The effect of posture and positive pressure breathing on the hemodynamics of the internal jugular vein.
Bibliographic record
Abstract
BACKGROUND: Mathematical and mechanical models of cerebral circulation indicate that the resistance of the collapsed internal jugular veins limits cerebral blood flow during high acceleration (+Gz) and that positive pressure breathing (PPB) restores cerebral blood flow by elevating blood pressure and preventing collapse of the vein. The effect of acceleration and PPB on the jugular resistance and flow can be estimated by documenting changes in the lumen area and blood velocity. METHODS: The right internal jugular vein was imaged with vascular ultrasound in supine and seated human subjects exposed to 0-50 mm Hg of PPB. For each of the PPB posture combinations the vein was imaged at four locations along the length; resistance and flow were calculated using Poiseuille flow approximation. RESULTS: For the supine subjects, the lumen area, just above the inferior bulb, was 1.0 +/- 0.49 cm2, the estimated resistance was 0.13 +/- 0.07 x 10(-3) mm Hg x cm(-3) x min(-1), and the estimated blood flow was 931 +/- 477 cm3 x min(-1). In the sitting position, the lumen narrowed to 0.11 +/- 0.07 cm2, the resistance increased to 6.3 +/- 4.9 x 10(-3) mm Hg x cm(-3) x min(-1), and the blood flow dropped to 372 +/- 194 cm3 x min(-1). However, the vessel of a sitting subject can be completely reopened with PPB of 30 mm Hg or higher, and the resistance can be brought to supine levels. CONCLUSIONS: The results demonstrate that the internal jugular vein collapses with transition from supine to sitting position. This implies a significant increase in resistance which is inversely proportional to the square of the lumen area. However, the collapse can be prevented with sufficiently high PPB.
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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 | 0.001 |
| 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) | 0.000 | 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".