Über die Sauerstoffversorgung des Gehirns und den Mechanismus von Mangelwirkungen

Inductive and Deductive Approaches to Acute Cell Injury

Many clinically relevant forms of acute injury, such as stroke, traumatic brain injury, and myocardial infarction, have resisted treatments to prevent cell death following injury. The clinical failures can be linked to the currently used inductive models based on biological specifics of the injury system. Here we contrast the application of inductive and deductive models of acute cell injury. Using brain ischemia as a case study, we discuss limitations in inductive inferences, including the inability to unambiguously assign cell death causality and the lack of a systematic quantitative framework. These limitations follow from an overemphasis on qualitative molecular pathways specific to the injured system. Our recently developed nonlinear dynamical theory of cell injury provides a generic, systematic approach to cell injury in which attractor states and system parameters are used to quantitatively characterize acute injury systems. The theoretical, empirical, and therapeutic implications of shifting to a deductive framework are discussed. We illustrate how a deductive mathematical framework offers tangible advantages over qualitative inductive models for the development of therapeutics of acutely injured biological systems.

Towards a dynamical network view of brain ischemia and reperfusion. Part I: background and preliminaries

The general failure of neuroprotectants in clinical trials of ischemic stroke points to the possibility of a fundamental blind spot in the current conception of ischemic brain injury, the "ischemic cascade". This is the first in a series of four papers whose purpose is to work towards a revision of the concept of brain ischemia by applying network concepts to develop a bistable model of brain ischemia. This first paper sets the stage for developing the bistable model of brain ischemia. Necessary background in network theory is introduced using examples from developmental biology which, perhaps surprisingly, can be adapted to brain ischemia with only minor modification. Then, to move towards a network model, we extract two core generalizations about brain ischemia from the mass of empirical data. First, we conclude that all changes induced in the brain by ischemia can be classified as either damage mechanisms that contribute to cell death, or stress responses that contribute to cell survival. Second, we move towards formalizing the idea of the "amount of ischemia", I, as a continuous, nonnegative, monotonically increasing quantity. These two generalizations are necessary precursors to reformulating brain ischemia as a bistable network.

Interaction of hypocapnia, hypoxia, brain blood flow, and brain electrical activity in voluntary hyperventilation in humans

Changes in various physiological measures in voluntary hyperventilation lasting three minutes or more in humans were studied and compared. Three-minute hyperventilation, in which the rate of external ventilation increased by an average factor of 4.5-5, produced similar phasic changes in central and brain hemodynamics. The rate of circulation, indicated by rheographic data, initially increased during hyperventilation, reaching a maximum at 1-2 min of the test; there was then a reduction, to a minimum 2-3 min after the end of the test; this was followed by a further slow increase. The rate of cerebral blood flow during all 3 min of hyperventilation remained elevated in most subjects as compared with baseline and decreased during the 5 min following the end of the test. Transcutaneous carbon dioxide tension changed differently - there was a decrease to a minimum (about 25 mmHg) by the end of the test, lasting 1 min from the end of the test, this being followed by an increase to a level of 90% of baseline at 5 min after the test. Blood oxygen saturation remained at 98-100% during the test, decreasing to about 90% 5 min after the test; this, along with the decrease in cerebral blood flow, was a factor producing brain hypoxia. In different subjects, changes in the spectral power of oscillations in different EEG ranges on hyperventilation were "mirrored" to different extents by the dynamics of transcutaneous carbon dioxide tension. The duration and repetition of hyperventilation were important factors for understanding the interaction between brain hemodynamics, hypocapnia, hypoxia, and brain electrical activity. After several repetitions of 3-min hyperventilation over a period of 1 h, the increasing brain blood flow could decrease significantly on the background of relatively small changes in brain electrical activity. The data presented here were assessed from the point of view of the important role of brain tissue oxygen utilization mechanisms in adaptation to hypoxia and hypocapnia.

