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Heat Production (heat + production)

Distribution by Scientific Domains

Life Sciences	54%
Earth and Environmental Science	21%
Medical Sciences	12%
4 Other Domains	13%

Kinds of Heat Production

metabolic heat production

Selected Abstracts

Metabolic Heat Production, Heat Loss and the Circadian Rhythm of Body Temperature in the Rat

EXPERIMENTAL PHYSIOLOGY, Issue 3 2003
Roberto Refinetti
Metabolic heat production (calculated from oxygen consumption), dry heat loss (measured in a calorimeter) and body temperature (measured by telemetry) were recorded simultaneously at 6 min intervals over five consecutive days in rats maintained in constant darkness. Robust circadian rhythmicity (confirmed by chi square periodogram analysis) was observed in all three variables. The rhythm of heat production was phase-advanced by about half an hour in relation to the body temperature rhythm, whereas the rhythm of heat loss was phase-delayed by about half an hour. The balance of heat production and heat loss exhibited a daily oscillation 180 deg out of phase with the oscillation in body temperature. Computations indicated that the amount of heat associated with the generation of the body temperature rhythm (1.6 kJ) corresponds to less than 1% of the total daily energy budget (172 kJ) in this species. Because of the small magnitude of the fraction of heat balance associated with the body temperature rhythm, it is likely that the daily oscillation in heat balance has a very slow effect on body temperature, thus accounting for the 180 deg phase difference between the rhythms of heat balance and body temperature. [source]

Adenosine A3 receptors regulate heart rate, motor activity and body temperature

ACTA PHYSIOLOGICA, Issue 2 2010
J. N. Yang
Abstract Aim:, To examine the phenotype of mice that lack the adenosine A3 receptor (A3R). Methods:, We examined the heart rate, body temperature and locomotion continuously by telemetry over several days. In addition, the effect of the adenosine analogue R- N6 -phenylisopropyl-adenosine (R-PIA) was examined. We also examined heat production and food intake. Results:, We found that the marked diurnal variation in activity, heart rate and body temperature, with markedly higher values at night than during day time, was reduced in the A3R knock-out mice. Surprisingly, the reduction in heart rate, activity and body temperature seen after injection of R-PIA in wild type mice was virtually eliminated in the A3R knock-out mice. The marked reduction in activity was associated with a decreased heat production, as expected. However, the A3R knock-out mice, surprisingly, had a higher food intake but no difference in body weight compared to wild type mice. Conclusions:, The mice lacking adenosine A3 receptors exhibit a surprisingly clear phenotype with changes in diurnal rhythm and temperature regulation. Whether these effects are due to a physiological role of A3 receptors in these processes or whether they represent a role in development remains to be elucidated. [source]

Increased coronary sinus blood temperature: correlation with systemic inflammation

EUROPEAN JOURNAL OF CLINICAL INVESTIGATION, Issue 4 2006
K. Toutouzas
Abstract Background, Recent studies have shown that patients with single vessel coronary artery disease (CAD) suffering from acute coronary syndromes (ACS) have increased coronary sinus (CS) blood temperature compared with the right atrium (RA). The aim of this study was to investigate whether there is a correlation between systemic inflammatory indexes and CS temperature and whether there is a difference in CS temperature between patients with single vs. multivessel disease. Materials and methods, We included consecutive patients scheduled for coronary angiography for recent-onset chest pain evaluation. We measured C-reactive protein (CRP) levels in the study population. Coronary sinus and RA blood temperature measurements were performed by a 7F thermography catheter. ,, was calculated by subtracting the RA from the CS blood temperature. Results, The study population comprised 53 patients with ACS, 25 patients with stable angina (SA) and 22 subjects without CAD (control group). ,, was greater in patients with ACS and with SA compared with the control group (0·22 ± 0·10 °C, 0·18 ± 0·04 °C vs. 0·14 ± 0·07 °C, P < 0·01 for both comparisons). The ACS group had greater ,, compared with the SA group, although the difference did not reach statistical significance (P = 0·09). Eighteen (39·1%) out of 46 patients with multivessel disease had three-vessel disease and 28 (60·8%) had two-vessel disease. ,, between patients with multivessel and single vessel disease was similar (0·22 ± 0·01 °C, 0·19 ± 0·01 °C, P = 0·17). The levels of CRP were well correlated with ,, (R = 0·35b, P < 0·01). Conclusions, Systemic inflammation is well correlated with CS temperature; thus, an inflammatory process could be the underlying mechanism for increased heat production from the myocardium. [source]

