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

Recent experimental and clinical studies from our institution have shown that the administration of cold, bicarbonate-buffered, hyperkalemic crystalloid cardioplegic solution resulted in a significant rise in intramyocardial pH. This rise could theoretically be caused by (1) the alkalinity of the solution administered (pH 8.2 at 25 degrees C), (2) the washout of acid metabolites with each administration, and (3) hypothermia per se. To investigate the relative effects of each of these three factors on intramyocardial pH, dogs on cardiopulmonary bypass received crystalloid cardioplegic solution either at 10 degrees C (n = 9) or at 37 degrees C (n = 8) every 30 min during 2 hr of aortic cross-clamping. Myocardial temperature, intramyocardial pH, and CO2 tension (Pmco2) were measured continuously. Needle biopsy specimens were taken every 30 min for biochemical and ultrastructural analysis. Before aortic cross-clamping, intramyocardial pH was 7.07 +/- 0.06 in both groups (+/- SEM). Upon each administration of cardioplegic solution, hearts in the 10 degrees C group cooled to 10 degrees to 15 degrees C and intramyocardial pH increased on the average by 0.31 +/- 0.03 units (p less than .001). In the 37 degrees C group intramyocardial pH was unaffected by cardioplegic solution. At the end of the cross-clamping period, intramyocardial pH had declined to 6.49 +/- 0.13 in the 10 degrees C group and to 5.60 +/- 0.08 in the 37 degrees C group, the fall in pH being significantly greater in the 37 degrees C group than in the 10 degrees C group (p less than .01).(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:The relative importance of alkalinity, temperature, and the washout effect of bicarbonate-buffered, multidose cardioplegic solution. 643 May 94

The effects of chronic naltrexone infusions on food intake and energy balance were examined in male rats. Animals were fed either Purina Chow, or chow plus a 32% sucrose solution. After one week of being maintained on these diets, animals were implanted (intrascapularly) with osmotic minipumps infusing either 200 micrograms/kg/hr naltrexone hydrochloride or saline. Sucrose + chow-fed animals exhibited increased O2 consumption, increased CO2 production and an elevation in the respiratory quotient (RQ) relative to chow-fed controls. When infused with naltrexone, sucrose + chow-fed animals decreased food intake and body weight gain. While chow-fed animals also suppressed food intake and body weight gain, these decreases were not as great as those observed in sucrose + chow-fed animals. As a function of naltrexone administration, both chow-fed and sucrose + chow-fed animals altered their metabolism as reflected by decreased RQ and adiposity as determined by skinfold measurements. In addition, sucrose feeding led to a hyperthermia which was reversed by naltrexone infusions. Thus, chronic naltrexone administration depressed appetite, reduced energy production and induced hypothermia in rats. As naltrexone is thought to block the endogenous opioid system, this suggests that the endorphins are involved in the regulation of food intake and thermogenesis.
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PMID:Modifications in food intake and energy metabolism in rats as a function of chronic naltrexone infusions. 643 49

In 28 children undergoing cardiopulmonary bypass with deep hypothermia for open heart surgery, an attempt was made to maintain pH at 7.4 not corrected for temperature by varying the CO2 concentration supplied to the oxygenator so that the PaCO2 was 5.33 kPa, not corrected for temperature. One to two percent CO2 gave satisfactory results. Five percent CO2 had previously been given. No adverse clinical side effects were noted, and the acid-base status remained stable for 24 hours in 16 patients. There are strong theoretical reasons for maintaining a pH of 7.4, uncorrected for temperature, during hypothermia and a clinical impression was gained of better myocardial function and improved systemic and cerebral perfusion.
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PMID:Acid-base control during hypothermia. Acid-base control in children during hypothermia without temperature correction of pH and PCO2. 643 44