ISOTT: roots, founding and beyond

The International Society on Oxygen Transport to Tissue (ISOTT) was founded in April, 1973 by Drs. Duane F. Bruley and Haim I. Bicher. However, the roots of ISOTT go back to Drs. Christian Bohr and August Krogh. Dr. Bruley first wanted to sponsor an international symposium on oxygen transport to tissue to highlight the research activity between his group at Clemson University and Dr. Melvin H. Knisely's group at the Medical College of South Carolina. It was also intended to honor Dr. Knisely for his ingenious development of the Quartz Rod Crystal technique for observing blood flow in-vivo. Later Dr. Bicher was selected to organize the program from the Medical College of South Carolina With an overwhelming response to the initial call for papers, Drs. Bruley and Bicher made the decision to found an International Society. They then decided on a name, developed the society logo, assigned a mission, developed a charter, sketched the by-laws, and contracted a publisher for the proceedings. The new society was to include a focus on inter and cross-disciplinary research involving theoretical and experimental investigations of oxygen transport to tissue in a single session format. The society meets annually at different venues throughout the world.

Pathophysiology and Therapy of Experimental Stroke

1. Stroke is the neurological evidence of a critical reduction of cerebral blood flow in a circumscribed part of the brain, resulting from the sudden or gradually progressing obstruction of a large brain artery. Treatment of stroke requires the solid understanding of stroke pathophysiology and involves a broad range of hemodynamic and molecular interventions. This review summarizes research that has been carried out in many laboratories over a long period of time, but the main focus will be on own experimental research. 2. The first chapter deals with the hemodynamics of focal ischemia with particular emphasis on the collateral circulation of the brain, the regulation of blood flow and the microcirculation. In the second chapter the penumbra concept of ischemia is discussed, providing a detailed list of the physiological, biochemical and structural viability thresholds of ischemia and examples of how these thresholds can be applied for imaging the penumbra. The third chapter summarizes the pathophysiology of infarct progression, focusing on the role of peri-infarct depolarisation, the multitude of putative molecular injury pathways, brain edema and inflammation. Finally, the fourth chapter provides an overview of currently discussed therapeutic approaches, notably the effect of mechanical or thrombolytic reperfusion, arteriogenesis, pharmacological neuroprotection, ischemic preconditioning and regeneration. 3. The main emphasis of the review is placed on the balanced differentiation between hemodynamic and molecular factors contributing to the manifestation of ischemic injury in order to provide a rational basis for future therapeutic interventions.

Dynamic observation of oxygenation-induced contraction of and transient fiber-network formation-disassembly in cultured human brain microvascular endothelial cells

Oxygenation-induced contraction of nonconfluent cultured human brain microvascular endothelial cells (HBECs, n = 30) was examined by video-enhanced contrast-differential interferential contrast microscopy. After administering a continuous gentle blow of pure oxygen gas to the surface of the medium just above the flattened HBEC, the plasma membrane exhibited tensioning and wrinkling, resulting in a strong contraction of the cell body by 14 +/- 7% (P < 0.001). When the cell stopped contracting, transient formation of a fiber network starting from certain spots (possibly adhesion plaques, though these were not visible in the majority of cases) and expanding to the whole cell was observed. The occurrence of fiber network formation was statistically significant (26 of 30 separate cells, P < 0.05). After cessation of oxygen delivery, the observed network of fibers broke up rapidly (in a period of 3.3 +/- 1.2 seconds) into small particles of <0.5 microm in diameter, which subsequently fused into the cellular structure. The HBEC completely recovered the control appearance. The sequential process was completed within 30 seconds and was reproduced in individual cells each time that oxygen gas was supplied. The authors conclude that the HBEC strongly contracts in response to a transient oxygenation stimulus, followed by rapid formation/disassembly of a network structure.

Effect of Irradiation on Enzymes of the Capillary Bed in Rat Ventricles

The effect of localized irradiation on the enzyme activity in rat cardiac capillaries was examined in experiments in which the arteriolar and venular portions of the capillary bed were distinguished by the double-staining method. This method shows that the endothelial cells of the former contain alkaline phosphatase (AP) and those of the latter, dipeptidylpeptidase IV (DPP). At both 1 week and 3 weeks after irradiation with 20 Gy, staining for AP was reduced but staining for DPP was unchanged. The loss of enzyme from the arteriolar portions may be a consequence of the greater radiosensitivity of tissues exposed to high oxygen tension, or it may indicate that AP is less stable than DPP when exposed to irradiation.

