Ralph Bågenholm

Scavengers of Free Oxygen Radicals in Combination with Magnesium Ameliorate Perinatal Hypoxic-Ischemic Brain Damage in the Rat

ABSTRACT: The effect of oxygen radical scavengers in combination with magnesium administered after a hypoxic-ischemic insult was evaluated in a model of perinatal brain damage. A mixture of scavengers of oxygen-derived free radicals (L-methionine, 0.2 g; mannitol, 0.5 g) and magnesium sulfate (0.3 g) per kg body weight was given to 34 1-wk-old rat pups immediately after a session of unilateral carotid artery ligation and 2 h of hypoxia (8% O2 in N2). Thirty-four littermates served as controls; they received a placebo. At 3 wk of age, there was a significantly smaller reduction of hemisphere weight ipsilateral to the ligation in the treated animals compared with the controls (0.7 versus 8.8% of contralateral hemisphere weight median values, p < 0.01). The difference was especially marked for the most severe degrees of brain damage. Only one of the 34 treated animals, compared with 13 of 34 control animals, had a reduction of ipsilateral hemisphere weight >25%. The protection offered by the mixture used was larger than in previously published studies using this model and treatment after the hypoxic exposure with only one protective agent. It is concluded that a combination of oxygen radical scavengers and magnesium administered in the phase of resuscitation mitigates perinatal postas-phyxial brain damage in the rat. An additive protective effect of different therapeutic strategies on the brain damage may be present in this situation.

Formation of free radicals in hypoxic ischemic brain damage in the neonatal rat, assessed by an endogenous spin trap and lipid peroxidation

The formation of free radicals and lipid peroxidation in the brain after hypoxic ischemia was investigated. Seven-day-old rats were subjected to unilateral (left) carotid artery ligation followed by 70 min of hypoxia with 8% oxygen at 36 degrees C. The animals were randomized into six groups as follows: control animals (no anesthesia, ligation or hypoxia) and animals decapitated at 0, 15, 30, 60 and 180 min into the reoxygenation period. Lipid peroxidation was quantified in brain homogenates using the thiobarbituric acid assay (TBA). The TBA-malondialdehyde (MDA) complex was measured with HPLC. The semi-dehydroascorbate radical was measured using electron spin resonance (ESR) spectroscopy. The semi-dehydroascorbate radical levels increased more than 3-fold in the left HI hemisphere compared to the left control hemisphere 15 min posthypoxic ischemia. The amount of MDA was significantly increased in the hypoxic ischemic (HI) hemisphere ipsilateral to the carotid ligation compared with contralateral hypoxic hemisphere. The MDA level in the left HI hemisphere was also significantly elevated at 0, 15, 30 and 60 min, but not at 180 min into the reoxygenation period. Reoxygenation after hypoxic ischemia thus induced formation of semi-dehydroascorbate radicals and lipid peroxidation.

Free Radicals Are Formed in the Brain of Fetal Sheep during Reperfusion after Cerebral Ischemia

Free radical production in the brain of acutely anesthetized, exteriorized lamb fetuses (n = 11, gestational age = 135 d) was measured using spin trap methodology. Communications between the vertebral and carotid circulations were tied, producing a two-vessel supply to the brain. Flow probes and occlusion slings were placed around each carotid. The spin trap 2-ethyl-3-hydroxy-2,4,4-trimethyloxazolidine (OXANOH) was infused intermittently into one carotid at a constant rate, and blood samples were taken at intervals from the sagittal sinus. These samples were analyzed for the stable radical OXANO˙ using electron spin resonance spectrometry. Six animals were subjected to 30 min of complete cerebral ischemia, and five fetuses served as shamoperated control animals. During postischemic reperfusion radical formation increased 2-fold during the first 20 min. However, the elevation of OXANO˙ in the venous effluent from the brain did not start until the transient hyperemia had passed. It is thus concluded that the increase of OXANO˙ observed is caused by an augmentation of free radical production during reperfusion. Because the spin trap agent was infused directly into the arterial supply and recovered directly from the venous effluent of the brain, the site of production could be the brain tissue, the endothelial cells of the cerebral circulation, and activated leukocytes. This is the first demonstration of increased radical production from the fetal brain. It is noteworthy that it takes place despite oxygen tension of the reperfusing blood of only 3-3.5 kPa.

Spectroscopy study of the dynamics of the transencephalic electrical impedance in the perinatal brain during hypoxia

Hypoxia/ischaemia is the most common cause of brain damage in neonates. Thousands of newborn children suffer from perinatal asphyxia every year. The cells go through a response mechanism during hypoxia/ischaemia, to maintain the cellular viability and, as a response to the hypoxic/ischaemic insult, the composition and the structure of the cellular environment are altered. The alterations in the ionic concentration of the intra- and extracellular and the consequent cytotoxic oedema, cell swelling, modify the electrical properties of the constituted tissue. The changes produced can be easily measured using electrical impedance instrumentation. In this paper, we report the results from an impedance spectroscopy study on the effects of the hypoxia on the perinatal brain. The transencephalic impedance, both resistance and reactance, was measured in newborn piglets using the four-electrode method in the frequency range from 20 kHz to 750 kHz and the experimental results were compared with numerical results from a simulation of a suspension of cells during cell swelling. The experimental results make clear the frequency dependence of the bioelectrical impedance, confirm that the variation of resistance is more sensitive at low than at high frequencies and show that the reactance changes substantially during hypoxia. The resemblance between the experimental and numerical results proves the validity of modelling tissue as a suspension of cells and confirms the importance of the cellular oedema process in the alterations of the electrical properties of biological tissue. The study of the effects of hypoxia/ischaemia in the bioelectrical properties of tissue may lead to the development of useful clinical tools based on the application of bioelectrical impedance technology.

