Healthy aging does not compromise the augmentation of cardiac function during heat stress
Bibliographic record
Abstract
During heat stress, stroke volume is maintained in young adults despite reductions in cardiac filling pressures. This is achieved by a general augmentation of cardiac function, highlighted by a left and upward shift of the Frank-Starling relation. In contrast, healthy aged adults are unable to maintain stroke volume during heat stress. We hypothesized that this would be associated with a lack of shift in the Frank-Starling relation. Frank-Starling relations were examined in 11 aged [69 ± 4 (SD) yr, 4 men/7 women] and 12 young (26 ± 5 yr, 6 men/6 women) adults during normothermic and heat stress (1.5°C increase in core temperature) conditions. During heat stress, increases in cardiac output were attenuated in aged adults (+2.5 ± 0.3 (95% CI) vs. young: +4.5 ± 0.5 l/min, P < 0.01) because of an attenuated chronotropic response (+30 ± 4 vs. young: +42 ± 5 beats/min, P < 0.01). In contrast to our hypothesis, a leftward shift of the Frank-Starling relation maintained stroke volume during heat stress in aged adults (76 ± 8 vs. normothermic: 74 ± 8 ml, P = 0.38) despite reductions in cardiac filling pressure (6.6 ± 1.0 vs. normothermic: 8.9 ± 1.1 mmHg, P < 0.01). In a subset of participants, volume loading was used to return cardiac filling pressure during heat stress to normothermic values, which resulted in a greater stroke volume for a given cardiac filling pressure in both groups. These results demonstrate that the Frank-Starling relation shifts during heat stress in healthy young and aged adults, thereby preserving stroke volume despite reductions in cardiac filling pressures.
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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 | 0.001 |
| 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".