Specific Gravity Method Research Articles

Evaluation of cerebral gas retention and oedema formation in decompressed rats by using a simple gravimetric method

Objective: The objective of the study is twofold: first, to develop a specific gravity method for distinguishing between bubbles and oedema following decompression, and, second, to evaluate the extent to which the change in specific gravity is due to retained gas in cerebral tissue. Methods: A brombenzene/kerosene gradient column was used to measure changes in brain specific gravity at 100 and 300 kPa, respectively. This study was performed on 23 rats. Non-exposed rats constituted the control group A (n = 6). The exposed animals were divided into two groups according to the number of bubbles they developed upon decompression; group B (bubble grade 0-2, n = 9) and group C (bubble grade 3-5, n = 8). Results: Cerebral gas retention was determined by increasing the pressure on the gradient column from 100 to 300 kPa. Median specific gravity of the brain at 300 kPa bar was significantly higher compared to 100 kPa for the decompressed groups B (p = 0.018) and C (p = 0.012), thus implying gas retention. The cerebral gas volume was significantly higher for rats with a high bubble score compared to rats with a low bubble score (p = 0.043). However, the major contribution to the change in specific gravity was due to oedema formation. Conclusion: The brombenzene/kerosene gradient column was found to be a sensitive method for distinguishing between gas retention and oedema formation in decompressed animals. There was a higher gas retention in rats with a high bubble score compared to rats with a low bubble score. The major contribution to the change in specific gravity in decompressed animals is due to oedema formation.

Correlation of cerebral hypoxic-ischemic T2 changes with tissue alterations in water content and protein extravasation.

Age-dependent changes in T2-weighted MR images have been reported in cerebral hypoxia-ischemia. However, the biophysical mechanisms responsible for the image changes remain poorly defined. We investigated whether cerebral hypoxia-ischemia-induced T2 changes correlate with alterations in either water content or protein extravasation. One- and 4-week-old rats were subjected to unilateral carotid artery occlusion plus hypoxia in 8% oxygen. T2 images were acquired before, during, and 1 or 24 hours after hypoxia-ischemia. Blood-brain barrier disruption and brain edema were evaluated by immunohistological detection of IgG extravasation and measurement of water content by dry-wet weight and specific gravity methods. In 1-week-old rats, T2 values, areas of hyperintensity on T2-weighted images, and water content in the ipsilateral hemisphere increased during hypoxia-ischemia, recovered at 1 hour after hypoxia-ischemia, and increased again at 24 hours after hypoxia-ischemia. Extravasation of IgG occurred during hypoxia-ischemia and remained detectable 24 hours after hypoxia-ischemia. In 4-week-old rats, an increase in T2 or extravasation of IgG did not occur until 24 hours after hypoxia-ischemia despite a comparable elevation in water content during and soon after hypoxia-ischemia. T2 imaging appears reliable for detecting edema associated with disruption of the blood-brain barrier but not necessarily an increase in cerebral water or plasma proteins alone. The different hypoxic-ischemic changes in T2 in immature and older brain are associated with differences in alterations in water content plus extravasation of protein, consistent with age-dependent differences in hypoxic-ischemic alterations in vascular permeability.

Polymerization shrinkage of dental composite resins.

Aesthetic materials have always been a priority for the restoration of anterior teeth; increasingly, they have also gained prominence in the restoration of posterior teeth. This has been due to their advantages as an alternative to amalgam. Their drawbacks however, can include poor marginal adaptation, postoperative sensitivity and cuspal movement. These are particularly associated with the polymerization shrinkage accompanying the placement of composite resins. Consequently, a variety of methods have been used for determining the polymerization shrinkage. These range from dilatometer methods, specific gravity methods and deflecting disc systems to optical methods. In this work a unique method for the qualitative analysis of polymerization shrinkage was undertaken. This method utilized a miniature transducer and provided details of the shrinkage from within the material. The results indicated movement of material towards the initiating light, followed by a return movement away from it. The study was expanded to incorporate clinical aspects, whereby the composite resin was in direct contact with dental tissue, as in a restoration. Tests were performed with surface-treated cavity moulds, as in restoration placement, and without surface treatment. Results indicated that the shrinkage was highly dependent upon the region under investigation, as well as on the state of the surface.

