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

Gibbon's rotating cylinder could not be enlarged to oxygenate an animal larger than a cat. The spinning disc oxygenator, introduced in 1947, had the capacity to perfuse a dog and the potential to increase oxygenation capacity by addition of more discs. When centers began to do three to four open-heart operations per day, the disposable bubble oxygenator was more practical. Bubble size was optimized to decrease the flow of oxygen relative to the blood flow and reduce trauma to blood. The bubble oxygenator is the type most commonly used today. Use of deep hypothermia with whole blood at an esophageal temperature of 10 degrees C was initially complicated by brain damage due to aggregation of white blood corpuscles and platelets. The introduction of hemodilution permitted safe utilization of hypothermic perfusion. Perfusion of infants should not be carried out at hematocrit below 25 ml/100 m. Early membrane oxygenators used nonporous silicone, or modified silicone membranes. High priming volumes, high pressure drop and marginal gas transfer efficiency characterized these devices. Recent advances in membrane technology have spawned a new generation of membrane oxygenators utilizing microporous polypropylene. In these new oxygenators, with either microporous hollow fibers or sheet membrane, the gas transfer characteristics are far superior to those of types produced in the past. The hollow-fiber devices typically have larger surface areas and higher pressure drop than in the new state-of-the-art flat plate models. An evaluation of one of these new-generation membrane oxygenators gave optimal oxygen and carbon dioxide exchange at a gas flow of 1 l/min of 60% oxygen in air at 30 degrees C and 2 l/min of 80% oxygen in air at normal temperature and rewarming for an adult. Today, after almost 40 years of oxygenator development, these new membrane device can offer better platelet preservation and reduced blood trauma as compared with types developed in the past. The new membrane oxygenators are fast becoming the preferred choice for use in infants and in protracted perfusion.
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PMID:From the spinning disc to the membrane oxygenator for open-heart surgery. 393 70

Moderate per- and postoperative hypothermia initiates an increased metabolism in the postoperative period. The subsequent demands on oxygen transport may be critical in poor risk patients. Nineteen healthy young women with moderate hypothermia after abdominal surgery were studied for 2 h postoperatively with or without external heating from a heating ceiling. Central and peripheral temperatures, oxygen consumption, plasma catecholamines and shivering were measured. A method for continuous measurement of oxygen consumption and carbon dioxide production during spontaneous breathing is described. The results suggest that postoperative external heating decreases oxygen consumption, shivering and plasma catecholamine levels. At the same time, the comfort of the patient is increased considerably.
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PMID:Effects of a thermal ceiling on postoperative hypothermia. 406 Oct 3

Nifedipine, a slow calcium-channel blocker, has been used to preserve myocardial function in the ischemic heart. To quantitatively evaluate the effectiveness of nifedipine as a cardioplegic agent during moderate hypothermia (28 degrees C), 15 pigs were evaluated on total and right heart bypass with measurement at normothermia and after 1 hour of hypothermic ischemia of stroke volume, coronary blood flow, myocardial oxygen consumption, and lactate extraction. Myocardial tissue gases (oxygen and carbon dioxide) were continuously monitored. Animals were divided into three groups: hypothermic ischemia, hypothermic ischemia with infusion of nifedipine carrier without nifedipine, and hypothermic ischemia with nifedipine and its carrier. A significant decrease in stroke volume was seen in all three groups; however, the depression was significantly greater following hypothermic ischemia than following cardioplegia with either nifedipine or its carrier. The mean recovery value of stroke volume was highest in the nifedipine group, but this difference between nifedipine and its carrier alone did not reach statistical significance. Coronary blood flow, myocardial oxygen consumption, lactate extraction, and tissue gases failed to substantiate a significant benefit when nifedipine was compared with its carrier alone. We conclude that under these hypothermic conditions, no proven statistically significant advantage was noted in the nifedipine group when compared with the nifedipine carrier group in swine. However, both nifedipine and the carrier were superior as a myocardial preservative when compared with hypothermic ischemic arrest alone.
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PMID:Quantitative evaluation of the myocardial preservative characteristics of nifedipine during hypothermic myocardial ischemia. 406 42

