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

Because disordered autoregulation of cerebral blood flow may underlie neurologic injury associated with cardiopulmonary bypass (CPB), we studied the effects of normothermic (37 degrees C) and hypothermic (18 degrees C) CPB on cerebral vascular reactivity in 6 to 8-week-old piglets. Hypothermic CPB animals were subdivided into alpha-stat and pH-stat groups (n = 6 animals each group) according to acid-base management protocol. Cerebral blood flow (CBF), cerebral oxygen consumption (CMRO2), cerebral vascular resistance (CVR), and CBF response to hypercapnia were examined before, during, and 1 hour after CPB and used to calculate CVR per millimeter of mercury change in arterial partial pressure of CO2: (CVRnormocapnia - CVRhypercapnia)/(PaCO2 hypercapnia - PaCO2 normocapnia). Before CPB, CBF, CMRO2, and vascular reactivity to elevated CO2 were similar in the three groups; these parameters remained unchanged by normothermic CPB. However, during hypothermic CPB, CBF and CMRO2 decreased in both alpha-stat and pH-stat groups; in the alpha-stat group, CBF decreased from 27 +/- 5 mL.min-1.100 g-1 (normothermic CPB) to 5 +/- 1 mL.min-1.100 g-1 (hypothermic CPB) (p < 0.05) and CMRO2 decreased from 1.8 +/- 0.21 to 0.24 +/- 0.04 mL.min-1.100 g-1 (p < 0.05), whereas in the pH-stat group CBF decreased from 28 +/- 2 to 9 +/- 1 mL.min-1. 100 g-1 (p < 0.05) and CMRO2 decreased from 1.63 +/- 0.07 to 0.31 +/- 0.09 mL.min-1.100 g-1 (p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Cerebral blood flow during cardiopulmonary bypass: influence of temperature and pH management strategy. 769 12

It is strange that some aspects of infant care have been strongly promoted by modern medicine while others have been neglected. Thus prone sleeping which has been strongly promoted is now related to an increase in SIDS, whereas the promotion of breast feeding in developed countries has been less successful. Unfortunately there has not been sufficient physiological investigation of many infant care practices and some of the proposed mechanisms for SIDS and prone sleeping have not been substantiated. Thus further work is needed on hypercapnia, hypothermia and periodic breathing and respiratory control. Studying infants alone may leave out important physiological mechanisms such as the effect on body warmth when the infant is close to the mother. More investigation is needed of antenatal factors related to SIDS and it is critically important that physiological investigation should not look for single mechanisms but be concerned with the interaction of many physiological factors.
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PMID:Infant care practices and the investigation of physiological mechanisms. 782 Dec 61

Anesthetized, paralyzed and mechanically ventilated pigs were hypoventilated to extreme hypercapnia (PaCO2 approximately 20 kPa) at FiO2 0.5, and allotted to receive hypothermia (approximately 31.5 degrees C) and buffer infusion, (HB-group, n = 6) or to a hypothermic control group (H-group, n = 6). The HB-group had higher arterial pH (7.34 vs 7.09, P < 0.01) and plasma bicarbonate (58.8 vs 35.4 mmol.l-1, P < 0.01) than the controls, but lower mean pulmonary arterial pressure (MPAP), (16 vs 23 mmHg (2.1 vs 3.1 kPa), P < 0.01) and pulmonary vascular resistance (PVR), (512 vs 699 dyn.s.cm-5 (5120 vs 6990 microN.s.cm-5), P < 0.05). Mixed venous PO2 (PVO2) was lower in the HB-group (5.1 vs 6.8 kPa, P < 0.01), as well as serum potassium (2.8 vs 3.7 mmol.l-1, P < 0.01) and ionized calcium (1.01 vs 1.29 mmol.l-1, P < 0.01). Subsequently, the inspired oxygen fraction (FiO2) was decreased stepwise (0.3, 0.25, 0.21, 0.15, 0.10) at 30 min intervals. At FiO2 0.3, the HB-group had lower PVO2 (6.6 vs 7.8 kPa, P < 0.01), O2 half saturation tension (3.6 vs 4.2 kPa, P < 0.01), MPAP (17 vs 25 mmHg (2.3 vs 3.3 kPa, P < 0.01) and PVR (598 vs 793 dyn.s.cm-5 (5980 vs 7930 microN.s.cm-5, P < 0.05) compared with the controls, but higher arterial O2 saturation (95.3 vs. 88.6%, P < 0.01) and O2 content (17.7 vs 15.7 ml.100 ml-1, P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Effects of hypothermia with and without buffering in hypercapnia and hypercapnic hypoxemia. 802 72

