25 Optic nerve sheath diameter during ascent to high altitude in Sherpa and Lowlanders
Bibliographic record
Abstract
Objectives Raised intracranial pressure is proposed to be a mediator of acute mountain sickness. However, establishing this is difficult due to the invasive nature of intracranial pressure measurement. In this study we used a non-invasive estimate of intracranial pressure, ultrasound of the optic nerve sheath diameter (ONSD), during ascent to high altitude in both low-altitude residents and high-altitude natives. Methods 42 (30 low-altitude, 12 high-altitude residents) participants ascended from 1300 to 5050m with ONSD, cerebral blood flow (CBF, duplex ultrasound), and arterial blood gas measurements at 1300, 2700, 3400, 4125 and 5050m. Lake Louise acute mountain sickness scores were collected at 5050m. Results Ascent to high-altitude was associated with an increase in median [IQR] ONSD (4.61mm [4.39–5.26] at 1300m to 6.47mm [5.78–7.34] at 5050m). At 5050m, those with more symptoms of acute mountain sickness had larger optic nerve sheath diameters (r =0.47, p=0.015). The increase in ONSD was related to an increase in CBF with altitude (p=0.005). High-altitude residents ascending to altitude had higher baseline ONSD, however this did not increase with altitude as much as low-altitude residents (interaction p=0.0001). Conclusions Increased optic nerve sheath diameter with ascent to altitude supports the theory that intracranial pressure rises during ascent to high altitude and that this may contribute to acute mountain sickness. The increases in ONSD are mediated in part by increased cerebral blood flow. The smaller increase in ONSD in Sherpa may protect against acute mountain sickness.
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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".