Aspects of manufacture, composition and safety of orubisi: a traditional alcoholic beverage in the north-western region of Tanzania

The processing technology and characteristics of orubisi/amarwa, an opaque beer commonly consumed in Kagera region in the north-western part of Tanzania is described in detail. The protein content of orubisi increased from 2.0 to 2.7% after 120 hours of fermentation. The maximum alcohol content of orubisi as determined by specific gravity method was 2.5%. The alcohol profile of orubisi analysed by gas liquid chromatography (GLC) was found to contain ethanol and iso-butanol. The test for methanol was negative. Orubisi was characterised as product with relatively high acidity ranging from 0.35-0.89 g/100 ml and a final pH of 3.7. The levels of fermentable sugars-sucrose, maltose, glucose and fructose-were 0.5, 0.7, 1.8 and 0.6 g/100 ml after 120 hours of fermentation, respectively. High microbial counts were encountered in orubisi. The viable counts included yeasts: 2.0 × 107 cfu/ml, moulds 7.4 × 106 cfu/ml, coliforms 1.18 × 102 cfu/ml, lactic acid bacteria 6.5 × 107 cfu/ml and total aerobic count 2.95 × 107 cfu/ml. Based on these results, orubisi poses a serious danger to public health due to the presence of high numbers of total count and coliforms. In order to improve the safety of orubisi the pasteurisation step is recommended in the process of preparing orubisi. Hygienic handling of the final product is necessary in order to avoid contamination before consumption. The presence of trace amount of iso-butanol can lead to irritation of mucous membranes and depression of central nervous system.

Effects of lecithinized SOD on sequential change in SOD activity after cerebral contusion in rats.

To analyze the effect of lecithinized superoxide dismutase (SOD) on superoxide accumulation after traumatic brain injury (TBI) in rats, we studied the SOD activity by NBT-reducing method and the expression of Cu,Zn-SOD mRNA by Northern blot analysis. As determined by the specific gravity method, the administration of lecithinized SOD decreased brain edema in the periphery of the lesion at 6 hr after contusion. SOD activity, without lecithinized SOD administration, increased at the peripheral portion at 30 min after contusion, but decreased to normal level at 6 hr after TBI. By administration of lecithinized SOD, the increase of SOD activity was preserved until 6 hr after TBI. The expression of Cu,Zn-SOD mRNA increased in the core lesion, peripheral portion, and contralateral hemisphere until 6 hr after TBI, then was suppressed in all three areas by lecithinized SOD. These results support the hypothesis that superoxide anions may play an important role in the development of brain edema after TBI, and that leciyhinized SOD appears to prevent brain edema through a protective effect against superoxide anions.

Characterization of organic matter in the Miocene turbidites and hemipelagic mudstones in the Niigata oil field, central Japan

The Teradomari Formation, a principal petroleum source rock in Japan, consists of turbidite (Et) and hemipelagic (Ep) mudstones of a Bouma sequence at the type section in Niigata Prefecture, central Japan. Maceral composition of immature kerogen shows characteristic differences between Et and Ep mudstones. Et kerogen consists mainly of vitrinite and non-fluorescent amorphous organic matter (NFA) both of terrestrial origin, while Ep kerogen mainly consists of weakly fluorescent amorphous organic matter (WFA) of marine plankton origin. Elemental analysis, Rock-Eval pyrolysis, FTIR spectra and stable carbon isotope ratios support the differences in maceral composition between Et and Ep kerogens. The carbon isotopic ratios of WFA from Ep kerogen, separated by centrifugation specific gravity method, were almost the same as for bulk Ep kerogen. This supports the case for their origin from marine plankton indicated by maceral analysis

Xylitol chewing gum in prevention of acute otitis media: Double blind randomised trial: Uhari M.; Kontiokari T.; Koskela M.; Niemela M.BR. MED. J. (FIN) (1996) 313/7066 (1180–1184)

