Older Adults Experience Greater Levels of Thermal and Cardiovascular Strain During Extreme Heat Exposures.
Bibliographic record
Abstract
Aging may cause changes in the body’s normal response to heat. This means that older adults may be at a greater risk of suffering from a heat-related injury or death. PURPOSE: We examined the effects of aging on whole-body heat loss and heat storage as well as cardiovascular responses during an extreme heat exposure (43 °C, 30% relative humidity). METHODS: Sixteen young (24 ± 3 years) and 16 older (64 ± 6 years) adults matched for body weight (young (Y): 79 ± 16 kg; older (O): 79 ± 13 kg) and body surface area (Y: 1.9 ± 0.2 m2; O: 1.9 ± 0.2 m2) rested for 3 hours in the heat. Whole-body heat loss and metabolic heat production were measured continuously by direct and indirect calorimetry respectively. This was paralleled by measurements of visceral and rectal temperatures. Body heat storage was calculated as the temporal summation of heat production and heat loss. Cardiovascular responses [cardiac output (CO), mean arterial pressure (MAP), stroke volume (SV), and heart rate (HR)] were measured prior to and following the exposure. RESULTS: Whole-body heat loss was lower for the older adults throughout the 3-hour exposure compared to their younger counterparts (p≤0.001). This resulted in a 1.9-fold greater heat storage in the older adults (Y: 193 ± 133 kJ; O: 372 ± 191 kJ; p=0.004). No differences in visceral or rectal temperature were observed. Despite differences in baseline cardiovascular responses between younger and older adults (CO: Y, 6.0 ± 1.1 L/min; O, 3.8 ± 1.1 L/min; MAP: Y, 87 ± 8 mm Hg, O, 94 ± 7 mm Hg, both p≤0.02), the percent change from baseline was similar between groups (CO: Y, −3 ± 13%; O, −6 ± 21%; MAP: Y, 6 ± 32%; O, 6 ± 12%, p>0.05). The lower CO measured in older adults was the result of a reduced SV (Baseline resting: Y, 82 ± 19 mL; O, 57 ± 18 mL; p=0.005; End of exposure Y, 59 ± 12 mL; O, 39 ± 12 mL; p=0.002) as no differences in HR were measured between groups (p>0.05). CONCLUSION: We show that older adults have an impaired capacity to dissipate heat during extreme heat exposures resulting in significantly greater body heat storage relative to their younger counterparts. However, this was not paralleled by a greater cardiovascular strain. Caution should be used when employing surrogate measures of body heat storage (visceral and rectal temperature) to evaluate the level heat strain in older adults. SUPPORT: Canadian Institutes of Health Research (grant # 286363).
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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) | 0.002 | 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".