Avraham Mayevsky

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.

Brain NADH redox state monitored in vivo by fiber optic surface fluorometry

A new approach for the evaluation of brain energy metabolism in awake animals became possible as UV transmitting optical fibers became available. A variety of surface fiber optic fluorometers / reflectometers which were developed during the past decade enabled the monitoring of intramitochondrial NADH redox state in unanesthetized animals. The bundle of flexible fibers was connected to the brain via a cemented light guide holder implanted epidurally. The two signals obtained, 366 nm reflectance and 450 nm fluorescence, are subjected to various artifacts not connected to the intramitochondrial NADH redox state. In our system, the effects of movement artifacts and changes in blood oxygenation are negligible while the effects of tissue absorption or blood volume changes are considerable and could be minimized by subtraction of the two signals (1:1 ratio) providing the corrected fluorescence signal. The brain was exposed to various physiological and pathological conditions which resulted in the increase or decrease in the level of NADH. Under anoxia, hypoxia and ischemia, oxygen availability decreased and the metabolic state of the brain became more reduced (state 4-5 transition). When the brain was activated by seizures, spreading depression of hyperbaric oxygenation NADH became more oxidized (state 4-3 transition).

Basic Principles of Tissue Oxygen Determination from Mitochondrial Signals

The importance of measuring intracellular oxygen concentrations in tissues has, over the years, emerged as a basic parameter in the physiology and biochemistry of living tissues. The credibility of oxyhemoglobin determinations, even as refined A/V differences, is taxed especially in cases where inhomogeneous tissues with variable oxygen demands and oxygen supply are served. The formation of lactic acid in the venous blood is often used as a criterion of anoxia, but it also lacks credibility where inhomogeneous circulatory pathways are served and in addition, is questionable from the standpoint of whether the appearance of excess lactate is an unequivocal criterion of oxygen insufficiency. To indicate my empathy with polarographic techniques as they have been developed at the Johnson Foundation, I wish to recall the pioneering works of Bronk(1) Brink (2), Davies and Remond (3) that stand as landmarks in the exploration of tissue oxygen tension by microelectrode methods. I served my apprenticeship with them.

Cerebral Blood Flow and Oxygen Consumption in Cortical Spreading Depression

We determined the effects of spreading depression on local cerebral O2 supply, oxygenation, and O2 consumption in the anesthetized rat. Spreading depression was induced by application of 0.5 M KCl to the frontal cortex. Regional cerebral blood flow was determined with [14C]iodoantipyrine and regional O2 extraction was determined microspectrophotometrically. The passage of the spreading depression wave was determined with a multiprobe assembly that recorded NADH redox state (surface fluorometry), extracellular K+ activity, and DC steady potential (surface minielectrodes). As the wave of spreading depression passed, there was an increase in extracellular K+ and a decrease in NADH. Cerebral blood flow was significantly increased (120 ± 51 ml/min/100 g, mean ± SD) during the wave as compared with other regions. In the affected cortex, blood flow was not different from that in the contralateral cortex (69 ± 28 ml/min/100 g) either before or after the wave of spreading depression passed. Arterial and venous O2 saturation were unaffected by the wave and the histogram of O2 saturations of examined veins followed a similar normal distribution in all regions. Oxygen extraction was not altered by the wave of spreading depression. Oxygen consumption was significantly increased during the wave to 7.4 ± 3.7 ml O2/min/100 g compared with the contralateral cortex (5.1 ± 2.6 ml/min/100 g) and other regions. It can be concluded that spreading depression caused an increase in cerebral O2 consumption that was adequately matched by an increase in local blood flow. Oxygen delivery was not limited during spreading depression and its effects were quickly over as evidenced by the lack of alteration in oxygenation after the wave of spreading depression passed.

Metabolic responses of the awake cerebral cortex to anoxia hypoxia spreading depression and epileptiform activity

Using the time sharing fluorometer/reflectometer the measurement of NADH fluorescence as well as the reflected light was obtained from the surface of the awake rat brain cortex. The light was transferred to and from the brain via a flexible light pipe (made of quartz fibers) connected to a cannula implanted permanently above the brain. Exposing the rat to pure nitrogen atmosphere increased the fluorescence (reduction of NADH) by 32.3 +/- 6.1% in comparison to the normoxic fluorescence level. During cortical spreading depression (SD) the NADH fluorescence decreased (oxidation of NADH) by 17.3 +/- 2.8%. Exposing the rat to nitrogen after SD was elicited blocked the oxidation cycle observed during SD. Exposing the awake ras to 10, 7.5 or 5% O2 did not block the response of the brain to spreading depression or to Metrazol applied locally to the cortex. Under hypoxic conditions the brain showed a typical response to SD, namely, an oxidation cycle of NADH except that the duration of the cycle was longer and the decrease in the NADH level was smaller. The EEG activity recovered to normal even under 5%. The same effect of hypoxia was found when Metrazol was applied and epileptic activity was developed.

