Ventilation Inhibits Sympathetic Neural Recruitment During Severe Chemoreflex Stress
Bibliographic record
Abstract
The current study investigated the effects of ventilation on sympathetic neural recruitment during severe chemoreflex stress. We measured, in six trained breath‐hold divers (one female; 35±11 yrs, 181±11 cm, 74±13 kg), muscle sympathetic nerve activity (MSNA; microneurography), heart rate (HR; electrocardiogram), blood pressure (BP; Finometer), and arterial hemoglobin saturation (HbSat; pulse oximetry) at baseline (2 mins) and during alternating periods (30 s) of functional residual capacity (FRC) apnea and asphyxic rebreathing, a protocol designed to elicit severe chemoreflex activation in the absence and presence of ventilation, respectively. Subjects were instructed to stop when they achieved ~85% of their self‐perceived ‘maximal’ tolerance for the protocol. The final FRC apnea and rebreathe periods were used for analysis. Sympathetic action potential (AP) discharge patterns were studied using a novel AP detection and analysis technique. This technique quantifies not only the number and morphology of APs within the integrated burst at rest, but also the emergence of latent (and larger) APs as stress develops. Compared to baseline, HbSat decreased to similar levels during FRC apnea and rebreathe (80±3 and 78±11%, respectively; P >0.05). Compared to baseline (18±7 bursts/min), MSNA burst frequency increased during FRC apnea (Δ35±6 bursts/min; P <0.01), but not rebreathe (Δ1±4 bursts/min; P >0.05), whereas burst amplitude (54±12 AU) increased during both FRC apnea (Δ82±30 AU) and rebreathe (Δ26±16 AU; both P <0.05), although the increase was greater during FRC apnea ( P <0.01). Compared to baseline (9±3 APs/burst), the mean AP content per integrated burst increased during both FRC apnea (Δ20±6 APs/burst) and rebreathe (Δ7±5 APs/burst; both P <0.01). Similarly, the number of active AP clusters per integrated burst (5±1 clusters/burst) increased during both FRC apnea (Δ4±1 clusters/burst) and rebreathe (Δ2±1 clusters/burst; both P <0.01). However, in both cases, the magnitude of increase was greater during FRC apnea (both P <0.01). Finally, when APs were binned according to peak‐to‐peak amplitude (i.e., into clusters), the number of total AP clusters detected (12±2 total clusters) increased during FRC apnea (Δ6±1 total clusters; P <0.01), but not rebreathe (Δ0±1 total clusters; P >0.05). As such, ventilation restrains sympathetic neural recruitment during severe chemoreflex stimulation. While the increased within‐burst firing frequency of previously active, lower‐threshold sympathetic axons appears preserved, but diminished, in the presence of ventilation (i.e., rebreathe), the recruitment of previously silent, higher‐threshold sub‐populations of larger‐sized sympathetic axons appears specific to apnea, and inhibited by ventilation. Support or Funding Information Supported by Natural Sciences and Engineering Research Council of Canada.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
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 | 0.000 |
| 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".