Brain energy metabolism during the process of dying and after cardiopulmonary resuscitation

In vivo 31P magnetic resonance spectroscopy study of mouse cerebral NAD content and redox state during neurodevelopment

Nicotinamide adenine dinucleotide (NAD) is an important cofactor of energy-producing pathways. The redox ratio (NAD⁺/NADH) reflects the cellular oxidoreductive state. Oxidative stress and redox dysregulation have been suggested to contribute to various neurological diseases. The assessment of NAD content has been recently demonstrated in large animals and human brains by ³¹P magnetic resonance spectroscopy. However, its measurement in small rodents has never been attempted. The purpose of this study was to investigate, in vivo, the NAD content during mouse brain neurodevelopment. ³¹P-MR-spectra were acquired in the mouse brain at postnatal days P20, P40, P90 and P250 at 14.1 T using a 3D-localization sequence. High spectral quality was achieved at 14.1 T. NAD⁺ and NADH were quantified with mean Cramér-Rao lower bound of 10% and 14%, respectively. An increase in NAD⁺/NADH was observed from P20 to P250 due to a decrease in [NADH]. The intracellular pH was significantly reduced with age, while the free [Mg²⁺] in the brain was significantly increased. This study demonstrates for the first time the feasibility of the measurement of NAD content in vivo in mouse brains during development, which opens the prospect of longitudinally studying energy metabolism and redox dysfunction in mouse models of brain pathology.

Brain energetics of cardiopulmonary cerebral resuscitation

Recovery of normal brain energetic conditions during and after resuscitation from cardiac arrest is critical for survival and good neurologic outcome. This review emphasizes the glucose-driven metabolic processes during and after ischemia and on the post-resuscitation development of secondary energy derangements. It also explores some potential therapeutic interventions designed to attenuate these energy derangements. The article summarizes some bench research and is not intended to provide treatment strategies for clinical application.

Magnetic resonance: a noninvasive approach to metabolism, circulation, and morphology in human brain death

Phosphorus (31P) magnetic resonance spectroscopy and magnetic resonance imaging were used to study the intracellular metabolism, circulation, and morphology in the brains of 3 patients with clinical brain death syndrome due to traumatic brain damage, subarachnoid hemorrhage, and acute occlusive hydrocephalus caused by a colloid cyst. Magnetic resonance spectra were characterized by a complete absence of ATP and were dominated by an intense inorganic phosphate signal. Magnetic resonance imaging revealed a uniform pattern of diffuse brain swelling and tentorial and foraminal herniation. Intracranial blood flow was absent on the magnetic resonance angiography projections. These preliminary findings suggest an important impact of magnetic resonance in the determination of human brain death.

The pathophysiology of brain ischemia

Brain ischemia due to a critical reduction in cerebral blood flow is a well recognized and common cause of irreversible brain damage. The observation that brain cells are more resistant to ischemia than was previously assumed on the basis of clinical experience has stimulated considerable investigative work designed to determine those factors responsible for irreversible ischemic cell damage. At this time, data from these investigations indicate that cellular acidosis and biochemical disturbances initiated by abnormal intracellular ion homeostasis may be especially important in determining the ultimate survival of nerve cells. This review examines the biochemical events initiated by ischemia and their potential role in determining the ultimate survival of brain cells.

The effect of mild microembolic injury on the energy metabolism of the cat brain

Moderate unilateral cerebral ischemia was produced by microembolism in 24 adult cats. Two million plastic microspheres with a diameter of 15 +/- 5 microns were injected into the left common carotid artery via the lingual artery. The physiological and metabolic responses to embolism were accessed by electrocorticography and by determining the cerebral energy state. Embolism caused an immediate slowing and voltage reduction of the ipsilateral electrocorticogram with a gradual recovery after 30 to 60 min. Some animals also had an immediate and short depression of the contralateral electrocorticogram. In spite of the market functional suppression, metabolites of the cerebral energy-producing metabolism in most of the animals changed only slightly. In the embolized hemisphere pyruvate increased from 0.06 to 0.10 mumol/g and lactate from 1.9 to 4.6 mumol/g within 5 min after embolization and remained at this level during the 4 h observation period. Phosphocreatine, adenosine triphosphate and the energy charge of the adenylate pool remained uncharged during this period. However, there was a slight increase of ATP in the non-embolized hemisphere during the early postembolic period. In two animals, the initial slowing of the electrocorticogram recurred and spread to the contralateral hemisphere, followed by bilateral flattening after a few hours. This delayed functional deterioration was accomplished by complete loss of energy-rich phosphates. These animals also had a progressive increase of cerebrospinal fluid (CSF) pressure and considerable brain swelling with cerebellar herniation after 4 h. It is concluded that unilateral cerebral embolism in the above concentration leads only to a slight increase of anerobic glycolysis without significant perturbation of the cerebral energy state, unless progressive brain swelling with cerebrellat herniation supervenes. This supports previous findings, that brain edema and not initial ischemia is the main pathogenetic factor for tissue damage in cerebral microembolism.

Incomplete versus complete cerebral ischemia: improved outcome with a minimal blood flow

It has been reported that incomplete cerebral ischemia with cerebral blood flow less than 10% of control may be more damaging than an equal period of complete ischemia. In this study, the effects of severe, incomplete cerebral ischemia on neurological outcome and cerebral metabolism were studied in dogs anesthetized with nitrous oxide. The results were compared with those of a previous study concerned with the effects of complete ischemia. Dogs could sustain only 8 to 9 minutes of complete ischemia with return of normal neurological function, whereas maintenance of a cerebral blood flow rate less than 10% of control extended this limit to 10 6o 12 minutes. Following a 10-minute exposure, only dogs undergoing incomplete ischemia regained a normal cerebral oxygen consumption within 90 minutes; similarly, animals subjected to incomplete ischemia enjoyed a faster return of EEG activity than dogs exposed to complete ischemia of the same duration. Cerebral metabolite levels did not prove to be a good index of return of neurological function. Within periods of cerebral ischemia in which meaningful neurological recovery might be expected, we conclude that some blood flow is better than no flow.

Complete cerebral recovery after prolonged circulatory arrest. A report of two cases

Two adult patients with severe heart disease regained full consciousness a few hours after circulatory arrest at normal temperature which lasted up to eighteen minutes, though both eventually died. Whilst the reason for their unusual cerebral recovery cannot be clearly established, it may have been primarily due to the cause of the circulatory arrest, exsanguinating haemorrhage during cardiac surgery, together with subsequent circulatory support. Several other factors may also have contributed to this outcome, but a review of present evidence suggests they were of much less importance.

Oxygen uptake following deep hypothermia

Oxygen uptake of the body (Vo2) was measured in 9 children undergoing surgical correction of congenital heart lesions using cardiopulmonary bypass and deep hypothermia at 20 degrees tc with circulatory arrest. Initial levels of Vo2 following circulatory arrest were found to be four times greater than would have been expected from the normal relationship between Vo2 and body temperature, but within 8-10 minutes had fallen to normal levels. The quantity of oxygen taken up by the body during this time is similar to theoretical values for the quantity of oxygen inphysical solution, at 20 degrees C, in the tissues. It is postulated that during deep hypothermia the increased amount of oxygen in physical solution in the body plays an important part in preventing tissue damage during circulatory arrest.