The Effect of Rapid and Slow Heat Acquisition on Heart Rate Variability
Bibliographic record
Abstract
Autonomic tone (AT), measured by heart rate variability (HRV), has shown to be linked to the risk of cardiovascular and other diseases. Firefighters are chronically exposed to environments and tasks that put them under acute bouts of thermal and cardiovascular stress, acutely affecting AT. HRV has been shown to respond to both heat stress and heavy exercise though it is not known if rapid heat acquisition caused by the microclimate of personal protective equipment (PPE) affects tonal response magnitude during exercise. PURPOSE: The aim of this study was to determine if PPE-induced rapid heat acquisition affected HRV differently than standard heat acquisition. METHODS: 15 healthy male subjects (mean age, 31.3 ± 11.7 years) completed an incremental graded treadmill walking test until a core temperature of 39.5°C, volitional maximum, or a 2-hour time limit was obtained in both an experimental (PPE) and a control (CON) test in a random crossover design. Pre- and post-exercise, participants completed a 10-minute supine rest period, during which heart rate and R-R intervals were continuously collected. HRV data was filtered and analyzed in the frequency domain. Low (LF) and high frequencies (HF) were reported in normalized units (nu) along with the VLF (very-low frequency), LF, HF, and LF/HF ratio as a unit of power (ms2). RESULTS: Post-exercise LFnu was significantly increased in both CON (pre=73.3±3.5, post= 80.7±3.6, p<0.05) and PPE (pre=7.4±230.1, post=84.2±2.4, p<0.01 ) conditions while HFnu was significantly lower (CON; pre=26.7±3.5, post= 19.2±3.6, p<0.05 and PPE; pre= 31.6±4.5, post= 15.7±2.4, p<0.01). LF/HF ratios were also significantly different pre- to post-exercise in both conditions (CON: pre= 3.9±0.7 ms2, post= 7.3±1.2 ms2, p<0.05; PPE: pre= 3.9±0.6 ms2, post= 7.7±1.0 ms2 p<0.01). There was no difference between the two conditions either pre- or post-exercise for any of the variables measured in ms2 except for post-exercise VLF which was significantly higher in PPE compared to CON. CONCLUSION: Results from the current study suggest that regardless of the rate of thermal acquisition, HRV response is similar, however the shift of HRV into the VLF domain during the PPE condition may have masked the magnitude of sympathetic response by lowering the LF frequency domain.
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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".