Acute Reduction of Ambient Air Pressure Enhances Arterial Vasodilation in Murine Resistance Arteries Independently of Endothelial Factors
Bibliographic record
Abstract
Introduction Epidemiological studies have found populations living at higher elevations are at lower risk for acute myocardial infarction (MI) than those at lower elevations, even after adjustments for confounders. The mechanism for this observation is not known. Since atmospheric air pressure varies inversely with elevation, and air pressure exerts compressive force on vascular structures, reduced compressive force on arteries due to elevation‐related reductions in atmospheric pressure might alter arterial function. This could be a potential mechanism. We hypothesized that acute exposure to lower air pressure will dilate arteries and increase arterial vasodilation to reduce peripheral vascular resistance. Methods Second order mesenteric arteries (n=7) were isolated from C57BL/6 male mice (n=7, age 3.2±0.9 months) and perfused with Ca2 + ‐free saline solution to assess passive properties of the vessels in a pressure myograph. This system was placed in a custom‐designed hypobaric chamber and arterial function was studied ex‐vivo at acute exposure to three barometric pressure steps: 754 mmHg (room pressure or control), 714 mmHg (p1) and 674 mmHg (p2). Active vessel responses in the presence of L‐NAME, a nitric oxide inhibitor, and Meclofenamate, a cyclooxygenase inhibitor, were assessed with mechanical manipulation of perfusion pressure (4–140 mmHg) or flow rate (0–70 μL/min). Lumen diameter was measured using a micrometer, with manometers for measurement of pressure drop across the vessel. Results Under static conditions, vessel diameters at p1 and p2 increased by 20.9±9.3% and 28.2±8.6% compared to baseline diameter at room pressure (p<0.01 vs. control for p1 and p2). Flow‐mediated vasodilation contributed little additional dilation. At a fixed flow rate of 70 μLmin −1 , vessels reached maximum diameters of 108.6 ±13.6μm at p1 and 120.5±13.0 at p2 versus 106.0±4.0 μm for the control condition. This observed vasodilation was not diminished in the presence of L‐NAME and Meclofenamate. Vascular resistance was significantly reduced at p2 compared to control (2.14±0.60 mmHg*min/μL vs. 3.21±0.49 mmHg*min/μL, p < 0.05). Conclusion We conclude that acute exposure to reduced barometric pressure increases artery diameter and decreases resistance across vessels ex‐vivo in an endothelium‐independent manner.
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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 | 0.000 |
| 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 | 0.001 |
| Insufficient payload (model declined to judge) | 0.002 | 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".