Sigal Meilin

Cortical spreading depression recorded from the human brain using a multiparametric monitoring system.

The number of parameters (i.e., EEG or ICP-intracranial pressure) routinely monitored under clinical situations is limited. The brain function analyzer described in this paper enables simultaneous, continuous on-line monitoring of cerebral blood flow (CBF) and volume (CBV), intramitochondrial NADH redox state, extracellular K+ concentrations, DC potential, electrocorticography and ICP from the cerebral cortex. Brain function of 14 patients with severe head injury (GCS < or = 8), who were hospitalized in the neurosurgical or general intensive care unit was monitored using this analyzer. Leao cortical spreading depression (SD) has been reported in many experimental animals but not in the human cerebral cortex. In one of the patients monitored, spreading depression was observed. This is the first time that spontaneous repetitive cortical SD cycles have been recorded from the cerebral cortex of a patient suffering from severe head injury. Typical SD cycles appeared 4-5 h after the beginning of monitoring this patient. During the first 3-4 cycles the responses of this patient were very similar to the responses to SD recorded in normoxic experimental animals. Electrocorticography was depressed whereas extracellular K+ levels increased. The metabolic response to spreading depression was characterized by oxidation of intramitochondrial NADH concomitant to a large increase in CBF. During brain death, an ischemic depolarization, characterized by decrease in CBF and an irreversible increase in extracellular K+, was recorded.

Multiparametric monitoring of brain oxygen balance under experimental and clinical conditions.

In order to evaluate the relationship between brain oxygen supply and demand (O2 balance) in real time, it is necessary to use a multiparametric monitoring approach. Cerebral blood flow (CBF) is a representative parameter of O2 supply. The extracellular level of K+ is a reliable indicator of O2 demand since more than 60% of the energy consumed by the brain is utilized by active transport processes. Mitochondrial NADH redox state can represent the balance between O2 supply and demand. In order to monitor the brain of experimental animals or patients, we constructed the multiparametric assembly (MPA) and the following parameters were monitored simultaneously and in real time: CBF, CBV, NADH redox state, extracellular K+, DC potential, EEG, tissue temperature and ICP. Animals were exposed to hypoxia, ischemia, hypercapnia, hyperoxia and spreading depression (SD) and the relative changes in CBF and NADH were calculated and found to be significant indicators of brain energy state. Monitoring these two parameters increases the possibility of differentiating between various pathophysiological states. Each added parameter increases the power of diagnosis and determination of the functional state of the brain. Preliminary results obtained in patients monitored in the ICU or in the OR show that the responses to hypercapnia, spreading depression or ischemia are similar to those measured in experimental animals.

Effect of aging on brain energy-metabolism

The aging process involves morphological and functional changes in cerebral vasculature and deterioration of mitochondrial number and function. Furthermore, slow oscillations of cerebral blood flow and oxidative metabolism occur in animals under different pathological conditions such as ischemia. The aim of this study was to evaluate the effect of aging on energy-metabolism of the rat brain during anoxia and normoxia and to further investigate the occurrence of oscillations under normoxia in the aging brain. Simultaneous hemodynamical (CBF), biochemical (NADH/NAD ratio) and electrical activity from the cerebral cortex were measured by means of a multiparametric assembly (MPA) system. Exposure of adult rats to anoxia (100% N(2)) resulted in a 36+/-2% elevation of NADH. Furthermore, exposure of the aged group to anoxia caused NADH elevation as low as 9.6+/-4% (P<0.05). The changes in the NADH levels were followed by an increase in CBF. In addition, during the normoxic periods, hemodynamic oscillations were recorded in the old animals. This study suggests that the structural and functional changes that occur in vessels in the aging brain cause disability of cerebromicrovessels to optimally deliver nutrients and oxygen to the brain, affecting the mitochondrial ability to respond to anoxia. Furthermore, this study supports the approach that the hemodynamic oscillations are related to the development of a pathological state and are not a normal cerebral function.