Mechanisms of spreading depression and hypoxic spreading depression-like depolarization

Spreading depression (SD) and the related hypoxic SD-like depolarization (HSD) are characterized by rapid and nearly complete depolarization of a sizable population of brain cells with massive redistribution of ions between intracellular and extracellular compartments, that evolves as a regenerative, "all-or-none" type process, and propagates slowly as a wave in brain tissue. This article reviews the characteristics of SD and HSD and the main hypotheses that have been proposed to explain them. Both SD and HSD are composites of concurrent processes. Antagonists of N-methyl-D-aspartate (NMDA) channels or voltage-gated Na(+) or certain types of Ca(2+) channels can postpone or mitigate SD or HSD, but it takes a combination of drugs blocking all known major inward currents to effectively prevent HSD. Recent computer simulation confirmed that SD can be produced by positive feedback achieved by increase of extracellular K(+) concentration that activates persistent inward currents which then activate K(+) channels and release more K(+). Any slowly inactivating voltage and/or K(+)-dependent inward current could generate SD-like depolarization, but ordinarily, it is brought about by the cooperative action of the persistent Na(+) current I(Na,P) plus NMDA receptor-controlled current. SD is ignited when the sum of persistent inward currents exceeds persistent outward currents so that total membrane current turns inward. The degree of depolarization is not determined by the number of channels available, but by the feedback that governs the SD process. Short bouts of SD and HSD are well tolerated, but prolonged depolarization results in lasting loss of neuron function. Irreversible damage can, however, be avoided if Ca(2+) influx into neurons is prevented.

Solitary tract nuclei in acute heart failure

BACKGROUND AND PURPOSE

Symmetrical necrosis of the brain stem nuclei has been described as a consequence of severe transitory cerebral hypoxia mainly in neonates or young adults who experienced an episode of acute ischemia due to transitory acute heart failure. We report selective bilateral lesions of the solitary tract nuclei in 5 adults with short survival intervals after acute heart failure.

METHODS

In 5 patients who died due to cardiovascular pathology, histological examination was performed on multiple samples of cerebral hemispheres, on transverse sections of the midbrain and pons, and on transverse serial sections of the medulla stained with hematoxylin-eosin, Klüver-Barrera, and Luxol fast blue. The 3-dimensional reconstruction of the extension and topography of the medullary lesions was obtained with computed image analysis.

RESULTS

In 4 subjects who died soon after an episode of acute heart failure (range of survival 10 hours to 2 days), the dorsal portion of the solitary tract nuclei showed an eosinophilic roundish aspect bilaterally. In their context, the neurons showed changes characteristic of ischemic coagulation necrosis. In a fifth patient, a 32-year-old man who died 15 days after an episode of cardiac arrest, 2 circumscribed symmetrical infarcts with macrophagic and astrocytic reactions were found at the same level. The topography of the lesions and the inflammatory reaction and gliosis of patient 5 suggest that the findings in the other 4 patients correspond to initial features of selective lesions of the solitary tract nuclei after acute heart failure: the short interval of survival prevented the evolution of the reactive process. The nucleus is localized at the watershed zone between the terminal branches of the medullary collateral vessels of the vertebral arteries, thus representing the last meadow in the case of sudden fall of the systemic blood flow due to acute heart failure. The absence of lesions of other medullary and pontine nuclei accounts for a selective vulnerability of the neurons of the solitary tract nuclei, and the selective dendritic lesions suggest an excitotoxic component to ischemic cell death.

CONCLUSIONS

The commonly accepted resistance of the medullary centers to ischemic hypoxia in adults apparently could be due to the rapidity of death, which prevents the evolution of lesions that can be diagnosed. In addition, minor lesions in the medullary tegmentum after acute heart failure could play a role in the prevention of the resumption of autonomous cardiac and respiratory functions despite life-saving procedures.

