Sex Differences in Orthostatic Tolerance Are Mainly Explained by Blood Volume and Oxygen Carrying Capacity
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Bibliographic record
Abstract
OBJECTIVES: The reduced orthostatic tolerance (OT) that is characteristic of the female sex may be explained by multiple phenotypic differences between sexes. This study aimed to elucidate the mechanistic role of blood volume (BV) and oxygen carrying capacity on sex differences in OT. DESIGN: Experimental intervention. SETTING: University of Calgary, Main Campus, Calgary, AB, Canada. SUBJECTS: Healthy women and men ( n = 90) throughout the adult lifespan (20–89 yr) matched by age and physical activity. INTERVENTIONS: Incremental lower body negative pressure (LBNP) in all individuals. Blood withdrawal and oxygen carrying capacity reduction in men to match with women’s levels. MEASUREMENTS AND MAIN RESULTS: Transthoracic echocardiography and central blood pressures were assessed throughout incremental LBNP for 1 hour or until presyncope. Blood uniformization resulted in a precise sex match of BV and oxygen carrying capacity ( p ≥ 0.598). A third of women (14/45) and two thirds of men (31/45) prior to blood uniformization completed the orthostatic test without presyncopal symptoms ( p -for-sex < 0.001). After blood uniformization, seven out of 45 men completed the test ( p -for-sex = 0.081). Left ventricular end-diastolic volume (LVEDV) and stroke volume (SV) were progressively reduced with LBNP in both sexes, with women showing markedly lower volumes than men ( p < 0.001). Blood uniformization did not eliminate sex differences in LVEDV and SV. CONCLUSIONS: Sex differences in OT are not present when BV and oxygen carrying capacity are experimentally matched between sexes throughout the adult lifespan.
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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 it