The amount of circumscribed brain edema and the degree of post-ischemic neuronal recovery do not correlate well

Protective effect of D-003 on experimental spinal cord ischemia in rabbits

D-003 is a natural mixture of long chain aliphatic acids isolated and purified from sugar cane wax. It possesses antiplatelet and antithrombotic effects as well as decreases plasma and serum levels of thromboxane B(2) (TxB(2)), meanwhile significantly and markedly raises prostacyclin (PgI(2)) levels in rats. This study was undertaken to investigate the effects of D-003 on spinal cord injury in rabbits. New Zealand rabbits were treated during 10 days with D-003 (25 and 200 mg kg(-1)) and ASA (2 mg kg(-1)) before spinal cord ischemia. Animals were subjected to 20 min of aortic occlusion and 24h of reperfusion. Clinical symptoms and histopathological changes of spinal cord were observed. The PgI(2) levels in thoracic aorta were quantified by bioassay. D-003 (25 and 200 mg kg(-1)) significantly increased the mean scores reached 4h after reperfusion, although no dose relation was observed. Twenty-four hours after reperfusion, no deaths occurred in both sham and D-003 treated groups, meanwhile in positive controls and ASA the mortality rate was 38.5% and 7.69% respectively. In addition, 100% of sham, 69% and 77% of rabbits treated with D-003 at 25 and 200 mg kg(-1), respectively, did not show histopathological changes. By the contrary, 100% of positive control animals showed severe damage and ASA-treated rabbits showed only a partial protection. Animals treated with both doses of D-003 showed PgI(2) levels significantly larger than those of positive and negative controls, an effect dose-related, while ASA 2 mg kg(-1) did not change PgI(2) values. The increase of PgI(2) levels achieved in the D-003 treated animals could be an important mechanism in the protection against the spinal cord ischemia.

Gas Embolism: Part II. Arterial Gas Embolism and Decompression Sickness

Gas emboli syndromes are known to occur in many different settings, and they may result in life-threatening emergencies. Venous gas embolization was discussed previously in Part I of this review. Gas emboli that gain access to the arterial circulation or that result from exposures to decreased ambient pressures in the environment are discussed in Part II. The prevalence of arterial gas emboli and decompression sickness are likely not as high as for venous gas emboli. Most cases are preventable, and prompt treatment is frequently effective. Once present, gas bubbles generally distribute themselves throughout the body based on the relative blood flow at the time, thus making the nervous system, heart, lung, and skin the primary organ systems involved. Both mechanical and biophysical effects lead to intravascular and extracellular alterations that result in tissue injury. The clinical manifestations of these disorders are varied, and a high index of suspicion in the appropriate settings will aid health care providers in prompt recognition of these problems and allow timely intervention with specific therapy. Management of arterial gas emboli and decompression sickness is similar, with a focus on hyberbaric chamber therapy and intermittent hyperoxygenation. Recompression schedules in current use have withstood the test of time. Research continues to refine our understanding of these diseases and to optimize the treatment regimens available.

Influence of isoflurane, fentanyl, thiopental, and alpha-chloralose on formation of brain edema resulting from a focal cryogenic lesion

The objective of this study was to analyze the effects of various anesthetics on the formation of brain edema resulting from a focal cryogenic lesion. Thirty rabbits (six per group) were anesthetized with isoflurane (1 minimum alveolar anesthetic concentration [MAC] 2.1 vol%), fentanyl (bolus 5 micrograms/kg; infusion rate 1.0-0.5 micrograms.kg-1.min-1), thiopental (32.5 mg.kg-1.h-1), or alpha-chloralose (50 mg/kg). Control animals (sham operation, no lesion) received alpha-chloralose (50 mg/kg). Regional cerebral blood flow (rCBF) in perifocal brain tissue was measured by H2-clearance. Animals anesthetized with isoflurane required support of arterial pressure by angiotensin II (0.15 micrograms.kg-1.min-1). Six hours after trauma the animals were killed. Formation of brain edema was studied by specific gravity of cortical gray matter, white matter, hippocampus, caudate nucleus, putamen, and thalamus. Brain tissue samples were collected at multiple sites close to and distant from the lesion. Mean arterial pressure, arterial PCO2 and PO2, hematocrit, body temperature, and blood glucose were not different between groups during the posttraumatic course (except for an increased arterial pressure with alpha-chloralose compared to thiopental 4-6 h after trauma). The specific gravity of cortical gray matter was significantly reduced up to a distance of 6 mm from the center of the lesion in animals anesthetized with isoflurane, thiopental, or alpha-chloralose and up to 9 mm in animals given fentanyl.(ABSTRACT TRUNCATED AT 250 WORDS)

