No Change of Mean Blood Velocities in Cerebral Arteries during Eucapnic, Passive Hyperthermia in Humans
Bibliographic record
Abstract
With mean arterial pressures between ∼60 and ∼160 mm Hg there is an autoregulation or maintenance of human cerebral blood flow. During hyperthermia, however, humans demonstrate thermal hyperpnea or hyperthermic-induced hyperventilation that reduces the partial pressure of arterial CO2 or end-tidal CO2 (PETCO2). This hypocapnia is suggested to give a cereobrovascular vasoconstriction and a reduced cerebral perfusion. Previous human studies in hyperthermia have, however, only examined the middle cerebral artery (MCA) blood velocity. It is not apparent how hyperthermia influences the blood velocities in other cerebral vessels during a clamping of the PETCO2 at eucapnic partial pressures. PURPOSE: It was hypothesized blood velocity in the middle cerebral artery (MCA), the posterior cerebral artery (PCA) and the basilar artery (BA) would remain constant in eucapnic, hyperthermic humans. METHODS: During eucapnic breathing, four male volunteers (Ht:178.0 ± 11.1 cm; Wt: 76.5 ± 5.8 kg; Age: 22.0 ± 1.4 yr; mean ± SD) with normothermic (N) and passive hyperthermic (H) core temperatures had blood velocities assessed in the MCA, PCA, and BA with a transcranial Doppler. Each volunteer was passively rendered hyperthermic in a climatic chamber (∼50°C, ∼25% RH) while clad in a vapor impermeable suit. Analyses included means comparisons with 2-tailed, paired t-tests with the significance level set at 0.05. RESULTS: Core temperature was raised from 37.0 ± 0.5°C to 38.2 ± 0.2°C (P=0.04). Pulmonary ventilation increased from 12.3 ± 1.1 L/min during normothermia to 16.2 ± 2.8 L/min during hyperthermia (P=0.03). No changes were evident in blood velocities for MCA (N: 44.8 ± 3.8 cm/s; H: 44.1 ± 6.3 cm/s; P=0.84), PCA (N: 39.5 ± 3.5 cm/s; H: 39.0 ± 4.0 cm/s; P=0.17) and BA (N: 30.3 ± 4.8 cm/s; H: 29.4 ± 3.0 cm/s: P=0.67). CONCLUSIONS: Eucapnic, passive hyperthermia in humans results in no changes in mean blood velocity in different cerebral arteries. This supports cerebral autoregulation is effective at maintaining cerebral perfusion in humans during eucapnia and passively-induced hyperthermia. Supported by the Natural Sciences and Engineering Research Council of Canada.
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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 | 0.001 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.001 | 0.002 |
| Science and technology studies | 0.000 | 0.003 |
| Scholarly communication | 0.000 | 0.001 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| 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".