UBC‐Nepal expedition: phenotypical evidence for evolutionary adaptation in the control of cerebral blood flow and oxygen delivery at high altitude
Notice bibliographique
Résumé
Key points Sherpa have lived in the Nepal Himalaya for 25–40 thousand years and display positive physiological adaptations to hypoxia. Sherpa have previously been demonstrated to suffer less negative cerebral side effects of ascent to extreme altitude, yet little is known as to whether or not they display differential regulation of oxygen delivery to the brain compared to lowland natives. We demonstrate that Sherpa have lower brain blood flow during ascent to and acclimatization at high altitude compared to lowlanders and that this difference in flow is not attributable to factors such as mean arterial pressure, blood viscosity and pH. The observed lower cerebral oxygen delivery in Sherpa likely represents a positive adaptation that may indicate a cerebral hypometabolic conservation of energy at altitude and/or decreased risk of other cerebral consequences such as vasogenic oedema. Abstract Debilitating side effects of hypoxia manifest within the central nervous system; however, high‐altitude natives of the Tibetan plateau, the Sherpa, experience negligible cerebral effects compared to lowland natives at extreme altitude. Phenotypical optimization of the oxygen cascade has been demonstrated in the systemic circulation of Tibetans and Sherpa, likely underscoring their adapted capacity to thrive at altitude. Yet, little is known as to how the cerebral circulation of Sherpa may be adapted. To examine potential differences in cerebral oxygen delivery in Sherpa compared to lowlanders we measured arterial blood gases and global cerebral blood flow (duplex ultrasound) during a 9 day ascent to 5050 m. Although cerebral oxygen delivery was maintained during ascent in lowlanders, it was significantly reduced in the Sherpa at 3400 m (−30.3 ± 21.6%; P < 0.01) and 4371 m (−14.2 ± 10.7%; P = 0.03). Furthermore, linear mixed effects modelling indicated that independent of differences in mean arterial pressure, pH and blood viscosity, race accounts for an approximately 100 mL min −1 (∼17–34%) lower cerebral blood flow in Sherpa compared to lowlanders across ascent to altitude ( P = 0.046). To ascertain the role of chronic hypoxia independent of the ascent, Sherpa who had not recently descended were also examined at 5050 m. In these Sherpa, cerebral oxygen delivery was also lower compared to lowlanders (∼22% lower; P < 0.01). We highlight new information about the influence of race and genetic adaptation in the regulation of cerebral oxygen delivery. The lower cerebral oxygen delivery in the Sherpa potentially represents a positive adaptation considering Sherpa endure less deleterious cerebral consequences than lowlanders at altitude.
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Comment cette classification a été obtenuedéplier
Prédiction distillée sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Apprise à partir de 10 348 étiquettes directes de Codex et de 10 348 étiquettes directes de Gemma. Le mode candidate est l'union des têtes enseignantes seuillées; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont ni des étiquettes humaines ni des étiquettes directes de modèles de pointe.
Scores Codex et Gemma par catégorie
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,000 | 0,000 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,000 | 0,000 |
| Études des sciences et des technologies | 0,000 | 0,000 |
| Communication savante | 0,000 | 0,000 |
| Science ouverte | 0,000 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,000 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,000 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule tête enseignante, pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».