Pathophysiology of the ischemic penumbra--revision of a concept

1. The original concept of the ischemic penumbra surrounding a focus of dense cerebral ischemia is based on electrophysiological observations. In the cortex of baboons following middle cerebral artery occlusion, complete failure of the cortical evoked potential was observed at a cerebral blood flow (CBF) threshold level of approx. 0.15 ml/g/min--a level at which extracellular potassium ion activity was only mildly elevated. With a greater CBF decrement to the range of 0.06-0.10 ml/g/min, massive increases in extracellular potassium occurred and were associated with complete tissue infarction. Thus, the ischemic penumbra has been conceptualized as a region in which CBF reduction has exceeded the threshold for failure of electrical function but not that for membrane failure. 2. Recent studies demonstrate that the penumbra as defined classically by the flow thresholds does not survive prolonged periods of ischemia. The correlation of CBF autoradiograms with diffusion-weighted MR images and the regional distribution of cerebral metabolites reveals that the ischemic core region enlarges when adjacent, formerly penumbral, areas undergo irreversible deterioration during the initial hours of vascular occlusion. At the same time, the residual penumbra becomes restricted to the periphery of the ischemic territory, and its fate may depend critically upon early therapeutic intervention. 3. In the border zone of brain infarcts, marked uncoupling of local CBF and glucose utilization is consistently observed. The correlation with electrophysiological measurements shows that metabolism-flow uncoupling is associated with sustained deflections of the direct current (DC) potential resembling transient depolarizations. Such penumbral cell depolarizations, which are associated with an increased metabolic workload, induce episodes of tissue hypoxia due to the constrained collateral flow, stimulate anaerobic glycolysis leading to lactacidosis, suppress protein synthesis, and, finally, compromise energy metabolism. The frequency of their occurrence correlates with the final volume of ischemic injury. Therefore, penumbral depolarizations are regarded as a key event in the pathogenesis of ischemic brain injury. Periinfarct DC deflections can be suppressed by NMDA and non-NMDA antagonists, resulting in a significant reduction of infarct size. 4. The histopathological sequelae within the penumbra consist of various degrees of scattered neuronal injury, also termed "incomplete infarction." The reduction of neuronal density at the infarct border is a flow- and time-dependent event which is accompanied by an early response of glial cells. As early as 3 hr after vascular occlusion a generalized microglial activation can be detected throughout the ipsilateral cortex. Astrocytic activation is observed in the intact parts of the ischemic hemisphere from 6 hr postocclusion onward. Thus, the penumbra is a spatially dynamic brain region of limited viability which is characterized by complex pathophysiological changes involving neuronal function as well as well as glial activation in response to local ischemic injury.

Continuous monitoring of the partial pressure of oxygen in cerebral venous blood

OBJECTIVE

Clinical oxygen monitoring in the injured brain is somewhat difficult. However, ischemia is one of the major factors responsible for secondary tissue damage after head injury or subarachnoid hemorrhage. Therefore, the aim of the present study was to investigate the value of continuously monitoring the partial pressure of oxygen in cerebral venous blood (PcvO2) during changes in intracranial pressure (ICP).

METHODS

In eight domestic pigs with Clark type probes placed in the posterior third of the superior sagittal sinus, PcvO2 was continuously registered while ICP was stepwise elevated by an inflatable balloon placed below the tentorium. Arterial blood pressure was continuously monitored, cerebral perfusion pressure (CPP) was calculated, and arterial partial carbon dioxide pressure and partial pressure of oxygen were registered intermittently.

RESULTS

The mean intraparenchymal ICP before the start of balloon inflation was 5 +/- 1 mm Hg, the mean CPP was 80 +/- 15 mm Hg, and the mean PcvO2 was 36 +/- 3 mm Hg. At maximum ICP elevation, CPP decreased to 20 +/- 12 mm Hg, PcvO2 decreased to 10 +/- 6 mm Hg, and ICP increased to 90 +/- 10 mm Hg. Strong linear correlations between ICP and PcvO2 and between CPP and PcvO2 were revealed, and mean correlation coefficients of 0.89 for ICP/PcvO2 and 0.73 for CPP/PcvO2 were calculated.

CONCLUSION

The present study demonstrates that polarographic PcvO2 monitoring in the superior sagittal sinus is a reliable method for the early detection of reduced CPP during ICP elevation. This technique is capable of registering the global oxygen supply and oxygen consumption of the brain. It seems superior to jugular venous oxymetry and is better suited for clinical use because of a somewhat low artifact susceptibility.

