This study aims to determine the effects of \~12 weeks of repeated hot water immersion ("heat therapy") vs. thermoneutral water immersion on blood pressure and vascular function in late middle-life to older (≥40 years) adults. The study also aims to determine the effects of \~12 weeks of heat therapy on fluid cognitive and cerebrovascular function.
Able to provide informed consent (no clinical diagnosis of dementia or related diseases AND mini mental state exam score >20).
Willing to accept random assignment to intervention.
Aged 40+ years.
Premenopausal women must not be pregnant (confirmed by urine pregnancy test).
Individuals taking 3+ anti-hypertensive medications (rationale: these individuals typically have resistant or secondary hypertension. Individuals taking 1-2 anti-hypertensive medications will still be included, with the exception of beta-blockers.)
SBP 140-159 mmHg but not on anti-hypertensive medications. (rationale: ACC/AHA guidelines indicate that immediate pharmacotherapy is advised for these individuals. Potential subjects with SBP in this range will discuss options/receive recommendations from a CTRC physician and be referred to their primary care provider. If they begin anti-hypertensive medication, they will be eligible to participate in the study after they have been on them for at least 3 months, assuming they still qualify. If they decide not to begin anti-hypertensive medications, they must receive approval for their primary care provider that it is ok for them to participate in the study.)
Regular vigorous aerobic/endurance exercise: >4 bouts per week for >30 min per bout at a workload of >10 METS, determined based on screening surveys and workload confirmed by MAQ during Visit 1. (rationale: aerobic exercise training independently lowers blood pressure and improves arterial function33,74,75).
Body mass index (BMI) >40 kg/m2 (rationale: BP and vascular measurements can be inaccurate in severely obese subjects and these subjects may differ in many ways from normal weight, overweight, or less obese subjects).
Parallel
Heat therapy
Other intervention36 sessions (\~3x per week for 12 weeks) of hot water immersion in 40°C water, sufficient to raise body core temperature to 38.5°C, and 12 weeks of follow-up.
Thermoneutral water immersion
Other intervention36 sessions (\~3x per week for 12 weeks) of thermoneutral water immersion in 36°C water to prevent changes in body core temperature \>0.2°C, and 12 weeks of follow-up.
Change in casual systolic blood pressure from baseline to 2, 4, 6, 8, 10, and 12 weeks of heat therapy, and 4 and 12 weeks of follow-up.
Casual brachial artery systolic blood pressure, measured in triplicate (and averaged)
Change in 24-hour ambulatory systolic blood pressure from from baseline to 2, 4, 6, 8, 10, and 12 weeks of heat therapy, and 4 and 12 weeks of follow-up.
Brachial artery systolic blood pressure measured over 24 hours with an ambulatory monitor
Change in brachial artery flow-mediated dilation from baseline to 2, 4, 6, 8, 10, and 12 weeks of heat therapy, and 4 and 12 weeks of follow-up.
Measure of endothelial function
Change in carotid-femoral pulse wave velocity from baseline to 2, 4, 6, 8, 10, and 12 weeks of heat therapy, and 4 and 12 weeks of follow-up.
Measure of large elastic artery stiffness
Change in carotid artery beta-stiffness index from baseline to 2, 4, 6, 8, 10, and 12 weeks of heat therapy, and 4 and 12 weeks of follow-up.
Measure of large elastic artery stiffness
Safety of heat therapy, as assessed by recording incidence of adverse events
Safety, i.e., risk to the subject, will be assessed by recording incidence of adverse events, which will be defined as any heat-related symptom or event (e.g., lightheadedness, low SBP or high HR) that results in the subject either sitting up early (if previously fully submerged) or being removed from the tub early.
Tolerability of heat therapy, as assessed by the rate at which enrolled subjects drop out due to adverse events.
Tolerability of heat therapy, i.e., the degree to which overt adverse effects can be tolerated by our subjects, will be assessed by the rate at which enrolled subjects drop out due to adverse events.
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