UBC-Nepal Expedition: Markedly lower cerebral blood flow in high altitude Sherpa children compared to children residing at sea-level

Developmental cerebral hemodynamic adaptations to chronic high altitude exposure, such as in the Sherpa population, are largely unknown. To examine hemodynamic adaptations in the developing human brain, we assessed common carotid (CCA), internal carotid (ICA) and vertebral artery (VA) flow and middle cerebral artery (MCA) velocity in 25 (9.6±1.0 y, 129±9 cm, 27±8 kg, 14 girls) Sherpa children (3800m, Nepal) and 25 (9.9±0.7 y, 143±7 cm, 34±6 kg, 14 girls) age-matched sea-level children (344m, Canada) during supine rest. Resting gas exchange, blood pressure, oxygen saturation and heart rate were assessed. Despite comparable age, height and weight were lower (both P<0.01) in Sherpa compared to sea-level children. Mean arterial pressure, heart rate and ventilation were similar, whereas oxygen saturation (95±2 vs. 99±1%, P<0.01) and end-tidal PCO₂ (24±3 vs 36±3 mmHg, P<0.01) were lower in Sherpa children. Global cerebral blood flow was ~30% lower in Sherpa compared to sea-level children. This was reflected in a lower ICA flow (283±108 vs. 333±56 ml/min, P=0.05), VA flow (78±26 vs 118±35 ml/min, P<0.05) and MCA velocity (72±14 vs 88±14 cm/s, P<0.01). CCA flow was similar between Sherpa and sea-level children (425±92 vs. 441±81 ml/min, P=0.52). Scaling flow and oxygen uptake for differences in vessel diameter and body size respectively, led to the same findings. A lower cerebral blood flow in Sherpa children may reflect specific cerebral hemodynamic adaptations to chronic hypoxia.

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