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PubMedDate not supplied

Simulation of human thermoregulation during water immersion: application to an aircraft cabin water-spray system.

A model was developed of transient changes in metabolic heat production and core temperature for humans subjected to cold conditions. It was modified to predict thermal effects of the upper parts of the body being sprayed with water from a system designed to reduce the smoke effects of an airplane fire. Temperature changes were computed at 25 body segments in response to water immersion, cold-air exposure, and windy conditions. Inputs to the temperature controller were: (a) temperature change signals from skin segments and (b) an integrated signal of the product of skin and head-core (hypothalamic) temperature changes. The controller stimulated changes in blood flow to skin and muscle and heat production by shivering. Two controller parameters were adjusted to obtain good predictions of temperature and heat-production experimental data in head-out, water-immersion (0 degree-28 degrees C) studies in humans. A water layer on the skin whose thickness decreased transiently due to evaporation was added to describe the effects of the water-spray system. Because the layer evaporated rapidly in a very cold and windy environment, its additional cooling effect over a 60-min exposure period was minimal. The largest additional decrease in rectal temperature due to the water layer was < 1 degree C, which was in normal conditions where total decreases were small.

Aircraft↗
PubMed1999

Early postoperative complications following neurosurgical procedures.

PURPOSE: To assess the incidence and characteristics of early postoperative complications in patients following neurosurgical procedures. METHODS: All patients undergoing neurosurgery during a four month period were followed postoperatively for up to four hours in the post anesthetic care unit or intensive care unit. Patient information and all complications were documented by the investigators on a standardized form. Complications were classified as respiratory, cardiovascular, nausea and vomiting, shivering and other. Risk factors analyzed for the occurrence of complications included age, sex, ASA status, type of surgery, elective or emergency surgery and postoperative placement. RESULTS: Four hundred eighty six adult patients were followed, but in 55 patients the trachea remained intubated during the four hour study period and they were eliminated from the analysis of postoperative complications. At least one complication occurred in 54.5% of the remaining 431 patients. Respiratory problems occurred in 2.8%, trauma to the airway in 4.4%, cardiovascular complications in 6.7%, neurological in 5.7% and nausea and/or vomiting in 38%. The highest incidence of patients with complications was during spine (65%) and vascular (66%) surgery, compared with tumour (47%) and other (43%) surgery, P < 0.05. Other risk factors included age < 70 yr for nausea and vomiting (P < 0.02), and elective surgery for spine and vascular surgery (P < 0.001). CONCLUSION: There was a high incidence of early postoperative complications in neurosurgical patients. The most common problem was nausea and vomiting especially in the younger patient undergoing elective spine surgery.

Adult↗
PubMed1995

The management of temperature during hypothermic cardiopulmonary bypass: II--Effect of prolonged hypothermia.

In animals mild hypothermia (32-35 degrees C) reduces ischaemic brain injury, but this has not been investigated in humans. During hypothermic cardiopulmonary bypass (CPB) patients are made hypothermic (usually to 30-32 degrees C) but are then rewarmed at a time when they are still at risk of ischaemic brain injury. We investigated the feasibility and safety of maintaining mild hypothermia throughout the CPB period. Thirty adult cardiac surgical patients were randomized to either rewarming to 36-37 degrees C or to maintaining temperature at 34 degrees C without rewarming. On arrival in the recovery room, patients in the hypothermic group had a mean bladder temperature of 33.8 +/- 0.45 degrees C compared with 35.4 +/- 0.58 degrees C (mean +/- SD, P < 0.05) in the rewarmed patients. There were no differences between groups in intra- or postoperative blood loss or blood use, inotrope use, dysrhythmias, or myocardial infarction. The hypothermic group received more muscle relaxant for the treatment of shivering postoperatively. Our results suggest that mild hypothermia following CPB did not increase morbidity although larger studies are needed for confirmation.

Adult↗
PubMed2002

[Goose flesh and cold sensation. Symptoms of visceral epilepsy].

Goose flesh and cold shiver can be ictal signs of visceral epilepsies. These visceral epilepsies may occur with isolated ictal signs during a simple partial seizure or in combination with other autonomic signs or in complex partial seizures. Because of the unusual features of the ictal symptomatology, these visceral epilepsies often are masked and wrongly diagnosed as nonepileptic events, e.g., somatoform disorders. Five cases are reported with case history, neurological findings, and results of electroencephalography, MEG, and imaging. Interestingly, patients did not suffer from tumoral epilepsies and the epileptic focus was lateralized to the left (dominant) temporal lobe.