Central control of thermogenesis in mammals

EXPERIMENTAL PHYSIOLOGY, Issue 7 2008
Shaun F. Morrison
Thermogenesis, the production of heat energy, is an essential component of the homeostatic repertoire to maintain body temperature in mammals and birds during the challenge of low environmental temperature and plays a key role in elevating body temperature during the febrile response to infection. The primary sources of neurally regulated metabolic heat production are mitochondrial oxidation in brown adipose tissue, increases in heart rate and shivering in skeletal muscle. Thermogenesis is regulated in each of these tissues by parallel networks in the central nervous system, which respond to feedforward afferent signals from cutaneous and core body thermoreceptors and to feedback signals from brain thermosensitive neurons to activate the appropriate sympathetic and somatic efferents. This review summarizes the research leading to a model of the feedforward reflex pathway through which environmental cold stimulates thermogenesis and discusses the influence on this thermoregulatory network of the pyrogenic mediator, prostaglandin E2, to increase body temperature. The cold thermal afferent circuit from cutaneous thermal receptors ascends via second-order thermosensory neurons in the dorsal horn of the spinal cord to activate neurons in the lateral parabrachial nucleus, which drive GABAergic interneurons in the preoptic area to inhibit warm-sensitive, inhibitory output neurons of the preoptic area. The resulting disinhibition of thermogenesis-promoting neurons in the dorsomedial hypothalamus and possibly of sympathetic and somatic premotor neurons in the rostral ventromedial medulla, including the raphe pallidus, activates excitatory inputs to spinal sympathetic and somatic motor circuits to drive thermogenesis. [source]

Metabolic Heat Production, Heat Loss and the Circadian Rhythm of Body Temperature in the Rat

Cold-Induced Recruitment of Brown Adipose Tissue Thermogenesis

EXPERIMENTAL PHYSIOLOGY, Issue 1 2003
Martin Klingenspor
Non-shivering thermogenesis in brown adipose tissue is the main mechanism for thermoregulatory heat production in small mammals and newborns. During cold acclimation the sympathetic innervation triggers the recruitment of brown adipose tissue by hyperplasia, which involves the proliferation and differentiation of precursor cells, and by hypertrophy of mature brown adipocytes. Mitochondrial biogenesis and increased synthesis of the uncoupling protein 1 (UCP-1) are hallmarks of the thermogenic recruitment process. The severalfold increase of mitochondrial protein content during cold acclimation recruits a large capacity for oxidative phosphorylation. However, UCP-1 increases proton leakage across the inner membrane of brown adipocyte mitochondria and thereby dissipates proton motive force as heat instead of ATP synthesis. During recent years considerable progress has been achieved in the analysis of transcriptional mechanisms controlling Ucp1 gene expression. However, so far only little is known about the molecular basis of cold-induced mitochondrial biogenesis in brown adipose tissue. [source]

A Generalized System for Photoresponsive Membrane Rupture in Polymersomes

ADVANCED FUNCTIONAL MATERIALS, Issue 16 2010
Neha P. Kamat
Abstract Polymersomes are vesicles whose membranes comprise self-assembled block copolymers. It has recently been shown that co-encapsulating conjugated multiporphyrin dyes in a polymersome membrane with ferritin protein in the aqueous lumen confers photolability to the polymersome. In the present study, the photolability is shown to be extendable to vesicles containing dextran, an inert and inexpensive polysaccharide, as the luminal solute. How structural features of the polymersome/porphyrin/dextran composite affect its photoresponse is explored. Increasing dextran molecular weight, decreasing block copolymer molecular weight, and altering fluorophore-membrane interactions results in increasing the photoresponsiveness of the polymersomes. Amphiphilic interactions of the luminal encapsulant with the membrane coupled with localized heat production in the hydrophobic bilayer likely cause differential thermal expansion in the membrane and the subsequent membrane rupture. This study suggests a general approach to impart photoresponsiveness to any biomimetic vesicle system without chemical modification, as well as a simple, bio-inert method for constructing photosensitive carriers for controlled release of encapsulants. [source]

Horizontal and vertical movements of juvenile bluefin tuna (Thunnus orientalis) in relation to seasons and oceanographic conditions in the eastern Pacific Ocean