The gaseous microemboli (GME) production and gas transfer characteristics of two series of bubble oxygenators (Harvey H-1500 and Bentley BOS-10) were evaluated during clinical perfusion in 33 adult patients during open heart surgery for acquired valvular and ischaemic heart disease. For each oxygenator series, patients were divided into two groups, depending upon the method of measurement (intermittent or continuous) of the arterial PO2(PaO2). Using the data available, the perfusionist altered the gas:blood flow ratio in an attempt to maintain the PaO2 within the normal range. In the first group (I = intermittent), where PaO2 data were available only intermittently, the PaO2 values were well above normal, and large numbers of GME were detected in the arterial blood. In the second group (C = continuous), where the PaO2 data were available continuously, there was significantly better control of the PaO2 (P less than 0.001 and P less than 0.01 for the H-1500 and BOS-10, respectively) and significantly fewer GME (P less than 0.01 and P less than 0.05 for the H-1500 and BOS-10, respectively). The Bentley BOS-10 oxygenator used a lower gas:blood flow ratio to achieve physiological levels (range 9 to 13 kPa at 37 degrees C) of PaO2 than did the Harvey H-1500 oxygenator, but there was no difference in the number of GME detected. The lower gas:blood flow ratios for the BOS-10 oxygenators in group C resulted in significantly higher PaCO2 values well outside the physiological range (4 to 6 kPa at 37 degrees C) during the rewarming phase (mean PaCO2 = 7.6 +/- 0.8 kPa) of cardiopulmonary bypass than did the H-1500 oxygenator (mean PaCO2 = 6.3 +/- 0.7 kPa). Mean values for the PaCO2 for both oxygenators during other phases of bypass (cooling and hypothermia) were within the physiological range. If the CO2 retention was corrected by increasing the gas:blood flow ratio the PaO2 values and GME counts became elevated.
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PMID:A clinical evaluation of the gas transfer characteristics and gaseous microemboli production of two bubble oxygenators. 644 73

The relative effects of temperature and CO2 on the blood flow in the common carotid artery (CCBF) were investigated in vagotomized, paralyzed rabbits under urethane-chloralose general anaesthesia with artificial ventilation. During hypothermia a 52% fall of CCBF was observed in rabbits ventilated by the classic method. Administration of a hyperkapnic mixture for breathing caused a further 16% CCBF fall, with a simultaneous rise in PaCO2 by 23%. During ventilation with a respirator triggered by phrenic nerve activity hypothermia caused a 30% CCBF fall without changes in PaCO2 value. Administration of the hyperkapnic mixture for breathing caused, in these circumstances, a 9% CCBF fall with a 7% PaCO2 increase. Hyperthermia caused during ventilation by the classic method a 42% rise in CCBF and a 22% PaCO2 rise. The hyperkapnic mixture given for breathing decreased the CCBF by 9% and increased the PaCO2 by 15%. On the other hand, during ventilation with the respirator triggered by phrenic nerve activity no changes were observed in these parameters. This suggests that the thermic stimulus exerts a direct effect on the regulation of the blood flow to the brain, and during hypothermia it prevails over the stimulus produced by CO2.
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PMID:"Paradoxical" effect of carbon dioxide on common carotid artery blood flow in rabbits during hypothermia and hyperthermia. 644 50

Acidification of luminal fluid in the proximal convoluted tubule has been modeled as a pump-leak system. Using isolated perfused rabbit proximal convoluted tubules in a HCO-3/CO2-free in vitro environment, we studied "H+ leak" by imposing pH gradients across the tubule and measuring the change in pH from perfusate to collected fluid. Active acidification was inhibited by acetazolamide with and without hypothermia. At 21 degrees C a symmetrical H+ leak with an apparent permeability coefficient of approximately 0.15 cm X s-1 was found with either a lumen-to-bath or bath-to-lumen [H+] gradient. At 37 degrees C a much higher apparent permeability coefficient was found that was dependent on luminal lactate. Phosphate movement did not affect H+ fluxes significantly. Without luminal lactate, the apparent permeability coefficient was 0.31 cm X s-1. Although this permeability coefficient is larger than other ionic permeability coefficients in this segment, it is not sufficient to account for a significant H+ leak compared with rates of acidification or bicarbonate reabsorption. To investigate the role of Na+-H+ exchange in mediating the observed H+ leak, we perfused tubules with low [Na+] solutions with and without amiloride (10(-3) M). Neither the lower [Na+] nor the presence of amiloride diminished the apparent [H+] permeability coefficient. We conclude that a H+ leak pathway independent of Na+-H+ exchange is present in the proximal convoluted tubule.
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PMID:Hydrogen ion permeability of the rabbit proximal convoluted tubule. 669 75

