Effects of passive heat exposure on myocardial blood flow in healthy young and older adults
Bibliographic record
Abstract
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 ± 1.7vs. older: 3.6 ± 2.2 bpm·mmHg·10 3 , p<0.01), due to a blunted increase in heart rate (young: 50 ± 12vs. older: 34 ± 14 bpm, p<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·10 3 ,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.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".