Breathing maneuvers as a metabolic coronary vasodilator for first-pass perfusion MR imaging
Bibliographic record
Abstract
CMR can detect myocardial ischemia by first-pass perfusion and by oxygenation-sensitive CMR (OS-CMR) imaging. While the former can reliably determine myocardial blood flow, the latter integrates other determinants of myocardial oxygenation. Simple breathing maneuvers can trigger a coronary vascular response, which can be monitored by OS-CMR imaging. We studied 24 healthy volunteers (37 ± 12 years; 62.5% men) in a clinical 3T MRI system. Each exam included three sets of first pass perfusion images, (1) at rest and, after 1 minute of hyperventilation during (2) a short breath-hold (SBH) or (3) a long breath-hold (LBH), performed in random order. A reader blinded to the maneuver applied, analyzed signal intensity upslope, upslope index and time between 20 and 80% of maximal signal. For inter-observer variability, a different, blinded, reader repeated the analysis in 4 volunteers. Demographics and LV function data are presented in Table 1 . All volunteers tolerated the breathing maneuvers well and completed the study protocol. The average upslope at rest was 1.34 ± 0.58, and increased by 39% during the SBH (1.86 ± 0.70; p < 0.05), diminishing to 1.77 ± 0.82 at the LBH step. The upslope started at 13.8 ± 5.5 and 49.5 ± 7.3 seconds of breath-hold, respectively, on SBH and LBH. Figure 1 shows the relationship between time of breath-hold after hyperventilation and both the individual values of up-slopes and rate-pressure products (RPP). The upslope curve shows two peaks, a early one (15 seconds) coinciding with the peak of the RPP curve; a second one at about 50 seconds, not promoted by the RPP. The upslope index, which accounts for the arterial input, was higher at this late step (rest: 0.077 ± 0.016; SBH: 0.083 ± 0.015; LBH: 0.095 ± 0.019; p < 0.01), as was the myocardial perfusion reserve index (1.25 ± 0.22 vs. 1.09 ± 0.17). In a multiple regression model that included gender, RPP, breath-hold time, caffeine intake, BSA-indexed mass and set order, only gender, RPP and breath-hold time were independently and significantly related to the upslope (R= 0.771; p < 0.001). A different reader repeated the analysis in 4 volunteers; the intra-class correlation for the up-slope was excellent, of 0.990 (95% CI: 0.943-0.997; p < 0.001). Individual values of upslope and rate-pressure products trough time of breath-hold. The upslope curve (filled circles) shows two peaks. The blood flow response to simple breathing maneuvers can be demonstrated by first-pass perfusion CMR, with a early peak dependent on RPP increase, and a late peak due to the vasodilatory effect of long breath holds. Confounding effects of breathing may also have implications for CMR first-pass perfusion imaging performed with pharmacological vasodilators.
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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 | 0.001 | 0.002 |
| Meta-epidemiology (narrow) | 0.001 | 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 | 0.001 | 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".