Paper, which is one of the largest constituent of Municipal solid waste, has become a severe problem for disposal in developed and developing countries due to the shrinking landfill capacity. It is very important and challenging task in managing the solid waste. Newspaper, which is a cellulosic feed stock, is emerging as an attractive option for the production of bio-ethanol because of lower feedstock costs, higher potential for fossil fuel displacement and also there will be reduction in greenhouse gas emission as compared to production of ethanol from corn. The main objective of the current project is to minimize the newspaper load on municipal solid waste by efficiently utilizing the waste newspaper in the production of bio-ethanol. Experimental studies have been carried out to optimize the pre-treatment process for increasing the efficiency of bacterial hydrolysis, the efficient conversion of cellulose to sugars from cellulose degrading microorganisms and to convert the sugars released to Ethanol by using Fermentation process. Pretreatment, hydrolysis and fermentation are the steps involved in the production of Bioethanol. In the pre-treatment process, the Lignin, Hemicellulose and Cellulose are separated to enhance the hydrolysis process. The optimized condition for the pre-treatment was found to be 1.5% concentration of H2SO4 at 121 °C and 45 minutes. The bacteria CytophagaHuchnosonni was used for hydrolysis process, which helped in converting the cellulose to sugars and was analysed using DinitroSalicilicacid. The reducing sugars were fermented to produce Bioethanol using the Yeast Saccharomyces Cerevisae and the yield was estimated using specific gravity method and also by using HPLC.

Antioxidant, OPC-14117, attenuates edema formation and behavioral deficits following cortical contusion in rats.

Oxygen free radicals may contribute to tissue injury processes in the central nervous system following ischemia or trauma. Recent studies have suggested that inhibition of free radicals improves the outcome in experimental models involving such conditions, and antioxidant therapy appears promising. In the present study, behavioral changes and edema formation in rat cortical contusion model were investigated, and the effects of a superoxide radical scavenger, OPC-14117, were tested. Wistar rats were anesthetized with halothane inhalation. Cortical contusion was induced in the parietal cortex employing a controlled cortical impact device. Immediately following injury induction, OPC-14117 was administered (300 mg/kg, p.o.). Edema formation was assessed in the center and peripheral areas of the contusion by the specific gravity method. Behavioral changes were evaluated by the Morris water maze test and the habituation of exploratory activity. The results revealed that the vehicle-administered control showed progressive edema formation and behavioral deficits following the injury. These changes were significantly attenuated by the OPC-14117 treatment (p < 0.05). Further, OPC-14117 reduced the size of contusional necrosis (p < 0.05). These findings suggest that superoxide free radicals are involved in contusion-induced edema formation, necrosis formation, and behavioral deficits, and that OPC-14117 has a therapeutic potential to prevent secondary cell damage following traumatic brain injury.

Ischemia-induced brain iron delocalization: Effect of iron chelators

Tissue damage in cerebral ischemia may be produced by acidosis-induced delocalization of intracellular iron which acts as a catalyst in oxidative reactions. Acidosis was induced either by homogenization and incubation of rat cortical homogenates in acidified buffers or by submitting hyperglycemic rats to complete ischemia, a procedure that leads to intracellular lactic acidosis. The level of low molecular weight species (LMWS) iron was measured after filtration of tissue homogenates through a 10,000 Mr ultrafiltration membrane. When cortical tissue was homogenized in buffer pH 7, the level of LMWS iron was equal to 0.21 μg/g. It was significantly enhanced by acidification of the homogenization medium, reaching 0.34 μg/g at pH 6 and 0.75 μg/g at pH 5. When the tissue was homogenized in water, the LMWS iron level reached 0.17 μg/g in normoglycemic rats and 0.38 μg/g ( p < 0.5) in hyperglycemic rats. Both aerobic incubation of homogenates for 1 h at 37°C and inclusion of EDTA in the homogenization medium led to further increases in the iron level. In order to demonstrate the deleterious role of iron in brain ischemia, the effect of treatment with bipyridyl, an iron-chelating agent, was assessed by measuring regional brain edema by the specific gravity method, 24 h following induction of thrombotic brain infarction. The treatment significantly attenuated the development of brain edema, reducing the water content of the infarcted area by about 2.5%. Taken together, these results support the hypothesis that a significant component of brain ischemic injury involves an iron-dependent mechanism.

Therapeutic effects of local delivery of dexamethasone on experimental brain tumors and peritumoral brain edema.

To determine if dexamethasone administered by osmotic pump directly to brain tumors would control peritumoral edema and at the same time suppress tumor growth and prolong survival, the authors studied experimental brain tumors produced in 102 rabbits by implanting VX2 carcinoma cells. Of these, 58 animals were separated into three treatment groups: Group 1 included 15 untreated rabbits; Group 2 included 18 rabbits treated with systemic dexamethasone (4 mg/kg/day); and Group 3 included 25 rabbits treated with local dexamethasone (0.24 mg/day) delivered by osmotic pump. Systemic or local dexamethasone was administered from Day 3 or Day 7 after tumor implantation, and animals were sacrificed on Day 13. A survival study was performed with 44 rabbits separated into the same treatment groups, beginning drug delivery on Day 7. Brain water content in the white matter of sacrificed animals was measured by the specific gravity method. The length and width of the brain tumors in all animals were measured and the tumor volume estimated. Findings showed that systemic and local dexamethasone administered from Day 3 or Day 7 was associated with a significant (5% level) inhibition of tumor volume as well as a mean reduction of brain edema in most tested sites. Systemic and local dexamethasone therapy also resulted in a significant (5% level) increase in survival time relative to the untreated group. These short-term results suggest that locally delivered dexamethasone may constitute a clinically important therapeutic modality.