High energy phosphates and direct calorimetry as predictive parameters for metabolic recovery of the rat liver following ischemia

BACKGROUND AND METHODS

Alteration of the hepatocellular function following ischemic damage may play a crucial role in the limited recovery after reperfusion. In spite of numerous efforts, finding a simple technique for predicting recovery of the liver after ischemic damage is still an unresolved problem. During ischemic storage of isolated rat livers at 25 degrees C tissue concentrations of high energy phosphates and lactate were determined photometrically and interstitial pH was measured by glass electrodes. In comparison, the metabolic rate was measured continuously by direct calorimetry. In a second series of experiments these results were compared with functional recovery after ischemia and reperfusion. Following ischemic storage at 25 degrees C for 60, 120 or 240 min, the isolated livers were reperfused for 30 min in a non-recirculating system with a constant flow rate. During reperfusion functional recovery, as assessed by oxygen consumption and bile flow, was determined. At the end of reperfusion tissue samples were taken for biochemical analysis of adenine nucleotides. Furthermore, morphologic integrity was determined by electron microscopy.

RESULTS

Whereas the ATP concentration drops within 60 min of ischemia to 6.9% of the control value without further significant change, the continuously measured metabolic rate as assessed by direct calorimetry decreases in an exponential manner. Accordingly, a better correlation of hepatocellular secretory function and calorimetrically measured heat output (r2 = 0.85; P < 0.001) was observed than with high energy phosphates (r2 = 0.56; P < 0.001).

CONCLUSIONS

These data suggest that if the metabolism of the ischemic rat liver falls below a critical level, recovery is incomplete or impossible. Therefore, assessment of the global metabolic rate by direct calorimetry seems not only to be a very good predictor of recovery after ischemic damage but also a good tool in the laboratory for studies concerning the sequelae of ischemic metabolism and for improvement of tissue protection.

The persistent primitive hypoglossal artery: a rare anatomic variation with frequent clinical implications

The case of a persistent primitive hypoglossal artery (PHA) in a 72-year-old man dead from myocardial infarction is presented. The autopsy showed the presence of a semicircular marginal infarct on the surface of the left cerebral hemisphere. The PHA anastomized the basilar artery origin with the left internal carotid artery, running through the left hypoglossal canal together with the hypoglossal nerve. The vertebral and posterior communicating arteries were hypoplastic. The PHA represented the morphological base on which the cerebral vascular insufficiency acted, following the generalized circulatory insufficiency due to the myocardial infarct, causing the cerebral infarct. Based on the embryology of the cranial arteries and on the morphological findings we suggest that the persistence of the hypoglossal artery: 1) precedes the vertebral and posterior communicating arteries hypoplasia causing it by competition for the territory of distribution; 2) gives rise to an almost complete dependence of the cerebral circulation from the carotid system with predictable ischemic consequences in the case of a critical reduction of the carotid blood flow; 3) may be associated with an anomalous structure of the vessel wall and exposes the basilar trunk to an unusual haemodynamic stress, predisposing to the onset of aneurysms.

Importance of supravitality in forensic medicine

Based on physiological investigations on latency period, survival period and resuscitation period under complete temporary ischemia, supravitality can be defined as even longer survival period of tissues (compared to the resuscitation period) after complete irreversible ischemia. Supravitality is mostly defined by functional parameters (sensitivity to excitation). Parameters of supravital metabolism (substrates and metabolites of anaerobic glycolysis) as a basis for supravital reactions (sensitivity to excitation) are discussed. Particular supravital reaction patterns in comparison to physiological conditions are mentioned (Cannon-Rosenbluth's law of denervation, supersensitivity to pharmacological excitation, local contraction instead of propagated excitation). Lastly, morphological alterations which can be induced during the early supravital period (latency period, survival period) as well as their destination from local vital reactions will be briefly mentioned.

Viability thresholds and the penumbra of focal ischemia

The classic concept of the viability thresholds of ischemia differentiates between two critical flow rates, the threshold of electrical failure and the threshold of membrane failure. These thresholds mark the upper and lower flow limits of the ischemic penumbra which is thought to suffer only functional but not structural injury. Recent studies of the functional and metabolic disturbances suggest a more complex pattern of thresholds. At declining flow rates, protein synthesis is inhibited at first (at a threshold of about 0.55 ml/gm/min), followed by a stimulation of anaerobic glycolysis (at 0.35 ml/gm/min), the release of neurotransmitters and the beginning disturbance of energy metabolism (at about 0.20 ml/min), and finally the anoxic depolarization (< 0.15 ml/gm/min). The penumbra, as defined by the classic flow thresholds, does not remain viable for extended periods. Since viability of the tissue requires maintenance of energy-dependent metabolic processes, penumbra is redefined as a region of constrained blood supply in which the energy metabolism is preserved. Imaging of the penumbra by combining autoradiographic cerebral blood flow measurements with bioluminescent images of adenosine triphosphate (ATP) demonstrates a gradual expansion of the infarct core (in which ATP is depleted) into the penumbra until, after a few hours, the penumbra has disappeared. It is suggested that the limited survival of the penumbra is due to periinfarct depolarizations, which result in repeated episodes of tissue hypoxia, because the increased metabolic workload is not coupled to an adequate increase of collateral blood supply. This explains pharmacological suppression of periinfarct depolarizations lowering the threshold of metabolic disturbances and reducing the volume of the ischemic infarct.