Spinal cord edema following freezing injury in the rat: relationship between tissue water content and spinal cord blood flow

A spinal cord edema model was developed in the rat by inflicting a freezing injury at -40 degrees C for 3 minutes. Regional spinal cord blood flow, tissue water content, and histology were examined. White matter edema had extended several segments by 8 hours after the injury. Tissue water content increased by 20.6% at 24 hours. Spinal cord blood flow in surrounding tissues decreased by more than 25% 4 hours after the injury. The progression of spinal cord edema following freezing injury appeared to be due to disruption of the blood-spinal cord barrier.

Cortical microcirculation in a new model of focal laser-induced secondary brain damage

To study the causes of spatial and temporal evolution of progressive neuro-injury in focal brain ischemia, models with consistent lesion topography are required. In such models, continuous monitoring of the microcirculation in a penumbral area undergoing progressive damage could be possible. We used a fixed-pulse (1.0 s, 40 W) Nd-YAG laser (NYL) to produced discrete brain lesions in rats and monitored the cerebral blood flow (CBF) with laser-Doppler flowmetry (LDF) in nonirradiated areas directly adjacent to the maturing lesion. We also examined the time evolution of the lesion topography over a 4 day period. The lesion volume determined by histopathological methods increased from 3.1 +/- 0.5 to 4.5 +/- 0.5 mm3 (p less than 0.05) during the first 2 h. Simultaneously, LDF indicated severe hypoperfusion (-60 +/- 21%, p less than 0.01) at a zone (1 mm distance from the laser lesion) where progressive neuronal degeneration and increased tissue water content (80.0 +/- 3.3% versus 76.8 +/- 2.1% in normal tissue, n = 7, p less than 0.05) were also observed. At a 4 mm distance from the lesion, hyperemic CBF responses were observed, but no histopathological signs or edema. Secondary brain damage progressed up to 4 days (lesion volume of 6.0 +/- 0.7 mm3). The NYL-induced brain lesion produced a highly reproducible focal injury and progressive neuronal death in a spatial relationship with microcirculatory failure and edema formation. The model allows prospective study of tissue state at a discrete zone, which is separate from the initial injury, but susceptible to secondary brain damage.

Platelet-activating factor and progressive brain damage following focal brain injury

The effects of a platelet-activating factor (PAF) antagonist on brain edema, cortical microcirculation, blood-brain barrier (BBB) disruption, and neuronal death following focal brain injury are reported. A neodymium:yttrium-aluminum-garnet (Nd:YAG) laser was used to induce highly reproducible focal cortical lesions in anesthetized rats. Secondary brain damage in this model was characterized by progressive cortical hypoperfusion, edema, and BBB disruption in the vicinity of the hemispheroid lesion occurring acutely after injury. The histopathological evolution was followed for up to 4 days. Neuronal damage in the cortex and the hippocampus (CA-1) was assessed quantitatively, revealing secondary and progressive loss of neuronal tissue within the first 24 hours following injury. Pretreatment with the PAF antagonist BN 50739 ameliorated the severe hypoperfusion in 12 rats (increasing local cerebral blood flow from a mean +/- standard error of the mean of 40.5% +/- 8.3% to 80.2% +/- 7.8%, p less than 0.01) and reduced edema by 70% in 10 rats (p less than 0.05) acutely after injury. The PAF antagonist also reduced the progression of neuronal damage in the cortex and the CA-1 hippocampal neurons (decrease of neuronal death from 88.0% +/- 3.9% to 49.8% +/- 4.2% at 24 hours in the cortex and from 40.2 +/- 5.0% to 13.2% +/- 2.1% in the hippocampus in 30 rats; p less than 0.05). This study provides evidence to support progressive brain damage following focal brain injury, associated with secondary loss of neuronal cells. In this latter process, PAF antagonists may provide significant therapeutic protection in arresting secondary brain damage following cerebral ischemia and neurological trauma.

