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At least 1,333 records · Page 74Linked to original sources
PubMed1990

[A comparative neurophysiological analysis of thermoregulatory muscle activity in hibernating and nonhibernating animals during the development of hypothermia].

Comparative neurophysiological analysis of the motor units (MU) activity during hypothermia performed in ground-squirrels and rats, revealed a tendency of the MU firing rate to decrease whereas electromyographical patterns of thermoregulatory activity were found to be common both for hibernating and non-hibernating animals. The MU activity ceased in rats at their body temperature of 20-22 degrees C in contrast to 9-5 degrees C in ground-squirrels. Differences in thermoregulatory muscle tone distribution over muscle groups were found between those two species. Some mechanisms of neural regulation of cold shivering and of thermoregulatory muscle tone, are discussed.

Animals↗
PubMed1988

Induction of gap junctions and brain endothelium-like tight junctions in cultured bovine endothelial cells: local control of cell specialization.

The final development of specializations by brain capillary endothelial cells, which characterize them as distinct from non-central nervous system (CNS) endothelium, is thought to be controlled by astrocyte-derived factors produced locally within the CNS. One specialization, the complex intercellular tight junction, which is unique to these cells and a major component of the blood-brain barrier, is controlled by an astrocyte-derived factor(s) and a "competent' extracellular matrix (Arthur et al., 1987). In order to test whether these factors can also trigger development of brain endothelium-like tight junctions in non-CNS microvessel endothelial cells, passaged bovine aorta and pulmonary artery endothelial cells were cultured in either 50% astrocyte-conditioned medium and 50% alpha-MEM, or in alpha-MEM alone (control). Only endothelial cells maintained in conditioned medium exhibited ultrastructural features indicative of synthesis and plasma membrane-insertion of junction components (Shivers et al., 1985). No assembled tight junctions were seen in these cells. Endothelial cells plated onto coverslips coated with ECM (Cedarlane Labs., Hornby, Ont.) and maintained in astrocyte-conditioned medium, displayed large, complex tight junctions and extraordinarily large gap junctions. Cells plated onto plastic or fibronectin-coated substrates possessed no tight or gap junctions. Results of this study show that CNS astrocytes produce a soluble factor(s) that promotes synthesis and insertion of tight junction components in non-CNS endothelial cells. Moreover, an intact, endothelial-derived extracellular matrix is required for assembly of tight junctions to complete development of this brain capillary-like specialization. This study confirms the notions that: a) the final fine-tuning of cell differentiation is under local control, and b) that endothelial cells in general do not express their final destination-specific differentiated features until those features are induced by local environment-produced conditions.

Animals↗
PubMed1988

Temperature and metabolic responses to inhalation and bath rewarming protocols.

Rewarming of mildly hypothermic subjects was compared using three different techniques that have been suggested for use in field situations. Eight subjects were cooled for up to 1 h, on four occasions, in a filled whole-body water calorimeter controlled at 22 degrees C. Following cooling, rewarming was initiated by one of four procedures: inhalation of warmed and humidified air at 40 degrees C or 45 degrees C, immersion in 40 degrees C water, or spontaneously by shivering. Deep body temperature was recorded simultaneously at three different sites: rectal, esophageal, and auditory canal. Skin temperatures were recorded from four sites: chest, forearm, thigh, and calf. Results showed that rapid external rewarming in 40 degrees C water produced the quickest rate of rewarming and smallest magnitude and duration of afterdrop. Regardless of which rewarming protocol was followed, the esophageal site always showed the smallest afterdrop. Although there were no differences in the rewarming rates calculated for each of the three core temperature sites during inhalation and spontaneous rewarming, both auditory canal and esophageal sites rose significantly quicker than rectal during the rapid rewarming in 40 degrees C water. Inhalation rewarming led to a depressed metabolic rate, compared to spontaneous rewarming, which was not compensated by heat provided through the respiratory tract. It was concluded that for mildly hypothermic subjects, rapid rewarming in 40 degree C water was the most efficient procedure and that esophageal temperature--the closest approximation of aortic blood or cardiac temperature--is the most sensitive to change during rewarming by any procedure.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1986

Radioprotective effect of polyethylene glycol.

