Yamashita, K; Yamaguchi, S; Kobayashi, S
It has been noted that perfluorochemicals (PFC) which were developed as artificial blood substitutes, protect against ischemic brain injury by their ability to serve as oxygen carriers. It is also known that normovolemic hemodilution (HD) improves cerebral blood flow (CBF) and neurological symptoms in cerebral infarction. However, there are few reports concerning the effect of PFC on the collateral circulation via pial anastomoses in cases of middle cerebral artery (MCA) occlusion. The ability to record the pial arterial blood pressure (PAP) without interfering blood flow now makes it possible to measure the segmental resistance of cerebral vessels. By using this method, one can measure collateral vessel resistance through pial anastomoses following MCA occlusion. In this paper, we studied the protective effects of PFC combined with HD on ischemic brain injury with the focus on the collateral circulation via pial anastomoses following occlusion of the MCA. Twenty adult cats were studied: control, 8; HD, 5; Fluosol (Fluosol-DA), 7. The systemic arterial pressure (SAP) and PeCO2 were continuously monitored. Subsequently the MCA was occluded via the transorbital approach. CBF in the ectosylvian gyrus (central area of the ischemic lesion) was measured by the hydrogen clearance method. A small pial artery about 100 .mu.m in diameter on the exposed ectosylvian gyrus was punctured nonocclusively with a micropipette filled with 2 M sodium chloride which was connected to a servo-null micropressure system (Model 900, W-P Instruments, Inc. U.S.A.). The electroencephalogram (EEG) was recorded from the ectosylvian gyrus. EEG frequency was analyzed by Fast Fourier transform with a signal processor (7 TO 8, Sanei) and the spectral power of the EEG was calculated by summing the Fourier coefficients covering the frequency ranging of 2-12 Hz. In the HD group, hemodilution was performed as follows: About 20 ml of blood was removed from the femoral artery and simultaneously low molecular dextran was normovolemically infused into the femoral vein from 10 minutes after ischemia until the hematocrit (Hct) was reduced to 24%. In the Fluosol group, Fluosol was infused normovolemically beginning 10 minutes after ischemia until the Hct was reduced to 25% in the same way. Data were compared using Student's t-test. No significant differences in SAP and PAP were observed among the three groups throughout the experiment. On the other hand, the values of CBF in both the Fluosol and HD groups were significantly higher than in the control group at the 90-min point after MCA occlusion. Upstream resistance ((SAP-PAP)/CBF), which was considered as vascular resistance of the collateral circulation via pial anastomoses, was significantly lower in both the Fluosol and HD groups compared with the control group at the 90-min point after MCA occlusion. Furthermore, downstream resistance (PAP/CBF), which was also considered as vascular resistance in cerebral parenchyma, was significantly lower in the Fluosol group compared with the control group at the 30-min point after MCA occlusion. These significant differences persisted until the 180-min point. The spectral power of the EEG decreased in all groups after ischemia. Fluosol group showed a significantly greater recovery of spectrum power than the control group at both the 120-min and 180-min points, but there was no significant difference between the Fluosol group and HD group after MCA occlusion. These results suggest that PFC may improve CBF by improving collateral circulation in the ischemic lesion, but that PFC may not improve cerebral function.
Animals; Arteries; Blood Pressure/drug effects; Brain/drug effects/physiopathology; Brain Ischemia/drug therapy/physiopathology/therapy; Cerebrovascular Circulation/drug effects; Collateral Circulation/drug effects; Drug Combinations/therapeutic use; Electroencephalography; Fluorocarbons/therapeutic use; Hemodilution; Hydroxyethyl Starch Derivatives; Pia Mater/blood supply; Vascular Resistance/drug effects
