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At least 19 recordsLinked to original sources
PubMed1998

Isoflurane alters shivering patterns and reduces maximum shivering intensity.

BACKGROUND: Shivering can be characterized by its threshold (triggering core temperature), gain (incremental intensity increase with further core hypothermia), and maximum response intensity. Isoflurane produces a clonic muscular activity that is not a component of normal shivering. To the extent that clonic activity is superimposed on normal thermoregulatory shivering, the gain of shivering might be increased during isoflurane anesthesia. Conversely, volatile anesthetics decrease systemic oxygen consumption and peripherally inhibit skeletal muscle strength, which might limit maximum intensity despite central activation. The purpose of the present study was, therefore, to evaluate the effect of isoflurane shivering patterns and the gain and maximum intensity of shivering. METHODS: Ten volunteers were each studied in two separate protocols: (1) control (no drug) and (2) 0.7% end-tidal isoflurane. On each day, the mean skin temperature was maintained at 31 degrees C. Core temperature was then reduced by infusion of cold fluid until shivering intensity no longer increased. The core temperature triggering the initial increase in oxygen consumption defined the shivering threshold. The gain of shivering was defined by the slope of the core temperature versus oxygen consumption regression. Pectoralis and quadriceps electromyography was used to evaluate anesthetic-induced facilitation of clonic (5-7 Hz) muscular activity. RESULTS: Isoflurane significantly decreased the shivering threshold from 36.4 +/- 0.3 to 34.2 +/- 0.8 degrees C. The increase in oxygen consumption was linear on the control day and was followed by sustained high-intensity activity. During isoflurane administration, shivering was characterized by bursts of intense shivering separated by quiescent periods. Isoflurane significantly increased the gain of shivering (as calculated from the initial increase), from -684 +/- 266 to -1483 +/- 752 ml x min(-1) x degrees C(-1). However, isoflurane significantly decreased the maximum intensity of shivering, from 706 +/- 144 to 489 +/- 80 ml/min. Relative electromyographic power in frequencies associated with clonus increased significantly when the volunteers were given isoflurane. CONCLUSIONS: These data indicate that isoflurane anesthesia markedly changes the overall pattern of shivering during progressive hypothermia from a linear increase to an unusual saw-tooth pattern. They further suggest that clonic muscular activity combines with shivering to increase the initial gain of shivering during isoflurane anesthesia, but that isoflurane peripherally inhibits the maximum expression of shivering.

Adult↗
PubMed1968

Shivering and non-shivering therogenesis during summit metabolism in young lambs.

1. Summit metabolism of lambs declined steadily from about 3.5 l. O(2)/kg.hr during the first day of life, to about 2.0 l. O(2)/kg.hr at 2 months of age.2. The contributions of shivering and non-shivering thermogenesis to these changes were estimated by three independent methods; non-shivering thermogenesis was stimulated by catecholamines in a thermoneutral environment, shivering was suppressed by curariform drugs during summit metabolism, and an attempt was made to suppress non-shivering thermogenesis during summit metabolism by use of the sympatholytic drugs phentolamine and propranolol. Drugs were given by intravenous infusion during measurement of oxygen consumption in a closed circuit respiration chamber.3. ;Resting' metabolic rate of lambs during the first day of life was increased two to three-fold, from 1 l. O(2)/kg.hr, by either adrenaline or noradrenaline infused at 1-10 mug/kg.min. The increase declined with increasing age of lamb and was virtually absent by 3 weeks. The response to catecholamines appeared maximal at the dose levels used.4. Muscular paralysis induced by suxamethonium or gallamine reduced summit metabolism by about 2 l. O(2)/kg.hr in all lambs examined within the first 2 months of life. The residual metabolic rate, and the metabolic response to catecholamines under thermoneutral conditions, declined with age in the same manner, and their magnitudes were similar.5. Summit metabolism in lambs aged up to 2 months was depressed to varying degrees by the sympathetic inhibitors phentolamine, propranolol and hexamethonium. The depression with propranolol was greater, and the decline with age clearer, than with phentolamine. Hexamethonium and phentolamine depressed blood pressure, propranolol decreased heart rate and phentolamine and propranolol each suppressed shivering in some experiments.6. In 1 day-old lambs estimates of non-shivering thermogenesis, by the various methods, ranged from 0.8 to 1.4 l. O(2)/kg.hr (mean 1.1 l. or 31% of summit metabolism), and the estimates of shivering ranged from 1.3 to 1.9 l. O(2)/kg.hr (mean 1.6 l. or 46% of summit metabolism). However, in lambs 1-month old, estimates of non-shivering thermogenesis from sympathetic inhibition (0.6 and 0.8 l. O(2)/kg.hr) were considerably higher than estimates from muscular paralysis or stimulation by catecholamines (0.2 and 0.1 l. O(2)/kg.hr). It is suggested that the depression of summit metabolism by the sympathetic inhibitors is not solely due to specific inhibition of non-shivering thermogenesis, at least in the older lambs.7. The possession of a non-shivering thermogenic mechanism in addition to shivering is of clear survival value to new-born lambs.

