Abstract
In the acute stage of selected cerebrovascular occlusive disease, it is essential to prevent the irreversible neuronal changes caused by ischemic insult by restoring decreased cerebral blood flow through appropriate methods. As an active and non-surgical method for enhancement of perfusion flow, carbon dioxide, which is a potent cerebral vaso-dilator without reduction of systemic blood pressure in the intact brain tissue, has been considered. However, in spite of the numerous investigations done in the last decade, its effectiveness on the increase of cerebral blood flow into ischemic areas still remains controversial, partly because of excessively weighed assessment on luxury perfusion phenomenon and partly because of undifferentiated assessment of the results both from the infarcted and the ischemic tissues.
In the previous consecutive studies, the author clarified that hypercapnia between 45 and 55 mmHg was beneficial in the development of collateral flow in areas of ischemia and simultaneous use of Mannitol solution did not offer any additional benefit for enhancement of decreased perfusion flow. However, our studies in the past were performed with an open cranium, even though experiment done after craniectomy undoubtedly provided very valuable information, mainly on better understanding of the dynamics of epicerebral circulation by fluorescein angiography and cortical blood flow studies by the 85Kr clearance method. Since it is well known that elevation of PaCO2 tends to induce an additional increase of intracranial pressure, the results achieved with an open cranium must be confirmed using a model with an enclosed compartment simulating clinical conditions in order to offer a safer application of CO2, to humans.
Accordingly, a purpose of this part 3 was to measure cortical blood flow by 85Kr and global miniregional cerebral blood flow by 133Xe clearance under an environment of enclosed cranium, and also to monitor intracranial pressure (ICP) in the same model.
In results, between 43 and 50 mmHg of arterial carbon dioxide (PaCO2), rCBF measured with both 85Kr and 133Xe clearances increased significantly. However, as PaCO2 was elevated above this level, there was a definite dissociation in rCBF values from both isotopes. Cortical blood flow measured by 85Kr decreases and conversely, global miniregional cerebral blood flow measured with 133Xe continued to increase. Degree of elevation of ICP was 2.1 ±0.4 (SE) mmH2O in response to 1 mmHg elevation of PaCO2. Our conclusion, derived from the previous consecutive studies done with an open cranium, was confirmed in the investigation under enclosed compartment.
