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PubMed1996

[Temperature changes and thermoregulatory responses during epidural anesthesia in women undergoing cesarean delivery].

Eleven healthy pregnant women were studied to determine temperature changes after induction of epidural anesthesia during cesarean delivery. Epidural anesthesia was induced by 2% lidocaine 15-20 ml (T 5 level) at 25 degrees C ambient temperature. Tympanic membrane and skin surface temperature, skin-temperature gradients (forearm-fingerchip, calf-toe), thermal perception (1-10 scale VAS) and the presence or absence of shivering were measured. Sixty minutes after induction, tympanic temperature decreased for 0.52 +/- 0.26 degrees C and average skin temperature increased for 0.56 +/- 0.17 degrees C. Central hypothermia and shivering did not produce a cold sensation. Temperature gradients of upper limb increased to 2.0 +/- 3.7 degrees C (50 minutes after induction) and the lower limbs decreased to -1.4 +/- 0.55 degrees C (30 minutes after induction). Shivering occurred in 3 patients. We conclude that epidural anesthesia impaired thermoregulatory control and induced redistribution hypothermia as in nonpregnant individuals.

Adult↗
PubMed1978

Effects of total body core cooling on heat production of conscious goats.

Experiments were performed to investigate the effect of general body core cooling on heat production at various air temperatures between +1 degree C and +56 degrees C in conscious goats. An intravascular heat exchanger (IVHE) was used to alter body core temperature independently of air temperature. Heat loss via the IVHE caused a fall in body core temperature, the extent of which depended on the rate of extraction and air temperature. Irrespective of air temperature the decrease in body core temperature resulted in shivering and an increase in heat production, which eventually balanced the heat loss. During steady state conditions the extra heat production was approximately equal to that lost via the IVHE. The threshold body core temperature at which heat production increased in response to central cooling did not significantly alter with air temperature. However, the slopes of the curves describing this response were smaller at higher than at lower air temperatures, which indicated that central thermosensitivity decreased with increasing air temperature. Irrespective of air temperature the threshold temperatures for shivering were higher and the slopes of the curves were steeper than those previously found with combined cooling of the hypothalamus and spinal cord in the same species which indicated the existence of central thermosensors outside the above two mentioned areas.

Anesthesia, General↗
PubMed1998

Role of replacement fluids in the immediate complications of plasma exchange. French Registry Cooperative Group.

OBJECTIVE: Comparison of side effects (fever shivering and/or allergic reactions, collapse, symptomatic hypocalcaemia) of the different substitution fluids used during therapeutical plasmapheresis. DESIGN: Multicentric retrospective comparative study designed to explore the side effects due to the replacements fluids (albumin alone or associated with dextran 40, modified fluid gelatin, hydroxyethyl starch), and to determine the best combination in patients undergoing plasmapheresis. PATIENTS: 46,895 procedures were performed on 5,167 patients between 1990 and 1994. The analysis concerns 33,962 sessions, divided into two groups (group 1: 21,079 sessions from 1990 to 1992 comparing albumin alone versus combined albumin-macromolecules and the different combinations among these, group 2: 12,883 sessions in 1993-1994 comparing albumin alone versus albumin-hydroxyethyl starch). Because of the diversity of the products used, 13,029 sessions were not studied because groups of small sample sizes were formed. MEASUREMENTS AND RESULTS: In group 1, the comparison of albumin + macromolecules with albumin alone, shows the best haemodynamic tolerance, lower frequency of fever shivering and/or allergic reactions in the albumin alone subgroup. On the other hand, hypocalcaemia is significantly higher in this subgroup. The combinations albumin + dextran 40 (but after hapten inhibition) and albumin + hydroxyethyl starch are equivalent. Albumin + modified fluid gelatin is the combination presenting the highest incidence in terms of allergic manifestations. In group 2, albumin + hydroxyethyl starch versus albumin alone, the former is preferable in terms of the three side effects studied. CONCLUSION: The results of this study show a combination of albumin 4% hydroxyethyl starch to replace plasma during plasma exchange to be the method presenting the lowest morbidity and the best cost/effectiveness ratio.