FISHERIES OCEANOGRAPHY, Issue 5 2007
TAKASHI KITAGAWA
Abstract Electronically tagged juvenile Pacific bluefin, Thunnus orientalis, were released off Baja California in the summer of 2002. Time-series data were analyzed for 18 fish that provided a record of 380 ± 120 days (mean ± SD) of ambient water and peritoneal cavity temperatures at 120 s intervals. Geolocations of tagged fish were estimated based on light-based longitude and sea surface temperature-based latitude algorithms. The horizontal and vertical movement patterns of Pacific bluefin were examined in relation to oceanographic conditions and the occurrence of feeding events inferred from thermal fluctuations in the peritoneal cavity. In summer, fish were located primarily in the Southern California Bight and over the continental shelf of Baja California, where juvenile Pacific bluefin use the top of the water column, undertaking occasional, brief forays to depths below the thermocline. In autumn, bluefin migrated north to the waters off the Central California coast when thermal fronts form as the result of weakened equatorward wind stress. An examination of ambient and peritoneal temperatures revealed that bluefin tuna fed during this period along the frontal boundaries. In mid-winter, the bluefin returned to the Southern California Bight possibly because of strong downwelling and depletion of prey species off the Central California waters. The elevation of the mean peritoneal cavity temperature above the mean ambient water temperature increased as ambient water temperature decreased. The ability of juvenile bluefin tuna to maintain a thermal excess of 10°C occurred at ambient temperatures of 11,14°C when the fish were off the Central California coast. This suggests that the bluefin maintain peritoneal temperature by increasing heat conservation and possibly by increasing internal heat production when in cooler waters. For all of the Pacific bluefin tuna, there was a significant correlation between their mean nighttime depth and the visible disk area of the moon. [source]

Thermogenesis and respiration of inflorescences of the dead horse arum Helicodiceros muscivorus, a pseudo-thermoregulatory aroid associated with fly pollination

FUNCTIONAL ECOLOGY, Issue 6 2003
R. S. Seymour
Summary 1In central Corsica, Helicodiceros muscivorus (Schott ex. K. Koch) produces a protogynous inflorescence that resembles the anal area of a dead mammal and produces a foetid scent during the few hours after sunrise. Flies enter the floral chamber, pollinate the female florets and become trapped until the next morning, when pollen is shed from the male florets and the flies are released. 2The exposed appendix exhibits a strong, unimodal episode of thermogenesis associated with scent production, reaching a maximum of 30 °C at 15 °C ambient temperature. The male florets in the floral chamber are highly thermogenic throughout the second night and generally maintain stable floret temperatures of about 24 °C at ambient temperatures down to 13 °C. 3Maximum respiration rates of the appendix (0·45 µmol CO2 s,1 g,1) and the male florets (0·82 µmol s,1 g,1) may be the highest recorded for plant tissue. 4Thermogenesis of the appendix does not depend on ambient temperature, but that of the male florets increases with decreasing ambient temperature in most cases. However, the pattern of heat production by the males appears related more to time than to ambient temperature, hence the term ,pseudo-thermoregulation'. 5The behaviour and thoracic temperatures of flies emerging from captivity suggests that male floral warming does not enhance their activity. [source]

Numerical simulation of thermal runaway phenomena in silicon semiconductor devices

HEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 6 2002
Kazanori Shioda
Abstract A mathematical model for heat production due to thermal excitation of conductive electrons and positive holes in a semiconductor pn junction is derived and discussed. The model is applied to simulate the thermal runaway phenomena in power electronics semiconductor devices. Our discussion focuses especially on the modeling of unexpected huge currents due to an excessive temperature increase. Calculated dynamics of temperature distributions of a silicon wafer while cooling performance decreases proved it is possible for a silicon wafer to be heated over its melting point in a few milliseconds. Our results indicate that if a local hot spot arises in a wafer, the thermal intrinsic excitation carries an increased diffusion current of minor carriers and a recombination current in the depletion layer of a pn junction. Also it appears to be important that cooling performance should be uniform on the wafer to avoid the growth of hot spots and thermal-runaway itself. © 2002 Wiley Periodicals, Inc. Heat Trans Asian Res, 31(6): 438,455, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.10044 [source]

Metabolic phenotyping of mouse mutants in the German Mouse Clinic

INTEGRATIVE ZOOLOGY (ELECTRONIC), Issue 3 2006
Ralf ELVERT
Abstract The German Mouse Clinic was established as a phenotyping center to provide the scientific community with systematic standardized phenotyping of mouse models from various genetic backgrounds. We found metabolic phenotypes in nine out of 20 mutant lines screened in a primary screen. Based on these findings, the mutants were analyzed in secondary and tertiary screens. Mice of a sample mutant line, isolated from the ENU-screen at the National Research Center for Environment and Health in Munich, were found to have lower body weight, consume less food, but have higher ratios of metabolized energy per unit body weight compared with their wild-type littermates. Basal metabolic rate and heat production were simultaneously increased by 16,18%, whereas body fat content was reduced by 11,16%. The combination of various parameters of energy consumption, expenditure and energy storage illustrate the metabolic demands of the sample mutant mouse line and demonstrate the utility of the powerful phenotyping tool used at the German Mouse Clinic. [source]

Diurnal rhythm in heat production and oxidation of carbohydrate and fat in pigs during feeding, starvation and re-feeding

