Regional Cerebral Pulsatile Hemodynamics During Isocapnic and Poikilocapnic Hyperthermia
Bibliographic record
Abstract
Hyperthermia reduces cerebral blood flow, but its impact on pulsatile hemodynamic forces is unknown. Thus, the objective of this secondary analysis was to assess cerebrovascular hemodynamic buffering (damping factor; DFi) during poikilocapnic (HT) and isocapnic (HT-C) hyperthermia. We hypothesized that HT would reduce posterior and anterior DFi, while HT-C would attenuate the reduction in DFi by limiting decreases in flow and increases in resistance. Ten healthy males were passively heated +2 °C from normothermia (BL). Mean arterial pressure was collected using an intra-radial catheter. Blood flow through the extracranial internal carotid artery (ICA) and vertebral artery (VA) was measured using vascular duplex ultrasound. Blood velocity through the middle cerebral artery (MCA) and the posterior cerebral artery (PCA) was measured using transcranial Doppler (TCD) ultrasound. DFi was calculated as the ratio of proximal to distal pulsatility index (PI): Anterior DFi = PI ICA / PI MCA ; Posterior DFi = PI VA / PI PCA . Mean arterial pressure decreased from BL (112±6.0 mmHg) during HT (96±9.7 mmHg, p =<0.001) and HT-C (99±9.6 mmHg, p =<0.001). Intravenous jugular pressure increased from BL (7.0±3.2 mmHg) during HT (8.3±3.0 mmHg, p =0.019) and HT-C (10.3±3.0, p =<0.001). Anterior PI increased in both ICA and MCA from BL (1.0±0.2 a.u; 0.8±0.2 a.u, respectively) during HT (1.6±0.4 a.u; 1.4±0.3 a.u; both p=<0.001), but only PI MCA increased from BL during HT-C (1.1±0.2 a.u, p=0.003). Both ICA and MCA PI HT-C (1.2±0.2 a.u; 1.1±0.2 a.u) was lower than HT (1.6±0.4 a.u; 1.4±0.3 a.u), p =0.001. Posterior PI increased in both the VA and PCA from BL (1.4±0.6 a.u; 0.8±0.2 a.u, respectively) during HT (2.3±0.5; 1.7±0.5 a.u, p =<0.001), but only PI VA increased from BL during HT-C (1.8±0.5 a.u; p =0.003). Both HT PI VA and PCA values were greater than HT-C (1.8±0.5 a.u [ p =<0.001]; 1.0±0.2 a.u [ p =0.006]). BL Anterior DFi (1.3±0.1 a.u) decreased in both HT (1.1±0.2 a.u; p =0.007) and HT-C (1.1±0.2 a.u; p =0.021). Posterior DFi did not change, p =0.116. BL CVC MCA (1.8±0.4 mmHg.ml.min -1 ) increased during HT (2.4±0.5 mmHg.ml.min -1 ; p = <0.001). Irrespective of P a CO 2 clamping, both hyperthermic conditions reduced anterior DFi, suggesting other mechanisms (i.e., intracranial pressure or myogenic tone) are responsible for cerebrovascular hemodynamic buffering. Furthermore, because posterior DFi responses were not observed, preferential buffering of the posterior cerebral circulation protects against deleterious pulsatile hemodynamic forces caused by hyperthermia. NSERC This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.
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How this classification was reachedexpand
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 itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, 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".