Measurement error of cardiac output determined by nitrous oxide rebreathing and impedance cardiography in healthy adults
Bibliographic record
Abstract
Cardiac output (Q̇) is a fundamental physiological variable but remains challenging to measure. Exercise Q̇ is commonly measured by inert gas rebreathing using acetylene or nitrous oxide (Q̇ N 2 O-IGR ) and impedance cardiography (Q̇ IC ), but device measurement error has not been assessed at different workloads or in females. This study determined the precision of Q̇ N 2 O-IGR (Innocor, COSMED Inc., USA) and Q̇ IC (Physioflow Enduro, Manatec Biomedical, France) in duplicate in 60 adults (30 females; 22 ± 5 years; V̇O 2max : 41.2 ± 8.6 mL . kg −1. min −1 ) during upright rest and cycling at 50 W and 90% peak power output (PPO) (277 ± 71 W). Measurement variance was higher for Q̇ N 2 O-IGR vs. Q̇ IC ( p < 0.0001), at 90% PPO compared to 50 W at rest ( p < 0.001), and in males vs. females at 50 W with Q̇ N 2 O-IGR ( p = 0.005). At rest the typical error (TE), coefficient of variation (CV), and intraclass correlation (ICC) were 0.6 L/min (12.4%), 11.6 ± 8.5%, and 0.75 [0.62–0.82] for Q̇ N 2 O-IGR and 0.4 L/min (6.9%), 7.5 ± 8.4, and 0.87 [0.79–0.92] for Q̇ IC . At 50 W, the TE, CV, and ICC were 0.8 L/min (7.7%), 5.4 ± 5.8%, and 0.79 [0.68–0.87] for Q̇ N 2 O-IGR and 0.5 L/min (5.6%), 3.7 ± 3.8%, and 0.85 [0.76–0.91] for Q̇ IC . At 90% PPO, TE, CV, and ICC were 1.2 L/min (7.5%), 5.4 ± 4.3%, and 0.89 [0.82–0.93] for Q̇ N 2 O-IGR and 0.7 L/min (4.0%), 5.0 ± 3.2%, 0.96 [0.93–0.98] for Q̇ IC . Duplicate Q̇ N 2 O-IGR differed up to ∼4 L/min (38%) and Q̇ IC ∼3 L/min (24%). In conclusion, group-level measurement precision was generally better for Q̇ IC than Q̇ N 2 O-IGR but depended on workload and sex. Duplicate Q̇ N 2 O-IGR and Q̇ IC differed substantially; therefore, repeat measures are important.
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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) | 0.001 | 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".