Cerebral water and electrolytes. Effect of asphyxia, hypoxia, and hypercapnia

Cerebral blood flow and regional potassium distribution during focal ischemia of gerbil brain

In 8 gerbils (Meriones unguiculatus) focal cerebral ischemia was produced by occlusion of the left common carotid artery and the opposite external carotid artery. After two hours blood flow was measured with iodoantipyrine labeled with carbon 14, and evaluated by means of quantitative autoradiography. Thereafter the same brain sections were stained for regional potassium by means of a histochemical technique. Changes in tissue potassium content were assessed by measuring the differences in optical densities in homotopic brain regions of the stained sections. The correlation between blood flow and tissue potassium level revealed that below a flow threshold of about 0.23 ml/gm/min, a definite potassium loss from the tissue was observed. The combination of autoradiographic methods with a technique for measuring the regional distribution of potassium may be useful in providing additional information on the occurrence of disturbed electrolyte homeostasis after the onset of focal ischemia.

Experimental regional cerebral ischemia in the middle cerebral artery territory in primates. Part 3: effects on brain water and electrolytes in the late phase of acute MCA stroke

Experimental regional cerebral ischemia was produced in the middle cerebral artery (MCA) territory in primates (M. mulatta) by macrosphere embolization. Determinations of percentage tissue dry weight and tissue sodium and potassium concentrations were obtained in samples from the ischemic and non-ischemic hemispheres at various time from 12 to 48 hours after the onset of cerebral ischemia. Samples from the cortex normally supplied by the occluded MCA showed maximal accumulation of edema fluid with fluxes in sodium and potassium in reciprocal directions at 12 hours and similar edematous changes in putamen at 24 hours after embolization By 48 hours after MCA occlusion and despite the presence of infarction, partial reversal was observed in the redistribution of water and electrolytes in these gray matter structures. In contrast to cerebral cortex and putamen, the adjacent subcortical white matter showed progressive increases in water content from 12 to 48 hours and definite increases in tissue sodium with decreases in potassium were not observed until 48 hours after MCA occlusion. This late severe white matter edema associated with cerebral infarction appears to be a major factor responsible for the hemispheric swelling observed at this state.

Experimental regional cerebral ischemia in the middle cerebral artery territory in primates. Part 2: Effects on brain water and electrolytes in the early phase of MCA stroke

Acute regional cerebral ischemia was produced in the middle cerebral artery (MCA) territory in monkeys (Macaca mulatta) by selective embolization of the internal carotid (ICA) bifurcation with minimum surgical intervention in the neck under sedated conditions. Two of five hours after embolization, brain water (measurement of dry weight) and tissue concentration of sodium and potassium were determined in the tissues of the sylvian cortex, putamen and subcortical white matter in the affected MCA territory. As early as three hours, initial increase in brain water was detected in the samples of the putament without noticeable change in tissue electrolytes in two of three animals. Gross ischemic swelling of the gray matter, in both the sylvian cortex and putamen, became obvious in six of eight animals after four to five hours. This swollen gray matter showed marked increase in brain water (up to 36% swelling), increase in tissue sodium (up to 100% of the control value), and decrease in tissue potassium (down to 55%). On the other hand, edema in the white matter, if present at all, was minimal without detectable change in tissue electrolytes and was always accompanied by much greater ( greater than two to seven times) edema in the gray matter. Thus, the gray matter edema, in both the deep subcortical structures and the cortex, appeared to play the major role in the development of hemispheric swelling of the brain which may begin within hours of the onset of the MCA stroke in monkeys. Microscopically, the swollen gray matter which showed more than 10% swelling with a definite shift of tissue sodium and potassium content appeared to be dead tissue. However, early edema in the gray matter which showed less than 10% swelling without detectable change in electrolytes might be caused by simple diffusion of water through the dysfunctional capillary wall or cell membrane with or without a permeability gradient between the intravascular cerebrospinal fluid and cerebral tissue compartment and might possibly be reversible.