Cost-Benefit Analysis↗
PubMed1996

Changes in thermal homeostasis in humans due to repeated cold water immersions.

The purpose of this study was to monitor changes in body and skin temperatures, heat production, subjective shivering, cold sensation and body fat content in humans after intermittent cold water immersion. Repeated exposures of young sportsmen to cold water (head out, 14 degrees C, 1 h, 3 times per week for 4-6 weeks) induced changes in regulation of thermal homeostasis. "Cold acclimated" subjects exhibited an hypothermic type of adaptation. Central and peripheral body temperatures at rest and during cold immersion were lowered. The metabolic response to cold was delayed and subjective shivering was attenuated. The observed hypothermia was due to the shift of the threshold for induction of cold thermogenesis to lower body temperatures. "Cold acclimated" subjects also showed a lowered cold sensation. Because of the observed physiological changes, about 20% of the total heat production was saved during one cold water immersion of "cold acclimated" subjects. Maximal aerobic and anaerobic performances were not altered. No change in the thermosensitivity of the body temperature controller, as assessed from the unchanged slope of the relation between the deep body temperature and total heat production, was observed. Changes in cold sensation and regulation of cold thermogenesis were noticed first after four cold water immersions and persisted for at least 2 weeks after termination of the adaptation procedure. A trend towards a small increase in the body fat content was also observed. This finding, as well as the increased vasoconstriction, evidenced by the lowered skin temperature, indicate that slight changes in body insulation may also occur after "cold acclimation" in humans.

Acclimatization↗
PubMed1975

The efficacy and safety of intramuscularly administered 15(S) 15 methyl prostaglandin E2 methyl ester for induction of artificial abortion.

The practicability of an intramuscular dose schedule of 10 mug of 15(S) 15 methyl prostaglandin E2 methyl ester [15(S) Me PGE2] administered every 4 hours was evaluated in 42 subjects from 7 to 20 menstrual weeks' gestation. Half of the subjects served as controls (Group I) and half of the subjects (Group II) were treated with a medication regimen of prochlorperazine, acetylsalicylic acid, diphenoxylate hydrochloride, and atropine sulfate to evaluate the regimen's effects. Although the 15(S) Me PGE2 dose schedule appeared to be effective (74 per cent aborted in 24 hours and 95 per cent aborted within 48 hours in a mean time of 18.9 hours), Group I (control) subjects frequently had side effects: 62 per cent had emesis, 86 per cent had diarrhea, 76 per cent had shivering, and 76 per cent had fever (greater than 100 degrees F.). Fewer Group II (medicated) subjects had side effects: 43 per cent had emesis, 19 per cent had diarrhea, 52 per cent had shivering, and 43 per cent had fever. The medication regimen did not appear to interfere with the abortifacient or oxytocic effects of the 15(S) Me PGE2 dose schedule, since Group I and Group II subjects had similar cumulative abortion rates, mean abortion times, and uterine activity. Although this 15(S) Me PGE2 dose schedule is effective in first-trimester patients, it is probably less satisfactory than the conventional method of vacuum aspiration. While intramuscularly administered 15(S) Me PGE2 with medications to attenuate side effects may be practicable for inducing midtrimester abortion, especially between 12 and 16 weeks' gestation, large controlled comparative studies of the intramuscular 15(S) Me PGE2 method and other experimental and conventional methods will be necessary to determine the most satisfactory method of performing midtrimester abortions.

Abortion, Induced↗
PubMed1985

The effect of epidural analgesia on maternal thermoregulation in labor.

Core and peripheral body temperatures were recorded in 24 parturients in labor with epidural analgesia and in 9 control parturients without analgesia. Shivering occurred in 11 (46%) of the women with epidural analgesia and in one parturient without analgesia. Twelve patients (50%) showed increase in leg and chest temperatures after injection of bupivacaine 0.35% into the epidural space. Lumbar epidural analgesia may produce shivering and temporary temperature changes in the periphery. Core temperature is not significantly altered.