Adolescent↗
PubMed2006

Motion sickness increases the risk of accidental hypothermia.

Motion sickness (MS) has been found to increase body-core cooling during immersion in 28 degrees C water, an effect ascribed to attenuation of the cold-induced peripheral vasoconstriction (Mekjavic et al. in J Physiol 535(2):619-623, 2001). The present study tested the hypothesis that a more profound cold stimulus would override the MS effect on peripheral vasoconstriction and hence on the core cooling rate. Eleven healthy subjects underwent two separate head-out immersions in 15 degrees C water. In the control trial (CN), subjects were immersed after baseline measurements. In the MS-trial, subjects were rendered motion sick prior to immersion, by using a rotating chair in combination with a regimen of standardized head movements. During immersion in the MS-trial, subjects were exposed to an optokinetic stimulus (rotating drum). At 5-min intervals subjects rated their temperature perception, thermal comfort and MS discomfort. During immersion mean skin temperature, rectal temperature, the difference in temperature between the non-immersed right forearm and 3rd finger of the right hand (DeltaTff), oxygen uptake and heart rate were recorded. In the MS-trial, rectal temperature decreased substantially faster (33%, P < 0.01). Also, the DeltaTff response, an index of peripheral vasomotor tone, as well as the oxygen uptake, indicative of the shivering response, were significantly attenuated (P < 0.01 and P < 0.001, respectively) by MS. Thus, MS may predispose individuals to hypothermia by enhancing heat loss and attenuating heat production. This might have significant implications for survival in maritime accidents.

Adult↗
PubMed1983

Human thermoregulatory behavior during a conflict between cold discomfort and money.

A conflict was contrived between thermal and non-thermal drives in humans to study the effects of varying degrees of voluntary suppression of behavioral temperature regulation. Five, young, near-nude males were paid 2, 5, 10, 20 or 40 cents per min to expose themselves to increasing cold (15 degrees to 0 degree C in 2 hours), after being instructed to terminate the exposure as soon as the cold discomfort exceeded the monetary reward. The duration of voluntary cold exposure was approximately linearly related to the logarithm of monetary reward. Reported cold discomfort was greater with high than with low rates of reward. Although V02 approached summit metabolism, the capacity for shivering did not appear to limit cold tolerance. Subjects adopted various strategies for coping with the conflict but, in general, greatest cold tolerance was recorded in subjects of large body mass and willing to tolerate low Tsk.

Adult↗
PubMed1984

Crustecdysone-induced modulation of electrical coupling and gap junction structure in crayfish hepatopancreatocytes.

Crustecdysone, the hormone responsible for onset and regulation of the molt cycle in Crustacea, causes an increase in ionic coupling of cells of the hepatopancreas concomitant with the events of the molt. Hepatopancreatic tissue incubated for up to 4 hr in modified Eagle Basal Medium containing crustecdysone, exhibited an approximate 29% decrease in intercellular resistance as compared with tissue incubated in control medium. This represents a 29% increase in ionic coupling between hepatopancreatocytes following treatment with crustecdysone. Examination of platinum replicas of freeze-fractured, crustecdysone-treated hepatocyte plasma membrane revealed that most of the gap junction plaques were round with tightly packed intramembrane particles; a condition indicative of highly coupled cells. Similar preparations of control plasmalemmae demonstrated many gap junction plaques which were round or irregular in shape with very loosely packed particles and were indicative of uncoupled junctions. Results of this study are identical to those from a previous investigation of the electrophysiology and freeze-fracture morphology of hepatopancreatocytes during the molt cycle (McVicar and Shivers, 1984), and are thus presumed to reflect a crustecdysone-controlled increase in cell communications in vivo.

Animals↗
PubMed1977

Quinine-induced hypothermia in cold-exposed rats.

Quinine HCl in doses from 10-50 mg/kg lowered the body temperatures of nonfebrile rats in the cold, primarily by suppressing shivering. However, if given an opportunity to turn on a heat lamp the rats worked much more than normal after a quinine injection and were theraby able to counteract the hypothermia to some extent. The effect of quinine is interpreted as an action on effector mechanisms rather than as an alteration of the thermal setpoint.