Age Factors↗
PubMed1984

Hypomyelination in the peripheral nervous system of shiverer mice and in shiverer in equilibrium normal chimaera.

In shiverer mice, the P1 component of myelin basic protein (MBP) is deficient in both the central nervous system (CNS) and peripheral nervous system (PNS) but compact myelin is more grossly defective in the CNS. In the PNS, myelin exhibits a normal periodic structure, and although examples of subtle abnormalities of shiverer Schwann cell ultrastructure have been described previously, myelin thickness has been reported as unremarkable when observed by light microscopy. We report a quantitative investigation of the myelin sheath thickness of shiverer Schwann cells in which a mild but apparently consistent hypomyelination of axons ensheathed by shiverer Schwann cells was observed. This abnormality was expressed both in the peripheral nerves of a homozygous shiverer mouse and in the shiverer Schwann cells populating the mosaic nerves of a mature shiverer in equilibrium normal mouse chimaera. In addition, multiple interlamellar gaps was found to be a highly consistent feature of shiverer myelin. These observations extend the description of the peripheral nerve defects expressed in shiverer mice and further define these abnormalities as direct consequences of the shiverer Schwann cells' intrinsic genotype. In light of these results, a significant role for P1 in the formation and/or maintenance of normal myelin in the PNS is suggested.

Animals↗
PubMed1999

Shivering and shivering-like tremor during labor with and without epidural analgesia.

BACKGROUND: Effective treatment and prevention of hyperthermia and shivering-like tremor during labor is hindered by a poor understanding of their causes. The authors sought to identify the incidence of nonthermoregulatory shivering-like tremor and the factors associated with this activity. METHODS: The authors studied women in spontaneous full-term labor who chose epidural analgesia (n = 21) or opioid sedation (n = 31). Shivering-like tremor and sweating were evaluated by observation. Core temperature was recorded in the external auditory canal using a compensated infrared thermometer. Arteriovenous shunt tone was evaluated with forearm minus fingertip skin temperature gradients; gradients less than 0 were considered evidence of vasodilation. Tremor was considered nonthermoregulatory when core temperature exceeded 37 degrees C and the arms were vasodilated. Pain was evaluated using a visual analog scale. RESULTS: Shivering-like tremor was observed in 18% of 290, 30-min data-acquisition epochs before delivery. The patients were both normothermic and vasodilated during 15% of these epochs. Shivering was observed in 16% of 116 postdelivery epochs and was nonthermoregulatory in 28%. Sweating was observed in 30% of predelivery epochs, and the patients were both hypothermic and vasoconstricted during 12%. The mean core temperature in patients given epidural analgesia was approximately 0.2 degrees C greater than in those given sedation. Hyperthermia was observed during 10 epochs (38.4+/-0.3 degrees C) during epidural analgesia and during 10 epochs (38.4+/-0.3 degrees C) with sedation. The patients were vasoconstricted in more than 50% of these epochs in each group. Multivariate mixed-effects modeling identified high pain scores and vasoconstriction as significant predictors of shivering. There were no predictors for shivering epochs in patients who were simultaneously normothermic and vasodilated. Significant predictors of sweating were time before delivery, high pain scores, hypothermia with vasoconstriction, high thermal comfort, and low mean skin temperature. There were no predictors for sweating epochs in patients who were simultaneously hypothermic and vasoconstricted. CONCLUSIONS: This study confirms the clinical impression that some peripartum shivering-like tremor is nonthermoregulatory. The authors also identified nonthermoregulatory sweating. These data indicate that shivering-like tremor and sweating in the peripartum period is multifactorial.

Adult↗
PubMed1978

The central control of shivering and non-shivering thermogenesis in the rat.

