Oxygen availability in ischemic brain following hypocarbia and hypercarbia. Polarographical depth electrode recordings in evolving and completed experimental stroke in the monkey

No intracerebral steal phenomenon in the ischemic brain following papaverine administration

The steal phenomenon due to a vasodilator was investigated in 6 cats in which cerebral ischemia had been produced by left middle cerebral artery (MCA) occlusion. The photoelectric method was employed for continuous recording of the cerebral blood volume together with frequent determinations of the cerebral blood flow (CBF) through the ischemic cerebral tissue at the following four stages: before MCA occlusion, 2 hours after MCA occlusion before the injection of papaverine, after the injection of papaverine, and when the systemic arterial blood pressure (SABP) was adjusted non-pharmacologically to the control level using a "vasculator". The administration of the vasodilator produced conflicting results for the CBF changes in the ischemic area with a decrease in SABP as reported previously in the literature. However, when the SABP was corrected to the control level, the CBF in the ischemic region became increased in all 6 cases to above the control ischemic flow values. It is concluded that the decreased CBF in the ischemic tissue after vasodilator administration was not due to the steal phenomenon, but simply to a fall in SABP.

The effect of Fluosol-DA on oxygen availability in focal cerebral ischemia

The effects of Fluosol-DA 35% (15 ml/Kg, IV) on cortical oxygen availability (O2a), a relative measurement of cortical oxygen tension, were examined in 16 cats subjected to temporary middle cerebral artery (MCA) occlusion. The cats were divided equally into control and treatment groups and half of each group underwent MCA occlusion at room air ventilation and the other half at 100% O2 ventilation. Prior to occlusion, Fluosol had no effect on arterial PO2 or cortical O2a at normoxia, however, there was a significant increase in both arterial PO2 and O2a following 100% O2 ventilation (pre vs post Fluosol). In an additional 5 cats, Fluosol resulted in a transient decrease in blood oxygen content due to hemodilution. Concurrent to this decrease, cerebral blood flow increased substantially resulting in a net increase in oxygen delivery. Within ipsilateral hemispheres, MCA occlusion resulted in decreased O2a to levels below the pre-occlusion normoxic values in all animals except those treated with Fluosol and ventilated with 100% O2. During reperfusion, O2a immediately recovered to hyperoxic levels in the Fluosol 100% O2 animals, whereas in the other three groups, O2a returned more gradually towards the pre-occlusion value. Since neither 100% O2 alone nor Fluosol plus room air ventilation significantly improved O2a in the ischemic cortex, we conclude that increased delivery of plasma plus Fluosol bound oxygen was responsible for the observed improvements in O2a following MCA occlusion.