Heat exposure ups myocardial blood flow in adults

Myocardial blood flow (MBF) tends to double in heat-exposed individuals who show an increase of 1.5°C in core temperature, reveals a study.

Although “changes in MBF do not differ by age or presence of coronary artery disease (CAD), some older adults with CAD may experience asymptomatic myocardial ischaemia,” the investigators said.

Sixty-one individuals, which included 20 healthy young adults (mean age 28 years), 21 healthy older adults (mean age 67 years), and 20 older adults with CAD (mean age 70 years) participated in this laboratory-based study. Participants were exposed to heat until their core temperature rose by 1.5°C.

The investigators measured MBF prior to heat exposure and at every increase of 0.5°C in core temperature. MBF measured by PET-CT was the primary outcome, while secondary outcomes were heart rate, blood pressure, and body weight change.

At an increase of 1.5°C in core temperature, MBF also increased in healthy young adults (change, 0.8 mL/min/g, 95 percent confidence interval [CI], 0.5‒1.0), healthy older adults (change, 0.7 mL/min/g, 95 percent CI, 0.5‒0.9), and older adults with CAD (change, 0.6 mL/min/g, 95 percent CI, 0.3‒0.8), which corresponded to a 2.08-fold, 1.79-fold, and 1.64-fold change from pre-exposure values.

Notably, post hoc analyses revealed imaging evidence of asymptomatic heat-induced myocardial ischaemia in seven adults with CAD (35 percent).

This study had certain limitations. First, heating was limited to about 100 min. Second, participants faced restrictions in movement and fluid intake. Finally, participants refrained from strenuous exercise and smoking; ceased alcohol and caffeine intake; and suspended their use of beta-blockers, calcium-channel blockers, and nitroglycerin before heating.

“Heat extremes are associated with greater risk for cardiovascular death,” the investigators said.