Spectral analysis of burst periods in EEG from healthy and post-asphyctic full-term neonates

OBJECTIVEnTo investigate whether the periodic EEG patterns seen in healthy and sick full term neonates (trace alternant and burst suppression, respectively) have different frequency characteristics.nnnMETHODSnBurst episodes were selected from the EEGs of 9 healthy and 9 post-asphyctic full-term neonates and subjected to power spectrum analysis. Powers in two bands were estimated; 0-4 and 4-30 Hz, designated low- and high-frequency activity, respectively (LFA, HFA). The spectral edge frequency (SEF) was also assessed.nnnRESULTSnIn bursts, the LFA power was lower in periods of burst suppression as compared to those of trace alternant. The parameter that best discriminated between the groups was the relative amount of low- and high-frequency activity. The SEF parameter had a low sensitivity to the group differences. In healthy neonates, the LFA power was higher over the posterior right as compared to the posterior left region.nnnCONCLUSIONSnSpectral power of low frequencies differs significantly between the burst episodes of healthy and sick neonates.nnnSIGNIFICANCEnThese results can be used when monitoring cerebral function in neonates.

Infraslow EEG activity in burst periods from post asphyctic full term neonates.

OBJECTIVEnTo investigate whether very low EEG frequency activity can be recorded from post asphyctic full term neonates using EEG equipment where the high pass filter level was lowered to 0.05 Hz.nnnMETHODSnThe time constant of the amplifier hardware was set to 3.2 s in order to enable recordings that equal to a high pass filter cut off at 0.05 Hz. Burst episodes were selected from the EEGs of 5 post asphyctic full term neonates. The episodes were analysed visually using different montages and subjected to power spectrum analysis. Powers in two bands were estimated; 0-1 and 1-4 Hz, designated very low- and low-frequency activity, respectively (VLFA, LFA).nnnRESULTSnIn all infants, VLFA coinciding with the burst episodes could be detected. The duration of the VLFA was about the same as that of the burst episode i.e. around 4s. The activity was most prominent over the posterior regions. In this small material, a large amount of VLFA neonatally seemed to possibly be related to a more favourable prognosis.nnnCONCLUSIONSnVLFA can be recorded from post asphyctic full term neonates using EEG equipment with lowered cut off frequency for the high pass filter.nnnSIGNIFICANCEnVLFA normally disregarded due to filtering, is present in the EEG of sick neonates and may carry important clinical information.

Brain electrical impedance at various frequencies: the effect of hypoxia

Non-invasive multi-frequency measurements of transcephalic impedance, both reactance and resistance, can efficiently detect cell swelling of brain tissue and can be used for early detection of threatening brain damage. We have performed experiments on piglets to monitor transcephalic impedance during hypoxia. The obtained results have confirmed the hypothesis that changes in the size of cells modify the tissue impedance. During tissue inflammation after induced hypoxia, cerebral tissue exhibits changes in both reactance and resistance. Those changes are remarkably high, up to 71% over the baseline, and easy to measure especially at certain frequencies. A better understanding of the electrical behaviour of cerebral tissue during cell swelling would lead us to develop effective non-invasive clinical tools and methods for early diagnosis of cerebral edema and brain damage prevention.

Spectral distance for ARMA models applied to electroencephalogram for early detection of hypoxia.

A novel measure of spectral distance is presented, which is inspired by the prediction residual parameter presented by Itakura in 1975, but derived from frequency domain data and extended to include autoregressive moving average (ARMA) models. This new algorithm is applied to electroencephalogram (EEG) data from newborn piglets exposed to hypoxia for the purpose of early detection of hypoxia. The performance is evaluated using parameters relevant for potential clinical use, and is found to outperform the Itakura distance, which has proved to be useful for this application. Additionally, we compare the performance with various algorithms previously used for the detection of hypoxia from EEG. Our results based on EEG from newborn piglets show that some detector statistics divert significantly from a reference period less than 2 min after the start of general hypoxia. Among these successful detectors, the proposed spectral distance is the only spectral-based parameter. It therefore appears that spectral changes due to hypoxia are best described by use of an ARMA- model-based spectral estimate, but the drawback of the presented method is high computational effort.

On evaluation of spectrum estimators for EEG

In the search for how neonatal EEG is affected by asphyxia it is of importance to find reliable estimates of EEG power spectra. Several spectral estimation methods do exist, but since the true spectra are unknown it is hard to tell how well the estimators perform. Therefore a model to generate simulated EEG with known spectrum is proposed and the model is used to evaluate performance of several parametric and Fourier based spectral estimators.

The difficulty of appreciating slowness

V.H.K. Jäntti Department of Anaesthesiology, Tampere University Hospital, Tampere, Finland Department of Anaesthesiology, Oulu University Hospital, Oulu, Finland Department of Neurosurgery, Oulu University Hospital, Oulu, Finland Department of Anaesthesiology, Central Finland Central Hospital, Jyväskylä, Finland Department of Clinical Neurophysiology, Tampere University Hospital, P.O. Box 2000, FIN-33521 Tampere, Finland E-mail address: ville.jantti@pshp.fi