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PubMed1999

Thermoregulatory responses to cold water at different times of day.

This study examined how time of day affects thermoregulation during cold-water immersion (CWI). It was hypothesized that the shivering and vasoconstrictor responses to CWI would differ at 0700 vs. 1500 because of lower initial core temperatures (T(core)) at 0700. Nine men were immersed (20 degrees C, 2 h) at 0700 and 1500 on 2 days. No differences (P > 0.05) between times were observed for metabolic heat production (M, 150 W. m(-2)), heat flow (250 W. m(-2)), mean skin temperature (T(sk), 21 degrees C), and the mean body temperature-change in M (DeltaM) relationship. Rectal temperature (T(re)) was higher (P < 0.05) before (Delta = 0.4 degrees C) and throughout CWI during 1500. The change in T(re) was greater (P < 0. 05) at 1500 (-1.4 degrees C) vs. 0700 (-1.2 degrees C), likely because of the higher T(re)-T(sk) gradient (0.3 degrees C) at 1500. These data indicate that shivering and vasoconstriction are not affected by time of day. These observations raise the possibility that CWI may increase the risk of hypothermia in the early morning because of a lower initial T(core).

Adult↗

PubMed2000

Effect of delivery temperature on endocrine stimulation of thermoregulation in lambs born by cesarean section.

We examined the hypothesis that exogenous stimulation with physiological doses of 3,5,3'-triiodothyronine (T(3)) and/or norepinephrine at birth can improve thermoregulation in near-term lambs delivered by cesarean section. This was achieved by investigating the effect of delivery temperature [i.e., warm (30( degrees )C) vs. cool (15( degrees )C) ambient temperatures] on hormonal stimulation on uncoupling protein-1 (UCP1) abundance in brown adipose tissue. In vivo measurements of temperature control (i. e., colonic temperature, oxygen consumption, and incidence of shivering) were made over the first 2.5 h after birth. Each lamb was injected with saline with or without T(3), norepinephrine, or T(3) plus norepinephrine. Irrespective of delivery temperature, abundance of UCP1 increased and incidence of shivering decreased by all hormonal treatments, but this only reduced the rate of decline in colonic temperature of cool-delivered lambs. Oxygen consumption was higher in cool-delivered lambs that were able to fully restore body temperature, an adaptation not observed in controls or any warm-delivered groups. Exogenous administration of endocrine stimulatory factors can enhance the abundance of UCP1 in cesarean-section-delivered lambs with the magnitude of thermoregulatory response being greater at cool than warm delivery temperatures.

Adipose Tissue↗

PubMed2006

Thermal effects of whole head submersion in cold water on nonshivering humans.

This study isolated the effect of whole head submersion in cold water, on surface heat loss and body core cooling, when the confounding effect of shivering heat production was pharmacologically eliminated. Eight healthy male subjects were studied in 17 degrees C water under four conditions: the body was either insulated or uninsulated, with the head either above the water or completely submersed in each body-insulation subcondition. Shivering was abolished with buspirone (30 mg) and meperidine (2.5 mg/kg), and subjects breathed compressed air throughout all trials. Over the first 30 min of immersion, exposure of the head increased core cooling both in the body-insulated conditions (head out: 0.47 +/- 0.2 degrees C, head in: 0.77 +/- 0.2 degrees C; P < 0.05) and the body-exposed conditions (head out: 0.84 +/- 0.2 degrees C and head in: 1.17 +/- 0.5 degrees C; P < 0.02). Submersion of the head (7% of the body surface area) in the body-exposed conditions increased total heat loss by only 10%. In both body-exposed and body-insulated conditions, head submersion increased core cooling rate much more (average of 42%) than it increased total heat loss. This may be explained by a redistribution of blood flow in response to stimulation of thermosensitive and/or trigeminal receptors in the scalp, neck and face, where a given amount of heat loss would have a greater cooling effect on a smaller perfused body mass. In 17 degrees C water, the head does not contribute relatively more than the rest of the body to surface heat loss; however, a cold-induced reduction of perfused body mass may allow this small increase in heat loss to cause a relatively larger cooling of the body core.

Adult↗

PubMed1985

Accidental hypothermia in a healthy quadriplegic patient.