Previous studies have shown that organic bases, including some drugs, are secreted by renal proximal tubules. The present studies examined the transport of the organic bases cimetidine and procainamide by rabbit proximal straight tubules perfused in vitro. Both drugs were secreted into the tubule lumen. [3H]cimetidine secretion was reduced by quinidine, procainamide, and N-acetylprocainamide. Previous studies showed that cimetidine secretion was reduced by other organic bases. Hypothermia and ouabain inhibited [3H]procainamide secretion as was shown previously for cimetidine secretion. [3H]procainamide secretion was also reduced by quinidine, cimetidine, procainamide, and N-acetylprocainamide but not by probenecid. High concentrations of cimetidine (10(-3) M) had no effect on the rates of fluid or total CO2 absorption. When analyzed in terms of Michaelis-Menten kinetics, the effect of cimetidine on procainamide secretion and procainamide on cimetidine secretion was consistent with competitive inhibition. The results suggest that both cimetidine and procainamide are secreted into the lumen of proximal straight tubules predominately by an organic base transport mechanism. These studies raise the possibility that some of these drugs might compete for a common secretory mechanism in renal tubules and reduce the elimination of each other.
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PMID:Cimetidine and procainamide secretion by proximal tubules in vitro. 617 96

In 1975 H. Rahn put forward a new concept of hydrogen ions regulation which explains acid-base regulation in relation to body temperature and applies to all animal species. At the root of this concept is the finding that maintenance of intracellular neutrality is governed by water dissociation and regulated by imidazole-rich protein buffers. The pH of the extracellular fluid, which receives acid by-products of cell activity, is kept higher than that of the intracellular fluid (relative alkalinity). The difference between extracellular pH and neutrality is constant for each species and ranges from 0.6 to 0.8 pH units. It is unaffected by changes in temperature, and the total CO2 content of extracellular fluid remains constant. The authors were able to confirm the value of this new concept in man by experimental studies of in vitro and in vivo blood of patients undergoing aorto-coronary bypass under controlled hypothermia. They draw the following practical conclusions: (1) in subjects under moderate or deep hypothermia for surgical purposes, the acid-base status can be controlled and the extracellular pH adjusted by ensuring intracellular neutrality; this is done by keeping PCO 2 at such a level that the arterial blood pH measured at 37 degrees C remains around 7.40; (2) the problem of correcting acid-base values (pH-PCO 2) according to body temperature is solved simply by using pH and PCO 2 values measured at 37 degrees C and interpreting them, as usual, in terms of metabolic or respiratory acidosis or alkalosis.
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PMID:[Relations between acid-base equilibrium and body temperature. Physiological concepts and practical applications]. 622 30

Fundamental physicochemical characteristics of the acid-base related constituents of extracellular and intracellular fluid spaces of vertebrates in relation to changes in temperature have been reviewed. Emphasis has been placed upon the dissociation constant of water, the solubility constant of CO2, the dissociation constant of histidine imidazole, the hydroxyl-hydrogen ion ratio, the protein charge state and the alpha-imidazole regulation concept. Because pN and pKIm change in parallel when temperature varies, the OH/H ratio and the alpha-imidazole value for any sample of blood or plasma held anaerobically in vitro are invariant with changing temperature, since a constant CO2 content is maintained. Thus, when blood or plasma cools, pH increases and PCO2 decreases, but relative alkalinity and the protein charge state remain constant. These responses are solely the consequence of physical constants, that is, equilibrium constants and gas solubility, changing with temperature. In vivo, the set of PCO2 is established in each poikilothermic species by its normal ventilatory pattern designed to maintain constant CO2 content. Regulation in vivo in poikilotherms consists of adjustments of ventilation per unit metabolism (VA/VCO2) appropriate to every temperature. When the ventilatory and renal mechanisms of human beings are suppressed by anesthesia and hypothermia, their extracellular and intracellular responses mimic those of poikilotherms. Clinical management of hypothermia in humans requires ventilatory control using oxygen-augmented room air without added CO2 monitored by pH measurements of arterial blood warmed anaerobically to 37 degrees C. Finally, the need for new techniques to measure intracellular pH as temperature is lowered and some areas for further investigation are suggested.
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PMID:The hydroxyl-hydrogen ion concentration ratio during hypothermia. 629 7

Intraoperative hypothermia has become a common occurrence. Postoperative rewarming often is accompanied by shivering and results in increased metabolic and circulatory demands. We examined the metabolic, hemodynamic, and biochemical variables in 2 groups of hypothermic (greater than 35.8 degrees C) patients requiring mechanical ventilation after a major operation. One was observed during routine medical management whereas the other group received 40 mg of metocurine iodide and then observed during routine medical management. All patients were allowed to rewarm passively. O2 consumption (VO2, ml/min, STPD), CO2 production (VCO2, ml/min, STPD) and respiratory quotient (RQ) measurements were made every 15 min using a Beckman Metabolic Measurement Cart. Esophageal temperature, arterial blood pressure, heart rate (HR), rate pressure product, CVP, arterial blood gases, serum lactate concentration, and duration of shivering also were recorded. Suppression of the shivering by metocurine increased rewarming time significantly and decreased VCO2, VO2, HR, rate pressure product, mean arterial pressure (MAP), and the O2 cost of rewarming. Thus, the elimination of shivering during postoperative rewarming is associated with a decrease in caloric, metabolic demands and myocardial work (as assessed by the rate pressure product) while rewarming time is prolonged. In the postoperative, hypothermic, critically ill patient, suppression of the shivering response in selected patients may be indicated.
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PMID:Physiologic requirements during rewarming: suppression of the shivering response. 640 3

