Simple nonperturbing temperature probe for microwave/radio frequency dosimetry

We present a simple readout device that fills the void produced by the gradual disappearance of the Vitck model 101 Electrothermia Monitor. The new device uses commercially available probes that are similar to Bowman's (IEEE Trans Microwave Theory Tech MTT-24:43-45, 1976) original design. As described, the device covers the range of 7 degrees to 45 degrees C with an accuracy and resolution of better than 0.1 degree C throughout. The digital readout (3 1/2 digits) is proportional to the thermistor resistance in the tip of the probe; it is converted to temperature through a formula or printed table. Outdoor dosimetric comparisons between the new and Vitek devices were conducted. Results showed no significant difference in the calculated specific absorption rates (SARs); moreover, variance was lower in the data collected from the new device.     

Head-body temperature differences in the Australian blue-tongued lizard, Tiliqua scincoides during radiant heating

When heated radiantly, head-body temperature gradients developed in both live and dead Tiliqua scincoides. The gradients were consistently larger in live than in dead individuals, indicating they were enhanced by a physiological component superimposed on the more basic physical components. Large gradients in the initial phases of heating represented a lag effect, the head core beginning to receive heat before the body core because it is closer to the heated surface. Once this lag effect subsided, the body heated more rapidly than the head because it presented a greater incident surface area per unit mass than did the head. Living lizards appeared to maintain head-body temperature differences until the maximum voluntary temperature was approached.     

Seasonal changes in the territorial behaviour of the satyrine butterfly Lethe diana are mediated by temperature

The territorial behaviour of butterflies often changes with temperature. The satyrine butterfly Lethe diana has three generations a year, and males display territorial behaviour in the May–June and September–October generations, but not in the July–August generation. This study investigated the relationship between this seasonal change in mate-locating behaviour and thermoregulation. When L. diana was able to hold a territory, thoracic temperature ranged from 23.8 to 33.6°C. This temperature was mainly influenced by environmental temperature based on air temperature, solar radiation, and wind, and metabolic heat was estimated to increase thoracic temperature by about 5°C in the May–June generation. When environmental temperature at a territorial site was within this range of the thoracic temperature minus the metabolic heat (approximately 5°C), L. diana males held territories. Since territorial sites were selected irrespective of the temperature, L. diana could not hold a territory when the temperature of the territorial site exceeded the threshold. In July–August, the temperature of the territorial site was almost always above the suitable range. These results suggest that seasonal change in territoriality of L. diana is due to behavioural thermoregulation. Electronic Publication     

A Comparative Study of Two Ambulatory Core Temperature Assessment Methods

Background. Given the need to identify reliable non-invasive solutions for core temperature ambulatory monitoring, the purpose of this study was to evaluate the performance of zero-heat-flux (ZHF) temperature sensor on the forehead ($T_{\mathrm{COzhf}}$) by comparing it with intestinal temperature ($T_{\mathrm{COpill}}$) in different ambient and physiological conditions.Methods. Seven trained male subjects were followed during a 45-min rest period (STA) and a 25-min self-regulated cycling exercise performed in neutral (TMP, 22.8?°C) and hot (HOT, 38.5 °C) ambient temperature.Results.$T_{\mathrm{COzhf}}$ values differed from $T_{\mathrm{COpill}}$ of ?0.23 ± 0.13 in STA, 0.15 ± 0.30 °C in TMP and $0.28\pm 0.38$?°C in HOT. The 95% limits of agreement showed an acceptable bias between $T_{\mathrm{COzhf}}$ and $T_{\mathrm{COpill}}$ in STA (±0.26?°C), but not in TMP and HOT (±0.60 and ±0.75?°C).Conclusion. The non-invasive ZHF sensor gave an accurate estimation of $T_{\mathrm{COpill}}$ in steady state but not during exercise. However, complementary results let suppose that ZHF performance is not affected by ambient conditions and could be a relevant alternative for deep body temperature measurement during whole-body heat stress.     

Effect of hypoxic breathing on cutaneous temperature recovery in man

Effect of hypoxia (12% O₂) on skin temperature recovery was studied on healthy young men. Forty male volunteers free of any respiratory disorder were randomly selected to participate in the study. Skin temperature, peripheral blood flow, heart rate and end expiratoryPO₂ andPCO₂ were measured. During hyoxic ventilation the peripheral blood flow was reduced and a corresponding drop in skin temperature occurred. This was partly due to hyperventilation associated with hypoxic ventilation. The recovery of skin temperature after cooling the hand for 2 min in cold water (10–12° C) took 5.5±0.1 min during normal air breathing; during hypoxic ventilation even after 9.1±0.3 min when the skin temperature recovery curve plateaued, the skin temperature remained about 2° C below control. The results of the present investigation indicate that hypoxia interferes with the normal functioning of the thermoregulatory mechanism in man. Hyperventilation associated with hypoxic ventilation is also partly responsible for incomplete recovery of skin temperature.     

