Left Ventricular Twist Is Augmented in Hypoxia by β <sub>1</sub> -Adrenergic–Dependent and β <sub>1</sub> -Adrenergic–Independent Factors, Without Evidence of Endocardial Dysfunction
Bibliographic record
Abstract
Background: Left ventricular (LV) twist mechanics are augmented with both acute and chronic hypoxemia. Although the underlying mechanisms remain unknown, sympathetic activation and a direct effect of hypoxemia on the myocardium have been proposed, the latter of which may produce subendocardial dysfunction that is masked by larger subepicardial torque. This study therefore sought to (1) determine the individual and combined influences of β 1 -AR (β 1 -adrenergic receptor) stimulation and peripheral O 2 saturation (Sp o 2 ) on LV twist in acute and chronic hypoxia and (2) elucidate whether endocardial versus epicardial mechanics respond differently to hypoxia. Methods: Twelve males (27±4 years) were tested near sea level in acute hypoxia (Sp o 2 =82±4%) and following 3 to 6 days at 5050 m (high altitude; Sp o 2 =83±3%). In both settings, participants received infusions of β 1 -AR blocker esmolol and volume-matched saline (double-blind, randomized). LV mechanics were assessed with 2-dimensional speckle-tracking echocardiography, and region-specific analysis to compare subendocardial and subepicardial mechanics. Results: At sea level, compared with baseline (14.8±3.0°) LV twist was reduced with esmolol (11.2±3.3°; P =0.007) and augmented during hypoxia (19.6±4.9°; P <0.001), whereas esmolol+hypoxia augmented twist compared with esmolol alone (16.5±3.3°; P <0.001). At 5050 m, LV twist was increased compared with sea level (19.5±5.4°; P =0.004), and reduced with esmolol (13.0±3.8°; P <0.001) and Sp o 2 normalization (12.8±3.4°; P <0.001). Moreover, esmolol+normalized Sp o 2 lowered twist further than esmolol alone (10.5±3.1°; P =0.036). There was no mechanics-derived evidence of endocardial dysfunction with hypoxia at sea level or high altitude. Conclusions: These findings suggest LV twist is augmented in hypoxia via β 1 -AR–dependent and β 1 -AR–independent mechanisms (eg, α 1 -AR stimulation), but does not appear to reflect endocardial dysfunction.
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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 | 0.001 | 0.000 |
| Meta-epidemiology (narrow) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.001 |
| 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".