Initial Orthostatic Hypotension Upon Rising From Squat Is Explained By Rapid Vasodilation In Leg Muscles
Bibliographic record
Abstract
Standing up is a frequent (3-10 %) trigger of loss of consciousness both in young and old subjects. This is due to an exaggerated transient BP (blood pressure) fall within 15 s upon standing, referred to as initial orthostatic hypotension (IOH). It is unclear what causes the marked increase in systemic vascular conductance that leads to IOH. Two possibilities have been proposed: 1) rapid vasodilation in the contracting leg muscles, and 2) systemic sympathetic withdrawal evoked by a sudden increase in right atrial pressure. PURPOSE: This study tested the hypothesis that IOH is due to rapid vasodilation in contracting leg muscles with the effort of standing. METHODS: 17 young healthy University undergraduates performed three different experimental conditions; standing up after a 10 s squat, a 1 min squat, or a 5 min squat. Beat by beat mean arterial blood pressure (MAP), cardiac output (CO), heart rate (HR) and stroke volume (finger photoplethysmography, Finometer) and right femoral artery blood flow (FABF; Doppler and Echo ultrasound) were recorded. RESULTS: data mean ±SE. Quiet standing represented baseline for all hemodynamic responses. Within 10 s of standing from squat, MAP (mmHg) fell to a nadir significantly below baseline in all conditions (baseline vs. standing from squat: 10 s squat 89.1 ±3.8 vs.72.0 ±3.9, 1 min squat 91.2 ±3.6 vs. 69.2 ±3.1, 5 min squat 91.1 ±3.1 vs. 62.8 ±4.4, all P<0.001). This occurred despite elevations in CO (L/min) (baseline vs. standing from squat: 10 s squat 4.2 ±0.3 vs. 6.7 ±0.5, 1 min squat 4.3 ±0.3 vs. 7.0 ±0.5, 5 min squat 4.1 ±0.3 vs. 7.6 ±0.5, all P<0.01) and was explained by large increases in total vascular conductance (TVC; (ml/min/100mmHg). The increase in TVC could be attributed primarily too increased 2-legged vascular conductance (LVC; ml/min/100mmHg) (TVC vs. LVC increase from standing baseline: 10 s squat 43.0 ±5.3 vs. 36.7 ±6.3, 1 min squat 47.8 ±4.5 vs. 44.6 ±6.8, 5 min squat 54.9 ±4.2 vs. 55.7 ±12.2) which co-insided with the MAP nadir. CONCLUSIONS: Rapid vasodilation in leg muscles with the effort of standing outstrips compensatory CO responses and is the cause of IOH.
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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 | 0.000 |
| 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".