Scrotal heating stimulates panting and reduces body temperature similarly in febrile and non-febrile rams (Ovis aries)

It is known that heating the ram scrotum stimulates heat loss resulting in a decrease in body temperature and that during fever core temperature increases, but local scrotal thermoeffectors operate to maintain normal scrotal temperature. We have investigated whether scrotal warming influences core body temperature and the panting effector during fever generation. We measured rectal temperature, intrascrotal temperature, scrotal skin temperature and respiratory frequency in four adult Merino rams following intravascular injection of saline or lipopolysaccharide at an ambient temperature of 18-20 degrees C while scrotal skin temperature was maintained at 33 degrees C or elevated to 41 degrees C. Compared to maintaining normal scrotal temperature, heating the scrotum increased respiratory frequency and reduced rectal temperature by a similar amount following LPS as following saline. Fever was associated with decreased respiratory frequency compared to saline at both 33 and 41 degrees C scrotal temperature, suggesting that the fever was generated mainly by decreasing respiratory heat loss. We conclude that scrotal thermal afferent stimulation resulted in an offset for the set-point of body temperature regulation in both normothermic and febrile rams.     

Effect of thermal tachypnoea and of its mechanical or pharmacological inhibition on hypothalamic temperature in the sheep

The abrupt inhibition of breathing in the panting sheep, by mechanical blockage of the nostrils or by the injection of noradrenaline or carbachol into a lateral cerebral ventricle, causes an immediate rise in hypothalamic temperature, followed by a rise in that of the carotid artery blood.

This confirms that evaporation from the surfaces of the upper respiratory tract has an immediate and local effect on brain temperature.

The significance of this relation in a species which controls its core temperature particularly well is discussed.     

Organ temperature measurement in a microwave oven by resonance frequency shift

An experimental system has been developed that can indirectly measure temperature in a high-intensity microwave field over a broad range of conditions. A RF amplifier connected closed-loop around a high Q cavity oscillates at one of the natural modes of the oven. A bandpass filter selects the mode of interest. As the frozen sample is thawed, an increase in dielectric constant occurs, decreasing the resonance frequency of the cavity. Calibration of the system is performed by measuring the frequency shift for samples whose temperatures are known, Rotation of samples during thawing often causes oscillations of the resonance frequency. These oscillations are generated by asymmetric sample properties and geometry, and hot spots developed during the thaw. Development of a method that would predict hot spot location from these resonance frequency oscillations and permit modulation of the magnetron or sample rotation to minimize thermal runaway is suggested.     

Core temperature response to cycling exercise: Effect of time of day and measurement site

This study evaluated the effect of time of day and temperature measurement site on core temperature response to exercise. Six trained cyclists performed a 1 h cycling exercise at a fixed power-output of 160 W in a controlled environment (ambient temperature of 21.5±1.6 °C and relative humidity of 31±6%) at batyphase +2 h (08:00 h) and acrophase +2 h (20:00 h) of their estimated circadian temperature rhythm; corresponding respectively to the heat gain and heat loss mode phases. Throughout the exercise, rectal and gastro-intestinal temperature data were collected. A two-way ANOVA was applied and a common nonlinear logistic-type function dependant on three parameters (asymptote, xmid and scale) was used to fit collected data. ANOVA only indicated a time of day effect without interaction with exercise duration. A nonlinear mixed-effect model allowed further analysis of temperature kinetics. The model indicated a higher theoretical increase in temperature at the end of morning exercise compared to the evening session. However, the circadian difference observed at rest persists throughout the exercise. Theoretical asymptotic temperature values at the end of the exercise and scale values (inversely proportional to the slope) are higher for the rectal measurement site than for the gastro-intestinal measurement. The model proposed offers a solution for refining the study of individual core temperature response to prolonged exercise. The main advantage is that it takes into consideration intra- and inter-individual variability in temperature kinetics.     

The effect of fleece on core and rumen temperature in sheep

Temperature loggers were implanted to record core body temperature (T_core) and rumen temperature (T_rumen) in sheep. The relationship between T_core and T_rumen was compared for fleeced and shorn Merino sheep over a range of environmental temperatures and during stressors involved with shearing. Fleeced sheep maintained higher T_core and T_rumen than shorn sheep in all environmental conditions tested (from thermoneutral up to 33 °C and 55% relative humidity). Shearing of the fleeced sheep resulted in those sheep having a lower T_core when exposed to hot conditions, compared to the previously shorn sheep. Respiratory rates of fleeced sheep followed similar patterns and were higher than shorn sheep under all environmental conditions. After the fleeced sheep were shorn, their respiratory rates decreased to rates similar to the previously shorn sheep when under heat load, suggesting heat loss other than respiratory evaporative heat loss was augmented.     

