[Changes in cerebral extracellular pH, cerebral blood flow and intracranial pressure induced by hypercarbic ventilation--assessment as a potential in vivo model of cerebral acidosis].

The effects of acidosis on ischemic brain damage are unclear and probably diverse. To establish an in vivo model of acidosis, the authors assess changes in extracellular brain pH (pHe), CBF and ICP induced by hypercarbic ventilation, and discuss the reliability and short comings of this experimental model. Acidosis was induced by increasing the inspired CO2 concentration in mechanically ventilated rats. pHe was measured with a pH-sensitive electrode implanted into the cortical mantle. The rats were divided into five groups according to the CO2 concentrations inspired: G-1, 0% control; G-2, -5-% CO2; G-3, -10-% CO2; G-4, -20-% CO2; G-5, -25-% CO2. Cortical blood flow was measured using a laser Doppler flowmeter, and ICP was also determined in each of the experimental groups. pHe decreased rapidly after the CO2 supply was turned on and remained almost constant at fixed concentrations of inspired CO2. pHe values diminished as the concentration of inspired CO2 decreased, as follows: G-2, -0.10 +/- 0.03; G-3, -0.31 +/- 0.08; G-4, -0.49 +/- 0.09; G-5, -0.64 +/- 0.10. The changes in pHe almost perfectly paralleled the changes in blood pH. The percentage increase in CBF was more than 200% in the G-2 groups and minimal increases in CBF, probably due to changes in blood pressure, were observed in from G-2 to G-5. Changes in CBF paralleled changes in systemic blood pressure, especially after the CO2 supply was turned off. ICP also rose after increasing the CO2 supply, and the pattern of changes was similar to that of CBF.(ABSTRACT TRUNCATED AT 250 WORDS)