1. Effects of moderate hypercapnia (10% CO2) on rectal temperature, oxygen consumption and body weight loss were examined during and after acute hypothermia induced by cold and helium-oxygen. 2. Hypothermia induction time was reduced significantly by hypercapnia. Rewarming tended to be faster in hypercapnic animals than in normocapnic animals. 3. Hypercapnia significantly reduced body weight loss when measured during hypothermia and during normothermia after rewarming. 4. Oxygen consumption during cooling was decreased by hypercapnia. 5. Exposure to 10% CO2 during cooling may spare energy substrate and favor survival in hypothermia.
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PMID:Effects of moderate hypercapnia on hypothermia induced by cold He-O2 in rats. 809 75

We tested the hypothesis that hypercapnia will induce behavioral hypothermia in toads and that central chemoreceptors are involved in this response. Animals were tested in an enclosed temperature gradient supplied with different gas mixtures. Fractional inspired CO2 (FICO2) between 0 and 0.05 had no significant effect on selected body temperature, but FICO2 between 0.06 and 0.10 reduced the selected body temperature from U approximately 28 to 18 degrees C. To determine if the hypercapnia-induced hypothermia is mediated by acidification of central chemoreceptors, the pH of the fourth ventricle was kept constant by perfusion with mock cerebrospinal fluid of pH 7.7 or 7.1 (normal and acidic values, respectively). Ventricular perfusion at pH 7.7 under normocapnic conditions had no effect on body temperature. Hypercapnia (FICO2 0.08) failed to induce hypothermia when the fourth ventricle was kept at pH 7.7 and when hyperoxia was present. Acidic ventricular perfusion under normocapnic conditions decreased selected body temperature from 27 to 25 degrees C, a significant drop but much less than that due to hypercapnia producing the same brain pH, suggesting an important role of peripheral chemoreceptors. The physiological significance of behavioral hypothermia and nature of the peripheral stimulus were evaluated by measuring the effect of hypercapnia on arterial oxygen saturation, PO2, and pH at 15 and 25 degrees C. Arterial oxygen saturation was higher at the lower temperature. Increasing FICO2 decreased oxygen saturation at 25 degrees C but not at 15 degrees C. Arterial PO2 increased with increasing inspired CO2. This increase was greater at 15 degrees C than at 25 degrees C. Arterial pH decreased at both temperatures.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Role of central chemoreceptors in behavioral thermoregulation of the toad, Bufo marinus. 820 24

A key element of neonatal regionalization is the establishment of transport links between centres of tertiary care and subregional centres. During the 11-year period 1982-92, 186 transports were undertaken from the neonatal unit, Vestfold Central Hospital, for a total of 180 patients, or 0.8% of all live born infants (n = 23,652). 64 patients (36%) were referred for prematurity/respiratory distress syndrome (IRDS), 81 (45%) for congenital malformations, and 35 (19%) for other conditions. Transports for prematurity/IRDS declined significantly from the the first 6-year period 1982-87 to the last 5-year period 1988-92 (3.6 vs. 1.8 per 1,000 live born infants; p < 0.01), owing to the establishment of a local respirator treatment programme for severe IRDS. In 71 (38%) transports the infants were mechanically ventilated. Seven (10%) suffered in-transport complications related to the endotracheal tube. At arrival, significantly more patients were anaemic (Hb < 14 g%; transports before 48 hours after birth), alcalotic (pH > 7.50), hypocapnic (PCO2 < 4 kPa) or had a base excess < -10 mmol/l than before transportation (p < 0.05). There was a tendency towards more patients with hypothermia (tp < 36 degrees C), acidosis (pH (< 7.20) and hypercapnia (PCO2 > 10 kPa) at arrival than before transportation (p > 0.05). No deaths occurred during transport. However, two infants died within two hours after arrival, giving a transport-related mortality rate of 1%. Transporting critically ill neonates implies discontinuity of treatment and monitoring of these infants. Optimal stabilization before transportation, and scrupulous work on technical details are of utmost importance.
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PMID:[Transport from a subregional neonatal unit. Experiences from Vestfold Central Hospital during an 11-year period 1982-92]. 825 80

