Preserved Exercising Muscle Oxygen Delivery: Demand Matching After High Altitude Acclimatization: Because of or In Spite of Elevated Sympathetic Activation?

Abstract

We read with interest the work by Hansen and colleagues (2022) investigating mechanisms responsible for reduced exercising muscle vasodilatation and blood flow after high altitude acclimatization (HA). In this letter we raise a number of points for the author’s and reader’s consideration, arguing against the conclusion that this study has “found” the purpose of chronic hypoxic induced elevations in sympathetic activity. We offer an alternate explanation consistent with the data, and more consistent with the nature of elevated sympathetic activation in chronic hypoxia. In summary, a different experimental approach is required to tease out whether hypoxia-induced chronic elevation in systemic sympathetic activity is responding to or causing elevated vasodilator activation in exercising muscle. Therefore, whether preserved ΔO2del:Δ ̇O2 in HA is because of or in spite of chronic hypoxia-induced elevations in sympathetic activity remains to be determined.