Effect of arterial PCO2 on local HbO2 and relative Hb concentration in the human brain--a study with the Erlangen micro-lightguide spectrophotometer (EMPHO)

Intraoperative investigations of local intracapillary haemoglobin oxygenation have been performed in 5 patients during neurosurgical interventions using the Erlangen microlightguide spectrophotometer (EMPHO). As the measurements can be performed in a very short period of time (approximately 60 s) the EMPHO enables rapid monitoring of local haemoglobin oxygenation in the brain. All patients received thiopental anaesthesia and were mechanically ventilated. The local measurements were performed during normoventilation (arterial PCO2--PaCO2 37.8 +/- 0.7 mm Hg) and hyperventilation (PaCO2 31 +/- 0.5 mm Hg). Hyperventilation caused a decrease in the mean SO2 from 47.8% to 41.1%. The number of SO2 values < 50% increased from 58% to 77.8%. The possible significance of the low local SO2 values is discussed.

Effect-kinetics on brain protection of two codergocrine-mesylate preparations (Aramexe retard® and Hydergine®) by EEG mapping and psychometry under hypoxia

In a double-blind, placebo-controlled study the effect-kinetics on brain protection of a new retard formulation of codergocrine-mesylate (CDM) (Aramexe retard, 5 mg) were investigated and compared with a standard CDM drug (5 mg Hydergine) utilizing blood gas analysis, EEG mapping and psychometry. A transient, reversible hypoxic hypoxidosis (i.e. impairment of cerebral metabolism due to hypoxia) was experimentally induced by a fixed gas combination of 9.8% oxygen (O(2)) and 90.2% nitrogen (N(2)) (found at an altitude of 6000 m), which was inhaled for 23 min under normobaric conditions by 18 healthy volunteers. After an adaptation session they received randomized 5 mg Aramexe retard, 5 mg Hydergine and placebo. Evaluation of blood gases, EEG mapping and psychometry was carried out at 0,2, 4,6, and 8 h after oral drug administration - each time under normoxic and hypoxic conditions. Blood gas analysis demonstrated a drop in SaO(2) from 99% under normoxia to 70% under hypoxia, in Po(2) from 100 to 33 mmHg, and in Pco(2) from 36 to 31 mmHg, while pH increased from 7.43 to 7.48. Base excess and standard bicarbonate remained stable. Under hypoxia EEG mapping exhibited an increase in delta/theta, a decrease of alpha and increase of beta activity, as well as a slowing of the centroid of the total power spectrum, which reflects deterioration of vigilance. Both CDM preparations significantly attenuated this vigilance decrement, with 5 mg Hydergine showing its encephalotropic peak effect in the second hour, 5 mg Aramexe retard in the sixth and eighth hours. At the behavioral level, hypoxic hypoxidosis induced a deterioration of the noo- and thymopsyche (by 53% under placebo), which was significantly mitigated by both 5 mg Aramexe retard (19%) and Hydergine (32%).

Spectrophotometric measurements of haemoglobin saturation and concentration in skin during the tuberculin reaction in normal human subjects

A non-invasive technique employing light-guide spectrophotometry is described for the measurement of haemoglobin concentration and oxygenation in human skin. Measurements were carried out in the visible wavelength range (500-620 nm) and a series of experiments were carried out in vitro and in vivo in order to calibrate the system. Indices were derived for the measurement of relative haemoglobin concentration and absolute oxygen saturation. The technique was applied to measure the changes in these parameters occurring during the course of the tuberculin reaction in human skin. The results are compared with those from laser Doppler flowmetry and transcutaneous oxygen measurements which were carried out concurrently. Divergence between the intracapillary and tissue oxygenation during the course of the reaction provides evidence for the existence of increased diffusion resistance for oxygen; a model is proposed. The study demonstrates the potential clinical usefulness of light-guide spectrophotometry for the non-invasive investigation of tissue oxygen supply.