Effects of acclimation and egg-incubation temperature on selected temperature by hatchling western painted turtles (Chrysemys picta bellii)

The ability of hatchling turtles to detect environmental temperature differences and to effectively select preferred temperature is a function that critically impacts survival. In some turtle species, temperature preference may be influenced by embryonic and post-hatching conditions, such as egg-incubation and acclimation temperature. We tested for effects of embryonic incubation temperature (27.5 °C, 30 °C) and acclimation temperature (20 °C, 25 °C) on the selected temperature and movement patterns of 32 Chrysemys picta bellii (Reptilia: Emydidae) hatchlings in an aquatic thermal gradient of 14-34 °C and in single-temperature (20 °C, 25 °C) control tests. Among 10-11 month old hatchlings, acclimation temperature and egg-incubation temperature influenced temperature selection and movement patterns. Acclimation temperature affected activity and movement: in thermal gradient and single-temperature control tests, 25 °C-acclimated turtles relocated between chambers significantly more frequently than individuals acclimated to 20 °C. Acclimation temperature also affected temperature selection: 20 °C-acclimated turtles selected a specific temperature during gradient tests, but 25 °C-acclimated turtles did not. Among 20 °C-acclimated turtles, egg-incubation temperature was inversely related to selected temperature: hatchling turtles incubated at 27.5 °C selected the warmest temperature available (34 °C); individuals incubated at 30 °C selected the coldest temperature (14 °C). These results suggest that interactions of environmental conditions may influence post-hatching thermoregulatory behavior in C. picta bellii, a factor that ultimately affects fitness.     

Body temperature and thermoregulation of Komodo dragons in the field

Komodo dragons from hatchlings (≈0.1 kg) to adults (≤80 kg) express the full magnitude of varanid species size distributions. We found that all size groups of dragons regulated a similar preferred body temperature by exploiting a heterogeneous thermal environment within savanna, forest and mangrove habitats. All dragons studied, regardless of size, were able to regulate a daytime active body temperature within the range 34–35.6 °C for 5.1–5.6 h/day. The index of effectiveness of thermoregulation (a numerical rating of thermoregulatory activity) was not different among size groups of dragons. However, the index of closeness of thermoregulation, which rates the variability of body temperature, suggests a greater precision for regulating a preferred body temperature for medium compared to small and large dragons. Reference copper cylinders simulating small, medium and large Komodo dragons heated and cooled at the same rate, whereas actual dragons of all size groups heated faster than they cooled. Larger dragons heated and cooled more slowly than smaller ones. The mean operative environmental temperatures of copper cylinders representing medium sized dragons were 42.5, 32.0 and 29.4° C for savannah, forest and mangrove habitats, respectively. The index for average thermal quality of a habitat as measured by the absolute difference between operative environmental temperature and the dragon’s thermal range suggests the forest habitat offers the highest thermal quality to dragons and the savannah the lowest. The percent of total daytime that the operative environmental temperature was within the central 50% of the body temperatures selected by dragons in a thermal gradient (Phillips, 1984) was 45%, 15%, and 9% for forest, mangrove and savannah, respectively. Forest habitat offers the most suitable thermal environment and provides the greatest number of hours with conditions falling within the dragon’s thermal activity zone.     

Body temperature and thermoregulation in two species of yellowjackets,Vespula germanica and V. maculifrons

In spite of the abundance and broad distribution of social wasps, little information exists concerning thermoregulation by individuals. We measured body temperatures of the yellowjackets Vespula germanica and V. maculifrons and examined their thermoregulatory mechanisms. V. germanica demonstrated thermoregulation via a decreasing gradient between thorax temperature and ambient temperature as ambient temperature increased. V. maculifrons exhibited a constant gradient at lower ambient temperatures but thorax temperature was constant at high ambient temperatures. Head temperature exhibited similar patterns in both species. In spite of low thermal conductances, a simple heat budget model predicts substantial heat loads in warm conditions in the absence of thermoregulation. Both species regurgitated when heated on the head. A smaller volume of regurgitant was produced at lower head temperatures and a larger volume at higher head temperatures. Small regurgitations resulted in stabilization of head temperature, while large ones resulted in 4°C decreases in head temperature. Regurgitation was rare when wasps were heated upon the thorax. Abdomen temperature was 3–4°C above ambient temperature, and approached ambient temperature under the hottest conditions. No evidence was found for shunting of hot hemolymph from thorax to abdomen as a cooling mechanism. The frequency of regurgitation in workers returning to the nest increased with ambient temperature. Regurgitation may be an important thermoregulatory strategy during heat stress, but is probably not the only mechanism used in yellowjackets.Abbreviations M _b body mass - M _th thorax mass - T _a ambient temperature - T _ab abdomen temperature - T _b body temperature - T _h head temperature - T _th thorax temperature - C _t thermal conductance     