Mechanisms of postischemic brain edema: contribution of circulatory factors

Controlled cerebral ischemia was produced in rabbits by bilateral occlusion of the common carotid arteries and restriction of collateral blood flow by a decrease of the systemic arterial pressure to a desirable level (by hemorrhage into a pressurized reservior system). The following circulatory parameters were simultaneously monitored: systemic arterial pressure (SAP), pressure in the circle of Willis (Pcw), systemic venous pressure (SVP), and pressure in the sagittal venous sinus of brain (Pvs). The cerebral blood flow (CBF) was measured by means of the H2-clearance method, and the brain volume (BrV) changes were evaluated with a mechanical system of the sterotaxic device. It has been concluded that the pre-edematous changes in the brain tissue arise during deep ischemis but an important factor in the brain edema development is the recovery of the CBF with and increase of the intravascular pressure closely related to the brain blood volume augmentation. The latter may be pronouced because of diminution of the blood outflow from the brain when the SVP is increased. The compensation for the BrV increase (caused either by brain blood volume augmentation or by brain edema) is obtained by Pcw decrease probably due to resistance rise in the internal carotid and vertebral arteries. The brain edema may be additionally compensated by an active decrease of the systemic arterial pressure.

[Cerebral vasoparalysis, arterial hypertension and brain edema (author's transl)]

The present studies were performed in order to determine whether "filtration edema" will develop as a consequence of cerebral vasoparalysis, vasoparalysis in combination with arterial hypertension or arterial hypertension alone. A series of dogs, anaesthetised with i.v. Chloralose-Urethane were exposed 1) to cerebral vasoparalysis, produced by hypercapnia (PaCO2 about 150 mm Hg) and hypoxaemia (PaO2 40-60 mm Hg); 2) to arterial hypertension and 3) to a combination of cerebral vasoparalysis and arterial hypertension. Following cerebral vasoparalysis and arterial hypertension, a significant decrease of total cerebrovascular resistance and moderate increase of venous resistance was observed. Regional cerebral blood flow (133Xe), intracranial pressure, as well as the pressure in postcapillary venous outflow (sinus sagittalis wedge pressure and confluence sinuum pressure) were increased. Neither normotonic vasoparalysis nor vasoparalysis in combination with slight arterial hypertension (MABP more than 90 min above 180 mm Hg) resulted in cerebral edema. In contrast, cerebral vasoparalysis in combination with severe arterial hypertension (MABP more than 90 min above 220 mm Hg) resulted in a statistically significant increase in the water content in the white matter without evidence of protein extravasation. Multiple small foci of Evans blue extravasates, however, were found in the cortex following arterial hypertension in combination with vasodilation, indicating a damage of the blood brain barrier. In these blue stained cortical areas the water content was significantly in creased. The following conclusions were drawn from the results. Vasoparalysis during normotension does not produce brain edema despite the slightly elevated hydrostatic pressure gradient between intravasal and extracellular space. Only considerable increase of this hydrostatic pressure gradient caused by a combination of vasoparalysis with severe arterial hypertension is able to produce brain edema in the white matter. In addition, acute hypertension may cause minor multifocal damage of the blood brain barrier in the cerebral cortex. It is concluded that so-called brain swelling, which has been described by several authors in states of cerebral vasoparalysis, is not predominantly caused by brain edema but by vascular congestion. The clinical aspects of the result are discussed.

Resuscitation of the monkey brain after one hour's complete ischemia. II. Brain water and electrolytes

Adult normothermic rhesus monkeys were submitted to one hour's complete cerebral ischemia, followed by periods of blood recirculation varying from 45 min to 24 h. The functional impact of ischemia and the subsequent recovery was monitored by electrophysiological recording and a distinction was made between animals with signs of functional recovery and animals without recovery. Prior to ischemia the water content of the gray matter was 81.1 plus or minus 0.3% (mean plus or minus S.D.) and of the white matter 68.9 plus or minus 0.8%. The sodium-potassium ratio in the gray matter was 0.43 plus or minus 0.02 and in the white matter 0.62 plus or minus 0.06. During one hour's ischemia brain water did not change significantly, but the differences in the sodium-potassium ratio in white and gray matter were reduced. Blood recirculation of the brain after ischemia caused a considerable increase in brain water content and a shift in the sodium-potassium ratio up to 1.0. Calculated brain swelling was maximal after 45 min when it reached 11.1% of the total brain volume in an animal with recovery and 12.2% in another one without recovery. In animals with signs of functional recovery brain swelling rapidly diminished, followed by a more gradual normalization of brain electrolytes within 24 h. In animals without functional recovery electrolyte shifts were irreversible or even progressed further. It is concluded that brain swelling and electrolyte derangements following one hour's cerebral ischemia are fully reversible when signs of functional recovery appear and brain metabolism returns.

