Duration at High Altitude Influences the Onset of Arrhythmogenesis During Apnea
Bibliographic record
Abstract
Excitation of both sympathetic and parasympathetic systems occur concurrently at high‐altitude (chronic hypoxia), via the carotid chemoreflex. We have demonstrated this autonomic conflict manifests as cardiac arrhythmias during voluntary apnea. We sought to determine the duration of hypoxic exposure at high‐altitude necessary to unmask cardiac arrhythmias during instances of voluntary apnea. We hypothesized that the occurrence of cardiac arrhythmias during apnea would be increased following 24 hours of high‐altitude exposure. Measurements of oxygen saturation (SpO 2 ; pulse oximetry) and continuous electrocardiogram (ECG; lead II) were collected in 22 participants (8 females) at low altitude (1045m) and over 8 consecutive days at high‐altitude (3800m). Following a 2 minute baseline participants performed an end‐expiratory apnea to volitional breakpoint. ECG rate and rhythm were evaluated at baseline and during apnea. The nadir heart rate was used to quantify bradycardia and abnormal ECG rhythm was classified based on origin (e.g., sinus node) and type (e.g., sinus arrest). Differences in resting ventilation, SpO 2 , and the heart rate response to apnea on each day at high‐altitude (Day 1‐8) were compared to that at low altitude (Day 0) using a repeated‐measures ANOVA design, with a Holm‐Sidak post‐hoc analysis where main effect of time was significant. Baseline SpO 2 was lower for all days at high‐altitude (average of all days, 89±3) compared to low altitude (98 ± 2) (p<0.01). At high‐altitude (all days), baseline heart rate was higher compared to low altitude (p<0.01). A main effect of time (p<0.01) was identified for the delta change in heart rate during apnea. At low altitude, the average apnea induced decrease in heart rate was ‐9±15bpm, whereas the average decrease in heart rate at high altitude (all days) was ‐24±16bpm. Bradycardia became more pronounced with acclimatization, with the greatest drop in heart rate (‐31±16bpm) occurring on Day 5. At low altitude 14% (3/22) of participants developed arrhythmias during apnea. At high‐altitude, cardiac arrhythmias during apnea became most prevalent (>50%) following Day 5. Changes in saturation during apnea and apnea duration were not associated with the magnitude of bradycardia during apnea (saturation, r= ‐0.007 p=0.92; apnea duration, r=0.005 p=0.94). Interestingly, the magnitude of bradycardia was correlated with the incidence (percentage) of arrhythmia per day (r=0.8; p=0.004), suggesting a similar underlying mechanism. Our data indicate chronic hypoxia is associated with a progressive increase in vagal tone, as indicated by augmented bradycardia during apnea and progressively increased incidence of arrhythmia at high‐altitude. Additionally, the increased incidence of arrhythmia with acclimatization suggests that chemoreflex sensitization may play a role in this phenomenon. This study provides insight into cardiac electrophysiology at high‐altitude and has implications as a future functional model for exploring the effects of heightened chemoreflex stress on autonomic control of heart.
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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".