Adult↗
PubMed1982

Acute thermoregulatory effects of unilateral electrolytic lesions of the medial and lateral preoptic area in rats.

Unilateral anodal lesions of the medial or lateral preoptic area (POA) in unanesthetized rats had opposite thermoregulatory effects immediately after the lesion were made. Lesions of the medial POA evoked hyperthermias and accompanying cold defense responses, including vasoconstriction of the tail, increased oxygen consumption, shivering, and heat conservation postures. The hyperthermias had latencies of 0-30 minutes and reached maximum values within 120 minutes postlesion. They were independent of ambient temperature and dissociable from the hyperactivity often seen after such lesions. Damage to the lateroventral POA elicited acute falls in body temperature, as well as vasodilation of the tail, decreased oxygen consumption, inhibition of shivering in cool environments, and prone body extension. Unilateral cathodal lesions throughout the POA yielded only hyperthermia. These results suggest a possible anatomical segregation of heat and cold defense functions within the anterior basal forebrain.

Animals↗
PubMed1985

Diaphragmatic, thoracic and limb motor effects of amyl nitrite inhalation.

In the pentobarbitone/urethane anaesthetized rabbit and pentobarbitone anaesthetized cat intratracheal inhalation of amyl nitrite, a non-specific smooth muscle relaxant, caused a vagally dependent depression of patellar reflex and spontaneous (thermal shivering and external intercostal inspiratory) motor activities. A prolonged vagally-independent potentiation succeeded the initial inhibition. The potentiation of intercostal activity may account for the increase in tidal volume produced by amyl nitrite after vagotomy. The patellar reflex potentiation survived thoracolumbar spinal transection but could not be attributed to a direct facilitation of neuromuscular or muscular events. A correlation existed between the relative dependence of fusimotor support of a muscle and its susceptibility to the inhibitory and subsequent facilitatory affects of amyl nitrite inhalation. The diaphragm and interchondral muscles, essentially independent of the autogenetic facilitation provided by muscle spindles, demonstrated neither of these effects. Conversely, the intercostal muscles depend greatly on such facilitation, as do the pectoral and limb muscles during thermal shivering.

Amyl Nitrite↗
PubMed1983

Temperature regulation and metabolism in developing white-necked ravens.

1. Nestlings less than six days old were ectothermic at ambient temperatures between 15 and 35 degrees C. Shivering was absent and panting sporadic and awkward. 2. At 7-14 days of age, shivering and panting responses were evident but body temperature was labile. 3. At 20 and 30 degrees C the rate of oxygen consumption increased with age to a peak of 3.5 ml/g per hr then decreased to around 2 ml/g per hr in the 400 g nestlings. At 40 degrees C the larger nestlings had a higher Vo2 than the younger birds. 4. Evaporative water loss (EWL) at Ta of 20-30 degrees C increased from approx 1 mg/g per hr in two-day-old ravens to 3-6 mg/g per hr in 11-20-day-old birds. At 40 and 45 degree C, EWL increased from approx 5 mg/g per hr in young nestlings to 10-34 mg/per hr in birds more than 11 days old. 5. Differentials in Vo2 between 20 and 30 degrees C show that the transition from ectothermy to endothermy occurred rapidly and completely in 12-14-day-old ravens. 6. At the onset of physiological thermoregulation the Vo2 of nestling birds was nearly twice that of a hypothetical adult. 7. The dry heat transfer coefficient decreased as weight increased indicating that young birds dissipate more heat passively than do older birds. Older birds dissipate heat predominantly by evaporative cooling.

Aging↗
PubMed1988

Thermally-induced activities of the mesencephalic reticulospinal and rubrospinal neurons in the rat.

