Does oxygen pulse represent a reliable surrogate for stroke volume during exercise? Insights from cardiopulmonary exercise test combined with echocardiography or invasive measurements
Bibliographic record
Abstract
Abstract Background While interpreting the mechanisms underlying exercise limitation in cardiopulmonary exercise testing (CPET), oxygen pulse (O2pulse) is often assumed to be a surrogate for stroke volume (SV). However, in the rearranged Fick’s equation, O2pulse represents the product of SV and arteriovenous oxygen difference (a-vO2diff). Consequently, interpreting O2pulse exclusively as a reflection of SV can be misleading, as it disregards one of its key determinants. Purpose To assess the effort response of the determinants of O2pulse (SV and a-vO2Diff) by simultaneous CPET and echocardiography (CPETecho) or invasive CPET (iCPET). Methods This observational study analysed the O2pulse in CPETecho and iCPET examinations conducted between July/15 and May/24. SV in CPETecho was measured using the ultrasound velocity time integral of the left ventricular outflow tract, and with VO2, a-vO2diff was calculated. For iCPET, a-vO2diff was directly measured using arterial and mixed-venous blood gas analyses, while SV was calculated. During CPETecho, measurements were taken at rest, intermediate, and peak exercise, whereas during iCPET, at rest, at 3, 6, 9 minutes, and at peak exercise. Variables were compared using one-way ANOVA with post hoc Tukey tests, with statistical significance set at p < 0.05. Results CPETecho: A total of 1,866 exams were analyzed (54.1% male; age: 65.4±13.9 y). The main indication was heart failure with preserved ejection fraction (HFpEF, 39.7%), valvular heart disease (35.5%), myocardial ischemia (6.3%), and others (18.5%). O2pulse increased significantly from rest to intermediate and peak (4.0±1.9, 9.0±3.3, and 10.9±3.9 mL/beat, respectively; p<.0001; Figure 1). SV increased from rest to intermediate load (70.2±18.1 vs. 84.5±20.9 mL/beat; p<.0001), with no further significant increase from intermediate to peak exercise (84.5±20.9 vs. 85.1±21.3 mL/beat; p=.07). In contrast, a-vO2 diff increased progressively from rest to intermediate and peak (p<.001). iCPET: A total of 68 exams were analyzed, primarily conducted in suspected HFpEF (age: 64.1±10.6 y). O2pulse increased progressively from rest to peak (p<.0001; Figure 2). SV significantly increased from rest to the 6-minute measurement, with no further significant changes thereafter. In contrast, a-vO2diff showed a continuous progressive increase from rest to peak exercise. Conclusion Analysis of the determinants of O2pulse (SV and a-vO2diff) using both CPETecho and iCPET demonstrated that the increase in O2pulse from intermediate to peak exercise is primarily driven by a rise in a-vO2diff, while SV remains relatively constant. Therefore, in cardiac patients, changes in O2pulse should not be assumed to reliably reflect changes in SV alone but rather represent the combined effects of SV and peripheral oxygen extraction. For a definitive interpretation of the O2pulse response during exercise, performing measurement of either SV or a-vO2diff is essential.Figure 1.Variables measured by CPETechoFigure 2.Variables measuredf by iCPET
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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 | 0.001 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.002 | 0.001 |
| Bibliometrics | 0.001 | 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".