Elevated inspired and end‐tidal PCO2 on the International Space Station
Bibliographic record
Abstract
The vision impairment intracranial pressure syndrome (VIIP) has recently been identified in astronauts living in space for long durations on the International Space Station (ISS). Although changes in hydrostatic pressure gradient resulting in chronic increases in cerebral artery and intracranial pressure are regarded as the most likely causes of VIIP, the elevated PCO2 in the atmosphere of the ISS is considered a potential contributor due to the vasodilatory effect of CO2 on cerebral and retinal arterioles. To date, there are no data published on the impact of elevated inspired PCO2 on arterial PCO2 during spaceflight. In the BP Reg study, we measured cardiac output by rebreathing providing an opportunity to obtain several breaths prior to rebreathing in which we could monitor inspired and expired PCO2. Here we report the averages from pre‐rebreathing PCO2 from inspiration and end‐tidal values (as indicators of the arterial PCO2) from 9 male astronauts during maneuvers in pre‐flight upright seated baseline testing and during spaceflight approximately 3 weeks before return to Earth. For each individual, all suitable breaths were averaged to a single value. Inspired PCO2 increased from pre‐flight baseline (0.6±0.12 mmHg) to inflight (3.8±0.44 mmHg, P<0.001). Expired, end‐tidal, PCO2 also increased from pre‐flight baseline (36.0±3.22 mmHg) to inflight (42.1±3.70 mmHg, P=0.004). The difference between end‐tidal PCO2 comparing inflight to pre‐flight (6.1±1.62 mmHg) was greater than the difference between inspired PCO2 comparing pre‐flight to inflight (3.3±0.46 mmHg, P<0.001). These data show that inspired PCO2 is elevated during spaceflight, but rather than an anticipated increase in alveolar ventilation to compensate for this increase in inspired PCO2, there might have been a reduction in alveolar ventilation resulting in an increase in end‐tidal PCO2 which is an indicator of arterial PCO2, although changes in ventilation‐perfusion should be considered. On Earth, a 6 mmHg increase in arterial PCO2 would be expected to increase brain blood flow over 15%; but, in spaceflight there appears to be no increase (Arbeille, 2001). Therefore, further studies are required to examine arterial PCO2 rather than end‐tidal, cerebrovascular reactivity to CO2 and cerebral blood flow to determine if elevated inspired PCO2 might contribute to the incidence of VIIP in astronauts. Support or Funding Information Supported by Canadian Space Agency
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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 | 0.000 | 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 | 0.000 |
| 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".