Effect of Voluntary End‐Expiratory Apnea During Varying Chemoreflex Stress on Sympathetic Neural Recruitment Strategies
Bibliographic record
Abstract
PURPOSE Sympathetic nervous system responses to voluntary apnea are increased by hypoxia and attenuated by hyperoxia. However, whether neural firing and recruitment strategies in response to apnea can be modified by hypoxia and/or hyperoxia were previously unknown. We examined the influence of chemoreceptor stimuli on sympathetic neural firing and recruitment strategies during voluntary end‐expiratory apnea. We hypothesized increases in the firing frequency and probability of low‐threshold axons during apnea would be exaggerated during hypoxia and attenuated during hyperoxia. METHODS Multi‐unit muscle sympathetic nerve activity (MSNA, microneurography) was measured in 10 young, healthy men (31±2 yrs, 25±1 kg/m 2 ). Data were collected at baseline and during maximal voluntary end‐expiratory apnea under normoxic (S p O 2 : 98±1%), hypoxic (F i O 2 : 0.17±0.01; S p O 2 : 82±1%), and hyperoxic (F i O 2 : 0.92±0.03; S p O 2 : 100±0%) conditions. Condition order was randomized and trials were separated by a minimum of 15‐min quiet normoxic rest. Action potential (AP) patterns were studied from the filtered raw signal using wavelet‐based methodology. Data are reported from the last 2‐min of baseline and during the second half of apnea, reflecting the time of highest MSNA. RESULTS There was an increase in multi‐unit MSNA (24±3 to 35±3 bursts/min, p=0.04) during normoxic apnea, which was due to an increase in the frequency and incidence of AP spikes (243±75 to 519±134 AP/min, p=0.048; 412±133 to 773±185 AP/100 heart beats, p=0.04). An increase in the probability of AP firing more than once per burst was also observed (p=0.01). There was an increase in multi‐unit MSNA (20±4 to 46±7 bursts/min, p<0.01) during hypoxic apnea that was due to an increase in the frequency and incidence of AP spikes (192±59 to 952±266 AP/min, p<0.01; 326±89 to 1212±327 AP/100 heart beats, p<0.01). Hypoxic apnea also resulted in an increase in the probability of AP firing more than once per burst (p<0.01). Hyperoxia attenuated any increase in MSNA with apnea, such that no changes in multi‐unit MSNA (24±4 to 28±5 bursts/min, p=0.14) nor frequency or incidence of AP spikes (155±35 to 253±71 AP/min, p=0.12; 249±61 to 502±188 AP/100 heart beats, p=0.28) were observed. Hyperoxia also attenuated any increase in the probability of AP firing more than once per burst (p=0.47). CONCLUSION These data are the first to show neural firing and recruitment strategies in response to voluntary end‐expiratory apnea are modified by hypoxia and hyperoxia. Our results demonstrate that hypoxic apnea increases the frequency and incidence of action potential spikes, as well as the probability of multiple within‐burst firing; whereas this response was suppressed when individuals were hyperoxic. These data may have important implications for neural control of the circulation in recreational activities (i.e. diving) and/or clinical conditions prone to apnea (i.e. sleep apnea). Support or Funding Information FUNDING: AHA #15SDG25080095, NIH HL130339, Natural Sciences and Engineering Research Council of Canada Discovery Grant program. 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) | 0.001 | 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".