Evidence against leukotrienes as mediators of brain edema

Leukotrienes are powerful metabolites of arachidonic acid which are known to increase the permeability of peripheral blood vessels. These substances are found in brain tissue in association with cerebral ischemia, and in brain tumors. Therefore, it has been proposed that leukotrienes have a mediator function in brain edema. This hypothesis was subjected to further experimental analysis in this study, in which the authors investigated whether: 1) superfusion of the exposed brain surface with leukotrienes increases the permeability of extraparenchymal blood vessels in vivo; 2) intraparenchymal infusion of leukotrienes induces brain edema; and 3) pharmacological inhibition of leukotriene formation by BW755C, an inhibitor of leukotriene synthesis, reduces formation of brain edema from a standardized traumatic insult. The pial vessels of the parietal cortex of cats were examined by fluorescence microscopy during cerebral superfusion with the leukotrienes C4 (LTC4), D4 (LTD4), or E4 (LTE4) by using an open cranial window preparation. Intravenous Na(+)-fluorescein served as an in vivo blood-brain barrier (BBB) indicator. Superfusion of the pia with leukotrienes (up to 2 microM) did not open the barrier to fluorescein, but was associated with a significant constriction (up to 25%) of arterial and venous vessels. In experiments with slow infusion of leukotriene B4 (LTB4) or LTC4 into the white matter of feline brain, the tissue water content was subsequently determined in serial brain slices using the specific gravity method. Tissue water profiles obtained after a 15-microM infusion of either LTB4 or LTC4 were virtually identical with those of control animals infused with mock cerebrospinal fluid. Thus, neither LTB4 nor LTC4 led to an augmentation of infusion-induced brain edema. In a final series, a cold lesion of the left parietal cortex was induced in rabbits. Twenty-four hours later, swelling of the exposed hemisphere was quantified by gravimetrical comparison of its weight with that of the contralateral nontraumatized hemisphere. Eight animals received BW755C intravenously prior to and after trauma to inhibit formation of leukotrienes. Seven rabbits were infused with an equivalent volume of saline as a control study. The resulting hemispheric swelling was 7.7% +/- 0.6% (mean +/- standard error of the mean) 24 hours later in animals receiving BW755C and 7.8% +/- 1.2% in the control group, indicating that inhibition of leukotrienes was ineffective in preventing formation of vasogenic brain edema. The findings demonstrate that leukotrienes administered to the brain in concentrations occurring under pathological conditions do not open the BBB nor do they induce brain edema.(ABSTRACT TRUNCATED AT 400 WORDS)

Potentiometric Determination of Ethanol in Alcoholic Beverages Using a Flow-Injection Analysis System Equipped with a Gas Diffusion Unit with a Microporous Poly(tetrafluoroethylene) Membrane

The selective determination of ethanol in alcoholic beverages is performed by a flow-injection analysis method using gas-diffusion separation. The determination is based on the oxidation of alcohol permeating across a porous membrane with dichromate and the reduction of excess dichromate with ferrous ion in a flow system. The concentration of ferric ion formed is potentiometrically measured with an oxidation-reduction potential electrode and is indirectly related to the alcohol content of the sample. Analytical results using the proposed method are in agreement with those obtained by a specific-gravity method (current official method in Japan) as well as by a gas-chromatographic determination.