An otherwise healthy 28-year-old quadriplegic patient was admitted to the hospital with a core temperature of 76 degrees F secondary to accidental hypothermia. Her neurologic disability was detrimental to thermoregulation by decreasing her ability to shiver actively and to vasoconstrict. The relationship between shivering and thermoregulation is discussed.

Accidents, Home↗

PubMed1990

Evaluation of a forced-air system for warming hypothermic postoperative patients.

Thirty adult surgical patients admitted to the recovery room with an oral temperature less than or equal to 35.0 degrees C were randomized into two groups. Group 1 patients were covered with cotton blankets warmed to 37.0 degrees C, and group 2 patients were treated with a forced-air warming system. Mean oral temperature on admission to the recovery room was the same in both groups (34.3 degrees C). Oral temperature and the presence or absence of shivering were recorded at 15-min intervals. After application of the selected warming method, patients in group 2 were warmer at all time intervals. Mean temperatures in the forced-air heating group and in group 1 were, respectively, 34.8 degrees C and 34.3 degrees C (P less than 0.05) at 15 min; 35.0 degrees C and 34.2 degrees C (P less than 0.01) at 30 min; 35.2 degrees C and 34.5 degrees C (P less than 0.05) at 45 min; 35.8 degrees C and 34.7 degrees C (P less than 0.001) at 60 min; 36.0 degrees C and 35.0 degrees C (P less than 0.01) at 75 min; and 36.0 degrees C and 35.0 degrees C (P less than 0.01) at 90 min. The incidence of shivering was significantly greater in group 1 at 15 and 45 min. In addition, time spent in the recovery room was significantly greater in group 1 than in group 2, 156.0 min versus 99.7 min (P less than 0.003).

Adult↗

PubMed2026

Effect of Local Anesthetic Solution at Different Temperatures for Epidural Labor Analgesia on Intrapartum Fever: A Randomized Clinical Trial.

BACKGROUND: Whether heating local anesthetic solutions to core body temperature (37°C) for epidural labor analgesia reduces intrapartum fever incidence remains undefined in the current literature. METHODS: This double-blind randomized controlled trial (RCT) enrolled 220 nulliparous parturients (18-35 years, American Society of Anesthesiologists [ASA] physical status II, term singleton pregnancy). Participants were randomized to receive epidural labor analgesia with 0.075% ropivacaine + 0.5 µg/mL sufentanil at 37°C (warmed group) or 22°C (room-temperature group). Epidurals were placed at L3-L4 with a test dose of 3 mL of 1.5% lidocaine at room temperature, followed by programmed bolus epidural analgesia (initial 10 mL, 10 mL/h) and patient-controlled epidural analgesia (PCEA) 5 mL (30-minute lockout). Tympanic temperature was measured every 30 minutes from epidural initiation to delivery, defining intrapartum fever as ≥38°C. The primary outcome was fever incidence, on which the power analysis was based, and also maximum temperature and shivering. Secondary outcomes comprised analgesia onset, block level, labor durations, neonatal Apgar scores, umbilical cord blood pH and BE, and maternal adverse events. RESULTS: A total of 220 parturients were included (warmed group, n = 110; room-temperature group, n = 110). The warmed group had a lower intrapartum fever incidence (15.5% [17/110] vs 30.9% [34/110], relative risk [RR] 0.5 [95% confidence interval {CI}, 0.298-0.840]; P = .007); however, the reduction of 49.8% did not reach the preset clinically meaningful difference of 60% reduction proposed in the power analysis. The maximum body temperature was also lower in the warmed group: median (interquartile range [IQR]) 37.4 (IQR, 37.2-37.7) °C vs 37.6 (IQR, 37.3-38.0) °C, median difference -0.2 (95% CI, -0.3 to -0.1) °C ( P = .006). Shivering incidence was not different between groups (10.9% [12/110] vs 14.5% [16/110]; P = .418). No statistically significant differences were observed between groups in any of the secondary outcomes assessed, including block characteristics, local anesthetic consumption, labor duration, neonatal outcomes, and maternal adverse events. CONCLUSION: Although we found a 50% reduction in the incidence of temperature rise using warmed (37°C) local anesthetics for epidural labor analgesia, this did not reach our preset threshold of 60% reduction.

Humans↗

PubMedDate not supplied

Adaptation to exercise in the cold.