Animals↗
PubMed1987

Physiological responses of vagotomized pigeons exposed to ambient temperatures gradually reduced from 34 degrees C to 2 degrees C.

In pigeons subjected to bilateral cervical vagotomy and sham-vagotomy, measurements of heart rate, breathing frequency, cloacal temperature (Tc), foot temperature (Tf), shivering and metabolic heat production (M) were made during gradual ambient cooling from 34 to 2 degrees C on Day 2 as well as on Day 3 post-surgery. Severe tachycardia was observed in both Day 2 and Day 3 vagotomized (VX) pigeons. Lowering of ambient temperature (Ta) below 28 degrees C produced increased heart rate in both Day 2 as well as Day 3 sham-vagotomized (SVX) and VX pigeons, except with Day 3 VX pigeons exposed to Ta below 12 degrees C when a reversal of the trend became apparent. Breathing frequency in VX pigeons was lower than that in SVX on both days tested, the difference being greater on Day 2 than on Day 3. On both days, the difference in breathing frequency between VX and SVX pigeons was minimal at Ta 30 degrees C and became increasingly greater with Ta above or below this point. Tc dropped significantly in both VX and SVX pigeons in response to ambient cooling on Days 2 and 3. The Day 2 VX pigeons in general had a lower Tc than that in SVX and as Ta continued to drop below 28 degrees C, Tc in VX pigeons dropped more rapidly than in SVX, showing the maximal difference in Tc between the two at Ta 2 degrees C.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1985

Oxygen consumption and carbon dioxide production following open heart surgery.

The VO2, VCO2 and RQ were measured in 24 patients after open heart surgery using a CO2 analyzer and O2 Consumption Calculator (Siemen Elma, Sweden). With prolonged ventilatory care, shivering was noticed in only one patient and VO2, VCO2 and RQ were rather stable and constant in patients in the Intensive Care Unit (ICU). With dopamine infusion the 3-5 kg body wt/min cardiovascular status was stable and the oxygen extraction ratio was a mean of 0.264. From those data we suggest that ventilatory support would be desirable for about 2 days for those patients in the post-operative period.

Adult↗
PubMed1994

Thermoregulatory responses to thermal stimulation of the preoptic anterior hypothalamus in the red fox (Vulpes vulpes).

The preoptic anterior hypothalamus (POAH) thermoregulatory controller can be characterized by two types of control, an adjustable setpoint temperature and changing POAH thermal sensitivity. Setpoint temperatures for shivering (Tshiver) and panting (Tpant) both increased with decreasing ambient temperature (Ta), and decreased with increasing Ta. The POAH controller is twice as sensitive to heating as to cooling. Metabolic rate (MR) increased during both heating and cooling of the POAH. Resting temperature of the POAH was lower than internal body temperature (Tb) at all temperatures. This indicates the presence of some form of brain cooling mechanism. Decreased Tb during POAH heating was a result of increased heat dissipation, while higher Tb during POAH cooling was a result of increased heat production and reduced heat dissipation. The surface temperature responses indicated that foxes can actively control heat flow from body surface. Such control can be achieved by increased peripheral blood flow and vasodilation during POAH heating, and reduced peripheral blood flow and vasoconstriction during POAH cooling. The observed surface temperature changes indicated that the thermoregulatory vasomotor responses can occur within 1 min following POAH heating or cooling. Such a degree of regulation can be achieved only by central neural control. Only surface regions covered with relatively short fur are used for heat dissipation. These thermoregulatory effective surface areas account for approximately 33% of the total body surface area, and include the area of the face, dorsal head, nose, pinna, lower legs, and paws.

Acepromazine↗
PubMed1984

Nonshivering thermogenesis.