A review of total brain ischaemia models in dogs and original experiments on clamping the aorta

Dog models of total brain ischaemia for the study of pathophysiological mechanisms and post-resuscitative therapy used since 1970 are reviewed. Attempts to produce isolated total cerebral ischaemia in dogs either failed to stop cerebral circulation completely because of the abundance of collateral vessels or involved complex operations with blood loss. Complete airway obstruction resulted in various periods of asphyxia preceding asystole. Total circulatory arrest by ventricular fibrillation for 12 min or longer, resulting in gross neurological deficit, required cardiopulmonary resuscitation of variable duration and often required thoracotomy to restart spontaneous circulation. An acceptable model for short-term studies was obtained by clamping the ascending aorta for 15 min. This resulted in control of perfusion pressure with precise timing of onset and termination of cerebral ischaemia, and an isoelectric electroencephalogram within a mean time of 37 (26-44) s; it retained its ability to restore spontaneous circulation promptly with special supportive therapy, and a severe neurological deficit was evident for 20 h after ischaemia. Reliable total brain ischaemia suitable for long-term survival studies could not be developed in the dog without major surgical procedures, as it has been in the rhesus monkey. Sixteen minutes of high-pressure neck occlusion with a tourniquet and special intensive care resulted in major neurological deficit with survival for at least 7 days, and proved suitable for simultaneous study of neurological, physiological and histological changes.

Total brain ischaemia in dogs: cerebral physiological and metabolic changes after 15 minutes of circulatory arrest

Cross-clamping of the ascending aorta in dogs for 15 min produced severe neurological deficit, observed for up to 20 h. Immediately after restoration of the circulation, the intracranial pressure in the cisterna magna increased transiently to a mean peak of 22.8 Torr (SD +/- 1.7) because of a compensatory increase in systemic arterial pressure, without a fall in cerebral perfusion pressure. The intracranial pressure returned to control values 15-30 min after ischaemia and showed no secondary rise during the 8 h of observation. The electroencephalogram became isoelectric 34 +/- 6.5 s (mean +/-SD) after circulatory occlusion, and was abnormal when it reappeared 5 h 36 min (SD +/- 2 h 4 min) after the circulation was restored. The electrical impedance of the brain increased immediately after ischaemia and returned rapidly towards pre-ischaemic values during re-perfusion. The cerebral water had not increased measurably 4 h after ischaemia. After ischaemia, the lactate concentration in the cerebrospinal fluid increased to 4.7 mequiv./1(SEM +/-0.1) and the pH decreased to 7.17 (SEM +/-0.02); both returned to control values after 3.5 h. The cerebral glucose uptake was decreased 35 min after ischaemia, cerebral oxygen uptake remained unchanged but cerebral blood flow decreased (P less than 0.05 at 90 min). Immediately after cardiac arrest, recovery was impaired more by the presence of focal abnormal brain perfusion than by intracranial hypertension.

Mechanisms of seizures and coma in hypoglycemia. Evidence for a direct effect of insulin on electrolyte transport in brain

The mechanisms involved in the production of hypoglycemic coma were studied in rabbits. Measurements were made in brain, cerebrospinal fluid (CSF), and plasma of osmolality, Na(+), K(+), Cl(-), water content, exogenous insulin, glucose, lactate, and glutamate, while pH, Pco(2), Po(2), and bicarbonate were evaluated in arterial blood, 35 min after i.v. injection of insulin (50 U/kg), plasma glucose did not change, but brain K(+) content increased significantly. Grand mal seizures were observed in unanesthetized animals (+/-SD) 133+/-37 min after administration of insulin, at a time when brain glucose was normal, but brain tissue content of Na(+), K(+), osmoles, and water was significantly greater than normal. Coma supervened 212+/-54 min after insulin injection, at which time brain glucose, lactate, and glutamate were significantly decreased. At both 35 and 146 min after insulin administration, exogenous insulin was present in brain, but not in the CSF. After 208 min of insulin administration, animals were given i.v. glucose and sacrificed 35 min later. Most changes in the brain produced by hypoglycemia were reversed by the administration of glucose. Hypoxia (Po(2) = 23 mm Hg) was produced and maintained for 35 min in another group of animals. Hypoxia caused brain edema but did not affect brain electrolyte content. However, brain lactate concentration was significantly greater than normal. The data indicate that the seizures noted early in the course of insulin-induced hypoglycemia are temporally related to a rise in brain osmolality secondary to an increased net transport into brain of Na(+) and K(+), probably caused by insulin, per se. As hypoglycemia persists, there is also depletion of energy-supplying substrates (glucose, lactate, glutamate) in the brain, an event which coincides with the onset of coma. The brain edema observed during hypoxia is largely due to an increase in brain osmolality secondary to accumulation of lactate.