The winter athlete has several potential tactics for sustaining body temperature in the face of severe cold. An increase in the intensity of physical activity may be counter-productive because of increased respiratory heat loss, increased air or water movement over the body surface, and a pumping of air or water beneath the clothing. Shivering can generate heat at a rate of 10 to 15 kJ/min, but it impairs skilled performance, while the resultant glycogen usage hastens the onset of fatigue and mental confusion. Non-shivering thermogenesis could arise in either brown adipose tissue or white fat. Brown adipose tissue generates heat by the action of free fatty acids in uncoupling mitochondrial electron transport, and by noradrenaline-induced membrane depolarisation and sodium pumping. The existence of brown adipose tissue in human adults is controversial, and although there are theoretical mechanisms of heat production in white fat, their contribution to the maintenance of body temperature is small. Acclimatisation to cold develops over the course of about 10 days, and in humans the primary change is an insulative, hypothermic type of response; this reflects the intermittent nature of most occupational and athletic exposures to cold. Nevertheless, with more sustained exposure to cold air or water, humans can apparently develop the humoral type of acclimatisation described in small mammals, with an increased output of noradrenaline and/or thyroxine. The associated mobilisation of free fatty acids suggests the possibility of using winter sport as a pleasant method of treating obesity. In men, a combination of moderate exercise and facial cooling induces a substantial fat loss over a 1- to 2-week period, with an associated ketonuria, proteinuria, and increase of body mass. Possible factors contributing to this fat loss include: (a) a small energy deficit; (b) the energy cost of synthesising new lean tissue; (c) energy loss through the storage and excretion of ketone bodies; (d) catecholamine-induced 'futile' metabolic cycles with increased resting metabolism; and (e) a specific reaction to cold dehydration. Current limitations for the clinical application of such treatment include uncertainty regarding optimal environmental conditions, concern over possible pathological reactions to cold, and suggestions of a less satisfactory fat mobilisation in female patients. Possible interactions between physical fitness and metabolic reactions to cold remain controversial.(ABSTRACT TRUNCATED AT 400 WORDS)

Adaptation, Physiological↗

PubMed1979

Thermoregulatory nonshivering thermogenesis in men, with special reference to lipid metabolism.

The existence of thermoregulatory nonshivering thermogenesis, with special reference to lipid metabolism, was investigated in men. Acute cold exposure (10 degrees C, 60 min) produced a marked increase in heat production, with concomitant elevation of plasma free fatty acid (FFA) level, modest increase of ketone body concentration and lowered respiratory quotient (R.Q.). The correlation of heat production to plasma FFA levels was significantly positive; that is, subjects with higher heat production showed higher plasma FFA levels. Moreover, correlation of either heat production or plasma FFA levels to R.Q. was significantly negative, respectively. On the other hand, exposure to cold after an administration of nicotinic acid, which has a suppressive effect on FFA mobilization from adipose tissue, resulted in less cold-elevated heat production, a significant fall of plasma FFA and ketone body concentrations, and no change in R.Q. Although no visible or only slight shivering was observed in control cold exposure study, greater shivering occurred in the nicotinic acid cold exposure study. These results appear to indicate that nonshivering thermogenesis as a source of heat production achieved by enhanced utilization of lipids is also present in men.

Adult↗

PubMed1983

Effects of restraint on baroreflex sensitivity in altering heart rate and heat production in rats.

When systemic arterial pressure was elevated with phenylephrine (PHE) at 13 degrees C, heart rate (HR), and heat production (M) associated with shivering were greatly suppressed in rats. The magnitude of suppression increased proportionally with increasing doses of PHE. During restraint, however, such a suppression of HR and M with PHE was attenuated, indicating that restraint reduced baroreflex sensitivity in altering HR and shivering in rats.

Animals↗

PubMed1976

Inhibition of adrenocortical function by intravenous administration of sodium pentobarbital in cocks.

The response of awake and anesthesized cocks with sodium pentobarbital to stressful stimuli has been examined. The stressful stimuli was immersion in cold water. In the awake cocks plasma corticosterone concentration was increased about 4 fold; they started shivering shortly after immersion and recovered after cessation of the treatment. In the anesthesized ones there was no increase in plasma corticosterone concentration, they did not shiver and died shortly after immersion.

Adrenal Cortex↗

PubMed2002

[Disorders of thermoregulatory mechanisms of the organism and their metabolic consequences. Part I. Hypothermia].