Thiopental induced cerebral protection during ischemia in gerbils

Temporary interruption or reduction of cerebral blood flow during cerebrovascular surgery may rapidly result in ischemia or cerebral infarction. Thiopental has been shown to have cerebroprotective effects. However, the cerebroprotective dose of thiopental causes burst suppression of the EEG, thus this parameter cannot be used continuously for the detection of metabolic changes in the brain during thiopental anaesthesia. This study was performed in order to examine whether the multiparametric assembly (MPA), which measures energy metabolism CBF and mitochondrial (NADH) as well as extracellular ion concentrations (K+), can shed light on the mechanism of the cerebroprotective effects of thiopental. The MPA was placed on the brain of Mongolian gerbils and burst suppression of the ECoG was induced by thiopental. Cerebral ischemia was induced by occlusion of carotid arteries after burst suppression. Burst suppression of the ECoG was accompanied by a significant decrease in cerebral blood flow. In animals that received thiopental prior to ischemia, NADH increased to a lesser degree and extracellular potassium ion concentration increased to a lesser degree than in the control animals, indicating that thiopental affords protection of the brain under ischemic conditions due to improved energy metabolism. This study also demonstrates that the MPA can monitor changes occurring in the cerebral cortex even after the ECoG can no longer be used. Those findings have a significant value in the development of a new clinical monitoring device.

Inter-relation between hemodynamic, metabolic, ionic and electrical activities during ischemia and reperfusion in the gerbil brain

The aim of this study was to examine the inter-relation between the hemodynamic events, energy metabolism, extracellular potassium and electrical activity during the acute phase of transient ischemia in the gerbil brain. It has already been shown that partial ischemia in the gerbil brain causes changes in the blood flow, oxygen tension, electrical activity and potassium ion efflux. However, the description of the event during brain recovery from transient ischemia is not documented. In order to enable a better understanding of the pathophysiology during the ischemia as well as during reperfusion, we used the multiparametric assembly system. This system enables simultaneous and continuous monitoring of CBF, intra-mitochondrial NADH, extracellular potassium, DC potential and ECoG. Twenty anesthetized gerbils underwent reversible carotid artery occlusion procedure for 3-4 min. While monitoring the various parameters until complete recovery was reached, we found high correlation between the CBF and the NADH during occlusion as well as during the reperfusion period. However, CBF at the reperfusion period increased above the basal level while NADH returned to base line without an undershoot, suggesting that the mitochondrial need for oxygen necessary for the production of ATP is not the only factor influencing CBF during reperfusion. Furthermore, NADH returned to its normal level before extracellular potassium ion levels recovered to the baseline. This may suggest that ATP was no longer the limiting factor and ion pump activity became the factor determining and affecting the recovery processes.

Blood flow and ionic responses in the awake brain due to carbon monoxide.

Abstract This study examined the effect of 2000 ppm CO on the brain of an awake rat. Measurements of regional perfusion as well as metabolic, ionic and electrical activities were used to examine whether mechanisms responsible for changes in brain perfusion were separable from those attributable to compromises in neuronal metabolism. Exposure to 2000 ppm CO resulted in elevation of cerebral blood flow. The stability of mitochondrial NADH redox level during CO exposure indicated that tissue hypoxia did not develop. The elevation in blood flow was inhibited by L-nitroarginine methyl ester, indicating that nitric oxide was responsible for the CO-induced elevation in blood flow. Exposure to 2000 ppm CO also triggered a significant decrease in pH and rise in extracellular potassium ion, possibly due to ion-pump inhibition. The amplitude of the electrocorticogram wave activity decreased, indicative of a compromise to physiological activity. These changes were not observed in rats anesthetized with pentobarbital during CO exposure, although anesthesia had no effect on the CO-induced elevation in blood flow and there was still no change in mitochondrial NADH redox level. We concluded that CO acts by separate mechanisms to alter cerebral vasoactivity and neuronal metabolic responses and that both processes are independent of hypoxic stress.

Optical Monitoring of Nadh Redox State and Blood Flow as Indicators of Brain Energy Balance

Real-time evaluation of brain vitality in situ could be done by monitoring different parameters, which are complementary to each other. During the last 40 years the following four minimally invasive techniques were developed and applied to monitor the brain in situ: (1) Cerebral Blood Flow (CBF) using laser Doppler flowmetry (Stern et al., 1977; Dirnagl et al., 1989). (2) Hemoglobin oxygenation or saturation (HbO2) by dual wavelength reflectometry (Rampil et al., 1992) or spectral analysis (Frank et al., 1989). (3) Brain average oxygenation using oxygen electrodes (Mayevsky et al., 1980). (4) Mitochondrial redox state by monitoring of NADH fluorescence using surface fluorometry (Chance et al., 1962; Jobsis et al., 1971b; Mayevsky and Chance, 1982).

