Impact of Extreme Heat on Myocardial Blood Flow and Flow Reserve in Young and Older Adults

Extreme heat causes a disproportionate number of hospitalizations and deaths in older adults relative to any other age group. Importantly, many hospitalizations and deaths are primarily due to cardiovascular events such as myocardial infarction. Previous data indicate that older adults have attenuated skin blood flow and sweating responses when exposed to heat, resulting greater increase in core body temperature. Despite these observations, relatively little is known about the risk for myocardial ischemia potentially contributing to the aforementioned higher morbidity and mortality in older adults during heat waves. The broad objective of this work is to determine the impact of ambient heat exposure on myocardial blood flow and flow reserve in young and older adults. Aim 1 will test the hypothesis that older adults exhibit attenuated myocardial flow reserve compared to young adults during heat stress. Aim 2 will determine if the percent of maximal myocardial flow reserve (assess via vasodilator stress) during heat exposure is higher in older adults compared to young adults. The expected outcome from this body of work will improve our understanding of the consequences of aging on cardiovascular responses to ambient heat stress.

Study Overview

• Status: Recruiting
• Conditions: Hyperthermia; Aging; Heat Stress; Heat Strain
• Intervention / Treatment: Other: Ambient heat stress

• Study Type: Observational
• Enrollment (Estimated): 24

Contacts and Locations

• Study Contact: Name: Zachary McKenna, PhD; Phone Number: 214-345-6557; Email: ZacharyMckenna@texashealth.org
• Study Contact Backup: Name: Taysom Wallace, MS; Phone Number: 214-345-5022; Email: taysomwallace@texashealth.org

Study Locations

• United States
  • Texas
    • Dallas, Texas, United States, 75231
      • Recruiting
      • Texas Health Presbyterian Hospital Dallas

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult; Older Adult
• Accepts Healthy Volunteers: Yes

• Sampling Method: Non-Probability Sample

Study Population

The study population will be healthy younger and older individuals identified from the general population.

Description

Inclusion Criteria:

• Healthy male and female individuals
• 18-35 years or 65+ years of age
• Free of any underlying moderate to serious medical conditions

Exclusion Criteria:

• Known heart disease; other chronic medical conditions requiring regular medical therapy including cancer, diabetes, neurological diseases, uncontrolled hypertension, and uncontrolled hypercholesterolemia.
• Taking of any medications (such as beta blockers and non-dihydropyridine calcium channel blockers) that have known influences on either cardiac function or sweating responses.
• Abnormalities detected on routine screening.
• Current smokers, as well as individuals who regularly smoked within the past 3 years.
• Body mass index of greater than 30 kg/m^2
• Pregnant individuals

Study Plan

How is the study designed?

Number of groups / cohorts

2

Cohorts and Interventions

Group / Cohort	Intervention / Treatment
Older participants; Individuals aged 65 years or older	Other: Ambient heat stress; 3-hour ambient heating in 44°C and 20% relative humidity
Young participants; Individuals aged 18-39 years	Other: Ambient heat stress; 3-hour ambient heating in 44°C and 20% relative humidity

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Myocardial flow reserve	Measured via myocardial contrast echocardiography.	The difference in the change from baseline to a vasodilator stress test and the change from baseline to after 3-hours of heat stress.
Myocardial blood flow	Measured via myocardial contrast echocardiography.	The change from baseline to after 3 hours of heat stress.

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Core temperature	Measured via ingestible telemetric pill.	The change from baseline to after 3 hours of heat stress..
Indices of left and right ventricular function	Measured via echocardiography.	At baseline and after 3 hours of heat stress.
Heart rate	Measured via electrocardiogram.	At baseline, during exercise- after 20 minutes and 2 hours in the heat, and at rest after 3 hours of heat stress.
Blood pressure	Measured via automated auscultation of the brachial artery.	At baseline, during exercise- after 20 minutes and 2 hours in the heat, and at rest after 3 hours of heat stress.

Collaborators and Investigators

• Sponsor: University of Texas Southwestern Medical Center
• Collaborators: National Institute on Aging (NIA); The American Society of Echocardiography

Study record dates

Study Major Dates

• Study Start (Actual): February 3, 2025
• Primary Completion (Estimated): February 1, 2026
• Study Completion (Estimated): February 1, 2027

Study Registration Dates

• First Submitted: February 18, 2025
• First Submitted That Met QC Criteria: February 18, 2025
• First Posted (Actual): March 25, 2025

Study Record Updates

• Last Update Posted (Actual): March 25, 2025
• Last Update Submitted That Met QC Criteria: February 18, 2025
• Last Verified: February 1, 2025

More Information

Terms related to this study

• Additional Relevant MeSH Terms: Wounds and Injuries; Body Temperature Changes; Heat Stress Disorders; Hyperthermia
• Other Study ID Numbers: STU_2019_1759_MCE; 1R01AG069005 (U.S. NIH Grant/Contract)

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No
• product manufactured in and exported from the U.S.: No