1. To test whether the preoptic area controls only non-shivering and the spinal cord only shivering thermogenesis, ten rats were chronically implanted with a preoptic and a spinal cord thermode each. The following were then studied: (a) the effect of propranolol (8 mg/kg.hr) on the metabolic response to cooling the preoptic area, and the spinal cord, (b) the effect of exogenous noradrenaline (0.5 mg/kg) on the metabolic response to cooling the preoptic area, and the spinal cord, and (c) the effect of warming the preoptic area on the metabolic response to cooling the spinal cord, and vice versa. 2. Administration of propranolol inhibited the metabolic response to cooling each of the thermosensitive areas, but the response to cooling the preoptic area was more strongly inhibited than that to cooling the spinal cord. 3. Administration of exogenous noradrenaline did not prevent the metabolic response to cooling either the preoptic area or the spinal cord. 4. Warming the spinal cord completely inhibited the metabolic response to cooling the preoptic area, and warming the preoptic area fully inhibited the metabolic response to cooling the spinal cord. 5. It is concluded that exogenous noradrenaline underestimates the capacity for non-shivering thermogenesis, and that both thermosensitive areas can control both forms of thermogenesis, but that the preoptic area threshold of non-shivering thermogenesis is probably lower than that of shivering, while the spinal cord threshold of shivering is probably lower than that of non-shivering thermogenesis.

Animals↗
PubMed1987

Human studies concerning thermal-induced shivering, postoperative "shivering," and cold-induced vasodilation.

Human reaction to cold stress and hypothermia involves shivering. Another form of overt shaking, postoperative shivering, has been attributed as a thermoregulatory response to postoperative hypothermia. Analysis of the normal human shivering pattern showed a synchronized, slow amplitude modulation (six to eight cycles/min) over all muscles sampled. In addition, there was a frequency of 8 to 10 Hz associated with each low-frequency amplitude modulation. EMG signals from postoperative patients revealed none of the major patterns seen in thermal-induced shivering. Cold-induced vasodilation also was studied and found to occur simultaneously in all cold-stressed fingers regardless of size or innervation. Thermal shivering and cold-induced vasodilation are considered to be manifestations of central neural oscillators.

Adolescent↗
PubMed1980

Cooling responses in shivering and non-shivering dogs during induced hypothermia.

1. Hypothermia to a temperature of 30 degrees C was induced in both shivering and non-shivering groups of dogs. 2. There was a sustained increase in oxygen consumption in the dogs allowed to shiver and this was up to 300% greater than the oxygen consumption in the relaxed dogs. 3. The increased tissue requirement for oxygen was met both by increased cardiac output and increased oxygen extraction from haemoglobin. 4. Oxygen utilization remained adequate in hypothermia, as shown by the absence of hypoxic acidosis. 5. Heart rate fell during cooling and stroke volume increased to meet the increased oxygen demands associated with shivering during the induction of hypothermia.

Animals↗
PubMed1994

Activation of shivering and non-shivering thermogenesis by electrical stimulation of the lateral and medial preoptic areas.

Experiments were conducted to determine if the area of stimulation within the preoptic area and/or the magnitude of the electrical stimulus applied to the preoptic region would selectively alter the evoked thermogenic responses of normothermic and hypothermic rats. Urethane anesthetized male, Long-Evans rats kept at 37 degrees C, and later cooled to 34 degrees C, were given unilateral electrical stimulation (0.5 ms pulses of 200 microA at 50 Hz for 30 and 300 s) into either the medial preoptic area (MPO) or the lateral preoptic area (LPO). Temperature changes of intrascapular brown adipose tissue, TIBATs; of gastrocnemius muscle, Tms, tail, Tts and colonic Tcs via thermistor probes were recorded before and after stimulation along with differential, multi-unit EMG activity of the gastrocnemius muscle via implanted stainless steel electrodes. The group kept at 37 degrees C and given MPO electrical stimulations evoked graded increases in TIBATs above core dependent on the duration of the electrical stimulus but shivering did not occur and Tms did not rise. When kept at 34 degrees C the MPO-stimulated group showed greater increases in TIBATs than respective responses seen when the same stimuli were applied at 37 degrees C. The group maintained at 37 degrees C and given LPO stimuli over 300 s increased Tms as shivering occurred, yet no change in TIBATs were observed. When cooled to 34 degrees C LPO stimulation (30 or 300 s duration) showed greater shivering activity. Interesting, LPO stimulation of animals maintained at 34 degrees C also caused TIBAT to increase.(ABSTRACT TRUNCATED AT 250 WORDS)

Adipose Tissue, Brown↗
PubMed1977

The control of shivering and non-shivering thermogenesis in the rat.

