Actin redistribution underlies the sparing effect of mild hypothermia on dendritic spine morphology after in vitro ischemia.

Brain hypothermia is at present the most effective neuroprotective treatment against brain ischemia in man. Ischemia induces a redistribution of proteins involved in synaptic functions, which is markedly diminished by therapeutic hypothermia (33 degrees C). Dendritic spines at excitatory synapses are motile and show both shape changes and rearrangement of synaptic proteins as a consequence of neuronal activity. We investigated the effect of reduced temperature (33 degrees C and 27 degrees C compared with 37 degrees C), on spine motility, length and morphology by studying the distribution of GFP-actin before, during and after induction of in vitro ischemia. Because high-concentration actin filaments are located inside spines, dissociated hippocampal neurons (7-11 DIV) from transgenic mice expressing GFP-actin were used in this study. The movement of the spines and the distribution of GFP-actin were recorded using time-lapse fluorescence microscopy. Under normal conditions rapid rearrangement of GFP-actin was seen in dendritic spines, indicating highly motile spines at 37 degrees C. Decreasing the incubation temperature to 33 degrees C or 27 degrees C, dramatically reduces actin dynamics (spine motility) by approximately 50% and 70%, respectively. In addition, the length of the spine shaft was reduced by 20%. We propose that decreasing the temperature from 37 degrees C to 33 degrees C during ischemia decreases the neuronal actin polymerization rate, which reduces spine calcium kinetics, disrupts detrimental cell signaling and protects neurons against damage.

NORCCAP (Norwegian colorectal cancer prevention): a randomised trial to assess the safety and efficacy of carbon dioxide versus air insufflation in colonoscopy.

BACKGROUND: To eliminate the risk of combustion during electrosurgical procedures and to reduce patient discomfort, carbon dioxide (CO2) insufflation has been recommended during colonoscopy. However, air insufflation is still the standard method, perhaps due to the lack of suitable equipment and shortage of randomised studies. AIMS: This randomised controlled trial was conducted to assess patient tolerance and safety when using CO2 insufflation during colonoscopy. PATIENTS: Over an eight month period a successive series of patients referred for a baseline colonoscopy due to findings in a flexible sigmoidoscopy screening trial were randomly assigned to the use of either air or CO2 insufflation during colonoscopy. METHODS: End tidal CO2 (ETCO2), a non-invasive parameter of arterial pCO2, was registered before and repeatedly during and after the examination. The patient's experience of pain during and after the examination was registered using a visual analogue scale (VAS). Sedation was not used routinely. RESULTS: CO2 insufflation was used in 121 patients (51%) and air in 119 patients (49%). The groups were similar in age, sex, and caecal intubation rate. No rise in ETCO2 was registered. There were statistically significant differences in VAS scores between the groups with less pain reported when using CO2. CONCLUSIONS: This randomised study of unsedated patients shows that CO2 insufflation is safe during colonoscopy with no rise in ETCO2 level. CO2 was found to be superior to air in terms of pain experienced after the examination.

Hyperglycemia and focal brain ischemia.

The influence of hyperglycemic ischemia on tissue damage and cerebral blood flow was studied in rats subjected to short-lasting transient middle cerebral artery (MCA) occlusion. Rats were made hyperglycemic by intravenous infusion of glucose to a blood glucose level of about 20 mmol/L, and MCA occlusion was performed with the intraluminar filament technique for 15, 30, or 60 minutes, followed by 7 days of recovery. Normoglycemic animals received saline infusion. Perfusion-fixed brains were examined microscopically, and the volumes of selective neuronal necrosis and infarctions were calculated. Cerebral blood flow was measured autoradiographically at the end of 30 minutes of MCA occlusion and after 1 hour of recirculation in normoglycemic and hyperglycemic animals. In two additional groups with 30 minutes of MCA occlusion, CO2 was added to the inhaled gases to create a similar tissue acidosis as in hyperglycemic animals. In one group CBF was measured, and the second group was examined for tissue damage after 7 days. Fifteen and 30 minutes of MCA occlusion in combination with hyperglycemia produced larger infarcts and smaller amounts of selective neuronal necrosis than in rats with normal blood glucose levels, a significant difference in the total volume of ischemic damage being found after 30 minutes of MCA occlusion. After 60 minutes of occlusion, when the volume of infarction was larger, only minor differences between normoglycemic and hyperglycemic animals were found. Hypercapnic animals showed volumes of both selective neuronal necrosis and infarction that were almost identical with those observed in normoglycemic, normocapnic animals. When local CBF was measured in the ischemic core after 30 minutes of occlusion, neither the hyperglycemic nor the hypercapnic animals were found to be significantly different from the normoglycemic group. Brief focal cerebral ischemia combined with hyperglycemia leads to larger and more severe tissue damage. Our results do not support the hypothesis that the aggravated injury is caused by any disturbances in CBF.

Hyperglycemia-exaggerated ischemic brain damage following 30 min of middle cerebral artery occlusion is not due to capillary obstruction.

