doubling at higher temperatures.

The research suggests that prevention strategies should consider previous day's heat levels and monitor various heat indices, not just WBGT, to better assess risks and implement effective control measures for heat stress illnesses.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Heat stress morbidity among US military personnel: Daily exposure and lagged response (1998-2019). Lewandowski, SA., Shaman, JL.[2022]

Wearable technology and predictive algorithms show high accuracy in predicting core body temperature (CBT), with 17 out of 18 algorithms meeting clinical validity standards, which could help prevent heat-related illnesses (HRI) in high-intensity environments.

Despite the promising results, most algorithms do not account for individual and environmental factors that affect CBT, indicating a need for more personalized and robust machine learning methods to enhance prediction accuracy and improve intervention strategies.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Wearable Sensor Technology to Predict Core Body Temperature: A Systematic Review. Dolson, CM., Harlow, ER., Phelan, DM., et al.[2023]

This systematic review identified 340 thermal stress indicators (TSIs) developed from 200 BC to 2019, providing a comprehensive resource for understanding their applications in monitoring heat stress, especially for physically active individuals.

Out of the identified TSIs, 187 can be calculated using only meteorological data, with 61 specifically suitable for occupational settings, making them practical tools for on-site monitoring and climate service analytics.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Indicators to assess physiological heat strain - Part 1: Systematic review. Ioannou, LG., Mantzios, K., Tsoutsoubi, L., et al.[2022]

An early identification tool for heat injuries can prevent the worsening of conditions from heat stress to more severe issues like heat exhaustion and heat stroke.

This proactive approach is crucial for ensuring safety, especially in environments where heat-related illnesses are a risk.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Monitoring Heat Injuries in a Hazmat Environment. Brown, DB., Smith, MJ., Kirkland, JB.[2020]

Older adults (ages 61-78) experience significantly greater heat storage and elevated core temperatures compared to younger adults (ages 19-31) during prolonged exposure to high temperatures (40°C) for 9 hours, indicating a higher risk of heat-related health issues.

The study highlights that common health conditions in older adults, such as type 2 diabetes and hypertension, further exacerbate their vulnerability to heat stress, suggesting that impairments in thermoregulation contribute to increased risks during heat waves.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Physiological responses to 9 hours of heat exposure in young and older adults. Part I: Body temperature and hemodynamic regulation. Meade, RD., Notley, SR., Akerman, AP., et al.[2023]

A study analyzing data from 1991 to 2018 found that higher annual temperatures are positively associated with increased rates of heat stress illnesses (HSI) among active-duty soldiers, particularly for outpatient encounters, with a 1°F increase linked to a 16% rise in such cases.

While outpatient HSI cases increased with rising temperatures, hospitalization rates for heat-related illnesses showed mostly no significant change, suggesting that while soldiers may experience more heat-related issues, severe cases requiring hospitalization are not as affected.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Heat stress illness outcomes and annual indices of outdoor heat at U.S. Army installations. Lewandowski, SA., Kioumourtzoglou, MA., Shaman, JL.[2023]

This study monitored heat exposure in grounds maintenance workers across three different climates in the southeastern U.S. over a 5-day period, revealing that individual factors like access to cooling areas and education level significantly influenced the risk of heat strain.

The research found a nonlinear relationship between temperature and heat strain, indicating that higher temperatures increase heat strain risk, but this risk is also affected by workers' adaptive behaviors, such as taking breaks during heat warnings.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Evaluation of wearable sensors for physiologic monitoring of individually experienced temperatures in outdoor workers in southeastern U.S. Runkle, JD., Cui, C., Fuhrmann, C., et al.[2019]

A simulation model using Australian weather data revealed that children and the elderly, particularly females aged 75 and older, are at the highest risk of heat strain in hot climates.

The model indicates that while cloudy days are generally safer, older women still face significant heat strain risks on hot, cloudy days or when indoors during high temperatures, highlighting the need for targeted public health interventions.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Estimating risks of heat strain by age and sex: a population-level simulation model. Glass, K., Tait, PW., Hanna, EG., et al.[2018]

Exposure to extreme heat events significantly increases the risk of hospitalization for acute myocardial infarction (AMI), with a 11% higher odds on the day of hospitalization based on a study of 32,670 AMI cases in Maryland from 2000 to 2012.