Nonshivering thermogenesis was originally defined as a cold-induced increase in heat production not associated with the muscle activity of shivering. Recent research shows it to be a metabolic process located primarily in brown adipose tissue and controlled by the activity of the sympathetic nervous supply of this tissue. Another stimulus to sympathetic nervous activity, the ingestion of food, promotes diet-induced thermogenesis in brown adipose tissue. Brown adipose tissue grows and regresses in accordance with the extent to which it is stimulated, either by cold or by diet, and the capacity of the animal for cold-induced nonshivering thermogenesis and diet-induced thermogenesis increases or decreases accordingly. In certain hibernators another stimulus, photoperiod, promotes growth or regression of brown adipose tissue. The neural regulation of thermogenesis in brown adipose tissue is thus not only part of the central control mechanisms involved in thermoregulation but also part of those involved in the regulation of energy balance. In hibernators , such as the hamster, the neural regulation of thermogenesis in brown adipose tissue includes, in addition, central components that control the function of brown adipose tissue during entry into and arousal from hibernation and pineal or melatonin-related components that control its growth in response to photoperiod. In animals which become intermittently torpid, such as the mouse, the regulation includes in addition central components that control the function of brown adipose tissue during entry into and arousal from torpor. The central neural components involved in control of thermoregulation are better understood than are those involved in the regulation of energy balance. Studies of animal with hypothalamic obesity indicate that the control of diet-induced thermogenesis in brown adipose tissue requires the participation of the ventromedial region of the hypothalamus whereas the control of cold-induced nonshivering thermogenesis does not. The importance of comparative studies in different species is emphasized since any neural model for the control of brown adipose tissue thermogenesis is likely to apply in detail only to the species for which it was developed.

Acclimatization↗
PubMed1995

Perinatal thermogenesis.

The rapid initiation of thermogenesis is crucial for the survival of newborn infants. At birth the fetus must adapt to cooling, increased oxygenation and separation from the placenta. An experimental approach in the chronically instrumental fetal sheep of 'simulated birth in utero' allowed the evaluation of each of these stimuli sequentially. Cooling stimulated shivering, cardiovascular and endocrine responses but not nonshivering thermogenesis (NST). Ventilation of the cooled fetus with oxygen caused only modest NST which was not altered by an infusion of triiodothyronine. Occluding the umbilical cord was followed by a rapid substantial rise in NST which was maintained until the placental circulation was re-established. Thus the placenta is secreting factors into the fetal circulation which inhibit the ability of the brown adipose tissue to respond to either hormonal or neural stimuli. Placental prostaglandin E2 and probably adenosine are tonic inhibitors of thermogenesis in utero. Effective thermogenesis after birth requires the combination of separation from the placental inhibitors of lipolysis, increased oxygenation from breathing and the stimulation of cutaneous cold receptors.

Adenosine↗
PubMed1989

Delivery temperature of heated intravenous solutions during rapid infusion.

Warming of intravenous fluids may help to prevent shivering and hypothermia in the surgical patient. Increasing the fluid temperatures to as high as 60 degrees C has been suggested. An in vitro study was performed in which temperature changes following the rapid infusion of heated lactated Ringer's solution within a vein were measured. When 1 L of solution was warmed to 55 degrees C and then was infused over 4 min, local model vein temperatures rose from 37 degrees C to 44 degrees C. This effect of possible regional tissue heating may well occur in vivo. It is known that the rate of human blood cell hemolysis and membrane enzymatic function is affected by temperature. Further efforts need to be directed toward appreciating the effects of warmed intravenous fluids upon intact physiologic preparations and red blood cells.

Hot Temperature↗
PubMed2006

Effect of subdiaphragmatic vagotomy on the noradrenergic and HPA axis activation induced by intraperitoneal interleukin-1 administration in rats.

