Peripheral Chemoreflex Regulates Post‐exercise Cardiac Vagal Reactivation in Healthy Humans and Patients with Pulmonary Arterial Hypertension
Bibliographic record
Abstract
The fast post‐exercise heart rate recovery (HRR) is valid, reproducible, and widely used in clinical practice to assess the cardiac vagal function. However, the mechanisms that regulate it remain unclear. As the peripheral chemoreflex regulates resting cardiac activity, and this reflex is sensitized by physical exercise, we hypothesized that the peripheral chemoreflex could regulate the post‐exercise cardiac vagal reactivation in healthy humans. Additionally, we hypothesized that the peripheral chemoreflex could contribute to the reduction of post‐exercise cardiac vagal reactivation in a clinical population that has been associated with high peripheral chemosensitivity. To test the first hypothesis, seven young men underwent ramp exercise tests then, during recovery, randomly inhaled either 1) 12% of O 2 to stimulate the peripheral chemoreflex (i.e., hypoxia), 2) 100% of O 2 to inhibit the peripheral chemoreflex (i.e., hyperoxia), or 3) 21% of O 2 as control (i.e., normoxia). To test the second hypothesis, 14 adults with pulmonary arterial hypertension (PAH) underwent the same protocol, but randomly inhaled 100% or 21% of O 2 during recovery. Of note, all the subjects were blinded about the inspired O 2 concentration, which was changed slightly before the onset of recovery, not to disturb physiological responses during ramp exercise. ECG was registered and cardiac vagal reactivation was assessed via: 1) HRR, calculated as the difference between peak HR (HR peak ) and HR after 30 s (HRR30s) and 1 min (HRR1min) of recovery, and 2) HR variability (HRV), calculated as the root mean square of successive R‐R intervals difference (RMSSD) of 30‐s data segments throughout 5‐min of recovery. The chemoreflex sensitivity was assessed by the ventilatory response to transient nitrogen inhalation at rest. Healthy subjects showed similar HR peak among conditions (hypoxia: 156 ± 10 vs. hyperoxia: 153 ± 7 vs. normoxia: 156 ± 9 beats/min, mean ± SD, P = 0.60). Their HRR30s was lower in hypoxia (5 ± 5 beats/min) than hyperoxia (22 ± 6 beats/min, P <0.01) and normoxia (17 ± 8 beats/min, P <0.01). HRR1min and RMSSD throughout the recovery period were lower in hypoxia than hyperoxia (HRR1min: 19 ± 10 vs. 35 ± 6 beats/min, P = 0.03; RMSSD: 3.5 ± 1.1 vs. 5.4 ± 1.3 ms, P = 0.04). Patients with PAH showed higher chemosensitivity than young healthy men. Their HR peak was similar between conditions (hyperoxia: 147 ± 17 vs. normoxia: 148 ± 18 beats/min, P = 0.78). HRR30s (10 ± 5 vs. 5 ± 4 beats/min, P <0.001) and HRR1min (19 ± 9 vs. 15 ± 8 beats/min, P = 0.01) were higher in hyperoxia than normoxia. RMSSD was similar between conditions ( P = 0.60). Therefore, collectively, these results indicate that the peripheral chemoreflex regulates the post‐exercise cardiac vagal reactivation in healthy humans, and, also, mediates reduction of cardiac vagal reactivation in patients with PAH. Support or Funding Information The study was supported by São Paulo Research Foundation, FAPESP (2014/24294‐6; 2015/22198‐2)
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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 | 0.001 | 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".