The effects of chemical kinetics on oxygen delivery to tissue

A mathematical model has been formulated to analyze the effect of nonequilibrium kinetics on oxygen delivery to tissue. The model takes into account molecular diffusion, facilitated diffusion in the capillary blood, convection, chemical kinetics of O2 with hemoglobin, and the rate of metabolic consumption. A line iterative technique is described to solve numerically the resulting coupled system of nonlinear partial differential equations with physiologically relevant boundary and entrance conditions. With nonequilibrium kinetics the end-capillary PO2 is found to be lower than that in the venous blood. The effect is more pronounced during hypoxia and anemia. It is found that the tissue PO2 at the lethal corner decreases with the decrease in blood velocity, arterial PO2, hemoglobin concentration, P50, and increase in COHb concentration or metabolic rate, while the difference between end-capillary PO2 and venous PO2 increases, which reflects the effect of nonequilibrium kinetics on the delivery of O2 to tissue. Thus, the consideration of venous PO2 as an indicator of tissue PO2 in clinical and experimental studies may be questionable.

Dose-response studies with co-dergocrine mesylate under hypoxia utilizing EEG mapping and psychometry

In a double-blind, placebo-controlled trial, human brain function and mental performance were studied under two different degrees of hypoxia after administration of two different doses (6 mg and 9 mg) of co-dergocrine mesylate (CDM) utilizing blood gas analysis, EEG mapping and psychometry. Hypoxic hypoxidosis (i.e. impairment of cerebral metabolism due to hypoxia) was experimentally induced by a fixed gas combination of 9.8% oxygen (O2) and 90.2% nitrogen (N2) (found in 6000 m altitude), and of 8.6% O2, 91.4% N2 (found in 7000 m altitude), which was inhaled for 23 min under normobaric conditions by 18 healthy volunteers. They received randomized after an adaptation session placebo, 6 mg and 9 mg co-dergocrine mesylate (CDM). Evaluation of blood gases, brain mapping and psychometry was carried out at 0, 2, 4, 6, 8 h after oral drug administration. Blood gas analysis demonstrated a drop in PO2 to 42 and 32 mm Hg 23 min after inhalation of the 9.8% and 8.6% gas mixture, respectively, PCO2 decreased to 32 and 31 mm Hg, pH increased to 7.46 and 7.47 and base excess increased to 0.50 and 0.90 nmol/l, respectively. EEG mapping demonstrated an increase in delta and decrease of alpha power and a slowing of the centroid over almost the whole brain. 6 mg and slightly less so 9 mg CDM attenuated this deterioration of vigilance (i.e. dynamic state of the neuronal network determining adaptive behavior). At the behavioral level, moderate hypoxia induced a deterioration of noopsychic performance, which was mitigated by 6 mg, but not by 9 mg CDM. A deepening of the hypoxia resulted in a loss of these brain protective effects of both doses. Decrement of the thymopsyche increased after both doses in the moderate hypoxic condition, while under marked hypoxia 6 mg CDM attenuated and 9 mg aggravated this deterioration. Time-wise, brain protective effects reached the level of statistical difference between the 2nd and the 6th hour. Somatic complaints like feeling dazed, giddiness and headache were mitigated dose dependently by CDM in the moderate, but not in the marked hypoxic hypoxidosis.

Brain protection of nicergoline against hypoxia: EEG brain mapping and psychometry