Unit activities of 226 midbrain reticulospinal (mRfS) and non-mRfS neurons and 238 rubrospinal (RbS) and non-RbS neurons were investigated during changes in temperatures of midbrain (Tmb), preoptic and anterior hypothalamus (Thyp) and skin (Ts) in the urethane-anesthetized rat. Responsiveness to Tmb, Thyp and Ts were found in 43.5%, 41.6% and 51.5% of neurons of midbrain reticular formation (mRf), and in 35.2%, 32.7% and 17.6% of neurons of red nucleus (Rb). Higher incidence of responsiveness to remote temperatures was found among Tmb responsive neurons than Tmb unresponsive neurons in both mRf and Rb. The mRf contains significantly greater numbers of neurons having such multiple thermal responsiveness and also of neurons which were activated by falls in temperatures (cold-responsive neurons) than the Rb. These characteristics were more conspicuously seen among mRfS neurons, showing a high degree of convergence of cold signals from different sites of body. On the other hand, RbS neurons did not differ from non-RbS neurons regarding thermal characteristics and showed no particular combinations of responsiveness to temperatures of different sites. Microinjection of procaine and glutamate into the mRf just dorsolateral to the Rb, but not into the Rb, decreased and increased cold-induced increase in EMG activity and shivering without changes in cardiovascular and respiratory parameters and pilomotor activity. The results suggest that mRfS neurons are involved in the control of thermoregulatory muscle tone and shivering.

Action Potentials↗
PubMed1994

Episodic spontaneous hypothermia with hyperhidrosis: implications for pathogenesis.

Unprovoked hypothermia is an unusual presenting sign. When occurring with diaphoresis it has been referred to as episodic spontaneous hypothermia with hyperhidrosis. Earlier reports described episodic, spontaneous hypothermia with hyperhidrosis in patients with agenesis of the corpus callosum and postulated a midline congenital malformation of the central nervous system. Since then, various endocrine, electrolyte, autonomic, and sleep disturbances have been described but the etiology remains undetermined. Three unrelated children are reported each of whom had an intact corpus callosum and normal endocrine function. Shivering was consistently absent despite marked symptomatic hypothermia. One child had spontaneous resolution of episodic spontaneous hypothermia with hyperhidrosis and two children responded to the antiserotonergic, cyproheptadine. It is hypothesized that specific serotonergic dysfunction in the anterior hypothalamic extrapyramidal shivering mechanism is central in the pathogenesis of this condition.

Body Temperature Regulation↗
PubMedDate not supplied

Do heated humidifiers and heat and moisture exchangers prevent temperature drop during lower abdominal surgery?

STUDY OBJECTIVE: To compare the effects of using a heated humidifier (HH), a heat and moisture exchanger (HME), or no warming device in maintaining body temperature during surgical procedures of 1 to 4 hours' duration. DESIGN: A randomized, controlled study. SETTING: Operating room, Thomas Jefferson University Hospital, Philadelphia, PA. PATIENTS: 51 ASA physical status I, II, and III patients, age 16 to 69 years, scheduled for a variety of lower abdominal procedures under general endotracheal anesthesia anticipated to last 1 to 4 hours. INTERVENTIONS: We randomly assigned patients to receiving an HH, an HME, or no warming device during the procedure. We then measured the patient's sublingual temperature every 5 minutes prior to induction, every 15 minutes intraoperatively, and every 15 minutes postoperatively until he or she was discharged from the postanesthesia care unit, (PACU). We also measured the esophageal temperature every 15 minutes intraoperatively. MEASUREMENTS AND MAIN RESULTS: Sublingual temperature or esophageal temperature probes placed at the site of maximal heart tones indicated that the patients' temperatures dropped significantly from baseline values in all three groups during the first 60 minutes of surgery, then remained constant during the next 120 minutes of surgery. Patients who had no warming device shivered and felt cold significantly more often than patients in the HH group but not more often than patients in the HME group. There was no difference in shivering between the HH and HME groups. The patients who received an HH tended to have a higher temperature (a mean of 0.5 degrees C) throughout the study, but this did not reach statistical significance. CONCLUSIONS: Results indicate that these warming devices provide little benefit in preventing a temperature drop during procedures of 1 to 4 hours' duration, although patients with an HH tended to have a higher temperature than those with an HME or no device.

