Myocardial blood flow during passive heat exposure in healthy young adults
Bibliographic record
Abstract
INTRODUCTION Extreme heat events, such as heatwaves, are associated with a greater risk of cardiovascular mortality. However, the pathophysiology that links extreme heat and cardiovascular mortality remains unknown. Upon exposure to a hot environment, cardiac contractility and heart rate increase thereby presumably increasing myocardial metabolism. Although greater oxygen extraction contributes, an increase in myocardial metabolism is primarily met by greater myocardial blood flow. It is therefore conceivable that the required myocardial blood flow during heat exposure exceeds the capacity for myocardial blood flow to increase in vulnerable individuals. However, the extent to which myocardial blood flow increases during heat exposure is unknown. The purpose of this study is to test the hypothesis that passive heat exposure increases myocardial blood flow. METHODS Five healthy adults (31 ± 3 years, 2 women/3 men) participated in 1 experimental visit during which myocardial blood flow was measured by positron emission computed/tomography. Measurements were performed at baseline and during passive heat stress (water‐perfused suit with water at 50°C) at an increase in core (rectal) temperature of 0.5°C, 1.0°C, and 1.5°C. Heart rate and rhythm (ECG) and blood pressure (automated auscultation) were also measured. RESULTS Relative to baseline, rate pressure product was greater at an increase in rectal temperature of 0.5°C (+4165 ± 623 bpm × mmHg, p=0.01), 1.0°C (+5015 ± 519 bpm × mm Hg, p<0.01) and 1.5°C (+7516 ± 261 bpm × mm Hg, p<0.01). The increase in rate pressure product was primarily due to an increase in heart rate (p<0.01), as systolic blood pressure was not affected by heat exposure (p=0.12). Relative to baseline values, myocardial blood flow increased at an increase in rectal temperature of 0.5°C (+0.45 ± 0.09 mL/min/g, p=0.03), 1.0°C (+0.61 ± 0.06 mL/min/g, p<0.01) and 1.5°C (+1.10 ± 0.22 mL/min/g, p=0.02). Overall, myocardial blood flow increased 2.7 ± 1.0‐fold relative to baseline at an increase in rectal temperature of 1.5°C. The change in myocardial blood flow during heat exposure correlated with the change in rate pressure product (r=0.78, p<0.01). CONCLUSION These results suggest that passive heat exposure increases myocardial blood flow in proportion with the increase in rate pressure product in young healthy adults.
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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 | 0.000 |
| 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".