Effect of Age on the Cerebrovascular Responses to the Initiation of Dynamic Exercise
Bibliographic record
Abstract
The rapid hemodynamic changes induced by the initiation of dynamic exercise robustly challenge the regulatory processes which ensure that cerebral perfusion is appropriately maintained. We sought to determine whether age alters the cerebrovascular responses to the initiation of dynamic exercise. Ten young (mean±SD, 23±2 years, 2 women) and eight older (65±3 years, 1 women) individuals performed a 5‐minute bout of semi‐recumbent leg cycling exercise at 75W. Blood pressure, cardiac output, total peripheral resistance (Finometer) and middle cerebral artery blood flow velocity (MCAv: transcranial Doppler ultrasound) were monitored. Gosling pulsatility index (PI) was calculated as; (systolic MCAv–diastolic MCAv)/mean MCAv. Beat‐to‐beat data during exercise were linearly interpolated at 1 Hz. At baseline, MAP (mean±SEM, young, 87±3; older, 93±4 mmHg), MCAv (young, 57±2; older, 56±3 cm/s) and PI (young, 0.88±0.4; older, 0.92±0.4 cm/s) were not different in young and older groups (P>0.05), while TPR tended to be lower (young, 16±1; older, 21±2 mmHg/L·min −1 , p=0.08) and CO tended to be higher (young, 5.6±0.4; older, 4.6±4 L·min −1 ; p=0.13) in the young. The initiation of exercise evoked a rapid and sustained increase in cardiac output and fall in total peripheral resistance, that was blunted in the older group. Blood pressure fell transiently at exercise onset, reaching a similar nadir (young, −9.9±2.8; older, −10.0±2.9 mmHg; p>0.05) after a similar duration (15±2; older, 13±2 s; p>0.05) in both groups. MCAv also fell transiently at the initiation of exercise (young, −5.3±1.5; older, −5.1±1.9 cm/s, p>0.05), but the nadir was reached later in the older group (young, 20±2; older, 29±2 s, p<0.05). PI increased rapidly at the onset of exercise in young individuals, but was elevated more sluggishly in older individuals. Collectively, these findings suggest that older individuals exhibit delayed cerebrovascular adjustments at the onset of exercise. Support or Funding Information This research was supported by a National Sciences and Engineering Research Council Discovery Grant and Canadian Research Chair in Cerebrovascular Physiology (PNA), the Swiss National Science Foundation (DF) and the British Heart Foundation (JPF).
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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) | 0.000 | 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) | 0.001 | 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".