Bibliographic record
Abstract
Across vertebrates, the maximal rate of oxygen consumption (V̇O2,max) defines the capacity of the respiratory and cardiovascular systems to transport oxygen from the environment to the cells. While V̇O2,max depends on multiple conductance steps in the oxygen transport pathway - ventilation, respiratory diffusion, circulatory convection and tissue diffusion - the relative importance of each step differs across species with varying gas exchange organs, cardiac morphologies and aerobic capacities. I analysed the determinants of V̇O2,max across vertebrates by conducting a sensitivity analysis of V̇O2,max limitations in a fish, and synthesizing published sensitivity analyses for an amphibian, a bird, the Thoroughbred racehorse, and humans of average and elite athletic ability. I also compared the effects of hypoxia on conductance contributions using data from birds and humans. To compare models, I calculated fractional limitations from modelled changes in V̇O2,max following perturbations to each conductance step. The results reveal similar patterns: circulatory conductance (cardiac output) dominates in species with lower aerobic capacity, while diffusive and ventilatory conductance become more influential in athletic species and in hypoxia. Athletic phenotypes appear to operate at the functional limits of the lung - a consequence, at least in part, of high cardiac output. These findings reinforce the importance of viewing oxygen transport as an integrative system with multiple components that can individually or jointly constrain V̇O2,max. Ultimately, the entire system serves to deliver oxygenated red bloods to the muscle capillaries, where the cumulative contributions of all upstream processes influence oxygen transfer from red blood cells to mitochondria.
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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 | 0.001 | 0.004 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.001 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 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".