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PubMed1985

Potential of brown adipose tissue type II thyroxine 5'-deiodinase as a local and systemic source of triiodothyronine in rats.

Previous reports suggest that a type II iodothyronine 5'-deiodinase may become the main enzymatic pathway for extrathyroidal triiodothyronine (T3) generation when the enzyme levels are sufficiently elevated and/or liver and kidney type I 5'-deiodinase activity is depressed. The present studies assessed the potential of brown adipose tissue (BAT) type II 5'-deiodinase to generate T3 for the plasma pool. BAT 5'-deiodination (BAT 5'D) was stimulated by either short- (4 h) or long-term (7 wk) cold exposure (4 degrees C). Long-term cold exposure increased thyroxine (T4) secretion 40-60% and extrathyroidal T3 production three-fold. In cold-adapted rats treated with propylthiouracil (PTU), extrathyroidal T3 production was 10-fold higher than in PTU-treated rats maintained at room temperature. Cold did not stimulate liver or kidney 5'D, but the cold-adapted rats showed a six- to eightfold higher BAT 5'D content. PTU caused greater than 95% inhibition of liver and kidney 5'D, but did not affect BAT 5'D. Thyroidectomized rats maintained on 0.8 micrograms of T4/100 g of body weight (BW) per day were acutely exposed to 4 degrees C. In rats given 10 mg of PTU/100 g of BW, 4 h of cold exposure still caused a 12-fold increase in BAT 5'D, a 2.3-fold increase in plasma T3 production, and a 4.8-fold increment in the locally produced T3 in BAT itself. All these responses were abolished by pretreatment with the alpha 1-antiadrenergic drug prazosin. Regardless of the ambient temperature, liver 5'D activity was greater than 90% inhibited by PTU. These results indicate that BAT can be a major source of plasma T3 under suitable circumstances such as acute or chronic exposure to cold. Furthermore, BAT 5'D activity affects BAT T3 content itself, suggesting that thyroid hormone may have a previously unrecognized role in augmenting the thermogenic response of this tissue to sympathetic stimulation. Such interactions may be especially important during the early neonatal period in humans, a time of marked thermogenic stress.

Adipose Tissue, Brown↗
PubMed2006

Temperature acclimation alters cardiac performance in the lobster Homarus americanus.

The American lobster is a poikilotherm that inhabits a marine environment where temperature varies over a 25 degrees C range and depends on the winds, the tides and the seasons. To determine how cardiac performance depends on the water temperature to which the lobsters are acclimated we measured lobster heart rates in vivo. The upper limit for cardiac function in lobsters acclimated to 20 degrees C is approximately 29 degrees C, 5 degrees C warmer than that measured in lobsters acclimated to 4 degrees C. Warm acclimation also slows the lobster heart rate within the temperature range from 4 to 12 degrees C. Both effects are apparent after relatively short periods of warm acclimation (3-14 days). However, warm acclimation impairs cardiac function at cold temperatures: following several hours exposure to frigid (<5 degrees C) temperatures heart rates become slow and arrhythmic in warm acclimated, but not cold acclimated, lobsters. Thus, acclimation temperature determines the thermal limits for cardiac function at both extremes of the 25 degrees C temperature range lobsters inhabit in the wild. These observations suggest that regulation of cardiac thermal tolerance by the prevailing environmental temperature protects against the possibility of cardiac failure due to thermal stress.

Acclimatization↗
PubMed2006

Ca2+-independent phospholipase A2-dependent gating of TRPM8 by lysophospholipids.

TRPM8 represents an ion channel activated by cold temperatures and cooling agents, such as menthol, that underlies the cold-induced excitation of sensory neurons. Interestingly, the only human tissue outside the peripheral nervous system, in which the expression of TRPM8 transcripts has been detected at high levels, is the prostate, a tissue not exposed to any essential temperature variations. Here we show that the TRPM8 cloned from human prostate and heterologously expressed in HEK-293 cells is regulated by the Ca(2+)-independent phospholipase A(2) (iPLA(2)) signaling pathway with its end products, lysophospholipids (LPLs), acting as its endogenous ligands. LPLs induce prominent prolongation of TRPM8 channel openings that are hardly detectable with other stimuli (e.g. cold, menthol, and depolarization) and that account for more than 90% of the total channel open time. Down-regulation of iPLA(2) resulted in a strong inhibition of TRPM8-mediated functional responses and abolished channel activation. The action of LPLs on TRPM8 channels involved either changes in the local lipid bilayer tension or interaction with the critical determinant(s) in the transmembrane channel core. Based on this, we propose a novel concept of TRPM8 regulation with the involvement of iPLA(2) stimulation. This mechanism employs chemical rather than physical (temperature change) signaling and thus may be the main regulator of TRPM8 activation in organs not exposed to any essential temperature variations, as in the prostate gland.