Oxygen-free radicals in traumatic brain oedema

Oxygen-free radicals have been implicated as causative factors in ischaemic and traumatic processes. Oxygen-free radical scavengers can be used potentially to treat brain oedema. We investigated the effects of superoxide dismutase and dimethylthiourea on brain oedema. Vasogenic brain oedema was produced in 44 cats by a cortical freezing lesion. Animals were separated into three groups: (1) cold-induced oedema with sacrifice at 6, 24 and 48 h; (2) cold-induced oedema with sacrifice at 6, 24 and 48 h: subgroup A was pretreated with 10,000 u./kg polyethylene glycol and superoxide dismutase; subgroup B received a bolus injection of free superoxide dismutase (4 mg/kg) and then 1 mg/kg/min for 20 min; (3) cold-induced oedema with sacrifice at 6 and 24 h: this group was pretreated with 500 mg/kg dimethylthiourea. Brain water content was measured by the specific gravity method. Detection of superoxide radicals was carried out by the direct cortical application of nitroblue tetrazolium. Free and polyethylene glycol-superoxide dismutase did not prevent the development of brain oedema, but superoxide radicals were detected in the cold lesion. Dimethylthiourea prevented the development of brain oedema in the white matter adjacent to the lesion at 6 h but not at 24 h. These findings indicate that oxygen-free radicals are generated by the brain following cold injury and the demonstration of these radicals offers an important clue in the genesis of traumatic brain oedema.

Protective effect of the iron chelator deferoxamine on cold-induced brain edema.

Oxygen free radicals such as superoxide radical and iron-catalyzed hydroxyl radical generated by the superoxide system have been implicated in the genesis of brain edema. Therefore, deferoxamine (DFO), an iron chelator, could potentially be used to treat brain edema. To examine this hypothesis, vasogenic brain edema was produced in 48 cats by a cortical freezing lesion. The animals were separated into three groups: Group 1 comprised 14 cats that received no DFO and were sacrificed at 6 or 24 hours; Group 2 consisted of 12 cats that were treated with DFO (50 mg/kg/ml, intravenously) at 15 minutes before the lesion was made and 60 minutes later and were sacrificed at 6 or 24 hours; and Group 3 included 12 cats that were treated with DFO (50 mg/kg/ml, intravenously) at 15 minutes after the lesion was produced and 60 minutes later and were sacrificed at 6 or 24 hours. The effect of DFO on arterial blood pressure was also studied in the remaining 10 cats. Brain water content in eight sampling areas was measured by the specific gravity method. Blood-brain barrier disruption was assessed by spread of Evans blue dye with planimetry. Specific gravity values at 6 and 24 hours were significantly higher in Group 2 than in Group 1 animals. Areas of Evans blue dye extravasation at 6 and 24 hours were significantly reduced in Group 2 relative to Group 1. Group 3 cats showed improvement in specific gravity values and Evans blue extravasation at 6 hours, but not at 24 hours. The iron chelator DFO prevented early development of brain edema; thus, this oxygen free radical scavenger may provide a foundation for a new therapy for brain edema.

Comparative study of different iron-chelating agents in cold-induced brain edema

Increasing numbers of reports demonstrate the importance of iron and oxygen free radicals in brain injury and brain edema. We investigated the protective effects of three different ferric and ferrous iron-chelating agents on cold-induced brain edema. Vasogenic brain edema was produced by a cortical freezing lesion. Thirty-eight cats were separated into five groups: Group 1 (N = 8): normal control group without lesion; Group 2 (N = 8): untreated group; Group 3 (N = 8): deferoxamine (extracellular and intracellular ferric iron chelator)-treated group; Group 4 (N = 8): 2,3-dihydroxybenzoic acid (extracellular ferric iron chelator)-treated group; and Group 5 (N = 6): 2,2-bipyridine (intracellular ferrous iron chelator)-treated group. In Groups 3, 4, and 5, each agent was administered intravenously 15 minutes before lesion production and 60 minutes later. Animals in Groups 2, 3, 4, and 5 were killed 6 hours after lesion production. Brain water content in 8 sampling areas was measured by the specific gravity method. Blood-brain barrier disruption was assessed by the spread of Evans blue dye measured by planimetry. Brain water contents and Evans blue dye extravasated areas were significantly reduced in Groups 3 and 5 in comparison to Groups 2 and 4. These data suggest that both ferrous and ferric iron-chelating agents, which can penetrate the cell membrane and, presumably, act intracellularly, are effective in reducing cold-induced brain edema. (Neurosurgery 24:820-824, 1989)

各種レーザー照射後の脳浮腫に関する研究

To examine the chronic effects of the laser exposure on the brain, CO2, Nd: YAG, or the combination of both lasers was exposed for one second and specific gravity method was used to measure water contents of material of the lesion 48 hours after the exposure. Nd: YAG laser exposure showed that water contents in the white matter were more extensive than those of the other modes of laser exposure. CO2 laser exposure showed that water contents in the gray matter were least extensive of the three modes of laser exposure. Effects on the white matter by CO2/YAG coaxial laser exposure were similar to those by CO2 laser exposure.