Polyethylene glycol of molecular weight 400 (PEG-400) had a radioprotective effect of about 20% against lethality when given ip 20 min prior to single or fractionated X-ray doses to the head and neck. Dose modification factors (DMF) based on LD50/15 values ranged from 1.14 to 1.24. A similar DMF of 1.12 based on LD50/30 values was obtained using single doses of whole-body X irradiation. Mice given head and neck irradiation had significantly reduced rectal temperatures (31.3 +/- 3.0 degrees C) 9 days post irradiation compared with unirradiated controls (35.4 +/- 0.6 degrees C). No such reduction was observed when PEG-400 was given with radiation (36.3 +/- 0.9 degrees C). PEG-400 also lessened, but not significantly, the frequency of shivering in irradiated animals. Histopathologic examination of the oral structures demonstrated only marginal protection by PEG-400. Estimation of the alpha/beta ratio from LD50 data on head and neck-irradiated mice yielded values of 4.4 +/- 1.9 (95% confidence limits) Gy without PEG-400 and 7.9 +/- 1.4 Gy with PEG-400. Since it is a non-thiol radioprotector, PEG-400 may be more useful when combined with more conventional thiol-containing radioprotectors.

Animals↗
PubMed1983

[Analysis of the mechanism of the hypothermic action of neurotropic drugs].

Hypothermic action of neurotropic drugs (Oxotremorine, Nicotine, Isoprenaline, Seduxene) is evaluated by means of suppression of shivering thermogenesis. The action is accounted for by their influence of the brain stem level of the postural muscular tension regulation rather than by selective action of these drugs on the hypothalamic thermoregulatory centre.

Animals↗
PubMed1983

[Changes in thermoregulation in the white mouse treated with endogenous substances from the intestinal tissue of hibernating animals].

Intraperitoneal administration of extracts of the small intestine epithelium of hibernating ground squirrels (C. Parryi Rich., C. undulatus) to white mice caused a decrease in oxygen consumption by 50-80%, the 5.5-14.0 degrees C drop in body temperature, inhibition of the muscle shivering thermogenesis, a decrease in heart rate, reduction of locomotor activity, development of hypnogenic effect and a closer dependence of body temperature on environmental fluctuations. The effects lasted for 30-40 hrs. Extracts from the small intestine tissue of non-hibernating ground squirrels caused insignificant changes of these parameters.

Animals↗
PubMed1980

Factors affecting the absorption of ampicillin administered intramuscularly in dwarf goats.

In nine healthy dwarf goats there were significantly higher serum concentrations of ampicillin after it was injected into the lateral neck muscles than after it was injected into the thigh. During fever, induced with Escherichia coli endotoxin, the rate of absorption of ampicillin from shivering muscles was faster, resulting in significantly higher serum concentrations of the antibiotic than in control non-febrile goats.

Absorption↗
PubMed1982

Thermogenesis in the avian body and the role of the pineal in thermoregulation.

In the absence of the brown adipose tissue, maintenance of body temperature (Tb) in birds is generally believed to be by shivering thermogenesis (ST), though evidence for nonshivering thermogenesis (NST) is becoming available. In ST, glycogen utilization by the anaerobic white muscle fibers forms the main energy process, while the aerobic red fibers appear to be largely involved in NST. Winter pigeons maintained on a 12 h photophase (PP) and 12 h scotophase (SP) had higher Tb during PP in both warm (25 degrees C) and cold (3 degrees C) acclimated birds. In pinealectomized (Px) pigeons Tb was higher than in controls during PP and SP without affecting the circadian thermal rhythm. This hyperthermic effect (HE) of pinealectomy was nullified with subcutaneous implantation of melatonin. These warm acclimated winter Px pigeons when examined for Tb next winter, did not show HE. Summer Px pigeons did not show HE as did the winter Px pigeons, indicating seasonal difference. No significant difference in circulating levels of T3 and T4 was seen in the summer as well as winter warm acclimated Px pigeons. These results suggest that the HE observed in warm acclimated Px winter pigeons was not mediated by the thyroid and that the pineal has no influence on the thyroid in the warm acclimated birds. The slightly higher HE seen in cold (3 degree C) acclimated Px pigeons may well be due to the influence of the thyroid.

Adaptation, Physiological↗
PubMed1978

[Bacteriemia due to acinetobacter calcoaceticus var. anitratus (author's transl)].

A serious bacteremia caused by Acinetobacter calcoaceticus var. anitratus could be observed. From the clinical point of view the most important symptoms were shivering, high tempeature up to 41 degrees C and clinical signs of acute hepatitis. There were pathological changes in the EEG. Certain signs of an outlayer damage of the heart could be seem in the ECG. The pathogenic microorganism isolated from the blood culture media was classified. Specific antibodies--agglutinines and precipitines--were demonstrated in the patient's serum. A contamination could be excluded so that the bacterium was the causative agent. The diagnostic value of finding antibodies in patient's serum having this type of bacterial infection is discussed.

Acinetobacter↗
PubMed1980

The effects of cold stress on neonatal calves. I. Clinical condition and pathological lesions.

