INFLUENCE OF CSF CALCIUM AND MAGNESIUM ON VENTILATORY RESPONSE TO CARBON-DIOXIDE DURING HYPEROXIA

Respiratory responses to inhaled CO2 were measured in anesthetized cats during perfusion of the ventriculocisternal system with artifical CSF. A study was performed to evaluate the effect of changes in the MG and/or Ca concentration of the CSF on the CO2 response curve which was described as .ovrhdot.VE [ventilation] = S [slope (sensitivity perameter to CO2)] (PCSF,CO2 - B) [concentration of CO2 in CSF in outflowing perfusate-constant]. A decrease of S was observed when the Mg concentration of the perfusion fluid was increased; the B-value remaining the same. The reverse was true down to Mg concentrations of 0.6 mmol .cntdot. l-1. Below this concentrations, S remained the same or decreased; the B-value was lowered. When both the Ca and Mg concentrations of the CSF were changed, the relation between S and these concentrations could be described as to be proportional to CCaa .cntdot. CMgb. The effect of changes in the Ca concentration was much more pronounced than comparable changes of the Mg concentration as reflected by the magnitude of the exponents a and b which were found to be -2.80 (S.D. 0.11) and -0.60 (S.D. 0.03), respectively.