JOURNAL OF ANIMAL PHYSIOLOGY AND NUTRITION, Issue 7-8 2004
A. Chwalibog
Summary Diurnal rhythm in heat production (HE), oxidation of carbohydrate (OXCHO) and fat (OXF) was calculated from daily measurements of gas exchange in 12 pigs [20,40 kg live weight, (LW)] during 6 days of near ad libitum feeding, followed by 4 days of starvation and 4 days of re-feeding. All measurements, divided in five times intervals from 12.00 to 8.00, showed the highest values of HE, reflecting the animals' energy requirements, between 12.00 and 16.00 gradually declining to the lowest values between 4.00 and 8.00. The values measured in the interval 4.00,8.00 were considered as a basal metabolic rate (BMR), being in all measurements 25% lower than during 12.00,4.00. The lowest BMR was measured on the fourth day of starvation (21.7 kJ/h·kg0.75). By transition from feeding to starvation, OXCHO declined gradually, but was for 16 h able to cover the energy requirement with no contribution from OXF. The decline in OXCHO proceeded for 40 h and reached zero between 4.00 and 8.00 on the first day of starvation with the energy requirement being covered by OXF. The HE during starvation was 25,30% lower than during feeding caused by absence of feed-induced thermogenesis and by the transition from OXCHO to OXF. Immediately after re-feeding dietary carbohydrates were oxidized, however, there was still a substantial OXF, proceeding until the next feeding. From the second day of re-feeding the contribution of substrates to the total HE was re-established with no OXF and the same level of HE as during feeding. [source]

Energy metabolism in young pigs as affected by establishment of new groups prior to transport

JOURNAL OF ANIMAL PHYSIOLOGY AND NUTRITION, Issue 5-6 2002
M. J. W. HEETKAMP
Energy metabolism was studied in 9-week-old-pigs as affected by mixing just before transport. In each of three trials, two groups of 20 pigs (two litters of 10) were randomly assigned to one of two treatments: control and mixing. Each group was housed in one of two climatic chambers with each subgroup in one of two pens. In each trial, the two litters within the mixing treatment were mixed, just before transport, at the start of a 2-week experimental period. In the control treatment, the social structure of both litters in each trial was not altered. In both treatments, large alterations of energy partitioning from week 1 to week 2, are probably signs of recovering from transportation and/or adaptation to new feeding and housing conditions. Mixing just before transport did not change total energy metabolism but only increased nonactivity-related heat production by 3.1% for the total experimental period. Most likely, long-term performance is also not affected negatively by mixing. Animals seem to be able to change energy expenditure on activity when more energy is required for other physiological processes. This symptom of possible reallocation of energy between different vital live processes (e.g. behavior, protein turn-over) might be one of the first indications of an impaired well-being. [source]

The role of viscous heating in Barrovian metamorphism of collisional orogens: thermomechanical models and application to the Lepontine Dome in the Central Alps

JOURNAL OF METAMORPHIC GEOLOGY, Issue 2 2005
J.-P. BURG
Abstract Thermal models for Barrovian metamorphism driven by doubling the thickness of the radiogenic crust typically meet difficulty in accounting for the observed peak metamorphic temperature conditions. This difficulty suggests that there is an additional component in the thermal budget of many collisional orogens. Theoretical and geological considerations suggest that viscous heating is a cumulative process that may explain the heat deficit in collision orogens. The results of 2D numerical modelling of continental collision involving subduction of the lithospheric mantle demonstrate that geologically plausible stresses and strain rates may result in orogen-scale viscous heat production of 0.1 to >1 ,W m,3, which is comparable to or even exceeds bulk radiogenic heat production within the crust. Thermally induced buoyancy is responsible for crustal upwelling in large domes with metamorphic temperatures up to 200 °C higher than regional background temperatures. Heat is mostly generated within the uppermost mantle, because of large stresses in the highly viscous rocks deforming there. This thermal energy may be transferred to the overlying crust either in the form of enhanced heat flow, or through magmatism that brings heat into the crust advectively. The amplitude of orogenic heating varies with time, with both the amplitude and time-span depending strongly on the coupling between heat production, viscosity and collision strain rate. It is argued that geologically relevant figures are applicable to metamorphic domes such as the Lepontine Dome in the Central Alps. We conclude that deformation-generated viscous dissipation is an important heat source during collisional orogeny and that high metamorphic temperatures as in Barrovian type metamorphism are inherent to deforming crustal regions. [source]

Interaction of metamorphism, deformation and exhumation in large convergent orogens