Transient focal ischemia of brief duration (15-30 min) gives rise to brain damage. In normoglycemic animals this damage usually consists of selective neuronal necrosis (SNN), and is largely confined to the lateral caudoputamen. In hyperglycemic subjects damage occurs more rapidly, involves also neocortical areas, and is often of the pan-necrotic type ('infarction'). Since experiments on forebrain ischemia of 30 min duration suggest that microcirculatory compromise develops during recirculation, we studied whether focal ischemia of the same duration, followed by reperfusion for 1, 2 or 4 h, leads to microcirculatory dysfunction. To test this possibility, we fixed the tissue by perfusion and counted the number of formed elements (leukocytes, macrophages and erythrocytes) in capillaries and postcapillary venules. Furthermore, capillary patency was evaluated following in vivo injection of Evan's blue. Histopathological examination of tissue fixed by perfusion after 1, 2 and 4 h of recirculation showed an increasing density of SNN in the caudoputamen of normoglycemic animals. Hyperglycemic, but not normoglycemic, animals showed pan-necrotic lesions ('infarction') after 4 h of recirculation. As a result, the total volume of tissue damage (SNN plus infarction) was larger in hyper- than in normoglycemic animals at 2 and 4 h of recirculation. In addition, hyperglycemic animals showed involvement of neocortex which increased with the time of reperfusion. In the ischemic hemisphere, between 5 and 10% of counted capillaries contained formed elements. However, since hyperglycemic animals contained an equal (or smaller) amount of cells the results did not suggest that capillary 'plugging' could explain the aggravated damage. Moreover, both normo- and hyperglycemic animals showed close to 100% capillary patency. The results thus fail to support the notion that the aggravation of focal ischemic damage by hyperglycemia is due to obstruction of microvessel by swelling or leukocyte adherence.

Influence of hypoglycemic coma on brain water and osmolality.

To study the effects of pronounced hypoglycemia on brain osmolality and brain edema formation, fasted rats were rendered hypoglycemic by injection of insulin, and subjected to 30 min of hypoglycemic coma. Recovery was accomplished by glucose administration. The change in water content in different brain regions was measured as a change in specific gravity after 30 min of hypoglycemic coma, or 30, 60, and 180 min after glucose administration. Plasma and brain tissue osmolality were measured in separate animals. The results show a significant decrease in specific gravity (increase in water content) in all structures measured (caudoputamen, neocortex, hippocampus, and cerebellum) at the end of the period of coma, as well as after 30 min and 60 min of recovery. At 180 min of recovery, brain water was normalized. The edema affected all structures to the same degree regardless of their vulnerability to hypoglycemic damage. Brain tissue osmolality showed a tendency to decrease with decreasing tissue glucose content. The decrease was significant (P<0.01) at 30 min of isoelectric coma. In the recovery phase, normal brain osmolality was restored within 30 min. Measurements of blood-brain barrier (BBB) permeability after 30 min of hypoglycemic coma showed no extravasation of Evan's blue, though a small but significant increase in the permeability for aminoisobutyric acid (AIB) in caudoputamen and in cerebellum was found. To analyze the importance of tissue acidosis for formation of edema, hypoglycemic animals were made acidotic by increasing the CO2 concentration in inspired air to produce an arterial plasma pH of 6.8-6.9. In these animals the edema was of a similar degree to the normocapnic animals, and the permeability for AIB was normal. We conclude that osmolytic mechanisms are not the primary cause of the selective neuronal vulnerability in hypoglycemic coma. Furthermore, the BBB is largely intact during a hypoglycemic insult.

Influence of preischemic hyperglycemia on osmolality and early postischemic edema in the rat brain.

Preischemic hyperglycemia, which raises tissue lactate content during ischemia, is known to aggravate ischemic brain damage. To explore the possibility that the enhanced lactic acidosis gives rise to osmotic damage, we studied the influence of a varied preischemic plasma glucose concentration on the early postischemic edema. Brain edema was measured by the specific-gravity technique. Brain and plasma osmolality were measured with a vapor pressure osmometer. We examined different brain regions in hyperglycemic and moderately hypoglycemic rats subjected to 15 min of forebrain ischemia, followed by recirculation for 5, 15, and 30 min. The decrease in specific gravity was compared with the increase in osmolality, to study whether the edema formation in the different groups correlated to the increase in tissue osmolality. We found edema formation to be most pronounced in frontoparietal cortex. In this structure and in hippocampus, statistically significant decreases of specific gravity were seen at all recirculation times studied. In caudoputamen, significant edema was seen only in the groups with 5 and 15 min of recirculation. Contrary to expectations, no difference was found between hyperglycemic and hyperglycemic animals. Tissue osmolality increased during ischemia in both the low and high glucose groups, but to a higher level in the latter (hypoglycemia 311 +/- 1 mmol kg-1, hyperglycemia 328 +/- 10 mmol kg-1; mean +/- SD, p less than 0.05). In the hyperglycemic group, brain osmolality remained elevated for the first 15 min of recirculation.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of two different anaesthetic agents on the newborn and the correlation between foetal oxygenation and induction-delivery time in elective caesarean section.

