Inspiratory CO2 increases orthostatic tolerance during repeated tilt.
Bibliographic record
Abstract
INTRODUCTION: The partial pressure of end tidal CO2 (PetCO2) is known to decrease with head-up tilt. Decreases in arterial CO2 reduce cerebral blood flow (CBF) and may increase the incidence of presyncope. We measured cerebral and central cardiovascular responses to repeated tilt where: 1) PetCO2 was allowed to change with tilt (eucapnic): and 2) PetCO2 was clamped at supine levels (isocapnic). METHODS: In eight healthy subjects breath-by-breath measurements were made of ventilation (VE) and PetCO2 along with beat-by-beat measurements of blood pressure (BP), heart rate (HR) and middle cerebral artery mean flow velocities (MFV). Following 30-min in the supine position, a series of six 10-min 90 degrees head-up tilts were performed, with 30-s of supine between each. Presyncopal subjects were returned immediately to the supine position. RESULTS: Statistical comparisons were made between the supine, and the first and last minute of the first tilt. BP, HR responses were not different between the eu- and isocapnic conditions; however, by the end of the first tilt VE was significantly higher than supine. MFV and BP at brain level decreased and HR increased from supine to tilt. MFV was higher in the isocapnic compared with the eucapnic condition but decreased from the beginning to the end of the first tilt in both conditions (i.e., tilt #1: eucap. 49.4 to 46.7; isocap. 65.0 to 59.6 cm s(-1); p < 0.05) while the BP remained constant. Five subjects were presyncopal in the study. With isocapnic tilt, presyncopal time was not reduced but was extended in four of the five subjects (2.2, 5.5, 6.3 and 31 min) yet at presyncope the values for MFV, BP and HR were the same in both conditions. CONCLUSIONS: Inspiratory CO2 contributed to increased MFV at the beginning of tilt and increased orthostatic tolerance.
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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) | 0.001 | 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) | 0.002 | 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".