JOURNAL OF METAMORPHIC GEOLOGY, Issue 1 2002
R. A. Jamieson
Abstract Coupled thermal-mechanical models are used to investigate interactions between metamorphism, deformation and exhumation in large convergent orogens, and the implications of coupling and feedback between these processes for observed structural and metamorphic styles. The models involve subduction of suborogenic mantle lithosphere, large amounts of convergence (, 450 km) at 1 cm yr,1, and a slope-dependent erosion rate. The model crust is layered with respect to thermal and rheological properties , the upper crust (0,20 km) follows a wet quartzite flow law, with heat production of 2.0 ,W m,3, and the lower crust (20,35 km) follows a modified dry diabase flow law, with heat production of 0.75 ,W m,3. After 45 Myr, the model orogens develop crustal thicknesses of the order of 60 km, with lower crustal temperatures in excess of 700 °C. In some models, an additional increment of weakening is introduced so that the effective viscosity decreases to 1019 Pa.s at 700 °C in the upper crust and 900 °C in the lower crust. In these models, a narrow zone of outward channel flow develops at the base of the weak upper crustal layer where T,600 °C. The channel flow zone is characterised by a reversal in velocity direction on the pro-side of the system, and is driven by a depth-dependent pressure gradient that is facilitated by the development of a temperature-dependent low viscosity horizon in the mid-crust. Different exhumation styles produce contrasting effects on models with channel flow zones. Post-convergent crustal extension leads to thinning in the orogenic core and a corresponding zone of shortening and thrust-related exhumation on the flanks. Velocities in the pro-side channel flow zone are enhanced but the channel itself is not exhumed. In contrast, exhumation resulting from erosion that is focused on the pro-side flank of the plateau leads to ,ductile extrusion' of the channel flow zone. The exhumed channel displays apparent normal-sense offset at its upper boundary, reverse-sense offset at its lower boundary, and an ,inverted' metamorphic sequence across the zone. The different styles of exhumation produce contrasting peak grade profiles across the model surfaces. However, P,T,t paths in both cases are loops where Pmax precedes Tmax, typical of regional metamorphism; individual paths are not diagnostic of either the thickening or the exhumation mechanism. Possible natural examples of the channel flow zones produced in these models include the Main Central Thrust zone of the Himalayas and the Muskoka domain of the western Grenville orogen. [source]

Frost boils and soil ice content: field observations

PERMAFROST AND PERIGLACIAL PROCESSES, Issue 4 2006
P. P. Overduin
Abstract Our aim is to measure and explain the seasonal changes in soil ice content in the frost boils of Galbraith Lake, Alaska. Instruments were installed in a frost boil to monitor the ground surface position and soil state over a period of 4 years. By comparing the subsidence and thaw rates, we calculate the soil ice content as a function of depth. Measured soil temperatures, liquid water contents and bulk apparent thermal conductivities are used to estimate latent heat production and release in the soil. The frost boil heaves during freezing and settles during thaw while the surrounding tundra heaves negligibly, but subsides measurably. Despite large changes in freezing rates from year to year, total heave and its distribution across the frost boil are similar between years. Winter air temperature and snow depth influence the freezing rate and ice distribution as a function of depth, but not the overall heave. This suggests that heave is controlled by water availability rather than the rate of heat removal from the soil. Areal ground subsidence rates between 2 and 5,cm/yr are due to the disappearance of ice at the base of the active layer, raising the possibility of ongoing thermokarst expansion around Galbraith Lake. Copyright © 2006 John Wiley & Sons, Ltd. [source]

Is the efficiency of mammalian (mouse) skeletal muscle temperature dependent?

THE JOURNAL OF PHYSIOLOGY, Issue 19 2010
C. J. Barclay
Myosin crossbridges in muscle convert chemical energy into mechanical energy. Reported values for crossbridge efficiency in human muscles are high compared to values measured in vitro using muscles of other mammalian species. Most in vitro muscle experiments have been performed at temperatures lower than mammalian physiological temperature, raising the possibility that human efficiency values are higher than those of isolated preparations because efficiency is temperature dependent. The aim of this study was to determine the effect of temperature on the efficiency of isolated mammalian (mouse) muscle. Measurements were made of the power output and heat production of bundles of muscle fibres from the fast-twitch extensor digitorum longus (EDL) and slow-twitch soleus muscles during isovelocity shortening. Mechanical efficiency was defined as the ratio of power output to rate of enthalpy output, where rate of enthalpy output was the sum of the power output and rate of heat output. Experiments were performed at 20, 25 and 30°C. Maximum efficiency of EDL muscles was independent of temperature; the highest value was 0.31 ± 0.01 (n= 5) at 30°C. Maximum efficiency of soleus preparations was slightly but significantly higher at 25 and 30°C than at 20°C; the maximum mean value was 0.48 ± 0.02 (n= 7) at 25°C. It was concluded that maximum mechanical efficiency of isolated mouse muscle was little affected by temperature between 20 and 30°C and that it is unlikely that differences in temperature account for the relatively high efficiency of human muscle in vivo compared to isolated mammalian muscles. [source]

