Initial orthostatic hypotension and cerebral blood flow regulation: effect of α<sub>1</sub>-adrenoreceptor activity
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Bibliographic record
Abstract
We examined the hypothesis that α(1)-adrenergic blockade would lead to an inability to correct initial orthostatic hypotension (IOH) and cerebral hypoperfusion, leading to symptoms of presyncope. Twelve normotensive humans (aged 25 ± 1 yr; means ± SE) attempted to complete a 3-min upright stand, 90 min after the administration of either α(1)-blockade (prazosin, 1 mg/20 kg body wt) or placebo. Continuous beat-to-beat measurements of middle cerebral artery velocity (MCAv; Doppler), blood pressure (finometer), heart rate, and end-tidal Pco(2) were obtained. Compared with placebo, the α(1)-blockade reduced resting mean arterial blood pressure (MAP) (-15%; P < 0.01); MCAv remained unaltered (P ≥ 0.28). Upon standing, although the absolute level of MAP was lower following α(1)-blockade (39 ± 10 mmHg vs. 51 ± 14 mmHg), the relative difference in IOH was negligible in both trials (mean difference in MAP: 2 ± 2 mmHg; P = 0.50). Compared with the placebo trial, the declines in MCAv and Pet(CO(2)) during IOH were greater in the α(1)-blockade trial by 12 ± 4 cm/s and 4.4 ± 1.3 mmHg, respectively (P ≤ 0.01). Standing tolerance was markedly reduced in the α(1)-blockade trial (75 ± 17 s vs. 180 ± 0 s; P < 0.001). In summary, while IOH was little affected by α(1)-blockade, the associated decline in MCAv was greater in the blockade condition. Unlike in the placebo trial, the extent of IOH and cerebral hypoperfusion failed to recover toward baseline in the α(1)-blockade trial leading to presyncope. Although the development of IOH is not influenced by the α(1)-adrenergic receptor pathway, this pathway is critical in the recovery from IOH to prevent cerebral hypoperfusion and ultimately syncope.
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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) | 0.002 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.002 |
| 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