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

Abstract

Changes in cerebrospinal fluid formation rate (VF) with hypocapnia were measured by the ventriculocisternal perfusion technique in 24 rhesus monkeys anesthetized with nitrous oxide. In addition cerebral blood flow (CBF) was measured by the hydrogen clearence methods, Vf in control animals declined at a mean rate of 2.3 mul/min each hour during the last 4.5 h of a 7-h perfusion although variables known to effect Vf remained stable. Three hours after perfusion began, Vf of normocapnic controls was 41.4 mul/min +/- 5.4; CBF, 59P ML/100 G PER MIN. When Pco(2) was reduced to half of control, Vf fell to 35.6 mul/min +/- 6.3 and CBF fell by 27%. When Pco(2) was doubled, Vf fell to 33.1 mul/min +/- 5.3 and CBF increased threefold. The difference in Vf id significant only for the hypercapnic group (p=0.01). When animals were used as their own controls, three were no significant differences in Vf with hypercapnia compared to normocapnia. These results indicated that in the monkey variations of Pco(2) within broad physiologic limits, which are sufficient to cause large changes in CBF, have little effect of Vf.

Effects of pCO2 on the CSF Turnover Rate in Rats Monitored by Gd-DTPA Enhanced T1-Weighted Magnetic Resonance Imaging.

“…The sharp increase in this rate might explain the discrepancies among previous studies in the hypocapnia. Even though we should be aware of the differences between species, Oppelt et al [6] reported significant inhibition by using the lowest pCO 2 (10 mmHg), and negative results were reported with a relatively higher pCO 2 (16 and 20 mmHg) [2,5]. No effect on the CSF secretion rate resulting from hypercapnia was shown in our experiments, which is in agreement with most of the previous reports [3,4,6].…”

“…There are conflicting reports on the effects of respiratory alkalosis and acidosis on the dynamics of CSF. In the hypocapnia, Oppelt et al [6] reported a 46% decrease in dogs (pCO 2 ϭ10 mmHg), and Martins et al [5] reported a tendency for a decrease in monkeys (pCO 2 ϭ16Ϯ4.2 mmHg). Meanwhile, the effect of hypocapnia was not observed in a report on an experiment on dogs (pCO 2 ϭabout 20 mmHg [2]).…”

“…In the hypercapnia, no effects were found on the CSF production in three reports on studies employing rabbits (18% CO 2 inhalation [3]), dogs (pCO 2 ϭ76 mmHg [6]), and cats (pCO 2 ϭ 80.9 mmHg [4]). However, Martins et al [5] found a 20% inhibition in monkeys (pCO 2 ϭ58Ϯ9.5 mmHg), and Heisey et al [12] reported on a complicated relationship between the CSF production rate and the perfusion pressure of the cerebrocisterna in cats (pCO 2 ϭ 51Ϯ3.5 mmHg).…”

“…Vasoconstriction induced by hypocapnia might decrease CSF production. Martins et al [5] demonstrated a gradual decrease of cerebral blood flow (CBF) rate in the pCO 2 range of 40 to 20 mmHg. However, hypercapnia revealed a much more significant effect: The amount of CBF was increased more than 2 times when pCO 2 increased from 40 to 60 mmHg.…”

“…This suggested that the formation of CSF might be altered by carbon dioxide. However, we have seen conflicting results in regard to the influence of hypercapnia and hypocapnia on CSF formation [2][3][4][5][6]. To confirm the effects of CO 2 , we developed a new method to measure local CSF turnover rate in the lateral ventricle of the rat brain.…”