Calcium↗
PubMed1984

Suction blister device with regulation of temperature: demonstration of histamine release and temperature change in cold urticaria.

A suction blister device with a sensitive thermometer and with a temperature regulator was constructed. Utilizing this device, it was demonstrated that the cold challenge induces an increase in the skin temperature in cold urticaria patients during the cold challenge and a simultaneous release of histamine into the suction blisters. The skin temperature increases faster after the cold challenge period in cold urticaria patients than in normal control persons. This could be explained by vasodilatation and increased circulation in the skin, following the release of histamine in the cold urticaria reaction.

Cold Temperature↗
PubMed2001

The influence of thermal acclimation on power production during swimming. II. Mechanics of scup red muscle under in vivo conditions.

We have previously shown that the power output of red muscle from warm-acclimated scup is greatly reduced when the fish swim at low temperatures. This reduction occurs primarily because, despite the slowing of muscle relaxation rate at cold temperatures, warm-acclimated scup swim with the same tail-beat frequency and the same stimulation durations, thereby not affording the slower-relaxing muscle any extra time to relax. We hypothesize that power output during swimming could be increased if the stimulus duration were reduced or if the relaxation rate of the red muscle were increased during cold acclimation. Scup were acclimated to 10 degrees C (cold-acclimated) and 20 degrees C (warm-acclimated) for at least 6 weeks. Cold acclimation dramatically increased the ability of scup red muscle to produce power at 10 degrees C. Power output measured from cold-acclimated muscle bundles driven through in vivo conditions measured from cold-acclimated scup swimming at 10 degrees C (i.e. work loops) was generally much greater than that from warm-acclimated muscle driven through its respective in vivo conditions at 10 degrees C. The magnitude of the increase depended both on the anatomical location of the muscle and on swimming speed. Integrated over the length of the fish, the red musculature from cold-acclimated fish generated 2.7, 8.9 and 5.8 times more power than the red musculature from warm-acclimated fish while swimming at 30 cm s(-)(1), 40 cm s(-)(1) and 50 cm s(-)(1), respectively. Our analysis suggests that the cold-acclimated fish should be able to swim in excess of 40 cm s(-)(1) with just their red muscle whereas the warm-acclimated fish must recruit their pink muscle well below this speed. Because the red muscle is more aerobic than the pink muscle, cold acclimation may increase the sustained swimming speed at which scup perform their long seasonal migrations at cool temperatures. We then explored the underlying mechanisms for the increase in muscle power output in cold-acclimated fish. Contrary to our expectations, cold-acclimated muscle did not have a faster relaxation rate; instead, it had an approximately 50 % faster activation rate. Our work-loop studies showed that this faster activation rate, alone, can increase the mechanical power production during cyclical contractions to a surprising extent. By driving cold-acclimated muscle through warm- and cold-acclimated in vivo conditions, we were able to partition the improvement in power production associated with increased activation rate and the approximately 20 % reduction in the duration of electromyographic activity found in the accompanying study. Depending on the position and swimming speed, approximately 60 % of the increase in power output was due to the change in the red muscle's contractile properties (i.e. faster activation); the remainder was due to the shorter stimulus duty cycle of cold-acclimated scup. Thus, by both shortening the in vivo stimulation duration and speeding up the rate of muscle activation as part of cold-acclimation, scup achieve a very large increase in the power output of their red muscle during swimming at low temperature. This increase in power output probably results in an increase in muscle efficiency and, hence, a reduction in the energetic cost of swimming. This increase in power output also reduces reliance on the less aerobic and less fatigue-resistant pink muscle. Both these abilities may increase the swimming speed at which prolonged aerobic muscle activity can occur and thus reduce the travel time for the long seasonal migrations in which scup engage.

Adaptation, Physiological↗
PubMedDate not supplied

Novel method to measure access flow during hemodialysis by ultrasound velocity dilution technique.

