Influence of myocardial oxygen demand on the coronary vascular response to arterial blood gas changes in humans
Bibliographic record
Abstract
It remains unclear if the human coronary vasculature is inherently sensitive to changes in arterial Po 2 and Pco 2 or if coronary vascular responses are the result of concomitant increases in myocardial O 2 consumption/demand ([Formula: see text]). We hypothesized that the coronary vascular response to Po 2 and Pco 2 would be attenuated in healthy men when [Formula: see text] was attenuated with β 1 -adrenergic receptor blockade. Healthy men (age: 25 ± 1 yr, n = 11) received intravenous esmolol (β 1 -adrenergic receptor antagonist) or volume-matched saline in a double-blind, randomized crossover study and were exposed to poikilocapnic hypoxia, isocapnic hypoxia, and hypercapnic hypoxia. Measurements made at baseline and after 5 min of steady state at each gas manipulation included left anterior descending coronary blood velocity (LAD V ; Doppler echocardiography), heart rate, and arterial blood pressure. LAD V values at the end of each hypoxic condition were compared between esmolol and placebo. The rate-pressure product (RPP) and left ventricular mechanical energy (ME LV ) were calculated as indexes of [Formula: see text]. All gas manipulations augmented RPP, ME LV , and LAD V , but only RPP and ME LV were attenuated (4–18%) after β 1 -adrenergic receptor blockade ( P < 0.05). Despite attenuated RPP and ME LV responses, β 1 -adrenergic receptor blockade did not attenuate the mean LAD V vasodilatory response compared with placebo during poikilocapnic hypoxia (29.4 ± 2.2 vs. 27.3 ± 1.6 cm/s) and isocapnic hypoxia (29.5 ± 1.5 vs. 30.3 ± 2.2 cm/s). Hypercapnic hypoxia elicited a feedforward coronary dilation that was blocked by β 1 -adrenergic receptor blockade. These results indicate a direct influence of arterial Po 2 on coronary vascular regulation that is independent of [Formula: see text]. NEW & NOTEWORTHY In humans, arterial hypoxemia led to an increase in epicardial coronary artery blood velocity. β 1 -Adrenergic receptor blockade did not diminish the hypoxemic coronary response despite reduced myocardial O 2 demand. These data indicate hypoxemia can regulate coronary blood flow independent of myocardial O 2 consumption. A plateau in the mean left anterior descending coronary artery blood velocity-rate-pressure product relationship suggested β 1 -adrenergic receptor-mediated, feedforward epicardial coronary artery dilation. In addition, we observed a synergistic effect of Po 2 and Pco 2 during hypercapnic hypoxia.
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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 | 0.001 |
| 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 | 0.000 |
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".