Newborn Holstein-Friesian calves were cold stressed by immersion in water at 15 to 17 degrees C until the core body temperature was lowered by 10 degrees C. Non-cold stressed calves were immersed in water at thermoneutral temperature (35 to 37 degrees C). The time required to lower the core body temperature of the cold stressed calves by 10 degrees C was 172 +/- 87 minutes (mean +/- SD). The time required for the core body temperature of the cold stressed calves to return to normal after immersion was 400 +/- 140 minutes (mean +/- SD). Differences were observed between cold and noncold stressed calves in the shivering response during immersion and the clinical condition after immersion. Cold-induced pathological lesions were confined to tissues located peripherally, particularly in the hind legs. Significant differences were observed between cold and noncold stressed calves in the incidence of subcutaneous edema in the ventral sternum (P less than or equal to 0.025), subcutaneous hemorrhage in the hind legs (P less than or equal to 0.025), synovitis (P less than or equal to 0.025) and hemorrhage (P less than or equal to 0.05) of the synovial membranes of the hock joints and hemorrhage (P less than or equal to 0.05) into the hock joint cavities.

Animals↗
PubMed1995

[Regulation of thermoregulatory thermogenesis].

Two modes of heat production exist which are involved in body temperature regulation with decreasing environmental temperature: shivering thermogenesis and more efficient nonshivering thermogenesis (NST). Enhanced NST is mediated by the activated sympathetic nervous activity and increased secretions of hormonal factors such as glucagon through an enhanced lipid utilization. Moreover, cold acclimation causes an increased responsiveness of the organism to these factors. Noradrenaline-induced secretion of glucagon is also enhanced by cold acclimation. Chronic administration of glucagon simulates cold acclimation, resulting in an improved cold tolerance by an increased NST. Brown adipose tissue (BAT) is a major site for nonshivering thermogenesis (NST) during metabolic cold acclimation. Cold acclimation causes a hyperplasia as well as an enhanced metabolic capacity of BAT cell. BAT function is mainly regulated by sympathetic noradrenaline and several hormonal factors such as glucagon. BAT possesses rich blood supply by which its high thermogenic capacity and an efficient transfer of heat are maintained. Noradrenaline and glucagon increases not only heat production, but also blood flow in BAT. Nitric oxide (NO), endothelium-derived relaxing factor, is involved in noradrenaline-, glucagon- and cold-induced increases of blood flow through BAT. Noradrenaline-induced BAT thermogenesis is suggested to be mediated by NO. NO synthase occurs in BAT cell in addition to endothelium of BAT vessel. These findings indicate that NO may be a signalling molecule for an enhanced NST during cold acclimation. Moreover, BAT contributes to adaptation to overfeeding, nonthermal stress and fever by means of producing heat, playing a role as adaptive organ in overall energy metabolism.

Acclimatization↗
PubMed1993

[The role of clonidine in anesthesia].

For decades the adrenergic alpha2 agonist clonidine has been considered to be one of the classical, centrally acting antihypertensive agents. In addition to its antihypertensive and sympathicolytic effects, in recent studies clonidine has been demonstrated to be an effective sedative and analgesic and to reduce the amount of anaesthetic agents required. Therefore, a reconsideration of possible new indications for clonidine in clinical anaesthesiology seems to be justified. This paper presents the pharmacological basis for treatment with clonidine and reviews the extensive literature on its clinical indications in anaesthesia. Clonidine apparently produces its sedative and anaesthetic-sparing effects by stimulation of centrally located alpha2 adrenoceptors. Analgesia seems to be mediated mainly by activation of alpha2 adrenoceptors in the dorsal horn of the spinal cord. Considering its clinical indications, clonidine is often used as a supplement in the treatment of alcohol withdrawal syndromes. Future indications for clonidine may be the treatment of postoperative shivering and chronic pain management. Administration of clonidine in combination with a local anaesthetic prolongs analgesia and motor blockade. Its use in premedication and postoperative pain management may be limited by its principal effects of hypotension and bradycardia. In future, cardiovascular side effects may be minimized if all the subtypes of alpha2 adrenoceptors, their distribution within the central nervous system, and their specific action are clearly defined. This could result in a detailed therapeutic index of more selective and potent alpha2 agonists.

Analgesics↗
PubMed1995

Metabolic changes during cold water immersion.

This study was conducted in order to compare the metabolic responses of individuals exposed to long duration cold water immersion under two experimental conditions: 1) Heat loss compensated by shivering thermogenesis, and 2) heat loss compensated by intermittent periods of exercise. Nine subjects participated in two experimental trials 1) Subjects wearing insulated survival suits who did perform mild leg cycling during immersion 2) Subjects wearing insulated survival suits who did not perform exercise. Blood was sampled pre- and postimmersion. Blood was assayed for free fatty acids (FFA), lactate, creatine kinase and glucose. Intermittent periods of physical activity during cold water immersion resulted in a higher increase in FFA than during inactivity. In lactate, glucose, and creatine kinase there were no significant differences between the changes from pre- to postimmersion under the two conditions.