This article presents the theory and bench validation of access flow measurement by ultrasound velocity dilution. Reversal of dialysis lines creates a zone of mixing in the vascular access, allowing the use of dilution technique for access flow measurement. The method of sound velocity dilution sensor calibration was analyzed. A single sensor system was investigated for blood circulation and isothermal injections. A dual sensor system was investigated with heated hypertonic saline circulation for both body temperature (isothermal) and room temperature (cold) injections. The accuracy of in vitro access flow measurement was studied on a two pump bench model, dialysis line flow was varied from 200 to 400 ml/min, access flow was varied from 300 to 2500 ml/min. For the dual sensor system, dilution access measurements tracked a gravimetrically calibrated in-line flow sensor within 3.25 +/- 0.34% for isothermal injections, and within 5.81 +/- 0.43% for cold injections. Measurements were repeatable within 3% independent of the temperature of the injected saline. For the single sensor system, results tracked the in-line flow sensor within 3.83 +/- 0.79%. These data show that access flow can be accurately measured by sound velocity dilution technique.

Animals↗
PubMed2004

Sensibility of the abdomen after abdominoplasty.

Abdominal skin hypesthesia may occur after abdominoplasty. The purpose of this study was to find out (1) which sensibility modalities are decreased and (2) which areas of the abdominal wall are affected, so that patients can be warned preoperatively about this condition. Forty patients were divided in two groups of 20 patients each. In the control group, patients had no previous abdominal incisions. The sensibility evaluation of patients from the experimental group was made from 12 to 60 months after abdominoplasty, with an average of 31.5 months. These patients were divided into two groups of 10 patients each, a short-term follow-up group (12 to 30 months postoperatively) and a long-term follow-up group (31 to 60 months postoperatively). The abdominal skin was divided into 12 areas; nine were above the abdominoplasty incision and three were below it. Sensibility to superficial touch, superficial pain, and hot and cold modalities was recorded as positive in all areas by a variable number of patients of the experimental group. However, in area 8 (hypogastric area), a statistically significant number of patients had decreased sensibility in all sensibility modalities (Fisher's test and t test). Patients in the experimental group also showed decreased sensibility to hot and cold temperature in area 11 (pubic area). Sensibility to pressure decreased significantly in all areas of the abdomen when compared with the control group (t test). When patients of the short-term follow-up group were compared with those of the long-term follow-up group, there was no statistically significant difference for all modalities of sensibility in the areas studied, except for area 5. In this area it was found that long-term follow-up patients recovered sensibility to cold and hot temperatures. These findings help plastic surgeons to orient their patients about possible risk of exposure to injuries in the areas with decreased sensibility after abdominoplasty. Most importantly, as these patients have decreased sensibility to pressure and hot temperature in a more extensive area of the abdomen, they are exposed to a higher risk of burn injury.

Abdominal Wall↗
PubMed2001

The influence of thermal acclimation on power production during swimming. I. In vivo stimulation and length change pattern of scup red muscle.

Ectothermal animals are able to locomote in a kinematically similar manner over a wide range of temperatures. It has long been recognized that there can be a significant reduction in the power output of muscle during swimming at low temperatures because of the reduced steady-state (i.e. constant activation and shortening velocity) power-generating capabilities of muscle. However, an additional reduction in power involves the interplay between the non-steady-state contractile properties of the muscles (i.e. the rates of activation and relaxation) and the in vivo stimulation and length change pattern the muscle undergoes during locomotion. In particular, it has been found that isolated scup (Stenotomus chrysops) red muscle working under in vivo stimulus and length change conditions (measured in warm-acclimated scup swimming at low temperatures) generates very little power for swimming. Even though the relaxation of the muscle has slowed greatly, warm-acclimated fish swim with the same tail-beat frequencies and the same stimulus duty cycles at cold temperatures, thereby not affording the slow-relaxing muscle any extra time to relax. We hypothesize that considerable improvement in the power output of the red muscle at low temperatures could be achieved if cold acclimation resulted in either a faster muscle relaxation rate or in the muscle being given more time to relax (e.g. by shortening the stimulus duration or reducing the tail-beat frequency). We test these hypotheses in this paper and the accompanying paper. Scup were acclimated to 10 degrees C (cold-acclimated) and 20 degrees C (warm-acclimated) for at least 6 weeks. Electromyograms (EMGs) and high-speed cine films were taken of fish swimming steadily at 10 degrees C and 20 degrees C. At 10 degrees C, we found that, although there were no differences in tail-beat frequency, muscle strain or stimulation phase between acclimation groups, cold-acclimated scup had EMG duty cycles approximately 20 % shorter than warm-acclimated scup. In contrast at 20 degrees C, there was no difference between acclimation groups in EMG duty cycle, nor in any other muscle length change or stimulation parameter. Thus, in response to cold acclimation, there appears to be a reduction in EMG duty cycle at low swimming temperatures that is probably due to an alteration in the operation of the pattern generator. This novel acclimation probably improves muscle power output at low temperatures compared with that of warm-acclimated fish, an expectation we test in the accompanying paper using the work-loop technique.

