Elevated Cardiorespiratory Fitness is Associated with Blunted Cerebral Pressure‐Flow Relationships
Bibliographic record
Abstract
There appears to be a “hemodynamic paradox” associated with elevated cardiorespiratory fitness; in that it has a differential impact on cerebral blood flow and orthostatic tolerance. A reduction in orthostatic tolerance with high cardiorespiratory fitness may be related to a blunted cerebral pressure‐flow relationship during rapid changes in blood pressure, and not only a consequence of inadequate cerebral perfusion. However, research on how cardiorespiratory fitness influences cerebral pressure‐flow relationships during rapid changes in blood pressure, and the consequences for orthostatic tolerance remain equivocal. Mean arterial pressure (MAP; finger photoplethysmography) and middle cerebral artery flow velocity (MCAv; transcranial Doppler ultrasound) were continuously monitored in 19 male endurance athletes (V̇O 2 max: 56±5 mL·kg −1 ·min −1 ) and 8 inactive/moderately active control participants (39±5 mL·kg −1 ·min −1 , P<0.01). Orthostatic tolerance was assessed by the prevalence of presyncope during a 20‐min 70° head‐up tilt. Cerebral pressure‐flow relationships were assessed by: [1] the time delay before onset of regulation (increase in the cerebrovascular conductance index (MCAv mean /MAP)) and [2] rate of regulation, after transient hypotension induced by bilateral thigh‐cuff release and sit‐to‐stand, and transfer function analysis (TFA) of blood pressure and MCAv responses during [3] spontaneous and [4] forced oscillations induced via 5‐min of repeated squat‐stand maneuvers at both 0.05 and 0.10 Hz. Prevalence of presyncope was not different between groups (p=0.41). The time delay before onset of regulation tended to be longer in athletes compared to controls after thigh‐cuff deflation (p=0.11) and prolonged after sit‐to‐stand (3.2 ± 1.6 vs. 1.4 ± 1.1 s; p=0.01), and the latter correlated with V̇O 2max (r=0.46, p=0.03). Rate of regulation was similar between groups irrespective of the technique employed. Athletes had lower TFA phase in the low frequency (p<0.01) range and higher TFA gain during 0.1 Hz squat‐stand compared to controls (p=0.01). Metrics describing cerebral pressure‐flow relationships did not correlate with orthostatic tolerance. These results indicate an attenuated ability of the cerebral vasculature to react to slow rhythmical oscillations as well as rapid and large changes in blood pressure in fit individuals. However, these functional cerebrovascular adaptations do not influence orthostatic tolerance. Support or Funding Information The present study was funded by the Ministère de l'Education, du Loisir et du Sport du Québec, and the Foundation of the Institut universitaire de cardiologie et de pneumologie de Québec
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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 | 0.002 |
| 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) | 0.002 | 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".