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Query: UMLS:C0020672 (hypothermia)
 17,327 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Neurophysiological, neurochemical and behavioral studies of the effects of ethanol on the nervous system have so far failed to identify specific, direct, primary mechnisms of action that may account for the typical pattern of alcohol intoxication in vivo. Electroencephalogram and evoked response studies indicate biphasic effects in the intact subject, which may correlate better with the level of arousal than with a specific drug action. Effects on spinal reflexes are also biphasic, probably representing the net result of direct influence on resting membrane potential, primary afferent depolarization, and neurotransmitter release. With the exception of its inhibitory effect on release of oxytocin, vasopressin and possibly other hypothalamic peptides, ethanol does not appear notably different in its spectrum of effects from a wide range of other hypnotics, anesthetics and minor tranquilizers. Interpretation of the findings is complicated by the fact that functional alteration of any given neuronal system by ethanol in vivo may reflect a) direct local action of ethanol on the cells under study, b) change in the input to those cells because of an action elsewhere in the nervous system, c) effects of ethanol metabolites, or d) indirect consequences of decreased blood flow, oxygen or metabolite supply, hormonal action, or hypothermia, due to disturbances of homeostasis in the whole body as a result of deep intoxication. To date, attempts to circmvent b, c and d by the study of brain tissue in vitro have shown consistent effects of ethanol only at concentrations well above those that are meaningful in vivo. Relatively specific patterns of action of different drugs in vivo may prove to be largely dependent on their customary rates and routes of administration, and on summation of minor differences in the dose-response curves with different types of neuron, even though the basic types of molecular action may be essentially similar.
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PMID:Direct effects of ethanol on the nervous system. 109 39

The authors review the intraoperative use of elective hypotension to reduce the probability of hemorrhage, to increase pliability of the aneurysmal sac for ease of clip application, and to control hemorrhage. The optimum agent and techniques for lowering systemic blood pressure remain controversial, but trimethaphan, sodium nitroprusside, and halothane have been found most useful. When cerebral blood flow falls below the brain's capacity to autoregulate, distinct time-related alterations occur biochemically and histologically. The profile of prolonged reduced adenosine triphosphate (ATP), low phosphocreatine, low glucose, and elevated lactate and lactate/pyruvate ratio is associated with swelling of perivascular astrocytes and "blebbing" of vascular endothelial cells with subsequent cerebral damage. To prevent permanent alteration it is desirable to observe time constraints and to employ other means of protection such as hypothermia, although the authors believe the latter unnecessary for short hypotensive periods. It has been proposed, but not substantiated, that anesthetics which depress rate of cerebral oxygen consumption but do not affect cerebral ATP level protect the brain from hypotension. Several investigations suggest that halothane, a vasodiltor, satisfies the safety requirement. The most prominent contraindication to halothane, however, is elevation of intracranial pressure. At present hypotensive surgery for aneurysmorrhapy is usually performed when intracranial pressure has returned to normal. Experimentally the electroencephalogram has been observed to show alterations prior to biochemical parameters for following brain vulnerability, so that it conceivably could be an effective monitoring technique during prolonged profound hypotension.
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PMID:Systemic hypotension in neurosurgery. 110 33