Adaptation, Physiological↗
PubMed2001

Interpretation of the finger skin temperature response to cold provocation.

OBJECTIVES: To compare alternative methods of interpreting the response of finger skin temperature (FST) to cold provocation for the detection of the abnormal cold response observed in vibration-induced white finger (VWF). METHOD: The FST response to cold provocation was measured in 36 male subjects: 12 office workers, 12 manual workers and 12 manual workers with symptoms of VWF. The FSTs were monitored continuously on the distal phalanges of all five fingers of a test hand for 2 min before, for 5 min during, and for 10 min following, immersion of the test hand in water at 15 degrees C. Of the fingers investigated, 147 were reported not to exhibit blanching and 33 were reported to exhibit blanching. Twenty-one alternative methods of interpreting the response of FSTs to cold provocation were assessed. These were grouped as: (1) areas above the response profile (i.e. the area above the curve showing the FSTs as a function of time during cooling and recovery), (2) areas below the response profile, (3) absolute temperatures during and following cold provocation, (4) percentage differences in FSTs, (5) the times taken for FSTs to rise by specified amounts and (6) rates of change of FSTs. Differences in the response to cooling between those fingers reported to blanch and the fingers not reported to blanch were tested, and receiver operating characteristics (ROCs) were used to compare the sensitivity and specificity of the various measures to symptoms of VWF. RESULTS: The areas above the response profile, areas below the response profile, percentage FSTs, absolute FSTs and rates of change of FSTs tended to discriminate between healthy and unhealthy subjects on a group basis. However, some of these methods of interpreting the FST response to cold provocation did not show a high sensitivity or specificity to vascular dysfunction on individual fingers. The area above the response profile, the percentage of initial temperature at the fifth minute of recovery and the maximum temperature during the 10-min recovery period, were found to show the highest sensitivity and specificity to symptoms of vascular dysfunction. CONCLUSIONS: The method chosen to interpret the FST response to cold provocation affects the ability of the test to detect an abnormal cold response. The area above the response profile, the percentage of initial temperature at the fifth minute of recovery and the maximum temperature achieved during a 10-min recovery period appear to be the most suitable measures for monitoring vascular function in workers exposed to hand-transmitted vibration. It is suggested that the FST response to cold provocation should be interpreted with respect to the state of initial blood flow.

Adult↗
PubMed2000

A phase model of temperature-dependent mammalian cold receptors.

We present a tractable stochastic phase model of the temperature sensitivity of a mammalian cold receptor. Using simple linear dependencies of the amplitude, frequency, and bias on temperature, the model reproduces the experimentally observed transitions between bursting, beating, and stochastically phase-locked firing patterns. We analyze the model in the deterministic limit and predict, using a Strutt map, the number of spikes per burst for a given temperature. The inclusion of noise produces a variable number of spikes per burst and also extends the dynamic range of the neuron, both of which are analyzed in terms of the Strutt map. Our analysis can be readily applied to other receptors that display various bursting patterns following temperature changes.

Algorithms↗
PubMed1994

THE ONTOGENY OF SHIVERING THERMOGENESIS IN THE RED-WINGED BLACKBIRD (AGELAIUS PHOENICEUS)