The maintenance of thermal equilibrium depends on the normal functioning of numerous body systems and their appropriate interaction with the environment. Man has a complicated neural and neuroendocrine control system that is designed to maintain a constant core temperature despite changes in environmental temperature or level of activity. Heat exchange is a bidirectional process involving the transfer of heat between an object and its environment. There are four mechanisms of heat dissipation: evaporation, conduction, convection, and radiation. Heat production is the sum of basal metabolism and shivering and non-shivering thermogenesis. The hypothalamus is the central control centre that ensures thermal homeostasis. Although many schemes exist for the classification of hypothermia, from the clinical point of view it is recommended to consider any temperature below 35 degrees C significant. Accurate temperature measurement and core temperature monitoring are essential for diagnosing hypothermia.

Body Temperature Regulation↗

PubMed2002

[Development of deep hypothermia in rats with limited motor activity].

Changes of the main organism functions (breathing frequency, heart rate and shivering) were investigated under hypothermia in two groups of rats. Animals of the first group were fixed rigidly on the special platform with fixing of head and limbs, and those of the second one--the rats, were placed in a punched cylindrical chamber, inside which they could move freely forward and back. In 2.5-3.0 hours after anaesthesia the rats were placed in a refrigerator (-5 degrees C) until they stop breathing. Cessation of breathing of the first group rats occurred in 1.7 +/- 0.3 hours from the beginning of cooling at body temperature 17.3 +/- 0.6 degrees C and the brain temperature 15.7 +/- 0.5 degrees C. In the second group, a prolonged activation of the frequency of breathing, heart rate and intensity of electrical activity of muscles during 2.5-3.0 hours, was observed. Only in 4.5-5.0 hours, the breathing stopped at rectal temperature 12.3 +/- 1.1 degrees C and the brain temperature 12.9 +/- 0.9 degrees C. In these animals, the time of survival in the cold environment increased considerably and the temperature thresholds of the termination of breathing were lowered. Thus, the activation in the thermo-regulative muscle tone and in shivering muscles provides the most effective resistance against cooling of rats, reducing a surface of heat, dissipation and keeping the temperature of internal areas of body.

Animals↗

PubMed2002

Physiological responses to cold exposure in men: a disabled submarine study.

A disabled submarine (DISSUB) lacking power and/or environmental control will become cold, and the ambient air may become hypercapnic and hypoxic. This study examined if the combination of hypoxia, hypercapnia, and cold exposure would adversely affect thermoregulatory responses to acute cold exposure in survivors awaiting rescue. Seven male submariners (33 +/- 6 yrs) completed a series of cold-air tests (CAT) that consisted of 20-min at T(air) = 22 degrees C, followed by a linear decline (1 degrees C x min(-1)) in T(air) to 12 degrees C, which was then held constant for an additional 150-min. CAT were performed under normoxic, normocapnic conditions (D0), acute hypoxia (D1, 16.75% O2), after 4 days of chronic hypoxia, hypercapnia and cold (D5, 16.75% O2, 2.5% CO2, 4 degrees C), and hypoxia-only again (D8, 16.75% O2). The deltaTsk during CAT was larger (P < 0.05) on D0 (-5.2 degrees C), vs. D1 (-4.8 degrees C), D5 (-4.5 degrees C), and D8 (-4.4 degrees C). The change (relative to 0-min) in metabolic heat production (deltaM) at 20-min of CAT was lower (P < 0.05) on D1, D5, and D8, vs. D0, with no differences between D1, D5 and D8. DeltaM was not different among trials at any time point after 20-min. The mean body temperature threshold for the onset of shivering was lower on D1 (35.08 degrees C), D5 (34.85 degrees C), and D8 (34.69 degrees C), compared to D0 (36.01 degrees C). Changes in heat storage did not differ among trials and rectal temperature was not different in D0 vs. D1, D5, and D8. Thus, mild hypoxia (16.75% F1O2) impairs vasoconstrictor and initial shivering responses, but the addition of elevated F1CO2 and cold had no further effect. These thermoregulatory effector changes do not increase the risk for hypothermia in DISSUB survivors who are adequately clothed.

Adult↗

PubMed1992

Relationship between physique and rectal temperature cooling rate.