Abdomen↗
PubMed1995

Postoperative hemodynamic and thermoregulatory consequences of intraoperative core hypothermia.

STUDY OBJECTIVE: To evaluate the postoperative hemodynamic and thermoregulatory consequences of intraoperative core hypothermia. DESIGN: Prospective, randomized clinical trial. SETTING: Operating room and postanesthesia care unit of a university hospital. PATIENTS: 74 healthy, ASA status I, II, and III patients (average age 58 yrs) undergoing elective colon surgery. INTERVENTIONS: Patients were randomly assigned to be kept normothermic or approximately 2.5 degrees C hypothermic during surgery. Anesthesia was maintained with isoflurane, nitrous oxide, and fentanyl. Postoperatively, surgical pain was treated with patient-controlled analgesia (PCA) opioid. MEASUREMENTS AND MAIN RESULTS: An observer blinded to group assignment and core temperatures evaluated shivering, thermal comfort, surgical pain, heart rates (HRs), and blood pressures (BPs) during the first six postoperative hours. Morphometric characteristics, oxygen saturation, fluid balance, PCA-administered opioid, and visual analog pain scores were comparable in the two groups. Hypothermic patients felt uncomfortably cold during recovery, and their postoperative core temperatures remained significantly less than in the normothermic patients for more than four hours. Peripheral vasoconstriction and shivering were common in the hypothermic patients but rare in those kept normothermic. HRs and BPs were comparable in the two groups. CONCLUSIONS: These data confirm that the effects of intraoperative hypothermia on postoperative HR and BP are modest in relatively young, generally healthy patients. In contrast, intraoperative hypothermia caused substantial postoperative thermal discomfort, and full recovery from hypothermia required many hours. Delayed return to care normothermia apparently resulted largely from postoperative thermoregulatory impairment.

Analgesia, Patient-Controlled↗
PubMed2005

Thermoregulatory model for prediction of long-term cold exposure.

A multi-segmental mathematical model has been developed for predicting shivering and thermoregulatory responses during long-term cold exposure. The present model incorporates new knowledge on shivering thermogenesis, including the control and maximal limits of its intensity, inhibition due to a low core temperature, and prediction of endurance time. The model also takes into account individual characteristics of age, height, weight, % body fat, and maximum aerobic capacity. The model was validated against three different cold conditions i.e. water immersion up to 38 h and air exposure. The predictions were found to be in good agreement with the observations.

Adult↗
PubMed2006

Mole-rats from higher altitudes have greater thermoregulatory capabilities.

Subterranean mammals (those that live and forage underground) inhabit a challenging microenvironment, with high levels of carbon dioxide and low levels of oxygen. Consequently, they have evolved specialised morphological and physiological adaptations. For small mammals that inhabit high altitudes, the effects of cold are compounded by low oxygen partial pressures. Hence, subterranean mammals living at high altitudes are faced with a uniquely demanding physiological environment, which presumably necessitates additional physiological adjustments. We examined the thermoregulatory capabilities of two populations of Lesotho mole-rat Cryptomys hottentotus mahali that inhabit a 'low' (1600 m) and a 'high' (3200 m) altitude. Mole-rats from the high altitude had a lower temperature of the lower critical point, a broader thermoneutral zone, a lower thermal conductance and greater regulatory non-shivering thermogenesis than animals from the lower altitude. However, minimum resting metabolic rate values were not significantly different between the populations and were low compared with allometric predictions. We suggest that thermoregulatory costs may in part be met by animals maintaining a low resting metabolic rate. High-altitude animals may adjust to their cooler, more oxygen-deficient environment by having an increased non-shivering thermogenesis whilst maintaining low thermal conductance.

Acclimatization↗
PubMed2006

Serotonin syndrome in a case of depression with various somatic symptoms: the difficulty in differential diagnosis.

