Comparative Assessment of Central and Peripheral Chemoreceptor Reflex Regulation of Muscle Sympathetic Nerve Activity and Ventilation
Bibliographic record
Abstract
We tested the hypothesis that central and peripheral chemoreceptor‐mediated sympathetic activation elicited by increases in CO 2 tension (PCO 2 ) mirror concurrent ventilatory responses. Twelve healthy young men (mean±SD; age: 24±4 yr; BMI: 24.5±1.3 kg·m −2 ) performed a modified rebreathing protocol designed to equilibrate central and peripheral chemoreceptor PCO 2 tensions with end‐tidal PCO 2 (P ET CO 2 ) at two isoxic end‐tidal PO 2 (P ET O 2 ) tensions such that central chemoreceptor reflex responses (hyperoxia) can be isolated from additive peripheral responses (i.e., hypoxia minus hyperoxia). Subject's ventilation (volume turbine) and muscle sympathetic nerve activity (MSNA; microneurography, right fibular nerve) responses to rebreathing at isoxic P ET O 2 tensions of 150 mmHg (hyperoxia) and 50 mmHg (hypoxia) were recorded continuously. During rebreathing, the P ET CO 2 (mmHg) at which ventilation (L·min −1 ) and total MSNA (au) began to rise were identified as the P ET CO 2 recruitment thresholds (RT). Slopes of these responses above RT also were determined. In hyperoxic rebreathing (i.e., the central chemoreflex response), the mean RT for ventilation (46±3 mmHg) and MSNA (45±4 mmHg) did not differ (p>0.05). Mean slopes were 2.3±0.9 L·min −1 ·mmHg −1 and 2.1±1.5 au·mmHg −1 , respectively. In hypoxic rebreathing (i.e., the summed central and peripheral chemoreflex response), the RT for both ventilation and MSNA were not different (41±3 mmHg vs 41±3 mmHg, p>0.05) but were lower (p<0.05) compared to hyperoxia. Mean slopes for ventilation (4.0±1.8 L·min −1 ·mmHg −1 ) and MSNA (5.1±3.4 au·mmHg −1 ) in hypoxia were greater than in hyperoxia yielding a mean peripheral chemoreflex sensitivity (hypoxic slope minus hyperoxic slope) of 1.7±0.1 L·min −1 ·mmHg −1 for ventilation and 3.0±2.6 au·mmHg −1 for MSNA. The 95% limits of agreement of RT between ventilation and MSNA for the central chemoreflex were −7 to 6 mmHg (bias=−1 mmHg, p>0.05) and −5 to 5 mmHg (bias=0 mmHg, p>0.05) for the peripheral chemoreflex. There was no relationship (p>0.05) between the ventilatory and MSNA sensitivity for either the central (r 2 =0.16) or peripheral (r 2 =0.01) chemoreceptor reflexes. These data highlight two novel findings: 1) ventilatory and sympathetic arms of the central and peripheral chemoreceptor reflexes are initiated at similar P ET CO 2 recruitment thresholds and 2) sympathetic responsiveness cannot be predicted from the sensitivities of the ventilatory central and peripheral chemoreceptor reflexes. Support or Funding Information Experiments were funded by a Project Grant from the Canadian Institutes of Health Research (PJT 159491). Dr. Floras holds the Canada Research Chair in Integrative Cardiovascular Biology. This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .
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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) | 0.002 | 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".