The present study examined the effects of exposure of rats to elevated environmental levels of CO2 on norepinephrine metabolism in the hypothalamus and other regions of the brain. In confirmation of previous findings by others CO2 at 10 or 15% was found to elevate both dopa accumulation after dopa decarboxylase inhibition and norepinephrine utilization after tyrosine hydroxylase inhibition. These effects however were found to be transient occurring only during the first 30 min of 2.5 h exposure. In this regard CO2 differs from another form of stress, restraint which produces a sustained 2.5 h increase of dopa accumulation and NE accumulation. Restraint was also more effective than CO2 in depleting endogenous stores of hypothalamic NE. The factor responsible for the adaptation of the catecholamine response to CO2 was not identified although it was shown not to be hypothermia and it was reversed by a 2 h CO2-free recovery period.
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PMID:Rapid adaptation of the stimulatory effect of CO2 on brain norepinephrine metabolism. 642 Jul 12

The effect of experimental hypothermia on changes of the electrophysiological equivalent of minute ventilation (Veq) was studied in rabbits under urethane-chloralose general anaesthesia with muscle relaxation and artificial ventilation. The animals were subjected to bilateral vagotomy prior to the experiment. During normothermia (37.5 +/- 0.7 degree C) and hypothermia (29.9 +/- 1.7 degrees C) the animals were given for breathing a hypercapnic mixture of gases (CO2 5% with O2 95%) and asphyxia was produced by switching off the respirator. The arterial blood pressure, blood flow in the common carotid artery, end-expiratory CO2 concentration, "integrated" phernic nerve activity and brain-stem temperature were recorded. The partial pressure of carbon dioxide and oxygen, hydrogen ion concentration and arterial acid-base balance were determined with correction for temperature changes. The equivalent of minute ventilation (being the product of the frequency and amplitude of "integrated" phrenic nerve activity) decreased in hypothermia by 91%, with a simultaneous fall of PaCO2 from 33,48 +/- 3.84 mmHg to 23.40 +/- 3.59 mmHg (by 30%). The hypercapnic stimulus applied during hypothermia produced a fivefold lower Veq value than in normothermia and under control conditions (despite a similar value of PaCO2 of 28.89 +/- 3.12 mmHg). The Veq value approaching that found under normal conditions in normothermia was observed during hypothermia only when asphyxia was induced when the value of PaCO2 was 37.07 +/- 8.74 mm Hg and that of PaO2 was 37.41 +/- 29.11 mmHg. During hypothermia the blood flow in the common carotid artery decreased by 16% when the animals were breathing the hypercapnic mixture. The analysis of the obtained results showed a direct effect of temperature on respiratory activity generation and regulation of arterial blood flow to the brain. It may be supposed also that hypothermia raises the response threshold to CO2 level in the breathed air.
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PMID:Minute ventilation changes in rabbits during experimental hypothermia. 642 Oct 87

It was tried in this study to determine the effects of temperature and carbon dioxide on the respiratory drive under experimental hypothermia in rabbits under urethane-chloralose anaesthesia after muscle-relaxant administration, after bilateral vagotomy and during artificial ventilation with a biologically-controlled respirator. Hypercapnia was produced in the animals during normothermia (37.3 +/- 0.7 degrees C) and hypothermia (30.0 +/- 1.5 degrees C). The basic physiological parameters and efferent activity of the phrenic nerve were recorded, and arterial blood gasometric parameters were determined. The electrophysiological equivalent of minute ventilation (Veq) decreased during hypothermia by 33% on the average while the PaCO2 value was unchanged. The hypercapnic stimulus applied during hypothermia failed also to raise the Veq value to its initial level. A 9% fall of blood flow was observed in the common carotid artery when the animals received a hypercapnic gas mixture for breathing during hypothermia. The results obtained in this study and earlier observations confirm unequivocally the hypothesis of a direct influence of temperature lowering on respiratory rhythm generation and regulation of arterial blood flow to the brain.
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PMID:Effect of lowered temperature on respiratory rhythm generation in rabbit. 642 Oct 88


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