Effect of blood pressure on blood flow in ischemic and in nonischemic cerebral cortex

170

Summary:We measured the relationships between changes in extracellular pH (pHe)' potassium (Ke), and calcium (Cae) activities and DC potential (DCe) in pro gressive ischaemia of rat cerebral cortex, pHe and Ke, or Cae and Ke, were measured at the same point simulta neously, using triple-barrelled, double-ion-sensitive mi croelectrodes. Ischaemia was produced using bilateral ca rotid artery occlusion and hypotension in rats under 50% N 2 0-0.4% halothane anaesthesia. Unilateral carotid ar tery occlusion did not affect blood flow, but bilateral oc clusion reduced flow to �40% of normal. Autoregulation of blood pressure (BP) changes was lost after bilateral occlusion, and so progressive hypotension produced a linear decrease in flow. pHe began to decrease at high

Section: Blood Flowsupporting

confidence: 89%

Extracellular pH, Potassium, and Calcium Activities in Progressive Ischaemia of Rat Cortex

Harris

Symon

1984

170

“…To examine autoregulation, SAP must be manip ulated either through alterations of blood volume and/or through administration of vasoactive drugs. Unfortunately, the drugs used to change blood pres sure as well as anesthetic agents may also influence CBF directly, without crossing the blood-brain bar rier (Waltz, 1968;Acar and Pickard, 1980), through alterations of vascular smooth muscle contraction. Three drugs were used in our study: nitroprusside, norepinephrine, and halothane.…”

Section: Methodological Problemsmentioning

confidence: 99%

Autoregulation of Cerebral Blood Flow in Experimental Focal Brain Ischemia

Dirnagl

Pulsinelli

1990

166

Summary:The relationship between systemic arterial pressure (SAP) and neocortical microcirculatory blood flow (CBF) in areas of focal cerebral ischemia was stud ied in 15 spontaneously hypertensive rats (SHRs) anes thetized with halothane (0.5%). Ischemia was induced by ipsilateral middle cerebral artery/common carotid artery occlusion and CBF was monitored continuously in the ischemic territory using laser-Doppler flow me try during manipulation of SAP with I-norepinephrine (hyperten sion) or nitroprusside (hypotension). In eight SHRs not subjected to focal ischemia, we demonstrated that 0.5% halothane and the surgical manipUlations did not impair autoregulation. Autoregulation was partly preserved in ischemic brain tissue with a CBF of > 30% of preocclu sion values. In areas where ischemic CBF was <30% of It is controversial whether increasing systemic arterial pressure (SAP) can improve the neurologi cal outcome after acute stroke (Olsen, 1982;Yatsu, 1982;Grotta, 1987; Meyer et aI., 1987). Studies in experimental animals have shown that raising SAP to hypertensive levels after induction of cerebral ischemia can lessen brain damage (Safar et aI., 1976; Hayashi et aI., 1984; Aspey et aI., 1987; Drummond et aI., 1988). Clinical data showing im proved neurological outcome associated with hy pertension after stroke are anecdotal (Farhat and Schneider, 1967 327 preocclusion values, autoregulation was completely lost. Changes in SAP had a greater influence on CBF in tissue areas where CBF ranged from 15 to 30% of baseline (9% change in CBF with each 10% change in SAP) than in areas where CBF was <15% of baseline (6% change in CBF with each 10% change in SAP). These findings dem onstrate that the relationship between CBF and SAP in areas of focal ischemia is highly dependent on the sever ity of ischemia. Autoregulation is lost in a gradual manner until CBF falls below 30% of normal. In areas without autoregulation, the slope of the CBF/SAP relationship is inversely related to the degree of ischemia. Key Words: Arterial blood pressure-Cerebral blood flow autoregula tion-Experimental focal cerebral ischemia. Van Dellen and Buchanan, 1977). PomerantzOn the other hand, there is experimental (Fenske et aI., 1975; Spatz et aI., 1976;Michenfelder and Milde, 1977; Bleyaert et aI., 1980; Kogure et aI., 1981) and clinical (Gottstein and Seel, 1977) evi dence for a worsening of outcome from increasing SAP above normal levels after cerebral ischemia. The enhanced formation of cerebral edema, intra cranial hypertension, cerebral hemorrhage, pulmo nary edema, and cardiac failure by arterial hyper tension might all contribute to this worsening. The potential benefit of increasing SAP during cerebral ischemia is based on the assumption that this measure will increase CBF in tissue where au toregulation has been lost (Meyer et aI., 1973a, b). Though it is generally accepted that autoregulation is lost in ischemic brain, little is known about the quantitative relationships among SAP, CBF auto regulation, and level of ischemia. Th...

“…Indeed, although Ginsberg et al (1977) showed that a zone of enhanced glycolysis does surround the area of ischaemia produced by occlusion of the middle cerebral artery, there is little experimental evidence that a marginal zone of hyperaemia develops, provided that conditions remain stable (Symon et al, 1974). Waltz (1968) believed that the reddening of venous blood that they observed in the pial circulation in focal ischaemia could be attributed in part to luxury perfusion, but they found this difficult to reconcile with their observation that the phenomenon was only rarely associated with an absolute increase in local blood flow. When they used autoradiographic measurements to identify areas of increased flow and then studied the same region histologically (Yamaguchi et al, 1971), they found that in hyperaemic sites there was usually evidence of established ischaemic brain damage.…”

Section: Hyperperfusionmentioning

confidence: 99%

Focal Cerebral Ischaemia in the Rat: 2. Regional Cerebral Blood Flow Determined by [¹⁴C]Iodoantipyrine Autoradiography following Middle Cerebral Artery Occlusion

Tamura

Graham

McCulloch

et al. 1981

300

Summary: Local cerebral blood flow has been measured by quantitative autoradiography, employing ['4Cjiodoantipyrine as tracer, in rats killed half an hour after occlusion of the middle cerebral artery. The results were compared with pattern of local cerebral blood flow (CBF) in sham-operated rats and with neuropathological findings. In every animal there was a profound reduction (to 13% of control levels) in blood flow in the neocortex previously supplied by the occluded artery. The level of blood flow in the areas in which ischaemic brain damage occurred was 0.24 ±0.03 ml g min (mean ± SEM). This level of CBF is considerably greater than that reported following a similar surgical procedure in cats and primates. Moderate reductions in blood flow were also seen outside the territory of the occluded artery and in parts of the opposite hemisphere. Absolute increases in blood flow (hyperaemia) were seen only in the substantia nigra and globus pallidus ipsilateral to the occlusion. It is suggested that this finding and the reductions in blood flow outside the territory of the middle cerebral artery are reflections of alterations in neuronal function and metabolic activity secondary to the ischaemic lesion. Key Words: Cerebrovascular circulationCerebral ischaemiaRat.In the past five years a range of reliable quantitative techniques have become available which permit accurate assessment of various neurochemical and cerebral circulatory parameters in discrete anatomical regions within the central nervous system.