The data show that the enucleated eye of the cat can be maintained in apparently physiologically functioning condition by appropriate arterial perfusion. Under appropriate conditions, photically evoked electrical mass responses can be recorded from various parts of the isolated, perfused eye for 8 to 10 hours. ERGs as well as responses from axonal bundles of the optic nerve exhibit shapes, amplitudes and time courses comparable to their counterparts in vivo. Homeostasis of the perfusion ensures the stability of these light-evoked electrical responses. Transient changes in biophysical parameters of the perfusate rapidly induce marked, although reversible, changes in the amplitudes of b-waves of the ERGs. Increases or decreases in the flow rate of the perfusate induce parallel increases or decreases in the amplitudes of the b-waves as well as of the optic nerve responses. Similar alterations in the oxygen concentration of the perfusate induce similar and proportional changes in the amplitudes of the b-waves. It is concluded, that low flow rates of hemoglobin-free perfusate induce hypoxia; consequently, acceleration of the flow can compensate for hypoxia in a certain range. Previous studies on the effects of and recovery after transient hypoxia in mammalian retina are in concordance with the present data. Progressive decrease of temperature induces gradual and reversible reductions in the amplitudes of the b-waves and increases their latencies and peak-times. It is suggested, that initial hypothermia, which occurs during the period of cannulation, reduces the deliterious effects of the coincident unavoidable hypoxia on retinal neuronal elements. Since light-evoked electrical responses can be maintained for many hours in these preparations and since movements of cardiovascular and respiratory origin, invariably present to varying extent in the in vivo experiments, are eliminated, this preparation is suitable for intracellular recordings from neuronal elements of the retina. Potentials were recorded from cells in various layers of the retina of the cat; intracellular recordings from horizontal cells (S-potentials) are described in detail. Spectral analysis of S-potentials allowed to distinguish between three types according to their inputs: a mixed, rod-cone type, which was most frequently encountered, a pure cone- and a pure rod-type. Light- and electronmicroscopic investigation of the retina after perfusion revealed that (1) the extent of cellular damage depends on the flow rate of the perfusate; (2) little cellular damage is observed if medium flow rates, which maintain physiologic responsiveness of the isolated eye to light, were applied for two hours; (3) high flow rates applied for two hours, or medium flow rates applied for 7 hours appear to induce cystic changes in the pigment epithelium, but only minor changes in the cells of the inner nuclear layer.
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PMID:The function of the retina in the perfused eye. 110 95

Changes in intramyocardial carbon dioxide tension (Pco2) and arterial oxygen tension (Po2) were recorded in dogs with a mass spectrometer after temporary occlusion of the aorta and the proximal part of the anterior descending coronary artery at normothermic and hypothermic levels. Patterns of hypoxic and hypercapnic changes and their recovery were favorably modified with moderate hypothermia. Deep levels of hypothermia seemed to enhance this protective effect and progressively slow the myocardial metabolism. Occlusion of the proximal part of the anterior descending coronary artery for 30 minutes had a regional effect similar to the general myocardial changes recorded after aortic clamping, while the posterior myocardial probe showed stable control values. These data support previous studies showing that moderate hypothermia halves the oxygen consumption and doubles the "safe" period of anoxic arrest.
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PMID:Myocardial perfusion and metabolism at normothermic and hypothermic levels. 111 22

Selection criteria, clinical data, and physiological measurements obtained during five extracorporeal membrane lung perfusions for acute respiratory insufficiency are presented. Four patients died and 1 survived. A new technique of femoral artery cannulation to allow aortic arch perfusion is described. When properly monitored, this route provides improved oxygen delivery to the brain during venoarterial (VA) perfusion. The importance of monitoring the equivalent of carotid artery Po2 during VA perfusion is emphasized. Recognition of the effects of high cardiac output in limiting the quality of extracorporeal perfusion, plus the use of hypothermia to reduce output, are stressed. We have confirmed that perfusion can be accomplished with small quantities of heparin, so that bleeding is reduced, but thrombocytopenia and occasional hemorrhage continue to be persistent problems.
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PMID:Extracorporeal perfusion for acute respiratory failure: recent experience with the spiral coil membrane lung. 111 37

The influence of halothane, ether, carbon dioxide, and perfusion rewarming on the electrocardiogram was studied in 37 dogs subjected to surface-induced deep hypothermia. Significant anesthetic-related differences in P-R, QRS, Q-T and R-R intervals during cooling were not apparent; however, reduced arterial pressure, ventricular fibrillation, and a greater tendency for bradycardia requiring supportive measures were noted at low temperatures with halothane anesthesia. The use of 95% O2/5% CO2 significantly reduced the QTc at low temperatures; Other phenomena, including the occurrence and significance of J waves, are discussed. The relationship of the electrocardiogram to clinical and pathological results was evaluated and indicates that (1) properly managed resuscitation (manual massage and defibrillation) is not a serious hazard, (2) ether in 100% oxygen is the agent of choice for surface-induced deep hypothermia with prolonged circulatory arrest, and (3) halothane may be used in a procedure combining surface cooling and perfusion rewarming if given in a mixture of oxygen and carbon dioxide.
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PMID:Electrocardiographic changes during surface-induced deep hypothermia. The influence of ether, halothane, carbon dioxide, and perfusion rewarming. 112 62