Mitochondrial function and energy metabolism in cancer cells: Past overview and future perspectives

The involvements of energy metabolism aspects of mitochondrial dysfunction in cancer development, proliferation and possible therapy, have been investigated since Otto Warburg published his hypothesis. The main published material on cancer cell energy metabolism is overviewed and a new unique in vivo experimental approach that may have significant impact in this important field is suggested. The monitoring system provides real time data, reflecting mitochondrial NADH redox state and microcirculation function. This approach of in vivo monitoring of tissue viability could be used to test the efficacy and side effects of new anticancer drugs in animal models. Also, the same technology may enable differentiation between normal and tumor tissues in experimental animals and maybe also in patients.

Factors in oxygen delivery to tissue

An animal model for evaluating oxygen delivery to tissue is based upon the determination of the intracellular oxygen tension by surface fluorometry of NADH under conditions where the inspired oxygen is reduced through the critical value for the particular organ. This procedure allows the evaluation of the overall efficiency of the pulmonocardiac tissue in delivering oxygen to tissue, and can be useful in new, quantitative measurements of the effect of various factors occurring between the inspired air and the final tissue oxygen tension.

Brain energy metabolism of the conscious rat exposed to various physiological and pathological situations

Using a time-sharing fluorometer-reflectometer, pyridine nucleotide (NADH) and flavoprotein (Fp) fluorescence, as well as reflected light at the excitation wavelength, were measured and correlated with the electrical activity of an awake cerebral cortex. Exposure of the rat to a nitrogen atmosphere (anoxia) led to an increase in signals representing the reduction of pyridine nucleotides and flavins, with very similar kinetics. Inducement of partial ischemia by bilateral carotid artery ligation led to an increase in NADH, accompanied by a very small effect on the electrical activity (ECoG). In most animals, 2-3h after ligation, the ECoG became flat or depressed. Exposure of this ischemic cerebral cortex to KC1 solution caused depression of the electrical activity without metabolic response probably due to the limitation of oxygen supply. The metabolic state of an awake cerebral cortex was identified by exposing the brain to various levels of oxygen, epileptoform activity, spreading depression, hyperbaric pressure of oxygen and an uncoupler. From our results we conclude that the awake cerebral cortex is close to the resting state, state 4, rather than to the active state, state 3.

Cerebral energy metabolism and oxygen state during hypoxia in neonate and adult dogs.

ABSTRACT: The relationship between a noninvasive determination of relative oxygen saturation of Hb circulating in brain tissue (StO2) and energy metabolism was investigated with respect to age dogs in three age groups (0 to 6- d-old, 7- to 21-d-old, and adults) and to severity of brain hypoxia using double beam spectroscopy of Hb deoxygenation and nuclear magnetic resonance spectroscopy of energy metabolism. The in vivo oxy-Hb dissociation was determined from the relationship between StO2 curve in the adult dog brain and sagittal sinus oxygen partial pressure during graded hypoxemia and found to be sigmoidal with an oxygen dissociation constant of 26.6 mm Hg. This agreed with an in vitro determination for oxygen dissociation constant of 28.2 mm Hg in adult dog red cells. The arterial oxygen pressure at which brain StO2 was reduced by 50% was shifted toward the right with increasing age (22.2,33.8, and 40.8 mm Hg, respectively). This correlated with an in vitro oxygen dissociation constant of red cell Hb of 17.0, 22.3, and 28.2 mm Hg in the three age groups, respectively. The phosphocreatine-inorganic phosphate ratio (PCr/Pi) was used to relate changes in cellular energy metabolism during hypoxia with changes in StO2. There was no change in PCr/Pi when StO2 had decreased to 50% of the control value. However, when the brain StO2 had decreased to between 7 and 15%, a reduction of PCr/Pi to 50% of the normoxic value occurred. The StO2 at which PCr/Pi falls should be considered a critical level of hypoxemia inasmuch as it represents a threshold of energy failure. There was no significant age dependence in the relationship between StO2 and PCr/Pi. Neonates had much smaller intravascular oxygen gradients than those in adults at a critical level of hypoxemia. However, compared with adults, the 1- to 3-wk-old age group requires a similar O2 availability and extraction for brain metabolic survival.

Effects of brain oxygenation on metabolic, hemodynamic, ionic and electrical responses to spreading depression in the rat.

The effect of cortical spreading depression (CSD) on oxygen demand (extracellular K(+)), oxygen supply (cerebral blood flow - CBF) and oxygen balance (mitochondrial NADH) was studied by a special multiprobe assembly (MPA), during hypoxia and partial ischemia. The MPA was constructed and applied to monitor the CSD wave from its front line until complete recovery, continuously and simultaneously. CSD under hypoxia or partial ischemia led to an initial increase in NADH levels and a further decrease in CBF during the first phase of the CSD wave, indicating a decrease of tissue capability to compensate for an increase in oxygen demand. Furthermore, the special design of the MPA enabled identifying the close interrelation between oxygen demand, supply and balance during CSD propagation. In conclusion, brain oxygenation was shown to have a clear effect on tissue responses to CSD.