The ontogeny of shivering thermogenesis was investigated in the altricial red-winged blackbird (Agelaius phoeniceus). Two indices of heat production &shy; the rate of oxygen consumption (V(dot)O2) of the bird and the electromyographic (EMG) activity of the pectoralis (PECT) and gastrocnemius (GAST) muscles &shy; were measured simultaneously in adult and nestling red-winged blackbirds as they were subjected first to thermoneutral temperatures and subsequently to progressively colder ambient temperatures (Ta). The ontogenetic changes in both indices indicated that the capability for thermogenesis in nestling red-winged blackbirds improved markedly with age. The metabolic rates of 3-day-old nestlings decreased during exposure to gradually falling ambient temperatures; at best, these nestlings were only able to maintain mass-specific V(dot)O2 at levels similar to or slightly above the resting metabolic rate at thermoneutral temperatures (RMR) for a short time before metabolic rates decreased with further cooling. Shivering was detected only in the PECT muscles and was of a relatively low intensity (maximum of sevenfold increase in intensity over basal levels). The 5-day-old nestlings increased mass-specific V(dot)O2 modestly (approximately 1.4-fold) above RMR and attained slightly higher maximal factorial increases in the EMG activity of the PECT (maximum of 18-fold basal levels) when exposed to the same experimental conditions. Shivering was also detected in the GAST muscles of these birds. The most striking improvements in both measures observed during the nestling period occurred between day 5 and day 8. Eight-day-old nestlings increased metabolic rates by approximately 2- to 2.5-fold over basal levels and sustained these elevated rates for longer before becoming hypothermic. Both the PECT and GAST muscles contributed significantly to shivering thermogenesis, and these older nestlings attained much higher factorial increases in the intensity of shivering (up to 72-fold) during exposure to cold temperatures. In addition, both the range and magnitude of the dominant frequencies of muscle activity in the PECT increased during postnatal development. The PECT muscles were a principal site of shivering thermogenesis in all nestling and adult red-winged blackbirds studied here. Shivering in these muscles was a 'first line defense' against cold; the threshold temperature for shivering in the PECT muscles coincided with the lower critical temperature for oxygen consumption (TLC), and the subsequent increases in EMG activity in this muscle with further cooling correlated well with the corresponding increases in mass-specific V(dot)O2.

Journal Article↗
PubMed2006

Cold-active winter rye glucanases with ice-binding capacity.

Extracellular pathogenesis-related proteins, including glucanases, are expressed at cold temperatures in winter rye (Secale cereale) and display antifreeze activity. We have characterized recombinant cold-induced glucanases from winter rye to further examine their roles and contributions to cold tolerance. Both basic beta-1,3-glucanases and an acidic beta-1,3;1,4-glucanase were expressed in Escherichia coli, purified, and assayed for their hydrolytic and antifreeze activities in vitro. All were found to be cold active and to retain partial hydrolytic activity at subzero temperatures (e.g. 14%-35% at -4 degrees C). The two types of glucanases had antifreeze activity as measured by their ability to modify the growth of ice crystals. Structural models for the winter rye beta-1,3-glucanases were developed on which putative ice-binding surfaces (IBSs) were identified. Residues on the putative IBSs were charge conserved for each of the expressed glucanases, with the exception of one beta-1,3-glucanase recovered from nonacclimated winter rye in which a charged amino acid was present on the putative IBS. This protein also had a reduced antifreeze activity relative to the other expressed glucanases. These results support the hypothesis that winter rye glucanases have evolved to inhibit the formation of large, potentially fatal ice crystals, in addition to having enzymatic activity with a potential role in resisting infection by psychrophilic pathogens. Glucanases of winter rye provide an interesting example of protein evolution and adaptation aimed to combat cold and freezing conditions.

Amino Acid Sequence↗
PubMed1998

Fundamental cryobiology of selected African mammalian spermatozoa and its role in biodiversity preservation through the development of genome resource banking.

Fundamental cryobiological characteristics of spermatozoa from threatened or endangered species must be determined for successful cryopreservation techniques to be established. In this study, spermatozoa from four diverse species, impala (Aepyceros melampus), wart hog (Phacochoerus aethiopicus), elephant (Loxodonta africana), and lion (Panthera leo), were collected by electroejaculation or epididymal aspiration. Spermatozoal plasma membrane permeability to water (hydraulic conductivity, Lp) and the osmotically inactive fraction of the sperm cell (Vb) were determined from each species. Changes in cell volume were measured over time using an electronic particle counter. A Kedem-Katchalsky membrane transport model was used to theoretically characterize the data to determine Lp and Vb for each species. In addition to determining plasma membrane characteristics, spermatozoa were also studied to determine their sensitivity to low temperatures and to permeating cryoprotectant solutes. Cells maintained at room temperature (20-22 degrees C) were slowly or rapidly exposed to cold temperatures (1-4 degrees C), and percent motility was estimated to determine the sensitivity of the cells to cooling. Spermatozoa were also in media containing 1 M glycerol, dimethyl sulfoxide or ethylene glycol, and percent motility was measured at 15, 30 and 60 min intervals to determine the sensitivity of the cells to the cryoprotectant agent over time. Results indicate that sperm motility is significantly effected by decreased temperatures and the presence of cryoprotectant agents.

Animals↗
PubMed1988

Embryonic temperature determines adult sexuality in a reptile.