Evaluation of a Specific Gravity Method for Estimating the Total Carcass Fat of New York-Dressed Broiler Chickens

Four trials were conducted to determine the applicability of a specific gravity method to estimate total New York-dressed carcass fat. Specific gravity values were compared to abdominal fat pad measurements, and total carcass moisture and fat values. Carcasses were produced over a very wide range of total carcass fat, from 6.5 up to 18.8%, by feeding one of five test diets with calorie-to-protein ratios ranging from 61 to 260. Total carcass fat was estimated on each New York-dressed carcass using specific gravity and abdominal fat pad weight. Each carcass was then ground, homogenized, and analyzed for total moisture and total fat. Results indicated that total carcass moisture had the best correlation with total analyzed carcass fat (r = −.95). Abdominal fat pad percent and weight resulted in the next best correlations (r = +.92 and r = +76, respectively), while specific gravity resulted in the poorest correlation (r = −.73). The low correlation value for specific gravity is thought to be due primarily to entrapped air in the lungs and air sacs of the New York-dressed carcasses.

Screening technique for differentiating the degree of spikelet filling in rice

Fully filled spikelets were determined by specific gravity method in some rice varieties. As specific gravity increased, the filled spikelets decreased while the test weight (1000-grain weight) increased. The potential test weight was found to be more than the weight known for the variety. Different grades of grain were characterised as (i) average (ii) good and (iii) Very good based on the degree of spikelet filling. The fully fitted spikelets were found to be lower in all the varieties tested and the partially filled but useful for yield calculations were higher. The grain grade index denotes the proportion of fully filled spikelets recovered at 1.18 specific gravity to the total number of spikelets formed. It was suggested that this inded is useful as a screening tool in varietal improvement programme for identifying high yield potential plants.

The role of cerebral blood volume changes in brain specific-gravity measurements

Cerebral blood volume (CBV) was calculated in gerbils from specific-gravity (SG) changes between normal and saline-perfused brains. Furthermore, changes in CBV were investigated during ischemia using carbon-14-labeled dextran (MW 70,000) as an intravascular marker. Both data were used to evaluate the possible error due to a change in CBV on the measurement of ischemic brain edema by the SG method. The methodological error found was 0.0004 for a 100% CBV change. This error is insignificant, being less than the standard deviation in the SG measured for the gerbil cortex (SG 1.0494 +/- 0.0006). Thus, CBV changes are not responsible for the SG variations observed during the first phase of ischemia. These variations are better explained as an increase of brain water content during ischemia.

Evolution and resolution of oedema following severe temporary cerebral ischaemia in the gerbil.

Regional cerebral blood flow (rCBF) and oedema following profound temporary ischaemia were studied in the gerbil. Ninety-four per cent of animals died within 24 hours of reperfusion; 50% by 4 hours. Regional differences in oedema (specific gravity method), Evans blue (EB) staining and rCBF (hydrogen clearance technique) occurred. Oedema developed during arterial occlusion, being inversely proportional to residual flow and was markedly exacerbated during reperfusion. Reperfusion hyperaemia was maximal in the parietal and hippocampal regions (ischaemic rCBF 4 ml 100 g-1 min-1). Oedema was disappearing in all areas by 3 hours of reperfusion and autoregulation returned in the occipital region (mean ischaemia rCBF 8 ml 100 g-1 min-1). EB staining and haemorrhage appeared in the thalamus (rCBF 10 ml 100 g-1 min-1) as oedema was decreasing. It is suggested that the amount of oedema and hyperaemia during reperfusion are dependent on the severity of the ischaemia. Areas of moderate ischaemia (8-10 ml 100 g-1 min-1) show little hyperaemia and greater oedema resolution during reperfusion as compared to areas of severe ischaemia (circa 4 ml 100 g-1 min-1) where there is marked hyperaemia with less oedema resolution. Early in the reperfusion period, oedema is not associated with EB staining and indicates a cytotoxic mechanism. The vasogenic component, with macroscopic haemorrhages and leakage of EB occurs later. In this model it is concluded that the early cytotoxic oedema formation and hyperaemia are phenomena with little bearing on mortality, which correlates better with later vasogenic changes.