Whole‐body heat stress does not appear to reduce β1‐adrenergic responsiveness in heat stressed older individuals
Bibliographic record
Abstract
Whole‐body heat stress increases cardiac output in younger and older individuals (i.e. ≥60 years), though the magnitude of that increase is attenuated in the older group. Recently, it has been identified that attenuated increases in cardiac output in older individuals during heat stress is primarily due to diminished heart rate responses. However, the mechanisms by which the increases in heart rate are attenuated in heat‐stressed older individuals remains unknown. The purpose of this study is to test the hypothesis that attenuated β1‐adrenergic responsiveness contributes to the lower increase in heart rate observed in older adults during heat stress. In ten healthy young (five females: age 23 ± 2 and five males: age 26 ± 3) and four older participants (two females: age 63 ± 2 and two males: age 70 ± 2) heart rate was measured prior to and during intravenous infusion, of a low (5 μg/kg/min) and a moderate (15 μg/kg/min) dose of dobutamine (a β1‐adrenergic receptor agonist) under normothermia (NT) and hyperthermia (HT; increase in internal temperature of 1.2 ± 0.1°C). The heart rate response to heat stress alone tended to be attenuated in older individuals (+24 ± 3 older: +33 ± 2 beats/min young, P = 0.06). The low dose of dobutamine during HT further increased HR in the older (Δ 23 ± 7 bpm) and young participants (Δ 12 ± 5 bpm) to a similar extent (older vs. young; P=0.15). Likewise, the infusion of the high dose of dobutamine during HT similarly increased HR in both groups (Δ 45 ± 8 vs. young: Δ 42 ± 5 beats/min, P = 0.80). Based upon these preliminary data, healthy aging does not reduce β1‐adrenergic responsiveness under normothermic and heat stress conditions. This finding suggests that attenuated increases in heart rate during heat stress in older individuals are likely neurally mediated.
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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".