Effects of cerebrospinal fluid acidity on cerebral blood flow and autoregulation in rats.

Using a ventriculocisternal perfusion method, the effects of cerebrospinal fluid (CSF) acidity of nonrespiratory origin on cerebral blood flow (CBF) and autoregulation of CBF were investigated. Three groups (six rats each) were studied: one group of sham operated rats, one control group with ventriculocisternal perfusion at normal pH (mean inflow pH +/- SD, 7.42 +/- 0.02), and one experimental group with ventriculocisternal perfusion at low pH (mean inflow pH +/- SD, 6.81 +/- 0.01). CBF was measured by the intracarotid xenon 133 method. Autoregulation was studied by repetitive measurements of CBF during an initial increase and then stepwise reduction of mean arterial blood pressure (MABP). No difference in CBF was found between sham operated and control rats with unperturbed pH (mean cisternal outflow pH +/- SD, 7.42 +/- 0.03) of CSF), and autoregulation was intact in both groups. In the experimental group, the mean CBF +/- SD was increased by 58%, from 127 +/- 33 mL/(100 g.min) before ventriculocisternal perfusion to 201 +/- 54 mL/(100 g.min) (P <.00001) during perfusion with acid CSF (mean cisternal outflow pH +/- SD, 7.23 +/- 0.04). In this group, the relationship between CBF and MABP was linear, thus indicating disrupted autoregulation. In conclusion, CSF acidity significantly increases CBF and impairs autoregulation of CBF.