Despite many attempts to relate components of physique to core temperature cooling rate, no consistent relationship has emerged. The inconsistencies among the reported findings may arise from unaccounted thermoregulatory responses or incomplete physique assessment or both. A study was designed to examine this relationship in the range of rectal temperatures (Tre) within which shivering and sweating are absent, defined as the null zone, thus minimizing the contribution of these effector responses. Twenty healthy subjects (10 male and 10 female), representing a variety of physiques, participated in the study. The anthropometric protocol included 5 heights, body mass, 8 skinfolds, 10 girths, and 4 breadths. This permitted derivation of a body surface-area-to-mass ratio and estimates of adipose and muscle tissue masses using a cadaver-validated mass fractionation model. Subjects were heated in a 40 degrees C bath followed immediately by cooling in a 30.6 degrees C bath. During the cooling, forehead sweating rate and oxygen uptake were monitored to establish the boundaries of the Tre null zone. In addition, on-line recordings were made of Tre, skin temperature, and surface heat flux at six sites. The rate of cooling of Tre (Tre), in the range of temperatures between thresholds for sweating and shivering, was correlated to the components of physique. Estimates of adipose and skeletal muscle tissue masses did not correlate to Tre in the range of core temperatures investigated. However, total mass exhibited a significant correlation (r = 0.5, P less than or equal to 0.05) with Tre, but gender seemed to distort this relationship, possibly due to differences in adipose tissue distribution.

Adipose Tissue↗

PubMed2005

[Stimulation of physiological functions in cooled rats without rewarming after introducing ethylenediaminetetraacetate into lateral ventricles of the brain].

On cooling the animals to the rectum temperature from approximately 37 to 24-28 degrees C the decreases were shown to occur in the frequency and amplitude of respiration motions, in the intensity of muscle electrical activity (thermoregulation muscle tone and cold muscle shivering), in the frequency of heart contractions. In 3-8 min after introducing ethylenediaminetetraacetate into a lateral ventricle of the rat brain the frequency and the amplitude of respiration motions increased statistically reliable and so did the intensity of thermoregulation muscle tone and cold muscle shivering (judging from the total muscle electrical activity). The doses of EDTA, which caused this effect, were by a factor of 30 - 100 less than the doses, which caused a similar stimulation of the functions in cooled animals after introduction into the blood.

Animals↗

PubMedDate not supplied

Anesthetic management of a parturient with myotonia dystrophica: a case report.

We report the case of a 22-year-old parturient with myotonia dystrophica. She underwent two separate intraabdominal surgical procedures in one day, both under lumbar epidural anaesthesia. Management was directed toward prevention of shivering, a known trigger of myotonic crises. Measures used included warm ambient atmosphere, warmed IV fluids, warming blankets and administration of epidural sufentanil, an opioid recently ascribed as an inhibitor of shivering in parturients.

Abdomen↗

PubMed1980

[Effect of high altitude on the thermoregulatory system].

The temperature range for specific thermoregulatory responses (shivering, sweat secretion) of the high altitude residents is narrower than in the lowland inhabitants, as well as the sensitivity of temperature centres of the formers is lower than in the latters. The absolute level of heat emission of the respiratory tract, internal and external gradients of temperature, are the important parts in mechanisms of shivering. The average level of body temperature domineers in the response of thermal sweat secretion.

Acclimatization↗

PubMedDate not supplied

Circadian rhythm of thermoregulating responses in man exposed to thermal stimuli.

Circadian changes in man's thermoregulating responses were studied in two experimental runs during which 7 volunteer subjects were exposed at 8 equally spaced time points of the 24-h span to a quick rise in temperature (To = 40 degrees C, v = 1 m/sec, P H2O less than 1 kPa) or to progressive cooling, the final temperature being reached after 45 min (To = 20 degrees C, v = 0.2 m/sec, P H2O less than 1 kPa). Under heat exposure, a circadian rhythm was observed in the period preceding the onset of sweating, and also in rectal temperature and mean body temperature, both at the onset of sweating and at its steady state. The time constant of the sweating rate and the sweating rate at the steady state show no apparent changes. Under cold exposure there is no detectable circadian rhythm in the mean body temperature at the onset of shivering, however, a circadian evolution appears in rectal temperature at the onset of shivering and at the end of the experiment. A circadian rhythm also appears for the metabolic response at the end of the experiment. These results suggest the presence of a circadian rhythm of the set point with no change in the gain of sweat responses. They also imply that thermoregulating responses to cold follow circadian changes.

Body Temperature↗