PCO(2) and rate of formation of cerebrospinal fluid in the monkey

Abstract

Changes in CSF formation rate (Vf) with hypocapnia and hypercapnia were measured by the ventriculocisternal perfusion technique in 24 rhesus monkeys [Macaca mulatta] anesthetized with nitrous oxide. In addition cerebral blood flow (CBF) was measured by the hydrogen clearance method. Vf in control animals declined at a mean rate of 2.3 .mu.l/min each hour during the last 4.5 h of a 7 h perfusion, although variables known to affect Vf remained stable. Three hours after perfusion began, Vf of normocapnic controls was 41.4 .mu.l/min .+-. 5.4; CBF was 59 ml/100 g per min. When PCO2 [CO2 tension] was reduced to half of control, Vf fell to 35.6 .mu.l/min .+-. 6.3, and CBF fell by 27%. When PCO2 was doubled, Vf fell to 33.1 .mu.l/min .+-. 5.3, and CBF increased 3-fold. The difference in Vf was significant only for the hypercapnic group (P = 0.01). When animals were used as their own controls, there were no significant differences in Vf with hypercapnia compared to normocapnia. In the monkey variations of PCO2 within broad physiologic limits, which are sufficient to cause large changes in CBF, apparently have little effect on Vf.