High temperature does not alter fatigability in intact mouse skeletal muscle fibres

THE JOURNAL OF PHYSIOLOGY, Issue 19 2009
Nicolas Place
Intense activation of skeletal muscle results in fatigue development, which involves impaired function of the muscle cells resulting in weaker and slower contractions. Intense muscle activity also results in increased heat production and muscle temperature may rise by up to ,6°C. Hyperthermia is associated with impaired exercise performance in vivo and recent studies have shown contractile dysfunction and premature fatigue development in easily fatigued muscle fibres stimulated at high temperatures and these defects were attributed to oxidative stress. Here we studied whether fatigue-resistant soleus fibres stimulated at increased temperature show premature fatigue development and whether increasing the level of oxidative stress accelerates fatigue development. Intact single fibres or small bundles of soleus fibres were fatigued by 600 ms tetani given at 2 s intervals at 37°C and 43°C, which is the highest temperature the muscle would experience in vivo. Tetanic force in the unfatigued state was not significantly different at the two temperatures. With 100 fatiguing tetani, force decreased by ,15% at both temperatures; the free cytosolic [Ca2+] (assessed with indo-1) showed a similar ,10% decrease at both temperatures. The oxidative stress during fatigue at 43°C was increased by application of 10 ,m hydrogen peroxide or tert-butyl hydroperoxide and this did not cause premature fatigue development. In summary, fatigue-resistant muscle fibres do not display impaired contractility and fatigue resistance at the highest temperature that mammals, including humans, would experience in vivo. Thus, intrinsic defects in fatigue-resistant muscle fibres cannot explain the decreased physical performance at high temperatures. [source]

Electromechanical reshaping of septal cartilage,,

THE LARYNGOSCOPE, Issue 11 2003
Ki-Hong Kevin Ho BS
Abstract Objectives: This study describes the process of tissue electroforming and how shape changes in cartilage can be produced by the application of direct current (DC). The dependence of shape change on voltage and application time is explored. Study Design: Basic investigation using ex vivo porcine septal cartilage grafts and electromechanical cartilage deformation focused on development of a new surgical technique. Methods: Uniform flat porcine nasal septal cartilage specimens were mechanically deformed between two semicircular aluminum electrodes. DC current was applied to establish charge separation and electrical streaming potential. Voltage (0,3.5 V) and application time (0,5 minutes) were varied. Shape change was measured, and shape retention was calculated using analytic representation. The effect of the direction of applied current on shape change was evaluated by switching the polarities of electrodes and using parameters of 0 to 5.5 V and 5 minutes. Temperature during reshaping was monitored with a thermocouple, and surface features were evaluated using light microscopy. Results: Reshaped specimen demonstrated mechanical stability similar to native cartilage tissue. Shape retention strongly correlated with increasing voltage and application time. Only a small current (<0.1 A) through the tissue was measured. Temperature change was less than 2°C during electroforming, suggesting that electroforming likely results from some nonthermal mechanisms. Surface features indicated that electrodeposition may occur depending on electrode material and magnitude of the applied voltage. Conclusions: These findings demonstrate that cartilage can be reshaped through the process we have described as "electroforming" by generating intrinsic differences in charge separation with negligible heat production. [source]

Productivity and energy partition of late lactation dairy cows during heat exposure

ANIMAL SCIENCE JOURNAL, Issue 1 2010
Kyoung Hoon KIM
ABSTRACT Three late-lactation Holstein cows were used to determine the effects of environmental temperature on performance and energy partitioning. Each cow was housed in a respiratory chamber for 30 consecutive days and exposed to three different conditions of environmental temperature: (i) 20°C and 20°C (20°C), (ii) 25°C and 20°C (25°C), (iii) 30°C and 25°C (30°C) during the day and night, respectively. The temperature was switched in an interval of 10 days. Humidity in the chamber was maintained at 55,65% through the entire experimental period. The daily mean as well as morning and evening rectal temperatures of Holstein cows increased linearly (P < 0.05) as chamber temperature increased. There was a significant linear reduction in dry matter (DM) intake (P < 0.05) and an increase in DM digestibility (P < 0.05). The response in milk yield, however, was not affected by heat stress. There were no significant differences among treatments for intake energy, heat production, net energy for lactation and net energy for gain. This results of this study disagreed with the assumption that late lactation cows gave priority to increasing body tissue at the expense of milk production under thermal stress. [source]

