Session: 757 APS Thermal stress, thermoregulation, and hydration Poster Session
(757.26) Effects of passive heat exposure on myocardial blood flow in healthy young and older adults
Monday, April 4, 2022
10:15 AM – 12:15 PM
Location: Exhibit/Poster Hall A-B - Pennsylvania Convention Center
Poster Board Number: E475
Hadiatou Barry (Montreal Heart Institute, Montreal Heart Institute), Georgia Chaseling (Université de Montréal, Université de Montréal), Caroline D’Oliviera-Sousa (Montreal Heart Institute), François Harel (Montreal Heart Institute, Montreal Heart Institute), Matthieu Pelletier-Galarneau (Montreal Heart Institute, Montreal Heart Institute), Daniel Gagnon (Université de Montréal, Université de Montréal)
Presenting Author Montreal Heart Institute, Montreal Heart Institute Montréal, Quebec, Canada
INTRODUCTION. Extreme heat is associated with a greater risk of cardiovascular mortality in older adults (≥60 years). However, the pathophysiology that links extreme heat and cardiovascular mortality remains unknown. One possibility is that myocardial oxygen requirements during heat exposure cannot be met by sufficient increased in myocardial blood flow (MBF) thereby predisposing to ischemia. However, the extent to which MBF increases during heat exposure, and whether age alters this increase, is unknown. The objective of this study was to test the hypothesis that passive heat exposure increases MBF and that this increase is attenuated in healthy older adults.
METHODS. MBF was measured during passive heat exposure (water-perfused suit) in 15 young (27 years, range: 24-30) and 14 older (68 years, range: 64-72) healthy adults with 82-Rubidium positron emission tomography. Four MBF measurements were performed: prior to heat exposure (baseline) and at an increase in rectal temperature of 0.5°C, 1.0°C, and 1.5°C. Heart rate (ECG) and blood pressure (automated auscultation) were also measured to calculate rate pressure product (RPP; heart rate x systolic blood pressure). MBF reserve (MFR) was calculated by dividing the MBF at 1.5°C by baseline MBF.
RESULTS. Baseline MBF was 0.76 ± 0.19 mL/min/g in young adults and 0.88 ± 0.21 mL/min/g in older adults (p=0.14). MBF increased similarly in both groups during heat exposure (interaction, p=0.31). Nonetheless, older adults displayed a lower MFR at an increase in rectal temperature of 1.5°C (young: 2.3 ± 0.7 vs. older: 1.8 ± 0.4, p=0.03). The lower MFR in older adults was paralleled by an attenuated increase in RPP during passive heating (at +1.5°C, young: 6.8 ± 1.7 vs. older: 3.6 ± 2.2 bpm·mmHg·103, plt;0.01), due to a blunted increase in heart rate (young: 50 ± 12 vs. older: 34 ± 14 bpm, plt;0.01). When the change in MBF was plotted against the change in RPP, the slope of the regression lines did not differ between young (0.11 [95% CI; 0.07, 0.15]) and older (0.08 [95% CI; 0.04, 0.11] mL/g/min/ bpm·mmHg·103, p=0.24) adults.
CONCLUSION. These results show that passive heat exposure roughly doubles MBF in healthy young and older adults. Furthermore, the results demonstrate that the increase in MBF during passive heat exposure is not altered by age and is proportional to the increase in RPP.
