Cardiovascular and Hematological Responses to Simulated Dynamic Apnea in Breath Hold Divers
Bibliographic record
Abstract
The mammalian dive reflex, characterized by bradycardia and peripheral vasoconstriction, occurs in all mammals, including humans, in response to apnea or facial submersion in water. However, the dive reflex to a single, maximal effort dynamic apnea (DYN), and how it compares to a time-matched exercise control trial (EX), has not been studied. We examined the hypotheses that, when compared to EX, (a) the magnitude of the cardiovascular response, including reduced heart rate (HR), increased systolic-, diastolic-, and mean arterial- pressure (SBP, DBP, and MAP, respectively) would be greater during DYN, and; (b) red blood cells (RBCs), hemoglobin (Hb), and hematocrit (Hct) would also all be elevated following DYN. Twenty-three (F=6) apnea divers performed a maximal DYN and time-matched EX on a swimming ergometer without facial submersion. For the DYN protocol, participants were instructed to exercise maximally while holding their breath which the EX trial was then time and distance matched. Trial duration was similar between DYN (126±7s [mean±SE]) and EX (126±7s;P>0.3), however the change in venous lactate (DYN 1.8±0.3mmol/l, EX: 0.2±0.2mmol/l) and peripheral oxygen saturation (DYN: -15±3%, EX: -1.8±0.5%;p<0.05, both comparisons) were greater during DYN compared to EX. During DYN ΔSBP (DYN: 107±6mmHg, EX: 45±6 mmHg), ΔDBP (DYN: 46±3mmHg, EX: 17±3mmHg) and ΔMAP (DYN: 66±3mmHg EX: 26±3mmHg) were increased compared to EX, while ΔHR was greater during EX (DYN: -24±5bpm, EX: 36±5bpm;p<0.0001, all comparisons). Similarly, the change in estimated stroke volume was further reduced in DYN (DYN: -15.2±3.3mL, EX: -1.0±3.3m;p<0.005) while Δcardiac output was reduced during DYN (-2.9±0.4l/min) and elevated during EX (2.9±0.4l/min;p<0.0001). The change in RBCs (DYN: 0.20±0.04x10 6 cells/μL, EX: 0.06±0.04x10 6 cells/μL) and Hct (DYN:1.7±0.3%, EX:0.5±0.3%) were greater during DYN than EX (p<0.02, both comparisons), whereas ΔHb (DYN: 4.0±0.9g/dL, EX: 1.9±0.8g/dL) and spleen volume (DYN: -9.1±7.4cm 3 , EX:-8.3±6.4cm 3 ;P>0.1, both comparisons) was comparable between the two trials. There was a main effect of sex for ΔDBP (Female: 36±3mmHg, Male: 27±2mmHg), and ΔMAP (Female: 52±5mmHg, Male: 40±3mmHg) indicating that females overall had a greater blood pressure response to both DYN and EX (p<0.05, both comparisons). Together, these data indicate that DYN elicits a greater cardiovascular and hematological response than EX alone, likely due to the combined activation of the metabo- and chemo-reflex during DYN. The mechanism(s) that may elicit greater changes in blood pressure response to DYN and EX in females when compared to males warrant future investigation. NSERC, University Research Chair. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| 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) | 0.000 | 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 teacher head, 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".