Effects of Hypercapnia on Myocardial Blood Flow in Healthy Human Subjects
Bibliographic record
Abstract
Elevation of the end-tidal partial pressure of CO<sub>2</sub> (P<sub>ET</sub>co<sub>2</sub>) increases cerebral and myocardial blood flow (MBF), suggesting that it may be a suitable alternative to pharmacologic stress or exercise for myocardial perfusion imaging. The purpose of this study was to document the pharmacodynamics of CO<sub>2</sub> for MBF using prospective end-tidal targeting to precisely control arterial Pco<sub>2</sub> and PET to measure the outcome variable, MBF. <b>Methods:</b> Ten healthy men underwent serial <sup>82</sup>Rb PET/CT imaging. Imaging was performed at rest and during 6-min hypercapnic plateaus (baseline; P<sub>ET</sub>co<sub>2</sub> at 50, 55, and 60 mm Hg; repeat of P<sub>ET</sub>co<sub>2</sub> at 60 mm Hg; and repeat of baseline). MBF was measured using <sup>82</sup>Rb injected 3 min after the beginning of hypercapnia and a 1-tissue-compartment model with flow-dependent extraction correction. Results were compared with those obtained during an adenosine stress test (140 μg/kg/min). <b>Results:</b> Baseline P<sub>ET</sub>co<sub>2</sub> was 38.9 ± 0.8 (mean ± SD) mm Hg (range, 35–43 mm Hg). All P<sub>ET</sub>co<sub>2</sub> targets were sustained, with SDs of less than 1.5 mm Hg. Heart rate, systolic blood pressure, rate × pressure product, and respiratory frequency increased with progressive hypercapnia. MBF increased significantly at each level of hypercapnia to 1.92-fold over baseline (0.86 ± 0.24 vs. 0.45 ± 0.08 mL/min/g; <i>P</i> = 0.002) at a P<sub>ET</sub>co<sub>2</sub> of 60 mm Hg. MBF after the administration of adenosine was significantly greater than that with the maximal hypercapnic stimulus (2.00 vs. 0.86 mL/min/g; <i>P</i> < 0.0001). <b>Conclusion:</b> To our knowledge, this study is the first to assess the response of MBF to different levels of hypercapnia in healthy humans with PET. MBF increased with increasing levels of hypercapnia; MBF at a P<sub>ET</sub>co<sub>2</sub> of 60 mm Hg was double that at baseline.
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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".