Gonadal differentiation in amniote vertebrates is controlled by one of two mechanisms: genotypic sex determination (GSD) or environmental sex determination (ESD). After differentiation the fetal gonad produces sex steroid hormones which govern the development of other components of sexuality. Thus, the primary sex determiner is thought to operate solely as a trigger that initiates a cascade of events culminating in adult sex differences. In the leopard gecko (Eublepharis macularius), gonadal and morphological sex is determined by incubation temperature, with relatively 'hot' temperatures (32 degrees C) resulting in mostly male offspring and relatively 'cold' temperatures (26 degrees C) resulting in only female offspring. We report here that the reproductive behaviour and endocrine physiology of an adult is influenced by the temperature experienced as an embryo. Also, the perception of a female to courtship by a male is influenced by incubation temperature. These data indicate that incubation temperature, the primary determiner of sex in this species, has differential effects on adult sexuality.

Animals↗
PubMed1999

Hypothermia: a natural cause of death.

Deaths due to hypothermia are usually accidental and are the result of exposure to extreme environmental temperatures. Often these individuals are intoxicated, elderly, or exposed to severe cold temperatures. We report the case of a blind, nonambulatory, elderly man who was found alive in his home in an unresponsive state. Core body temperature at hospital was 24 degrees C (75 degrees F). At autopsy, punctate hemorrhages were present in the stomach mucosa. A 4- x 7-cm pituitary adenoma extended from a dilated sella turcica, obliterated the optic chiasm, and compressed the base of the brain in the region of the hypothalamus. Compression in this region of the brain would disrupt the temperature regulatory function of the hypothalamus and create an individual who would be susceptible to minor fluctuations in ambient temperature. The manner of death was designated as natural. This is an unusual presentation of a pituitary adenoma in the current era of advanced imaging techniques in which microadenomas are often detected and treated.

Adenoma↗
PubMed1993

Isolation and characterization of hydroxylamine-induced mutations in the Erwinia herbicola ice nucleation gene that selectively reduce warm temperature ice nucleation activity.

Cells of ice nucleation active bacterial species catalyse ice formation over the temperature range of -2 to -12 degrees C. Current models of ice nucleus structure associate the size of ice nucleation protein aggregates with the temperature at which they catalyse ice formation. To better define the structural features of ice nucleation proteins responsible for the functional heterogeneity of ice nuclei within a genetically homogeneous collection of cells we used in vitro chemical mutagenesis to isolate mutants with reduced ability to nucleate ice at warm assay temperatures but which retain normal or near normal nucleation activity at cold temperatures (WIND, i.e. warm ice nucleus-deficient mutants). Nearly half of the mutants obtained after hydroxylamine mutagenesis of the iceE gene from Erwinia herbicola had this phenotype. The phenotypes and location of lesions on the genetic map of iceE were determined for a number of mutants. All WIND mutations were restricted to the portion of iceE encoding the repetitive region of the polypeptide. DNA sequencing of two WIND mutants revealed single nucleotide substitutions changing a conserved serine or glycine residue to phenylalanine and serine, respectively. The implications of these findings in structure/function models for the ice nucleation protein are discussed.

Amino Acid Sequence↗
PubMed2006

Performance of three systems for warming intravenous fluids at different flow rates.

This study compared the intravenous fluid warming capabilities of three systems at different flow rates. The devices studied were a water-bath warmer, a dry-heat plate warmer, and an intravenous fluid tube warmer Ambient temperature was controlled at 22 degrees to 24 degrees C. Normal saline (0.9% NaCl) at either room temperature (21 degrees to 23 degrees C) or at ice-cold temperature (3 degrees to 5 degrees C) was administered through each device at a range of flow rates (2 to 100 ml/min). To mimic clinical conditions, the temperature of the fluid was measured with thermocouples at the end of a one metre tube connected to the outflow of the warmer for the first two devices and at the end of the 1.2 m warming tubing for the intravenous fluid tube warmer The temperature of fluid delivered by the water bath warmer increased as the flow rate was increased up to 15 to 20 ml/min but decreased with greater flow rates. The temperature of the fluid delivered by the dry-heat plate warmer significantly increased as the flow rate was increased within the range tested (due to decreased cooling after leaving the device at higher flow rates). The temperature of fluid delivered by the intravenous fluid tube warmer did not depend on the flow rate up to 20 ml/min but significantly and fluid temperature-dependently decreased at higher flow rates (>30 ml/min). Under the conditions of our testing, the dry heat plate warmer delivered the highest temperature fluid at high flow rates.

Anesthetics, Intravenous↗