Resting Left Ventricular Volumes Do Not Predict Inter-Individual Differences In Submaximal Cardiac Output-Oxygen Consumption Relationships
Bibliographic record
Abstract
During exercise, cardiac output (Q̇) increases along with the rate of oxygen consumption (V̇O2). This relationship can be represented as the amount of Q̇ required to facilitate an increase in V̇O2 by 1 L/min (Q̇-V̇O2 relationship). Previous work identified that inter-individual variability in this relationship during submaximal cycling was mediated by stroke volume (SV) as opposed to heart rate, yet how resting left ventricular (LV) structure contributes to inter-individual differences in the Q̇-V̇O2 relationship is unknown. PURPOSE: To determine whether resting LV volumes predict the slope of the Q̇-V̇O2 relationship during submaximal cycling. METHODS: Ten healthy, recreationally active individuals (26 ± 5 yr, 70% male) completed semi-upright cycling on a tilt-recline stress echocardiography table ergometer. Cycling began at 40 W and increased by 40 W/5 min until 120 W. Exercise intensity was then increased by 25 W/min until volitional exhaustion. 2D echocardiography was completed at rest and during steady state up to 120 W. SV was assessed using the LV outflow tract diameter and the velocity time integral. All images were analyzed over three cardiac cycles. V̇O2 (pulmonary gas exchange) was assessed throughout. Q̇-V̇O2 was assessed as the slope between 40-120 W (Δ from rest). A resting venous blood sample was collected to compute arterial oxygen content (CaO2). Data are mean ± SD and range (min-max). RESULTS: The Q̇-V̇O2 relationship differed by 7.6 L/min between individuals (3.3-10.9 L/min). Resting EDV was 86 ± 20 ml (56-133 ml) while resting ESV was 34 ± 9 ml (20-51 ml). Differences in Q̇-V̇O2 were not related to CaO2 (r = 0.267, p = 0.49), nor were they predicted by resting EDV (r = -0.007, p = 0.99) or ESV (r = 0.017, p = 0.96). Indexing LV volumes to body surface area did not improve prediction of Q̇-V̇O2. As expected, EDV was positively correlated with V̇O2peak (r = 0.668, p = 0.03). CONCLUSION: Inter-individual differences in submaximal Q̇-V̇O2 are unexplained by resting LV volumes. Additional work is required to determine how individuals match oxygen delivery to oxygen demand throughout submaximal intensities. Future investigations should explore the contributions of LV function to submaximal Q̇-V̇O2 while deconstructing potential cardiac reserves recruited during exercise. Supported by NSERC DG and NSERC CGS M.
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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 | 0.002 |
| 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 | 0.001 |
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".