Responses of cerebral arteries to the changes in cerebral perfusion pressure

The responsiveness of cerebral pial arteries and arterioles to changes in systemic arterial blood pressure (SAP) was investigated. Using 9 cats anesthetized with chloralose and urethane, direct, simultaneous measurements of pial arterial pressure (PAP) and cerebral blood flow (CBF) were made during changes in SAP. SAP was varied between 25 and 140 mmHg by the hemorrhage and blood infusion methods. After a partial craniotomy. PAP was measured with a micropipette connected to a servo-controlled micropressure recording system. Punctured pial arteries were grouped into three types according to their diameters, 1A (291 +/- 33 microns), 2A (16 +/- 26 microns), and 3A (70 +/- 10 microns). CBF on the exposed cortex was measured with hydrogen clearance method. The PAPs measured were a linear function of SAP; PAP (1A) = 0.73/SAP-6.6 (r = 0.96), PAP (2A) = 0.62 X SAP-6.6 (r = 0.90), PAP (3A) = 0.61 X SAP-6.4 (r = 0.93). The result indicates that PAPs are entirely dependent on SAP and that SAP induced changes in PAPs are less in the smaller pial arteries. Regional CBF remained constant (55 +/- 4 ml/100 g/min) between 60 and 140 mmHg of SAP. A significant decrease in CBF was observed below 60 mmHg of SAP. Cerebrovascular resistances were calculated segmentally using the following formulas; large vessel resistances (LVR) = (SAP-PAP(1A]/CBF, middle vessel resistance = (PAP (1A)-PAP (3A]/CBF, and small vessel resistance = PAP (3A)/CBF. The changes in LVR, MVR, and SVR were almost identical between 70 and 140 mmHg of SAP. Below 70 mmHg of SAP, SVR showed the greatest decrease in resistance.(ABSTRACT TRUNCATED AT 250 WORDS)