Does pulse contour analysis provide a valid estimate of cardiac output during spaceflight?
Bibliographic record
Abstract
Model flow is a pulse contour analysis method that provides non‐invasive ambulatory cardiac output, which can characterize potential degradation of cardiovascular function due to long‐duration spaceflight. However, the model flow algorithm has not been tested in altered gravitational environments. The purpose of this study was to use a standard rebreathing measure of cardiac output (COre) to validate the model flow cardiac output (COmf) and to detect potential changes in cardiovascular physiology during spaceflight using the stiffness index, model flow Aortic Age (AGEmf). Data were collected from nine male astronauts (45 ± 7 years old) who were aboard the International Space Station for 6 months. Testing occurred pre‐flight and inflight approximately 3 weeks before returning to Earth. Rebreathing cardiac output was collected using the Pulmonary Function System. The arterial pressure waveform was collected using finger photoplethysmography for the determination of COmf and AGEmf. Changes in COmf with spaceflight did not match changes in COre (p < 0.001). COre increased from pre‐flight to inflight (4.8 ± 0.7 L/min and 7.0 ± 1.4 L/min, respectively; p < 0.01) while COmf remained constant with spaceflight (pre‐flight: 6.2 ± 1.4 L/min and inflight: 5.8 ± 1.1 L/min, respectively; p > 0.05). The model flow algorithm assumes central arterial properties based on age but as changes in COmf were not similar to COre with spaceflight, this assumption appears to have been violated. As well, the stiffness index AGEmf decreased with spaceflight (pre‐flight: 68 ± 16 years old and inflight: 41 ± 9 years old; p < 0.01). These results suggest changes in cardiac function and in arterial properties that invalidate pulse contour analysis during spaceflight. Support or Funding Information The research was supported by the Canadian Space Agency, Natural Sciences and Engineering Research Council of Canada, and the American Physiological Society.
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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 | 0.002 | 0.011 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.001 | 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".