1. The effect of intraperitoneal administration of propranolol (4, 8 and 12 mg/kg) on colonic temperature was studied in twelve rats during exposure to ambient temperatures of 30, 15 and 5 degrees C. 2. At 30 degrees C, propranolol had no effect on colonic temperature; at 15 and 5 degrees C, however, 4 mg propanolol/kg induced a fall in colonic temperature of about 0-8 degrees C, whereas 8 and 12 mg propanolol/kg induced a fall of about 1-5-2-0 degrees C. 3. Assuming that the temperature regulations system of the rat has a proportional controller and that the effect of propranolol was due to the blockade of non-shivering thermogenesis, the results are interpreted as showing that shivering is activated only when heat loss exceeds the capacity for non-shivering thermogenesis.

Animals↗
PubMed1983

P1 deficiency in shiverer myelin is expressed by Schwann cells in shiverer dystrophic normal mouse chimaera nerves.

The myelin basic protein (P1) deficiency in shiverer myelin is expressed in shiverer reversible normal mouse chimaera nerves. Chimaera examined with immunocytochemical techniques have revealed populations of both densely labeled and unreacting myelinated Schwann cells. Single axons can innervate both Schwann cell types, demonstrating that the expression of P1 in Schwann cell myelin is unrelated to the shiverer or normal genotype of the neuron. The coexistence of both Schwann cell types in single nerves indicates that multiple progenitor Schwann cells are allocated to developing nerves and the mosaic patterns expressed further suggest that such cells tend to proliferate relatively small coherent clones of Schwann cells.

Animals↗
PubMed1988

Quaking shiverer double mutant mice: morphological phenotypes support possible dual actions of the shiverer locus.

Mice doubly homozygous for the two different hypomyelination mutations, quaking (qk) and shiverer (shi) or shiverer myelin-deficient (shimld) (abbreviations: qk*shi and qk*shimld), both have much less myelin than either single mutant ancestor, myelin morphology resembling shi or shimld rather than qk, and abundant shi-type oligodendrocytic microprocesses. The qk*shimld double mutant differs from qk*shi only in having small amounts of normal or abnormal major dense line, in keeping with the morphologic difference between the shi and shimld single mutants. By contrast, shi*jp and shimld*jp have clearly different morphological phenotypes; unexpectedly the major dense line is present in the CNS myelin of shi*jp but not shimld*jp. When shi and shimld act alone, their different DNA abnormalities produce similar protein abnormalities. We speculate that the two mutations interact with qk at a different, later step of DNA expression than they interact with jp. In the interaction with qk, the similar proteins produce similar morphologies. In the interaction with jp, the different DNAs are somehow caused to produce protein differences that are reflected in different morphologies. In this study we have observed for the first time a morphological effect of these mutant genes in heterozygous animals. Of particular importance, animals whose genomes combine shi/+ or shimld/+ with qk/qk produce qk-type, compacted myelin but abundant shi-type oligodendrocyte microprocesses. We consider this as evidence that both shi and shimld have two effects: non-production of a normal structural protein, myelin basic protein, and production of an abnormal protein which perturbs the cytogogic function we postulate to be normally exercised by the myelin basic protein gene.

Animals↗
PubMed1984

Cultures of shiverer mutant cerebellum injected with normal oligodendrocytes make both normal and shiverer myelin.

Earlier reports suggested that injecting normal optic nerve into organotypic cerebellar cultures from three of the central nervous system hypomyelinated mutant mice resulted in striking local increases in myelination of mutant axons. It has been questioned whether this myelin was produced by the introduced normal glia because there was no "marker" by which the genotype of an individual myelin sheath could be rigorously determined. The present study shows that the myelin sheaths of the central nervous system hypomyelinated mutant shiverer (shi/shi) can be distinguished in vitro from genetically normal myelin by their immunocytochemical reactions and ultrastructure. When shi/shi cultures are injected with normal optic nerve, they produce two kinds of myelin as distinguished by these techniques: shi/shi myelin throughout and, in addition, ultrastructurally and immunocytochemically normal myelin near the optic nerve. These results suggest that the primary defect of the shi/shi mutation involves the oligodendrocyte and support the earlier conclusion that in all of the glial injection experiments to date the genotype of the oligodendrocyte determines the phenotype of the myelin produced.

Animals↗
PubMed1997

Substrate utilisation during exercise and shivering.