Rahn's concepts of acid-base balance during hypothermia were tested in humans by studying eleven men who required extra-corporeal cooling for surgery. Hypothermia was moderate (27-28 degrees C) and maintained for 60-70 min. Extracorporeal blood perfusion (ECBP) was performed with a bubble-oxygenator which allowed changes in blood flow and gas concentrations. Arterial pH (pHa) at the person's body temperature was controlled by varying CO2 flow to the oxygenator in order to maintain in vitro pH measured at 37 degrees C in the normal range. During hypothermia and after rewarming to 37 degrees C, bicarbonate concentration and total CO2 content of arterial and mixed venous blood remained constant. A physiologic solution was introduced into the peritoneal cavity which was used as a tonometer; the values of equilibrated CO2 content in peritoneal fluid were constant. Neither metabolic acidosis nor hypercapnia developed. Blood acid-base balance in vivo during hypothermia was therefore identical to the behavior of blood in vitro. In addition, the interpretation of the results of acid-base studies, in humans with abnormal central temperature is facilitated when measurements are performed at 37 degrees C.
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PMID:Control of acid-base status during hypothermia in man. 678 9

It is shown that the amount of ATP in rats under hypothermia up to heat stroke lowers and that of ADP and AMP somewhat rises. Ionol administration normalizes the ATP level and increases the ADP and AMP contents. Inhalation of CO2 and especially administration of ionol contribute to a higher resistance of the animals to hyperthermia.
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PMID:[Influence of hyperthermia and protective effect of ionol and carbon dioxide gas on ATP, ADP and AMP content of the rat brain]. 678 22

Circulatory dynamics during surface- induced deep hypothermia using the halothane-diethyl ether azeotrope in 100% oxygen (O2) without circulatory arrest and 95% O2 and 5% carbon dioxide (CO2) with and without 60 minutes of arrest were evaluated in 15 adult mongrel dogs. Mean arterial pressure was lower in animals given 5% CO2 than in animals given 100% O2 during cooling. Cardiac output in the 5% CO2 groups increased until 30 degrees C cooling and then gradually decreased to 29% of control at 20 degrees C. Cardiac output in the 100% O2 group progressively decreased to 16% of control at 20 degrees C cooling and was 51 to 77% of the output in the 5% CO2 animals at comparable temperatures throughout the hypothermia procedure. The differences in cardiac output were attributed primarily to changes in stroke volume since heart rates were not significantly different. These changes were probably secondary to differences in systemic vascular resistance, which had increased sixfold in the animals given 100% O2 and had only doubled in the 5% CO2 groups at 20 degrees C during cooling. Hemodynamic variables in animals given 5% CO2 did not reveal significant differences in arrested versus nonarrested animals during early rewarming. However, with further warming, cardiac output, stroke volume, left ventricular stroke work, and mean pulmonary arterial and pulmonary artery wedge pressures were lower, and systemic and pulmonary vascular resistances were higher in the arrest group. We conclude that the improved results with halothane-diethyl ether azeotrope in 95% O2 and 5% CO2 during surface hypothermia are due to a greater cardiac output and reduced peripheral vascular resistance.
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PMID:Circulatory dynamics during surface-induced hypothermia under halothane-ether azeotrope anesthesia. 680 89

The purpose of this study was to determine the effects of a specific dopamine receptor agonist (apomorphine) and antagonist (pimozide) on thermoregulation when the heat loss pathway was activated by the stress of exercise. Apomorphine or its control vehicle (0.9% wt/vol saline) was injected systemically (0.5, 1.0, 1.5 mg/kg ip) or within the preoptic-anterior hypothalamus (5, 10, 20 micrograms) immediately before the start of treadmill exercise at 21.5 m/min. Colonic, tailskin, and ambient temperatures were recorded each minute. Oxygen consumption was calculated from on-line measurements of percent O2 and CO2. Pimozide injected systemically (0.5 mg/kg ip) had no effect on resting colonic temperature, but caused a significant (P less than 0.05) hyperthermia during treadmill exercise compared to saline controls. Central and systemic injections of apomorphine caused a dose-dependent hypothermia that was blocked by pretreatment with pimozide. Oxygen uptake values during exercise following the central injection of apomorphine were virtually identical to those following the injection of saline, but colonic temperature was significantly (P less than 0.05) lower than saline controls, indicating that the hypothermia observed was not due to a reduction in metabolic rate. These data indicate that dopamine receptors in the preoptic-anterior hypothalamus of the rat participate in the mediation of heat dissipation when the animal is challenged with a heat stress.
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PMID:Effects of apomorphine and pimozide on temperature regulation during exercise in the rat. 720 55


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