The study highlights the need for community-specific strategies to address the varying vulnerability to heat-related AMI across different ethnic and geographic populations, especially as extreme weather events become more common due to climate change.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Summertime extreme heat events and increased risk of acute myocardial infarction hospitalizations. Fisher, JA., Jiang, C., Soneja, SI., et al.[2022]

In a study involving 26 firefighters, it was found that physiological heat strain, indicated by a higher core temperature, was significantly greater on the second day of back-to-back fire suppression work, despite no differences in hydration or heart rate between the two days.

Firefighters reported increased perceived exertion and thermal sensation on the second day, suggesting that even with full recovery, the demands of consecutive days of intense work can lead to greater heat strain and fatigue.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Heat Strain Is Exacerbated on the Second of Consecutive Days of Fire Suppression. Schlader, ZJ., Colburn, D., Hostler, D.[2022]

The heat stress standard ISO 7243, based on the wet bulb globe temperature index (WBGT), is a reliable and valid method for assessing hot environments globally, but it has limitations regarding metabolic heat estimation and clothing effects.

To enhance its applicability, especially outdoors, the standard recommends using a WBGT equation that factors in solar absorptivity and introduces a 'clothed WBGT' to better account for clothing effects.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Heat stress standard ISO 7243 and its global application. Parsons, K.[2022]

The study found that different heat stress assessment metrics significantly affect the estimated workability (WA) of labor in hot outdoor environments, with metrics like Wet Bulb Globe Temperature (WBGT) showing varying constraints based on workload and time of day.

Physiological models like Predicted Heat Strain (PHS) and Universal Thermal Climate Index (UTCI)-Fiala provide a more comprehensive understanding of cumulative physiological strain during extended work hours, suggesting that current WBGT standards may not adequately account for these factors.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Estimated work ability in warm outdoor environments depends on the chosen heat stress assessment metric. Bröde, P., Fiala, D., Lemke, B., et al.[2018]

Citations

1. United States pubmed.ncbi.nlm.nih.gov

Heat stress morbidity among US military personnel: Daily exposure and lagged response (1998-2019). [2022]

2. Switzerland pubmed.ncbi.nlm.nih.gov

Wearable Sensor Technology to Predict Core Body Temperature: A Systematic Review. [2023]

3. United States pubmed.ncbi.nlm.nih.gov

Indicators to assess physiological heat strain - Part 1: Systematic review. [2022]

4. United States pubmed.ncbi.nlm.nih.gov

Monitoring Heat Injuries in a Hazmat Environment. [2020]

5. United States pubmed.ncbi.nlm.nih.gov

Physiological responses to 9 hours of heat exposure in young and older adults. Part I: Body temperature and hemodynamic regulation. [2023]

6. United States pubmed.ncbi.nlm.nih.gov

Heat stress illness outcomes and annual indices of outdoor heat at U.S. Army installations. [2023]

7. Netherlands pubmed.ncbi.nlm.nih.gov

Evaluation of wearable sensors for physiologic monitoring of individually experienced temperatures in outdoor workers in southeastern U.S. [2019]

8. Switzerland pubmed.ncbi.nlm.nih.gov

Estimating risks of heat strain by age and sex: a population-level simulation model. [2018]

9. United States pubmed.ncbi.nlm.nih.gov

Summertime extreme heat events and increased risk of acute myocardial infarction hospitalizations. [2022]

10. United States pubmed.ncbi.nlm.nih.gov

Heat Strain Is Exacerbated on the Second of Consecutive Days of Fire Suppression. [2022]

11. Japan pubmed.ncbi.nlm.nih.gov

Heat stress standard ISO 7243 and its global application. [2022]

12. United States pubmed.ncbi.nlm.nih.gov

Estimated work ability in warm outdoor environments depends on the chosen heat stress assessment metric. [2018]