Passive Heat Therapy and Age-associated Physiological Function

Study Overview
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Brief Summary
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This study aims to determine the effects of 8-10 weeks of repeated hot water immersion (heat therapy) vs. thermoneutral water immersion on vascular function in late middle-aged to older (55-79 years) adults.

Detailed Description
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Advancing age is the primary risk factor for cardiovascular diseases (CVD), which remain the leading cause of death in the developed world. The key process that links aging to increased risk of CVD is the development of arterial dysfunction, including impaired endothelial function and arterial stiffening. In addition, age-associated impairments in arterial function have been linked to other diseases/disorders of aging, including cognitive impairments, Alzheimer's disease and dementia, and motor disorders/disability. Passive heat therapy, in the form of repeated use of hot baths and saunas, has been used by several cultures for centuries; however, the physiological benefits are only now being elucidated. For example, recent studies have found that lifelong habitual sauna use is associated with considerably reduced risk of all-cause mortality, sudden cardiac death, CVD-related death, and Alzheimer's disease and dementia. In addition, 8-10 weeks of hot water immersion in young adults has been shown to improve endothelial function and reduces arterial stiffness and blood pressure. Therefore, the investigators expect heat therapy to similarly improve vascular function, as well as cognitive and motor function, in middle-aged to older adults who are at greater risk of CVD and related diseases/disorders.

Official Title
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Passive Heat Therapy and Age-associated Physiological Function

Conditions
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Aging

Intervention / Treatment
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* Behavioral: Heat therapy
* Behavioral: Thermoneutral water immersion


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: Ability to provide informed consent. Aged 55-79 years. Women must be postmenopausal and not taking hormone replacement therapy within the past year. Sedentary to recreationally active: participating in vigorous aerobic exercise <4x/wk for ≥ 3 yrs. Able to refrain from the use of dietary supplements, anti-inflammatory medications, and prescription medications for 24-48h prior to experimental testing. Generally healthy (no overt clinical disease), as determined by medical history, physical examination, blood and urine chemistries. Ankle-brachial blood pressure index >0.7 Total cholesterol <240 mg/dl (<6.2 mmol/L) Fasting plasma glucose <126 mg/dl (<7.0 mmol/L) Systolic blood pressure < 160 mmHg and >100 mmHg Glomerular filtration rate > 60 ml/min/1.73 m2 Mini mental state exam score > 20 points Body mass index (BMI) <30 kg/m2 Weight stable in the prior 3 months (≤ 2 kg weight change) and willing to remain weight stable over the course of the study Free from alcohol dependence or abuse, as defined by the American Psychiatry Association, Diagnostic and Statistical Manual of Mental Disorders (DSM-IV). Exclusion Criteria: Current use of certain prescription medications that may interfere with thermoregulation and/or blood pressure control during heat stress. These include anti-hypertensives (in particular beta-blockers), nitrates and nitrites (e.g. nitroglycerin), PDE5 inhibitors (e.g. Viagra), anticholinergics (e.g. amitriptyline), and alpha-blockers (e.g. Flomax). Orthostatic hypotension Current or past smoking within the last 5 years Recent major change in health status within previous 6 months (i.e. surgery, significant infection or illness). Chronic clinical diseases (e.g., inflammatory bowel diseases/irritable bowel syndrome, coronary artery/peripheral artery/cerebrovascular diseases, diabetes, chronic kidney disease requiring dialysis, neurological disorders or diseases that may affect motor/cognitive functions [multiple sclerosis, Parkinson's disease, polio, Alzheimer's disease, dementia or other brain diseases of aging]). History of heat-related illness Open wounds or skin lesions. History of skin-related conditions or sensitivities to prolonged water immersion or exposure to pool chemicals. Blood donation within the past 2 months Inability to tolerate blood draws, intravenous catheters, and/or fingertip blood sampling, including past fainting in response to blood sampling. Rectal, anal, vaginal, or prostate surgery within the last 6 months, current or recent (within the last 6 months) hemorrhoids, or related concerns regarding use of rectal thermistor

Ages Eligible for Study
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Minimum Age: 55 Years
Maximum Age: 79 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: Parallel Assignment
Interventional Model Description: Randomized, controlled (parallel design), single-blind
Masking: Single


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Experimental: Heat therapy<br>Hot water immersion 3-4x per week for 8-10 weeks | Behavioral: Heat therapy<br>* 30 sessions (3-4x per week for 8-10 weeks) of hot water immersion in 40°C water, sufficient to raise body core temperature to 38.5°C.<br>|
| Sham Comparator: Thermoneutral water immersion<br>Thermoneutral water immersion 3-4x per week for 8-10 weeks | Behavioral: Thermoneutral water immersion<br>* 30 sessions (3-4x per week for 8-10 weeks) of hot water immersion in 36°C water to prevent changes in body core temperature >0.2°C.<br>|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Brachial artery flow-mediated dilation | Measure of endothelial function | 0 and 8 weeks | 
| Carotid-femoral pulse wave velocity | Measure of central arterial stiffness | 0 and 8 weeks | 
| Mean arterial blood pressure | Brachial artery blood pressure, measured in triplicate (and averaged) following 20 min of supine rest | 0 and 8 weeks | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Cerebrovascular reactivity | Measure of cerebral vascular function; magnitude of increase in blood flow through the middle cerebral artery in response to breathing 5% CO2 | 0 and 8 weeks | 
| Fluid cognition composite score | Multiple domains of cognitive function (incl. executive function, memory, processing speed) assessed using the NIH toolbox (aggregated into one reported value) | 0 and 8 weeks | 
| Motor function composite score | Multiple domains of motor function (incl. endurance, strength, dexterity) assessed using the NIH toolbox (aggregated into one reported value) | 0 and 8 weeks | 

 Terms related to the study
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Keywords Provided by Centre Hospitalier Valida
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endothelial function, arterial stiffness, heat, hot water immersion