Aging Resets the Spontaneous Baroreflex Control of Sympathetic Action Potential Subpopulations in Humans
Bibliographic record
Abstract
Currently, the effect of aging on sympathetic baroreflex control is equivocal, with some studies finding that integrated sympathetic baroreflex threshold gain is not affected by age, and others finding that it is blunted in older compared to young adults. While these studies evaluated the effect of aging on baroreflex control of integrated sympathetic burst frequency, it remains unclear how aging modulates the baroreflex control of postganglionic action potentials (AP). In young adults, the arterial baroreflex exerts non‐uniform control over varying‐sized APs spontaneously firing within bursts of muscle sympathetic nerve activity (MSNA), with the strongest control over medium sized AP clusters, and less control over the smallest and largest APs. Therefore, we tested the hypothesis that resting baroreflex control of AP subpopulations and integrated sympathetic bursts would be blunted in older compared to young adults. Baroreflex threshold relationships for integrated MSNA bursts and the underlying subpopulations of AP clusters (obtained using microneurography and a continuous wavelet transform) were assessed during 5 minutes of supine rest in eleven older (45‐75 years, 5 females) and eleven young (21‐30 years, 5 females) adults. Baroreflex threshold was quantified as the slope of the linear regression between AP probability (%) and MSNA burst probability (%) versus diastolic blood pressure (DBP, mmHg; Finger plethysmography). AP discharge was greater in older compared to young adults (Older: 614 ± 327 spikes/100 beats vs. Young: 211 ± 107 spikes/100 beats, P < 0.001), and the baroreflex control of AP subpopulations was reset towards greater firing probabilities in older adults (group‐by‐cluster effect: P < 0.001). Specifically, the arterial baroreflex threshold gain of medium AP clusters was greater in older compared to young adults (e.g. Cluster 4, Older: ‐7.8 ± 3.1 %/mmHg vs. Young: ‐4.1 ± 2.9 %/mmHg, P = 0.010), whereas the baroreflex threshold gains for the smallest (e.g. Cluster 1, Older: ‐1.2 ± 1.1 %/mmHg vs. Young: ‐0.7 ± 0.4 %/mmHg, P = 0.197) and largest (e.g. Cluster 10, Older: ‐0.5 ± 0.4 %/mmHg vs. Young: ‐0.6 ± 0.6 %/mmHg, P = 0.673) AP clusters were not modified by aging. Additionally, integrated sympathetic burst threshold gain was greater in older compared to young adults (Older: ‐7.9 ± 3.8 %/mmHg vs. Young: ‐3.9 ± 1.8 %/mmHg, P = 0.005), and the operating point was shifted rightward towards a higher DBP (Older: 76 ± 8 mmHg vs. Young: 68 ± 7 mmHg, P = 0.021). Contrary to our hypothesis, the strength of baroreflex control over medium sized AP clusters as well as integrated sympathetic baroreflex threshold gain was greater in this group of older adults compared to young adults.
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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".