The Effect of Aging and Rapid Saline Infusion on Compensatory Reserve during Whole‐Body Passive Heat Stress
Bibliographic record
Abstract
The compensatory reserve is defined as the physiological capacity to compensate for reductions in central blood volume. It is measured by a machine learning algorithm, called CRI, which analyzes continuous changes in the features of a photoplethysmographic signal obtained by finger pulse oximetry. The purpose of this study was 2‐fold. First, we examined the effect of healthy aging on compensatory reserve during normothermic and heat stress conditions. Second, we examined the effect of rapid saline infusion during heat stress on compensatory reserve. Eleven young (6 males/5 females; mean ± SD: age, 25 ± 4 years; height, 165 ± 6 cm; weight, 63 ± 9 kg) and ten aged (4 males/6 females; age, 69 ± 4 years; height, 165 ± 9 cm; weight, 68 ± 9 kg) adults were exposed to central hypovolemia via 15 and 30 mmHg of lower‐body negative pressure (LBNP) under normothermic and heat stress (increase in core temperature of 1.5°C) conditions. Approximately 10 min after the heat stress LBNP challenge, warm saline was rapidly infused (15 ml/kg in ~6 min) while subjects remained hyperthermic. Absolute CRI values (Table) range between 0 and 1, where 0 represents little to no reserve for cardiovascular compensation and 1 represents maximal physiological reserve to compensate for central hypovolemia. Under normothermic conditions, an age × LBNP level interaction was observed ( P <0.01). Relative to baseline, CRI was reduced during 15 mmHg LBNP in young ( P <0.01) but not aged ( P =0.21) adults. During 30 mmHg LBNP, CRI was reduced in both groups ( P ≤0.01). During whole‐body passive heat stress, CRI was lower relative to normothermic baseline in both groups ( P <0.01). During subsequent LBNP, CRI was further reduced in young adults during 15 and 30 mmHg ( P <0.01). In aged adults, CRI was further reduced at 30 mmHg during heating ( P =0.06), but not at 15mmHg ( P =0.27). Relative to heat stress, rapid saline infusion did not affect CRI in young ( P =0.47) or aged ( P =0.99) adults. These results demonstrate that CRI responses at low levels of central hypovolemia (i.e. 15 mmHg ≈ 250 ml) differ between young and aged adults under normothermic and heat stress conditions. Furthermore, CRI is unaffected by rapid saline infusion performed under heat stress conditions in both young and aged adults. Support or Funding Information Funded by the Department of Defense (W81XWH‐12‐1‐0152). CRI responses in young and aged adults. Normothermic baseline LBNP15 LBNP30 Heat stress LBNP15 LBNP30 Infusion Young 0.88±0.06 0.77±0.11 0.53±0.17 0.43±0.27 0.31±0.20 0.18±0.13 0.40±0.18 Aged 0.84±0.20 0.79±0.21 0.67±0.24 0.45±0.20 0.40±0.20 0.35±0.23 0.41±0.15 Values are mean ± SD. different from baseline at P ≤0.05; different from heat stress at P ≤0.06.
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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".