Adult↗
PubMed1997

Prediction of survival time at sea based on observed body cooling rates.

The prediction of survival time (ST) of individuals stranded at sea is particularly difficult since reliable controlled data are unavailable. An individual's rate of body cooling is governed by the difference between heat loss and heat production. It has been suggested that the rate of deep body cooling can be extrapolated to estimate ST. The observed linearity of this cooling rate against water temperature is consistent with the predictions of an independently-developed mathematical model of ST. This model has been extended to simulate conditions of partial immersion and wet clothing, and subsequently calibrated against observed human cooling rates. The resultant modification allows a much broader range of ST predictions involving calm and rough seas, and non-immersion wet conditions. Predictions are presented for lean vs. fat individuals, a "worst" case scenario where shivering is absent, and partial immersion. While these predictions must be considered speculative and subject to change as better information becomes available, the model can be useful as a decision aid. It would be prudent, however, to consider the predictions in a relative vs. absolute sense; i.e., for comparative purposes.

Body Temperature↗
PubMed1997

Perioperative fever.

Unlike normal thermoregulatory control, which is largely neuronally mediated, fever is activated by circulating pyrogens. Pyrogens are triggered by either infectious or non-infectious etiologies, all of which may be present in patients undergoing ambulatory surgery. Fever is a regulated elevation in the setpoint temperature for all thermoregulatory responses (warm and cold defenses). To increase core temperature according to the newly elevated setpoint, cold defenses such as vasoconstriction and shivering are activated. In contrast, anesthesia widens the interthreshold range, thus resulting in hypothermia. As a result, general anesthesia impairs the febrile response to pyrogenic stimulation. However, the precise nature of the interaction between fever and anesthesia has yet to be determined. Postoperative fever continues to be a major problem. Wound infections are responsible for many such fevers, although numerous other etiologies contribute. Initial diagnosis should thus focus on determining the etiology of fever. Once that is established, treatment can focus on the specific cause.

Ambulatory Surgical Procedures↗
PubMed1997

[Electromyographic characteristics of postanesthetic tremor].

Postanesthetic tremor is a frequent complication during recovery from surgery. Its etiopathogenesis is poorly understood and its electromyographic characteristics have scarcely been studies. We report the electromyographic characteristics of three normothermic patients with postanesthetic tremor. Electromyography revealed tremor to be consistent with that recorded for patients with exacerbated physiological tremor. None of the three patients had electromyographic signs typical of hypothermic patients with tremor. We conclude that the electromyographic signs of postanesthetic tremor should be studied further and consider it noteworthy that the recordings we made could be attributable to high levels of circulating catecholamines, leading to exacerbation of physiologic tremor manifested in the form of postanesthetic shivering.

Adult↗
PubMed1998

The implications of hypothermia for early tracheal extubation following cardiac surgery.

Thermoregulation is impaired during anesthesia for cardiac surgery. Redistribution of body heat and heat loss to the environment result in mild hypothermia before cardiopulmonary bypass. Maintenance of normothermia, rather than hypothermia, may facilitate early tracheal extubation. Hypothermia alters the distribution and decreases the metabolism of most drugs, including anesthetic drugs and muscle relaxants, thus prolonging recovery. Postoperative shivering increases metabolic rate and potentially leads to myocardial ischemia; prevention is therefore critical to the success of early tracheal extubation after cardiac surgery. Coagulopathies, increased incidence of surgical wound infection, and perioperative cardiac morbidity are other potential risk factors identified in noncardiac patients. Hypothermia, however, does have potential benefits to the patient, including protection from cerebral ischemia and hypoxemia. Mild core hypothermia (approximately 34 degrees C) may represent the optimal balance between risks and benefits for fast-track patients.

Anesthesia Recovery Period↗
PubMed1977

Hypothermia and persisting capacity to develop fever. Occurrence in a patient with sarcoidosis of the central nervous system.

A patient with central nervous system and systemic sarcoidosis had profound hypothermia and dementia with associated lymphadenopathy and hypernatremia. His capacity to develop fever remained; despite the persistent marked hypothermia, sweating and shivering in response to peripheral heating and cooling were maintained. Postmortem neuropathologic studies indicated that the hypothalamic region, generally considered to contain the primary temperature control, had been severely damaged by granulomatous sarcoid disease. These results confirm and extend previous findings of temperature disturbance in hypothalamic sarcoidosis and suggest that the integrity of the primary control of body temperature is not essential to fever production and "broad-band" regulation against environmental temperature extremes.

Central Nervous System Diseases↗