A brief episode of severe arterial hypertension induces delayed deterioration of brain function and worsens blood flow after transient multifocal cerebral ischemia

Transient arterial hypertension occurs sporadically following cerebral air embolism and may occur during the acute phase of stroke. This study used an animal model of multifocal cerebral ischemia induced by air embolism and reversed by recompression to assess the effect of induced hypertension on the evoked response recovery, local cerebral blood flow, intracranial pressure, and brain water in 19 anesthetized dogs (Canis familiaris). Six received 0.4 ml of air via the internal carotid artery, 8 received intracarotid air and 10 micrograms/kg norepinephrine to produce transient hypertension, and 5 received intracarotid saline and norepinephrine. The average evoked response recovery in the air-only group was 58.3 +/- 7.7% (mean +/- SEM) of control after 4 hours of recompression; the air plus hypertension group recovery was 15.4 +/- 2.7% (p less than 0.01). The final evoked response in the dogs receiving hypertension alone did not differ from control values. Seven of 8 dogs in the air plus hypertension group had very low blood flows; only 1 of 4 in the air-only group had very low flows. The amount of brain water and the intracranial pressure were not detectably different at the end of treatment among all 3 groups. These results support a role for endothelial damage produced by air and hypertension in potentiating the process of postischemic hypoperfusion.

Intracranial and systemic effects of osmotic and oncotic therapy in experimental cerebral edema

Experiments were carried out to compare the effectiveness of oncotic and osmotic therapy in dogs with experimental cerebral edema caused by a left parietal cold lesion. Animals were divided into five groups and treated for 6 hours with either crystalloid (control group), or mannitol, albumin, furosemide, or albumin/furosemide (treatment groups). The cerebral effects of therapy were evaluated by intracranial pressure (ICP) measurements and by postmortem evaluations of water content, using computerized tomography (CT) density measurements and wet-dry weight measurements. The ICP was significantly reduced by all treatments except albumin alone, and was reduced equally by mannitol, furosemide, and albumin/furosemide. The CT density of the lesion area was significantly increased by all treatments. The density of the contralateral nonlesioned hemisphere was significantly increased by all treatments except albumin. The water content of the lesion area was significantly decreased by all treatments; water content of the opposite hemisphere was not significantly reduced. The systemic effects of therapy were evaluated by measuring net fluid balance, wedge pressures, hematocrits, free water clearance, and vasopressin. Negative fluid balance without an increase in hematocrit or in vasopressin secretion occurred only in dogs treated with albumin/furosemide. Such oncodiuretic therapy seems to cause normovolemic dehydration and to have cerebral effects similar to mannitol and furosemide, without their undesirable systemic effects.

Several new aspects of bubble-induced central nervous system injury

Ischaemia is a major mechanism underlying central nervous system (c.n.s.) damage in decompression sickness. Some recent experimental observations on the effect of bubble-induced ischaemia on c.n.s. tissue sharpen and extend our understanding of the pathophysiology of decompression sickness. After bubble-induced brain ischaemia, a measurable increase in 111In-labelled leucocytes occurs in the injured hemisphere. By 4 h into the recovery period the cells are concentrated in zones of low blood flow, as measured by the [14C]iodoantipyrine technique. The presence of these cells during the critical early hours of c.n.s. ischaemia suggests that they may contribute to the evolution of neuronal damage. Oedema is often cited as the cause of clinical deterioration after c.n.s. ischaemia or trauma. Recent evidence indicates that the presence and degree of circumscribed brain oedema is not a good predictor of the amount of nerve cell recovery (by using cortical sensory evoked response) after bubble-induced brain ischaemia. This brings into question the role of circumscribed oedema of the c.n.s. in dysfunction of post-ischemic nerve cells.