Substrate oxidation and retention in pigs and poultry

ANIMAL SCIENCE JOURNAL, Issue 2 2002
André CHWALIBOG
ABSTRACT A model combining data from gas exchange measurements with nutrient balances, demonstrating energy transfer between the pools of protein, carbohydrate and fat and their partition in the body, is described. Data from energy metabolism experiments with growing pigs and laying hens is incorporated into the model in order to illustrate methods of calculations and interpretations of the model. The experiments with pigs were carried out with growing pigs (20,100 kg) measured alternately on high (ad libitum) and low (near maintenance) feed levels on diets with low or high fat concentration. When energy intake from digested carbohydrate covered the requirements for growth, heat from oxidation of carbohydrate contributed 85,90% to the total heat production, while there was no net oxidation of fat. When the intake of digested carbohydrate was not sufficient to cover requirements, fat was mobilized from the body and oxidized. Energy from oxidation of carbohydrate was in all measurements below the energy in the carbohydrate pool, indicating transfer of energy from carbohydrate to fat metabolism in the process of de novo lipogeneis. The experiments with hens were carried out with 62 hens during the laying period from 26 to 47 weeks of age. The hens originated from two strains (A and B); they were kept in battery cages either individually or 3 hens/cage and fed ad libitum with an identical commercial diet. The partition of the protein pool between oxidation and retention was not influenced by the housing system. However, the genetic origin of hens effected protein utilization with relatively lower oxidation and higher retention in Strain B. The main part of the carbohydrate pool was oxidized (45,60%), but the hens kept individually oxidized more carbohydrate than those kept 3 hens/cage. Further, there were significant differences between the strains. Generally, about half of the fat pool originated from de novo lipogenesis from carbohydrate, indicating the importance of this process for fat retention in eggs. Fat oxidation depended on the energy supply from carbohydrate, hence with higher use of carbohydrate for oxidation in Strain B less fat was oxidized and more was used for fat synthesis. The presented results indicate that by combining results from gas exchange measurements with nitrogen and energy balances it is possible to evaluate the contribution of nutrients to the oxidative processes and the energy transfer between substrate pools. [source]

Partial-body exposure of human volunteers to 2450,MHz pulsed or CW fields provokes similar thermoregulatory responses,

BIOELECTROMAGNETICS, Issue 4 2001
Eleanor R. Adair
Abstract Many reports describe data showing that continuous wave (CW) and pulsed (PW) radiofrequency (RF) fields, at the same frequency and average power density (PD), yield similar response changes in the exposed organism. During whole-body exposure of squirrel monkeys at 2450 MHz CW and PW fields, heat production and heat loss responses were nearly identical. To explore this question in humans, we exposed two different groups of volunteers to 2450,MHz CW (two females, five males) and PW (65,,s pulse width, 104,pps; three females, three males) RF fields. We measured thermophysiological responses of heat production and heat loss (esophageal and six skin temperatures, metabolic heat production, local skin blood flow, and local sweat rate) under a standardized protocol (30,min baseline, 45,min RF or sham exposure, 10,min baseline), conducted in three ambient temperatures (Ta,=,24, 28, and 31°C). At each Ta, average PDs studied were 0, 27, and 35,mW/cm2 (Specific absorption rate (SAR),=,0, 5.94, and 7.7,W/kg). Mean data for each group showed minimal changes in core temperature and metabolic heat production for all test conditions and no reliable differences between CW and PW exposure. Local skin temperatures showed similar trends for CW and PW exposure that were PD-dependent; only the skin temperature of the upper back (facing the antenna) showed a reliably greater increase (P,=,.005) during PW exposure than during CW exposure. Local sweat rate and skin blood flow were both Ta - and PD-dependent and showed greater variability than other measures between CW and PW exposures; this variability was attributable primarily to the characteristics of the two subject groups. With one noted exception, no clear evidence for a differential response to CW and PW fields was found. Bioelectromagnetics 22:246,259, 2001. © 2001 Wiley-Liss, Inc. [source]

Crustal Composition of China Continent Constrained from Heat Flow Data and Helium Isotope Ratio of Underground Fluid

ACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 1 2010
Yang WANG
Abstract: Based on conservation of energy principle and heat flow data in China continent, the upper limit of 1.3 ,W/m3 heat production is obtained for continental crust in China. Furthermore, using the data of heat flow and helium isotope ratio of underground fluid, the heat productions of different tectonic units in China continent are estimated in range of 0.58,1.12 ,W/m3 with a median of 0.85 ,W/m3. Accordingly, the contents of U, Th and K2O in China crust are in ranges of 0.83,1.76 ,g/g, 3.16,6.69 ,g/g, and 1.0%,2.12%, respectively. These results indicate that the abundance of radioactive elements in the crust of China continent is much higher than that of Archean crust; and this fact implies China's continental crust is much evolved in chemical composition. Meanwhile, significant lateral variation of crustal composition is also exhibited among different tectonic units in China continent. The crust of eastern China is much enriched in incompatible elements such as U, Th and K than that of western China; and the crust of orogenic belts is more enriched than that of platform regions. It can also be inferred that the crusts of eastern China and orogenic belts are much felsic than those of western China and platform regions, respectively, derived from the positive correlation between the heat production and SiO2 content of bulk crust. This deduction is consistent with the results derived from the crustal seismic velocity data in China. According to the facts of the lower seismic velocity of China than the average value of global crust, and the higher heat production of China continent compared with global crust composition models published by previous studies, it is deduced that the average composition models of global continent crust by Rudnick and Fountain (1995), Rudnick and Gao (2003), Weaver and Tarney (1984), Shaw et al. (1986), and Wedepohl (1995) overestimate the abundance of incompatible elements such as U, Th and K of continental crust. [source]

Self-regulating hyperthermia induced using thermosensitive ferromagnetic material with a low Curie temperature

CANCER SCIENCE, Issue 4 2008
Hajime Saito
Hyperthermia has been used for many years to treat a variety of malignant tumors. The Curie temperature (Tc) is a transition point at which magnetic materials lose their magnetic properties, causing a cessation of current and thus heat production. The Tc enables automatic temperature control throughout a tumor as a result of the self-regulating nature of the thermosensitive material. We have developed a method of magnetically-induced hyperthermia using thermosensitive ferromagnetic particles (FMPs) with low Tc (43°C), enough to mediate automatic temperature control. B16 melanoma cells were subcutaneously injected into the backs of C57BL/6 mice, after which tumors were allowed to grow to 5 mm in diameter. FMPs were then injected into the tumors, and the mice were divided into three groups: group I (no hyperthermia, control); group II (one hyperthermia treatment); and group III (hyperthermia twice a week for 4 weeks). When exposed to a magnetic field, the FMPs showed a sharp rise in heat production, reaching the Tc in tissue within 7 min, after which the tissue temperature stabilized at approximately the Tc. In groups I and II, all mice died within 30,45 days. In group III, however, 6 of 10 mice remained alive 120 days after beginning treatment. Our findings suggest that repeated treatment with magnetically-induced self-regulating hyperthermia, mediated by FMPs with a low Tc, is an effective means of suppressing melanoma growth. A key advantage of this hyperthermia system is that it is minimally invasive, requiring only a single injection for repeated treatments with automatic temperature control. (Cancer Sci 2008; 99: 805,809) [source]

Exercise-induced hyperthermia in childhood: a case report and pilot study

ACTA PAEDIATRICA, Issue 7 2009
T Kallinich
Abstract Hyperthermia is characterized by an increase of body core temperature due to exogenous heat exposure and/or endogenous heat production. Contrary to fever the hypothalamic-controlled temperature set point remains unchanged. Aim: To demonstrate that exercise-induced hyperthermia is a common phenomenon in childhood. Case: We describe a 5-year-old boy, who attended our outpatient clinic with a 6-month observation period of exercise-induced hyperthermia with rectal temperatures up to 39.0°C. Characteristically temperature dropped to normal values after cessation of exercise. Method: In eight children aged 5,8, tympanic and rectal temperatures were measured before and after exercise. Results: The rectal temperature increases frequently after exercise (p < 0.001), whereas tympanic temperature did not (p = 0.2). Conclusion:, Benign hyperthermia should be considered in children with increased body temperature of unknown sources. The site of temperature measurement might be critical in the identification of this condition. [source]

Kinetics of the Action of Na2SeO3 on Bacillus subtilis Growth as Studied by Microcalorimetry

CHINESE JOURNAL OF CHEMISTRY, Issue 2 2002
Yi Liu
Abstract Microcalorimetric bioassay for acute cellular toxicity is based on metabolic heat production from cultured cells. The biological response to toxicants is the inhibition of the heat production rate in cells, and toxicity is expressed as the concentration of toxicant that is 50% effective in this inhibition (IC50). In mis paper, the effect of Na2SeO3 on Bacillus subtilis growth was investigated at 37 °C by microcalorimetry. The relationship between growth rate constants (k) and concentration of Na2SeO3 (c) shows a logarithmic normal distribution, and lC50 is 20.3 ,g/mL. All these thermokinetic information is readily obtained by an LKB 2277,204 heat conduction microcalorimeter. Microcalorimetry is a quantitative, inexpensive, and versatile method for toxicology research. [source]