Fig. 1

Comparisons of solute levels and pH between venous blood and CSF. The distribution of pO₂ was higher in CSF than in venous blood, as were those of pCO₂ and lactic acid, indicating that the brain and spine discharge CO₂ and lactic acid into the CSF. The CSF was significantly more acidic than the venous blood. Levels of HCO³⁻ and Na⁺ ions did not differ significantly between the venous blood and CSF. The grey-filled areas show the generally accepted normal ranges in arterial blood. All p-values are the result of a paired t-test. CSF, cerebrospinal fluid; HCO₃⁻, bicarbonate ion; pCO₂, carbon dioxide partial pressure; pO₂, oxygen partial pressure