The vagus nerve is thought to participate in signal transduction from the immune system to the CNS. The role of the vagus in the physiological, behavioral and neurochemical responses to intraperitoneally (ip) injected interleukin-1beta (IL-1beta) was studied using awake subdiaphragmatically vagotomized rats. The rats were injected ip with saline and IL-1beta (1 microg/rat) in random order. For the next 2-4 h, they were monitored for locomotor activity, body temperature via abdominally implanted telethermometers, hypothalamic norepinephrine (NE) secretion using in vivo microdialysis and blood sampled via intravenous catheters to determine concentrations of ACTH and corticosterone to assess hypothalamo-pituitary-adrenocortical (HPA) axis activation. Saline injections were followed by transient increases in locomotor activity, body temperature, dialysate NE and plasma concentrations of ACTH and corticosterone. These responses were not significantly altered by vagotomy. IL-1beta injections resulted in short-lived increases in shivering and longer decreases in locomotor activity, as well as a delayed modest fever. IL-1beta also induced prolonged elevations of hypothalamic microdialysate NE, as well as plasma ACTH and corticosterone. Similar responses were observed regardless of the order of the saline and IL-1beta injections. Subdiaphragmatic vagotomy prevented the IL-1-induced increases in body temperature and the increase in dialysate NE, and markedly attenuated the increases in plasma ACTH and corticosterone. The results indicate close temporal relationships between the apparent release of NE and the increase in body temperature and the HPA activation. This together with the effects of vagotomy suggests that the activation of NE in turn increases body temperature and activates the HPA axis. However, because IL-1beta induces a limited HPA activation in subdiaphragmatically vagotomized rats, the vagus nerve does not appear to be the only route by which ip IL-1beta can activate the HPA axis. It is suggested that IL-1beta-induced vagal activation of hypothalamic NE is the major mechanism of HPA activation at low doses of IL-1beta. However, IL-1beta can also exert direct effects on IL-1 receptors on cerebral blood vessels, activating cyclooxygenases and hence synthesis of prostaglandins which in turn can affect body temperature, behavior and HPA axis activation.

Adrenocorticotropic Hormone↗
PubMed2004

Seasonal changes in thermal responses of urban residents to cold exposure.

To determine whether urban circumpolar residents show seasonal acclimatisation to cold, thermoregulatory responses and thermal perception during cold exposure were examined in young men during January-March (n=7) and August-September (n=8). Subjects were exposed for 24 h to 22 and to 10 degrees C. Rectal (T(rect)) and skin temperatures were measured throughout the exposure. Oxygen consumption (VO(2)), finger skin blood flow (Q(f)), shivering and cold (CDT) and warm detection thresholds (WDT) were assessed four times during the exposure. Ratings of thermal sensations, comfort and tolerance were recorded using subjective judgement scales at 1-h intervals. During winter, subjects had a significantly higher mean skin temperature at both 22 and 10 degrees C compared with summer. However, skin temperatures decreased more at 10 degrees C in winter and remained higher only in the trunk. Finger skin temperature was higher at 22 degrees C, but lower at 10 degrees C in the winter suggesting an enhanced cold-induced vasoconstriction. Similarly, Q(f) decreased more in winter. The cold detection threshold of the hand was shifted to a lower level in the cold, and more substantially in the winter, which was related to lower skin temperatures in winter. Thermal sensations showed only slight seasonal variation. The observed seasonal differences in thermal responses suggest increased preservation of heat especially in the peripheral areas in winter. Blunted vasomotor and skin temperature responses, which are typical for habituation to cold, were not observed in winter. Instead, the responses in winter resemble aggravated reactions of non-cold acclimatised subjects.

Adult↗
PubMed2005

EEG should be performed during induced hypothermia.

Induced hypothermia has improved neurological outcome after cardiac arrest. Even though anoxic insults to the brain often provoke epileptic activity, it is unclear whether EEG monitoring is necessary in these patients. We report the case of a 53-year-old female who suffered cardiac arrest. During induced hypothermia extensive shivering was managed by sedation and curare. After their discontinuation convulsions appeared and status epilepticus was disclosed on EEG recording, and was treated by thiopental infusion for 10 days. The patient recovered slowly and has now regained independent living (CPC 1). In induced hypothermia several factors including the use of curare, may conceal clinical signs of epileptic activity. We therefore suggest a broader use of EEG in these patients.

Curare↗
PubMed1997

Nocturnal digestion, cloacal excretion, and digestion-related thermogenesis in pigeons (Columba livia).

Two indicators of nocturnal digestive activity were identified in pigeons. Experiment 1 showed that a sizable amount of food empties from the crop while pigeons are inactive during the night. Experiment 2 showed that the number and volume of cloacal droppings during the night were directly related to the volume of food consumed during the day. The temporal pattern of cloacal droppings in the night was systematically related to features of the nocturnal body temperature (Tb) curves, suggesting that excretory activity is thermogenic in its own right and/or that it is a marker for a thermogenic process in the upper digestive tract. Questions about the relationship between digestion-related thermogenesis and shivering thermogenesis during the night in birds are highlighted by these findings.

Animals↗