The intraperitoneal administration of sodium salicylate, L-tryptophan, and tyrosine resulted in significant hypothermia when rats were exposed to a 4degree C ambient temperature. Salicylate and tryptophan increased plasma levels of nonprotein-bound tryptophan while total and bound tryptophan were reduced in salicylate-treated rats. Tryptophan concentrations were unaffected by tyrosine administration. Concomitant with increases in free plasma tryptophan, there occurred significant rises in brain levels of tryptophan in both groups of rats, while brain tyrosine levels were increased in those rats receiving tyrosine. Similarly, significant increments in hypothalamic serotonin levels in rats receiving salicylate or L-tryptophan and increases in hypothalamic norepinephrine in tyrosine-treated rats seem to reflect the increased availability of tryptophan and tyrosine for monamine synthesis. However, alternative mechanisms of hypothermiaseem to be operative since oxygen consumption studies demonstrate dissimilar results for tryptophan and salicylate administration.
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PMID:Salicylate, tryptophan, and tyrosine hypothermia. 113 May 45

Although the environmental stresses to which man is subjected on the ground are less than those commonly encountered in aviation or under water, they may still exceed an individual's powers of adaptation. Extremes of temperature, commonly encountered in the Arctic or the tropics, may occur in regions of normally temperate climate and lead to failure of temperature regulation, resulting in hypothermia, frostbite, heat exhaustion, or heat stroke. High mountains impose additional hazards due to high winds and lack of oxygen, and deep mines are dangerous work-places because of high temperature and humidity. Some physiological acclimatization occurs in extreme natural environments and the dangers may be reduced by appropriate clothing, diet and behaviour.
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PMID:Adaptation and failure of adaptation to extreme natural environments. 113 66

The dilution of whole blood leads to a significant improvement of its rheologic properties based on a decrease in hematocrit and, hence, blood viscosity. Under conditions of normovolemia and an adequate response of the cardiorespiratory system, the acute dilution of blood will enhance the venous return to the heart and thereby improve total and capillary blood flow significantly. In the hematocrit range of 25 to 30 per cent (limited hemodilution), this increase in flow rate is able to compensate fully for the diminished oxygen content of the blood. Changes in oxygen extraction or in oxygenhemoglobin affinity are only encountered at hematocrits below 20 per cent or if hemodilution is associated with hypovolemia. Since normovolemia is the condition sine qua non for the heart to increase its output compensatorily, intentional hemodilution should preferably be performed with colloid solutions which are capable of maintaining the colloid osmotic pressure of plasma and the circulating volume in normal limits. Limited normovolemic hemodilution with its beneficial effects on microcirculatory flow and tissue nutrition is emphasized for the treatment of impaired microcirculation as occurring in shock and low flow states, polycythemia, and high viscosity syndromes. Acute preoperative hemodilution is a means of reducing the use of bank blood and of avoiding the risks of blld transfusions in patients undergoing major elective surgery. Extreme hemodilution and total body washout in hypothermia appear to be effective clinical tools.
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PMID:Hemodilution. 113 50

The effect on reactive hyperaemia of variations in oxygen content of the inspired air and in tissue temperature, was studied by electromagnetic flowmetry in the hind limbs of rabbits. Flowmetry was used together with oxygen polarography to compare recovery time of blood flow and recovery time of oxygen tension in muscle tissue during reactive hyperaemia. After occlusions lasting more than 10 seconds; recovery time of oxygen tension was much shorter than recovery time of blood flow. Breathing of different oxygen concentrations induced relatively small changes of reactive hyperaemia. After increasing tissue temperature all variables of reactive hyperaemia were reduced following 10-60 seconds' occlusion. On the other hand, after 5 minutes' occlusion percentual repayment and recovery time increased significantly. During hypothermia, percentual repayment and recovery time were reduced significantly after 5 minutes' occlusion. Thus, the time-response curves for percentual repayment and recovery time during hyper-and hypothermia crossed each other when occlusion time was extended beyond 60 seconds. Normalization of oxygen tension when blood flow was still increased seems to exclude that oxygen deficiency per se is the only cause of reactive hyperaemia. Oxygen deficiency may be a contributory factor in the initiation of vasodilation during circulatory arrest and may possibly be of importance in the first part of reactive hyperaemia. The results of changing the tissue temperature suggested that metabolites which are accumulated during circulatory arrest, maintain the increased blood flow, at least after release of longer occlusions.
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PMID:Reactive hyperaemia in the hind limbs of rabbits. II. The effect of changes in oxygen tension and temperature. 115 78


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