In a double-blind, placebo-controlled trial human brain function and mental performance as well as the antihypoxidotic properties of nicergoline were studied utilizing blood gas analysis, EEG brain mapping and psychometry. Hypoxic hypoxidosis was experimentally induced by a fixed gas combination of 9.8% oxygen (O2) and 90.2% nitrogen (N2) equivalent to 6,000 m altitude, which was inhaled for 23 min under normobaric conditions by 16 healthy volunteers. They received randomized after an adaptation session placebo, 10 mg, 30 mg and 60 mg nicergoline (NIC). Evaluation of blood gases, brain mapping and psychometry was carried out at 0, 2, 4, 6, 8 hrs oral drug administration. Blood gas analysis demonstrated a drop in PO2 from 95 to 35 and 34 mm Hg in the 14 and 23 min of inhalation, respectively. PCO2 decreased too (38 to 34 and 34 mm Hg), while pH increased (7.39 to 7.44 and 7.44). Base excess increased (-0.6 to 0.6 and 0.4) while standard bicarbonate decreased (24.4 to 24.1 and 23.8 mmol/l). Thus, blood gases remained stable between the 14 and 23 min of hypoxia during which time the neurophysiological and behavioral evaluations were carried out. EEG brain mapping exhibited an increase in delta/theta activity mostly over the parietal, temporal and central regions (left more than right), while alpha activity decreased (mostly over the parietal, central, frontal, fronto-temporal and temporo-occipital regions). 30 and 60 mg NIC attenuated this deterioration of vigilance. At the behavioral level, hypoxic hypoxidosis induced a deterioration of the noo- and thymospsyche which was mitigated by NIC. Based on 13 psychometric variables, the hypoxia-induced performance decrement was on the overall (2nd-8th hr) 43% after placebo as compared with pretreatment normoxic values, while only 29, 24 and 31% after 10, 30 and 60 mg nicergoline, respectively. The difference between placebo and the optimal dosage of nicergoline 30 mg reached the level of statistical significance (p less than 0.01, multiple Wilcoxon).

Oxygen supply of the blood-free perfused guinea-pig brain in normo- and hypothermia measured by the local distribution of oxygen pressure

The O2 supply of the blood-free perfused brain cortex of the guinea pig was investigated by measuring polarographically the local distribution of tissue PO2 at 18 degrees C, 24 degrees C, and 37 degrees C. The perfusion was performed in situ, using a medium equilibrated by a gas mixture of 95% O2 and 5% CO2. Papaverine was added to prevent vasoconstriction during hypothermia. To avoid measuring artefacts thin micro electrodes with a small sharpened tip of ca. 4 microns in diameter were used and a special puncturing technique was applied. The experimental results indicate the presence of a large variation of local tissue PO2. Local mean PO2 increased up to a depth of 1000 microns, reached a plateau, and then decreased towards 3000 microns. This demonstrates that the O2 supply changes in dependence of the distance of the brain surface. This may partly be caused by the special vascularization pattern of the brain cortex. As it follows from the PO2 histograms, at 24 degrees C the tissue layer between 0-2000 microns (layer I) was well supplied with oxygen, whereas at the same time the layer between 2001-3000 microns (layer II) was hypoxic. At 37 degrees C, both layers were hypoxic, but layer III showed the more pronounced tissue hypoxia. To obtain a sufficient oxygen supply the temperature had to be reduced below 24 degrees C to sufficiently decrease tissue O2 consumption: at 18 degrees C, there was no sign of hypoxia any more. In comparison with the PO2 histogram of the tissue the PO2 histogram of the pial surface was shifted to higher PO2 values.(ABSTRACT TRUNCATED AT 250 WORDS)

"Angiodysgenetic necrotizing encephalopathy" and its different manifestations. Survey of age-related forms and clinico-pathological appearances

Various observations of diffuse meningo-cerebral angiomatoses, which cannot be satisfactorily classified with the common phakomatoses, have been reported. They may occur at any age, with familial accumulation or sporadically. Divry and van Bogaert were the first to draw attention to such conditions in adults, where meningo-cerebral angiomatoses seemed to be combined with sudanophilic leukodystrophy. However, subsequently the latter was considered to be due to hypoxic damage to the white matter. In other observations, the severe damage to the grey matter was more evidently of hypoxic origin. Observations on two newborn individuals, sporadic examples of diffuse meningo-cerebral angiomatosis and with severe necrotic changes in the grey and white matter, are reported and discussed. Published reports on the various age-related forms are summarized and a general designation is suggested, which includes the various observations under a general heading. A parallel will be drawn between the meningo-cerebral angiomatosis and Foix-Alajouanin's disease.

Dying and death, with special reference to brain death. A bibliography

A bibliography of dying and death has been made, with special reference to the brain. It does not claim to be comprehensive. Short references have been omitted unless they contained new information not published elsewhere. When books or papers have been written in other languages, their titles have been translated, and their original languages indicated. It has not always been possible to find the complete page references to these.