Effect of experimental ischemia on cerebral water and electrolytes

✓ In dogs, while the middle cerebral artery (MCA) was clipped, an apparent ischemia was demonstrated with fluorescein angiography when the dye was injected through the lingual artery. Injection of fluorescein into the femoral artery or perfusion of carbon black particles through the heart demonstrated considerable collateral blood supply to the affected area. Water, sodium, and potassium content of cerebral tissues normally supplied by the occluded artery remained unchanged. At 48 hours after clipping, focal areas of infarction developed in 70% of the animals; edema could then be demonstrated in tissue surrounding the infarction. The collateral blood supply was compromised by subjecting the dogs with clipped MCA to hemorrhagic hypotension for 1 hour. Following restoration of the systemic blood pressure by infusion of the shed blood, an area of ischemia in the territory normally supplied by the clipped artery could be easily demarcated by fluorescein angiography through the femoral and lingual arteries and by carbon perfusion. The involved cerebral cortex tissue showed marked changes that started immediately after restoration of the blood pressure, and which consisted of a fall in percentage dry weight and potassium content and an increase in sodium content. These findings were clearly correlated with gross and histological evidence of massive necrosis and were interpreted as indicating cell death rather than tissue swelling. In the underlying white matter, moderate delayed changes in water and electrolyte content were compatible with the development of vasogenic edema.

Water and electrolyte abnormalities in the human brain after severe intrapartum asphyxia

In a necropsy study of brain water, sodium, and potassium concentrations is newborn infants, abnormalities were found in 10 out of 16 cases who were severely asphyxiated at birth. It is concluded that, although frank cerebral cortical necrosis is not often recognizable in perinatal deaths, early anoxic-ischaemic cerebral damage is frequent after intrapartum asphyxia. Diffuse cerebral swelling was associated with marked electrolyte disturbances and may be regarded as a feature of anoxic-ischaemic encephalopathy in asphyxiated newborn infants.

Effects of experimental ischemia on electrolytes of cortical cerebrospinal fluid and on brain water

✓ A procedure for perfusion over the cortical surfaces of the cerebral hemispheres of monkeys (Macaca mulatta) was used in combination with a procedure for producing sudden, temporary circulatory arrest in one hemisphere while the carotid circulation to the other hemisphere remained intact. The underlying disturbance in brain metabolism subsequent to circulatory arrest for 60 minutes was reflected in part by a decrease in the concentration of sodium and an elevation in the concentration of potassium in the cortical cerebrospinal fluid (CSF) on the ischemic side. The changes occurred at or within 30 minutes of the onset of circulatory arrest. The concentration of chloride in the cortical CSF on the ischemic side did not show significant differences from the control values. The ischemic brain exhibited as much as 18% swelling of cortical gray matter and 16% swelling of subcortical white matter at 5 hours after reestablishment of the carotid circulation. Vascular injury pursuant to ischemia was reflected in a significantly increased permeability to 131I-albumin entering the cortical CSF from the cerebral blood vessels. It is suggested that the CSF and vascular water are the sources of increased brain water.

Hemodynamic and metabolic concomitants of brain swelling and cerebral edema due to experimental cerebral infarction

✓ Severe cerebral ischemia was produced in 25 baboons by clamping the carotid and vertebral arteries bilaterally for 10 minutes. Cerebral hemodynamics and metabolism were monitored throughout. Cerebral anoxia was less severe in animals in which a marked pressor response occurred due to ischemia of the vasomotor center, and a reversible type of brain swelling was usual. In those with more severe ischemic anoxia, progressive cerebral edema was a pathological entity. Evidence is presented that cerebral edema was caused by loss of autoregulation of cerebral blood flow (CBF) concomitant with hyperemia and an increase of water and chloride content of brain tissue. Cerebral edema began when CBF was reduced during occlusion and progressed for several hours after termination of occlusion. Evidence is adduced that uncoupling of oxidative phosphorylation may be an important concomitant of cerebral edema.