Local vascular response to change in carbon dioxide tension. Long term observation in the cat's brain by means of the hydrogen clearance technique.

Thirty six small hydrogen sensitive electrodes were inserted into the brains of 6 cats to evaluate the local vascular response to change in PaCO2, of cortex, subcortical white matter, and caudate nucleus. Repeated measurements (617) of local cerebral blood flow (ICBF) were performed over a period of 12 weeks. Within a PaCO2 range from 19 to 96 mmHg the local response of CBF was linear in most of the regions measured. The absolute local CO2 reactivity (CO2-R) showed a positive correlation to ICBF at PaCO2 = 40 mmHg (ICBF40) with the regression line: absolute CO2-R = 0.02 ICBF40 + 0.22, r = 0.71 (p less than 0.01). Therefore relative ICBF change was calculated in relation to ICBF40 to make comparisons between the CO2 response of different measuring days and of different regions examined. No significant change in relative CO2-R was observed during the 12 weeks interval. Differences of relative CO2-R between investigated regions were insignificant. The uniformity of relative CO2 response might support the hypothesis of a direct effect of PaCO2 or pH on the vessel wall. For comparison of CBF, the individual determination of CBF40 and relative CO2-R would be necessary.