Identification of Critical Thermal Environments for Aged Adults

Study Overview
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Brief Summary
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This study evaluates critical environmental limits (temperature and humidity) above which older adults are unable to effectively thermoregulate. Participants will exercise in a series of different environmental conditions to identify combinations of temperature and humidity above which age-related physiological changes cause uncompensable heat stress, resulting in increased risk of heat illness.

Detailed Description
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The earth's climate is warming well above historical averages, and there is an increased frequency, duration, and severity of heat waves. At the same time, the world's population is rapidly aging. Aging is associated with reductions in thermoregulatory capacity due to reductions in sweating and skin blood flow. For this reason, people ≥65 years exhibit exponentially larger increases in morbidity and mortality during heat waves than younger individuals, with the large majority of excess deaths during heat waves occurring in the elderly. Compounding the physiological effects of primary aging, co-morbidities and common classes of drugs taken by older adults can further compromise their thermoregulatory function. One such class of medications is cyclooxygenase inhibitors, including aspirin (ASA) and other platelet inhibitors. Provocative data published by our lab indicate that platelet inhibitors including ASA increase the rate of heat storage during passive heat stress by  25%. Following current clinical guidelines, nearly 40% of US adults over the age of 50 engage in an aspirin therapy regiment for the primary or secondary prevention of cardiovascular disease. Although there is compelling evidence that aging is associated with decreased heat dissipation and elevated risk of heat illness in hot ambient conditions, the significant question remains: In what specific environments does this age disparity begin to occur? The goal of the current study is to identify and model ambient conditions that are unsafe for older adults. A second aim of the study is to determine the effects of the commonly used platelet inhibitor, acetylsalicylic acid (ASA), on age-specific critical environmental limits.

Official Title
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Identification of Critical Thermal Environments for Aged Adults

Conditions
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Aging

Intervention / Treatment
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* Drug: Low dose ASA
* Other: Control


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: Adults aged 18 and older (those 40+ years of age must be cleared by collaborating physician) All premenopausal women will be eumenorrheic (by survey) Asymptomatic and no signs/symptoms of disease according to the American College of Sports Medicine 10th edition Guidelines for Exercise Testing and Prescription Exclusion Criteria: Medications that affect thermoregulatory or cardiovascular responses to exercise Any contraindications to low intensity physical activity on the Physical Activity Readiness Questionnaire Any mobility restrictions that interfere with low intensity physical activity Pregnant or planning to become pregnant in the next 12 months Prior diagnosis of cancer, cardiovascular disease, diabetes, or metabolic syndrome Illegal/recreational drug use History of Chron's disease, diverticulitis, or similar gastrointestinal disease Abnormal resting or exercise electrocardiogram (ECG)

Ages Eligible for Study
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Minimum Age: 18 Years

Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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Accepts Healthy Volunteers

Study Plan
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How is the study designed?
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Design Details

Primary Purpose: Basic Science
Allocation: Randomized
Intervention Model: Single Group Assignment
Interventional Model Description: Two groups of subjects (young, older) participate in twelve experiments; experimental conditions consist of six different combinations of temperature and humidity and are performed at two different exercise intensities. The experiments are conducted in randomized order and are separated by a minimum of three days. A subgroup of older adults will be asked to complete all trials after taking daily low-dose aspirin for seven days, and aspirin will be continued until all trials are complete.
Masking: None (Open Label)


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Experimental: Critical Environmental Limits<br>Subjects will perform exercise at  200-300W with ambient temperature or humidity increasing every 5 min throughout the trial until core temperature begins to rise. | Other: Control<br>* All participants will be tested with no treatment.<br>|
| Experimental: Aspirin Supplementation<br>After a minimum of 7 days of daily, low-dose aspirin ingestion, older subjects will repeat critical environmental limits trials. As before, subjects will perform exercise at  200-300W with ambient temperature or humidity increasing every 5 min throughout the trial until core temperature begins to rise. | Drug: Low dose ASA<br>* A sub-group of older adults will be re-tested after 7 days of treatment with low-dose aspirin.<br>* Other names: Low-dose aspirin;|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Temperature and humidity limits for maintaining stable core temperature | Core temperature will be measured throughout exercise. The point at which heat stress becomes uncompensable will be determined for each environmental and exercise condition by assessing the combination of temperature and humidity at which core temperature begins to rise. | Through study completion, an average of 1 year. | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Core temperature | Core temperature will be monitored throughout each experimental visit | Continuous throughout visit until completion of exercise; an average of 2 hours. | 
| Sweat rate | Sweat rate will be determined by measuring nude body mass before and after each experimental visit | Immediately before and immediately after exercise. | 
| Skin temperature | Skin temperature will be monitored throughout each experimental visit | Continuous throughout visit until completion of exercise; an average of 2 hours. | 

 Terms related to the study
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Keywords Provided by Centre Hospitalier Valida
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Aging, Thermoregulation, Heat stress