In Norway the number of deaths per year from drowning is approximately nine persons per 100,000, most of them men between 25 and 40 years of age. About 60% of these persons can swim, and 50% of the deaths are related to intake of alcohol. About 6% of the drowned are children, most of them boys. In disaster medicine, drowning is associated with accidents at sea, involving large vessels or small boats, or connected to offshore activities. The important pathological events are directly related to asphyxia, hypoxemia, hypercarbia, pulmonary oedema, and circulatory arrest. This paper describes various aspects of drowning and the pathophysiological processes involved, and discusses differences between drowning and near drowning in fresh water and salt water. Although treatment is basically centred on effective cardiopulmonary resuscitation, there are certain differences with regard to further treatment and fluid/electrolyte management. Hypothermia is often a prominent feature, and if cardiopulmonary resuscitation is successful, hypoxic brain damage may be ameliorated by the fall in body temperature.
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PMID:[Drowning--near drowning]. 826 93

We examined the oxygen tension, carbon dioxide tension, and pH in canine brains under profound hypothermia to evaluate the effects of perfusion (circulatory arrest for 1 hour; 25 and 50 mL.kg-1 x min-1 for 2 hours) with and without pulsatile assistance. The effects of pulsatile flow on cerebral blood flow and metabolism were also evaluated in dogs supported by low-flow perfusion (25 mL.kg-1 x min-1) for 2 hours. Profound hypoxia occurred in the brain after 20 to 60 minutes of circulatory arrest. Brain tissue acidosis with hypercapnia was moderated by perfusion at a rate of flow of 50 mL.kg-1 x min-1. Pulsatile low-flow perfusion (25 mL.kg-1 x min-1) moderated cerebral hypercapnia and made the cerebral metabolism aerobic without affecting the total cerebral blood flow and consumption of oxygen.
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PMID:Pulsatile low-flow perfusion for enhanced cerebral protection. 826 72

We examined changes in ventilation and metabolic rate during hypothermia (36-27 degrees C) induced with exposure to helium-oxygen and cold in halothane anesthetized ground squirrels (Spermophilus lateralis) and rats. As a consequence of proportionate decreases in VCO2 and breathing frequency, the VE/VCO2 in both species remained constant. The changes which occurred in breathing pattern were also similar in the two species; an increase in TI and TE along with emergence of apneic periods between breaths at body temperatures below 31 degrees C. VT/TI and TI/TTOT decreased but VT remained constant with progressive hypothermia. The ventilatory responses to hypercapnia and hypoxia decreased to the same extent as the ventilatory and metabolic requirements in the ground squirrel but not the rat. The changes in VE and VCO2 during hypothermia in the ground squirrel predicted well the values observed in deep hibernation. We conclude that regulation of ventilation at reduced body temperatures is tightly coupled to metabolic demand.
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PMID:Ventilation is coupled to metabolic demands during progressive hypothermia in rodents. 835 48

We investigated the effect of prolonged hypercapnia on human thermoregulation during immersion of seven male subjects in a 15 degrees C water bath until their esophageal temperature dropped to 35 degrees C or until 1 h had elapsed. In the control trial, subjects inspired room air, whereas in the other trial the inhaled gas mixture was a 4% CO2:20% O2:76% N2 gas mixture. Oxygen uptake (VO2, liter.min-1), inspired minute ventilation (VI, liter.min-1), esophageal temperature (Tes, degree C), mean unweighted skin temperature (Tsk, degree C), mean heat flux (Q, W.m-2), and electromyographic (EMG, mV) activity of the trapezius muscle were recorded. VO2 and integrated EMG (IEMG) activity were used as the primary indicators of shivering thermogenesis. There was a tendency for elevated VO2, albeit not significant, in the CO2 trial compared to the air trial. We observed no significant differences in the IEMG between the air and CO2 trials. These results suggest that prolonged inhalation of a gas mixture containing 4% CO2 does not have a significant inhibitory effect on shivering thermogenesis and does not enhance the cooling rate of the body core. The absence of any shivering attenuation is most likely due to the small blood PCO2 increase incurred by inhalation of 4% CO2, compensation of hypercapnic-induced respiratory acidosis, and a strong thermal drive from core and peripheral regions. It is unlikely that elevated PICO2 levels contribute significantly to the etiology of hypothermia in divers.
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PMID:Effects of prolonged CO2 inhalation on shivering thermogenesis during cold-water immersion. 840 Nov 51


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