It is generally assumed that exercise and shivering are analogous processes with regard to substrate utilisation and that, as a consequence, exercise can be used as a model for shivering. In the present study, substrate utilisation during exercise and shivering at the same oxygen consumption (VO2) were compared. Following an overnight fast, eight male subjects undertook a 2-h immersion in cold water, designed to evoke three different intensities of shivering. At least 1 week later they undertook a 2-h period of bicycle ergometry during which the exercise intensity was varied to match the VO2 recorded during shivering. During both activities hepatic glucose output (HGO), the rate of glucose utilisation (Rd), blood glucose, plasma insulin, free fatty acid (FFA) and beta-hydroxybutyrate (B-HBA) concentrations were measured. The VO2 measured during the different levels of shivering averaged 0.49 l.min-1 (level 1: low), 0.6 l.min-1 (level 2: low-moderate), and 0.9 l.min-1 (level 3: moderate), and corresponded closely to the levels measured during exercise. HGO and Rd were greater (P < 0.05) during exercise than during shivering at the same VO2 (9.5% and 14.7%, respectively). The average (SD). HGO during level 3 exercise was 3.0 (0.91) mg.kg-1.min-1 compared to 2.76 (1.0) mg.kg-1.min-1 during shivering. The values for Rd were 3.06 (0.98) mg.kg-1.min-1 during level 3 exercise and 2.68 (0.82) mg.kg-1.min-1 during shivering. Blood glucose levels did not differ between conditions averaging 5.4 (0.3) mmol.l-1 over all levels of shivering and 5.2 (0.3) mmol.l-1 during exercise. Plasma FFA and B-HBA were higher (P < 0.01) during shivering than during corresponding exercise (12.3% and 33.3%, respectively). FFA averaged 0.61 (0.2) mmol.l-1 over all levels of shivering and 0.47 (0.16) mmol.l-1 during exercise. The figures for L-HBA were 0.44 (0.13) mmol. l-1 during all levels of shivering and 0.32 (0.1) mmol.l-1 during exercise. Plasma insulin was higher (P < 0.05) during level 2 and 3 shivering compared to corresponding exercise; at these levels the average value for plasma insulin was 95.9 (21.9) pmol.l-1 during shivering and 80.6 (16.1) pmol.l-1 during exercise. On the basis of the present findings it is concluded that, with regard to substrate utilisation, shivering and exercise of up to 2 h duration should not be regarded as analogous processes.

3-Hydroxybutyric Acid↗
PubMed1998

Meperidine and alfentanil do not reduce the gain or maximum intensity of shivering.

BACKGROUND: Thermoregulatory shivering can be characterized by its threshold (triggering core temperature), gain (incremental intensity increase with further core temperature deviation), and maximum intensity. Meperidine (a combined mu- and kappa-agonist) treats shivering better than equianalgesic doses of pure mu-opioid agonists. Meperidine's special antishivering action is mediated, at least in part, by a disproportionate decrease in the shivering threshold. That is, meperidine decreases the shivering threshold twice as much as the vasoconstriction threshold, whereas alfentanil (a pure mu-agonist) decreases the vasoconstriction and shivering thresholds comparably. However, reductions in the gain or maximum shivering intensity might also contribute to the clinical efficacy of meperidine. Accordingly, we tested the hypothesis that meperidine reduces the gain and maximum intensity of shivering much more than alfentanil does. METHODS: Ten volunteers were each studied on three separate days: (1) control (no drug); (2) a target total plasma meperidine concentration of 1.2 microg/ml; and (3) a target plasma alfentanil concentration of 0.2 microg/ml. Skin temperatures were maintained near 31 degrees C, and core temperatures were decreased by central-venous infusion of cold lactated Ringer's solution until maximum shivering intensity was observed. Shivering was evaluated using oxygen consumption and electromyography. A sustained increase in oxygen consumption identified the shivering threshold. The gain of shivering was calculated as the slope of the oxygen consumption versus core temperature regression, and as the slope of electromyographic intensity versus core temperature regression. RESULTS: Meperidine and alfentanil administration significantly decreased the shivering thresholds. However, neither meperidine nor alfentanil reduced the gain of shivering, as determined by either oxygen consumption or electromyography. Opioid administration also failed to significantly decrease the maximum intensity of shivering. CONCLUSIONS: The authors could not confirm the hypothesis that meperidine reduces the gain or maximum intensity of shivering more than alfentanil does. These results suggest that meperidine's special antishivering effect is primarily mediated by a disproportionate reduction in the shivering threshold.

Adjuvants, Anesthesia↗