The PO2 and acid-base balance (pH, PCO2 and base deficit) of the newborn, determined at the moment of birth and at 10 and 60 min after birth, were compared in two series of elective caesarean section, anaesthesia being induced with thiopentone in one series (n = 12), and with ketamine in the other (n = 16). The PO2 and acid base values of umbilical cord blood at birth were correlated with the induction delivery (ID) times of the total series of patients subjected to elective caesarean section (n = 28). The ID-times were varied between 2 and 10 min. The PO2, acid-base values and Apgar scores did not differ between the thiopentone and ketamine groups. A significant negative correlation between the PO2 of the newborn at the moment of birth and the ID-time was found in the thiopentone group. The study suggests that ketamine is a good alternative to barbiturate as an induction agent for caesarean section.

Myocardial blood flow, oxygen uptake and carbon dioxide release of the human heart during hemodilution.

Myocardial blood flow, oxygen consumption and carbon dioxide release were studied before and during hemodilution in man. Dextran 70 was used as the dilutional agent to reduce hematocrit values from 37 to 28% (mean). The decrease of oxygen content in arterial blood after hemodilution was compensated by an increase of cardiac output. The myocardial blood flow increased proportionally more than the cardiac output, resulting in a virtually unchanged oxygen tension in coronary sinus blood. The metabolism of the heart was not affected as the respiratory quotient remained unchanged. This investigation suggests that blood losses up to 20% of the total blood volume can be replaced by dextran solutions, without a significant decrease of myocardial oxygen supply.

Computherm. A new device for measurement of coronary blood flow using the continuous thermodilution technique.

A new device for an automatic determination of coronary sinus blood flow using the thermodilution technique is presented. The measuring equipment consists of four main parts; a thermal dilution-catheter with two signal amplifiers of analogue type, an analogue/digital converter controlled by a microcomputer system, a pump for the control of the rate of injection flow and a control panel and display. The device has been tested in a model test with flow levels between 75 and 200 ml/min. The error between a number of measurements with all parameters unchanged except minor variations in temperatures was less than 5 per cent.

Evaluation of the continuous thermal dilution technique for measurement of coronary blood flow.

A continuous thermodilution technique has been used in a flow model. It has been difficult to determine the exact flow, but alterations of the flow have been reliably determined. For in vivo measurement the catheter is inserted into the vein of the actual organ. The indicator is injected against the bloodstream with a constant speed. The temperature of the indicator and the fall of blood temperature during the injection of indicator are measured with thermistors located at the catheter. The inability to measure the exact flow was mainly due to three factors; it turned out to be difficult to obtain the total and uniform mixing between the "blood" of the flow model and the indicator. Heat leakage occurs within the catheter as well as to ambient structures. The Wheatstone bridge was found not to be suitable, and a new type of instrument for determination of changes of resistance in the thermistors was used.

A gas chromatographic technique for determination of blood flow and metabolism in individual organs (with special reference to the heart).

A method for determining blood flow, oxygen uptake and carbon dioxide release in individual organs is presented. For blood flow measurement an inert gas (N2O) technique was used. Blood contents of O2, CO2 and N2O were measured by a gas chromatographic method with use of a special vacuum chamber for extracting the gases from blood. There was a strong correlation between the contents of O2 determined by the gas chromatographic and a spectophotometric method (correlation coefficient 0.953). Good agreement was found between CO2 in gas samples analysed by the Scholander technique and by the gas chromatographic method. A correlation coefficient of 0.998 was obtained between the N2O content calculated theoretically and that determined by the gas chromatographic technique. The new technique presented makes it possible to calculate blood flow in ml/100 g tissue/min, O2 uptake and CO2 production in an individual organ, whereby the predominant type of metabolism in the organ can be ascertained.

Early and late results of controlled ventilation in flail chest.

From 1967 through 1974, a consecutive series of 35 patients with flail chest were treated with intermittent positive-pressure breathing (IPPB). The controlled ventilation contributed to stabilization of the thoracic cage in a favorable position for healing of the fractures. Surgical stabilization of the chest was not attempted in any of the cases. During treatment with IPPB, one patient died from profuse bleeding due to a generalized coagulation disorder, but the remaining 34 were discharged in a satisfactory respiratory condition. A late follow-up study of the pulmonary function one to eight years after the trauma included x-ray films of the trachea and lungs, kymographic studies of the diaphragm, spirometric and radiospirometric testing, and arterial blood gas levels. Eighteen patients were examined. Spirometric testing revealed astonishingly little impairment of the total pulmonary function. The radiospirometric studies with 133xenon showed a significant reduction of the regional perfusion only in five patients (2 to 4.5 pulmonary segments). Kymographic study of the diaphragm gave no further information and was less selective compared with the other tests of pulmonary function. Owing to the encouraging early and late results in this study, early treatment with IPPB is considered to be the method of choice in flail chest with paradoxic respiratory movements.