Cerebral blood flow, brain metabolism and CSF acid-base balance in highlanders

Abstract

SUMMARY. Cerebral blood flow (Qc), local arterio-venous oxygen difference (0₂ AVD); and pH, O₂ and CO₂ partial pressures in arterial and jugular blood and in lumbar and cisternal cerebrospinal fluids (CSF) were measured in subjects born and residing at high altitude (3,800 - 4,800 m). Qc, was determined by 85Kr wash-out. Studies were made while subjects were breathing room air as control, while breathing gas mixtures or while voluntarily hyperventilating to alter Pao₂ and/or Paco₂. (1) Qc control values are lower than at sea level, 0₂ AVD larger and cerebral oxygen consumptions identical; cerebral respiratory quotient is close to 1.0, lactic acid production is negligible and glucose uptake fits with the local O₂ consumption. (2) Qc as function of Paco₂ describes a curve similar to that obtained at sea level but with a higher setting: therefore, for a given Paco₂. Qc is higher in highlanders than in lowlanders Correction of altitude hypoxia reduces highlanders' Qc to a lower value. Conversely, when deeper hypoxia is induced, Qc rises above control values. This influence of Pao₂, on Qc contrasts with what is observed at sea level. (3) A curvilinear relationship is found between cerebral mean circulatory transit time and hematocrits ranging from .35 to .84: sea level values fall on the same curve. Cerebral red cell flow is comparable at sea level and at altitude. (4) A consistent difference is found between cisternal and lumbar CSF : pH, and Po₂ are lower in lumbar CSF and Pco₂, higher than in cisternal fluid, whereas [HC03-] is not significantly different at the two sites: CSF heterogeneity is larger in highlanders than in lowlanders. Cisternal pH was not signilicantly different from sea level values.