Responses of rat brain to induced spreading depression following exposure to carbon monoxide

Until recently carbon monoxide (CO) was known only for its noxious effects. Exposure to CO results in an autoregulatory increase in cerebral blood flow (CBF). Little information is available on brain energy metabolism under low CO concentrations and on the effect of CO on the stimulated brain. In this study cortical spreading depression (SD) was induced in order to cause transient brain depolarization and increased energy demand. The multisite assembly (MSA), which contains four bundles of optical fibers for monitoring the intramitochondrial NADH redox state and tissue reflectance as well as four DC electrodes enabling measurement from four consecutive points on the cerebral cortex, was used to measure energy metabolism and the propagation of SD waves during exposure to CO. CBF in the contralateral hemisphere was measured using the laser Doppler technique. Three experimental groups of animals were examined: SD was induced during exposure to 1000 ppm CO, immediately after exposure to CO and 90 min after cessation of exposure to CO. Three control groups were also examined, in which the animals underwent the same procedures but were not exposed to CO. In all animals exposure to CO was followed by a significant increase in CBF. The greatest effect was found when SD was induced immediately after cessation of exposure to CO. SD wave frequency decreased when induced immediately after exposure to CO, whereas it increased when SD was induced 90 min after exposure. The amplitude of the NADH oxidation waves and their integral were smaller during SD induced immediately after exposure to CO. The DC potential did not change, suggesting that CO did not affect the SD initiation mechanism but rather resulted in energy depletion during recovery from SD. This study demonstrates that even at a concentration of 1000 ppm CO interferes with the metabolic activity of the brain during repolarization of the SD-induced negativity.

Multiparametric Responses to Cortical Spreading Depression Under Nitric Oxide Synthesis Inhibition

Cortical spreading depression (SD) described initially by Leao (1944a) is a multifactorial event affecting the electrical, ionic, metabolic and hemodynamic activities in the brain (Vyskocil et al., 1972; Mayevsky et al., 1974; Bures et al. 1974; Mayevsky and Weiss, 1991). Due to disturbances in the ion homeostasis, the Na+K+-ATPase activity and energy metabolism are stimulated in order to restore the normal extracellular ion levels (Mayevsky et al., 1974; Hansen, 1985; Mayevsky and Weiss, 1991). The hemodynamic response to SD was a challenge to many investigators since the initial observation of dilation of pial vessels (Leao, 1944b). He concluded that the vascular responses are secondary to the local changes in the activity of neural elements. The changes in cerebral blood flow (CBF) just before, during and after the depolarization wave of SD were described by various investigators (Van Harreveld and Stamm, 1952; Van Harreveld and Ochs, 1957; Burevsova, 1957; Hansen et al., 1980; Lauritzen et al., 1982; Mies and Paschen, 1984; Lauritzen, 1984; Lauritzen and Diemer, 1986) and have been reviewed by Lauritzen (1987a,b). In all studies, a large increase in cerebral blood flow was recorded during the wave. Lauritzen and collaborators descried a post-spreading depression wave hypoperfusion, while a preceding vasoconstriction (immediately before the wave) was not established or proved. The mechanism behind the changes in CBF due to the SD wave is not clear although recently nitric oxide NO was proposed to be involved (Goadsby et al., 1992; Duckrow 1993). NO was suggested as an important factor in CBF regulation (Beckman et al., 1991; Iadecola et al., 1994; Irikura et al.,1994) as well as having direct effects on neuronal elements (Culotta and Koshland 1992; Mayer et al., 1992). In order to

Metabolic and Hemodynamic Oscillations Monitored Optically in the Brain Exposed to Various Pathological States

Slow (<1 Hz) oscillations of cerebral blood flow (CBF) and oxidative metabolism have been previously reported in several animal species under different physiological/pathological conditions (Vern et al., 1998, Mayevsky and Ziv 1991, Hudetz et al., 1992, Deyoe et al., 1995). Spontaneous oscillations in cerebral circulation have been demonstrated as periodic variations of blood volume, oxygen availability, NAD+NADH oxidative state (Dora and Kovach 1981), cytochrome aa3 redox state (Jobsis 1978), ischemia and anesthesia.