Testing Ventilatory Acclimatization to High Altitude using the Hyperoxic Ventilatory Withdrawal Test
Bibliographic record
Abstract
Testing the transient hypoxic ventilatory response (HVR) is the most common method utilized for assessing ventilatory acclimatization in the setting of high altitude ascent, as the peripheral chemoreceptors become sensitized to hypoxia with chronic exposure. However, this test requires sophisticated equipment (e.g., gas tanks, feedback controllers) that lacks portability, and may lead to participant discomfort while already hypoxic while at altitude. The transient hyperoxic withdrawal (HVW) test is simple, portable and safe, using a small 100% O 2 tank available on most expeditions, and may better assess ventilatory acclimatization when participants are chronically hypoxic in high altitude fieldwork studies. We hypothesized that the HVW would be larger following 7‐days of ascent to 4240m while taking acetazolamide (Diamox; i.e., ventilatory stimulant) than an acute hypoxic control group at low altitude, thus having utility in detecting ventilatory acclimatization during ascent to high altitude. Using two separate recruitments, we tested two groups in two contexts. In Part A, we recruited 14 participants to assess the HVW in the context of acute, steady‐state hypoxia (~30‐min; F I O 2 13.5‐14%) in a laboratory context (1045m, P ATM ~665 mmHg). In Part B, 12 participants were recruited from a large research expedition to high altitude in the Nepal Himalaya, following 7 days of incremental ascent to high altitude (4240m, P ATM ~460 mmHg), while taking prophylactic Diamox (125 mg, BID). Participants were instrumented with a mouthpiece and bacteriological filter attached to a calibrated pneumotachometer (to measure inspired ventilation; V I ; L/min) and a peripheral pulse oximeter to measure oxygen saturation (SpO 2 ;%). First, while breathing roughly equivalent P I O 2 of ~85 mmHg at baseline (BL), both groups were exposed a single tidal breath of 100% O 2 from a 50L Douglas bag by switching a three‐way valve from room air to hyperoxia. The HVW was quantified as the change (delta) in V I from BL to the smallest instantaneous breath within 20‐sec of the hyperoxic stimulus indexed to the change in SpO 2 from BL to the peak following the hyperoxic breath, wherever it occurred (i.e., ventilatory response/oxygen change). We found that the HVW values from acute hypoxic participants had a mean of 0.34±0.23 L/min/%, while those who underwent acclimatization to high altitude hypoxia had a significantly larger HVW of 0.53±0.24 L/min/% (P=0.03). Our results suggest that the transient HVW test is a feasible method to detect peripheral chemoreceptor sensitization and ventilatory acclimatization in the context of high altitude ascent.
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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 | 0.001 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.004 | 0.001 |
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".