A 65-year-old female patient with major depressive disorder suffered from clonus, shivering and impaired visual acuity after 20 mg/day of paroxetine administration. The symptoms were initially regarded as further manifestations of her somatic symptoms of depression, and paroxetine was increased to 30 mg/day resulting in frequent clonus, increased shivering, serious dysarthria, ongoing impairment in visual acuity and agitation. These symptoms subsided upon paroxetine discontinuation. Ten mg/day of paroxetine rechallenge provoked dysarthria, tremor and headache, but these symptoms improved again upon paroxetine discontinuation. These findings indicate that the patient's symptoms were not somatic in origin but were in fact the symptoms of serotonin syndrome. In conclusion, the present case suggests the difficulty in diagnosing serotonin syndrome in a patient with somatic symptoms.

Aged↗
PubMed1999

Reduced thermoregulatory null zone in postmenopausal women with hot flashes.

OBJECTIVE: Most menopausal hot flashes are preceded by small elevations in core body temperature. If the thermoneutral zone between the thresholds for sweating and shivering is reduced in women with symptoms, the triggering mechanism for hot flashes could be explained. STUDY DESIGN: We studied 12 postmenopausal women with symptoms and 8 without symptoms. We measured body temperatures with a rectal probe, an ingested telemetry pill, and a weighted average of rectal and skin temperatures. Each woman underwent 3 experimental sessions: determination of the sweating threshold by body heating, determination of the shivering threshold by body cooling, and replication of the sweating threshold with exercise. RESULTS: The women with symptoms had significantly smaller interthreshold zones than did the symptom-free women for all 3 measures of body temperature: rectal temperature, 0.0 degrees C +/- 0.06 degrees C versus 0.4 degrees C +/- 0.18 degrees C (P <.005); telemetry pill temperature, 0.0 degrees C +/- 0.11 degrees C versus 0.4 degrees C +/- 0.18 degrees C (P <.005); and mean body temperature, 0.8 degrees C +/- 0.09 degrees C versus 1.5 degrees C +/- 0.20 degrees C (P <. 0006). Sweat rates were significantly higher among the women with symptoms (0.06 +/- 0.002 mg. cm(-2). min(-1)) than among the women without symptoms (0.03 +/- 0.001 mg. cm(-2). min(-1), P <.05). Sweating thresholds during exercise did not significantly differ from those during body heating. During exercise all the women with symptoms and none of the women without symptoms had hot flashes. CONCLUSIONS: Menopausal hot flashes in women with symptoms may be triggered by small elevations in body temperature acting within a reduced thermoneutral zone.

Body Temperature↗
PubMed2000

Warmed humidified inspired oxygen accelerates postoperative rewarming.

STUDY OBJECTIVE: To investigate the efficacy of warmed, humidified inspired oxygen (O(2)) for the treatment of mildly hypothermic postoperative patients. DESIGN: Prospective, randomized, unblinded clinical trial. SETTING: Postanesthesia care unit in a tertiary care hospital. PATIENTS AND INTERVENTIONS: 30 ASA physical status I, II, and III patients following intraabdominal surgical procedures were randomly assigned to receive either routine O(2) therapy (control group, n = 15), or warmed (42 degrees C) humidified O(2) (treatment group, n = 15) for the initial 90 postoperative minutes. MEASUREMENTS: Core (tympanic) temperature, dry mouth score and shivering score. MAIN RESULTS: Tympanic temperature was similar in both groups on admission ( approximately 35.8 degrees C). Rewarming rate in the first postoperative hour was greater in the treatment group (0.7 +/- 0.1 degrees C. hr(-1)) compared to the control group (0.4 +/- 0.1 degrees C. hr(-1)) (p = 0.03). Patients receiving the warmed, humidified O(2) had a lower incidence of dry mouth compared to the control group (p = 0.03). The incidence of shivering was low and similar in both groups. CONCLUSIONS: Warming and humidifying inspired O(2) hastens recovery from hypothermia in postoperative patients.

Female↗