Design and performance of a rugged standard operative temperature thermometer for avian studies

The lack of a truly satisfactory sensor which can characterize the thermal environment at the spatial scale experienced by small endotherms has hindered study of their thermoregulatory behavior. We describe a general design for a rugged, easily constructed sensor to measure standard operative temperature, T_es. We present specific designs for adult dark-eyed juncos (Junco hyemalis) and hatchling mallards (Anas platyrhynchos). Sensor response was stable and repeatable (±1.4%) over the course of several months. Over the range of conditions for which validation data were available (variable air temperature and wind with negligible net radiation), sensors predicted the mean net heat production of live animals to within ±0.023 W (equivalent to ±1°C at T_es=15°C). The main limit on accuracy was scatter in the data on metabolism and evaporative water loss in live animals. These sensors are far more rugged and easily constructed than the heated taxidermic mounts previously used to measure T_es. These characteristics facilitate the use of significant numbers of sensors in thermal mapping studies of endotherms.     

Wheel-running activity and energy metabolism in relation to ambient temperature in mice selected for high wheel-running activity

Interrelationships between ambient temperature, activity, and energy metabolism were explored in mice that had been selectively bred for high spontaneous wheel-running activity and their random-bred controls. Animals were exposed to three different ambient temperatures (10, 20 and 30°C) and wheel-running activity and metabolic rate were measured simultaneously. Wheel-running activity was decreased at low ambient temperatures in all animals and was increased in selected animals compared to controls at 20 and 30°C. Resting metabolic rate (RMR) and daily energy expenditure (DEE) decreased with increasing ambient temperature. RMR did not differ between control and selected mice, but mass-specific DEE was increased in selected mice. The cost of activity (measured as the slope of the relationship between metabolic rate and running speed) was similar at all ambient temperatures and in control and selected mice. Heat generated by running apparently did not substitute for heat necessary for thermoregulation. The overall estimate of running costs was 1.2 kJ/km for control mice and selected mice.     

Regulation of body temperature in the white shark, Carcharodon carcharias

Stomach temperatures of three white sharks, Carcharodoncarcharias, (one reported previously and two new individuals) were intermittently recorded by acoustic telemetry at the South Farallon Islands, central California. Temperature profiles of the water column were obtained concurrently. Stomach temperatures were elevated over ambient water temperatures by as much as 14.3 °C. Stomach temperatures varied within a narrow range while ambient water temperature fluctuated over a much larger range, showing that this species regulates its body temperature. These data, in combination with previous work on the physiology and anatomy of white sharks, indicate that the white shark is endothermic. It appears that the heat retention system in lamnid sharks has allowed them to inhabit cold water and remain active predators of swift and agile prey. Accepted: 17 February 1997     

Brain temperature measurements in rats: a comparison of microwave and ambient temperature exposures

In an effort to understand microwave heating better, regional brain and core temperatures of rats exposed to microwave radiation (2450 MHz) or elevated air temperatures were measured in two studies. In general, we have found no substantial evidence for temperature differentials, or "hot spots," in the brain of these animals. In the first study, after a 30-min exposure, no temperature differences between brain regions either after microwave or ambient air exposure were found. However, a highly significant correlation between brain and core temperatures was found and this correlation was the same for both microwave and ambient air heating. In the second study, time-temperature profiles were measured in rats exposed to either 30 mW/cm2 or 36.2 degrees C. In this study, the 30-min exposure period was divided into seven intervals and the change in temperature during each period was analyzed. Only the cortex showed significantly different heating rates between the air heating and microwave heating; however, this difference disappeared after the initial 5 min of exposure.     

The ear skin temperature as an indicator of the thermal comfort of pigs

The aim of the study was to investigate the relationship between the ear skin temperature and the behaviour of pigs. Fifty-four pigs weighing 75 ± 5 kg were used in three replications (18 pigs per replication) and housed in pens (six pigs per pen) in a controlled climate facility. The room temperature was changed by 2 °C from 18 °C down to 10 °C and up again to 22 °C. The ear skin temperature (EST) was continuously recorded and the activity, lying posture, location and contact with pen mates were scored by 12 min scan sampling for 24 h at the set point temperatures 18 °C, 10 °C and 22 °C. A diurnal rhythm in the EST, the posture and the lying behaviour was found. The EST was highest at night and lowest in the afternoon. During night the pigs had more physical contact to pen mates than during day time. For all three set point temperatures the predominant lying position during the night was the fully recumbent position. The room temperature affected the lying behaviour and the EST. With decreasing room temperature the pigs increased their contact to pen mates and fewer pigs were observed lying in the fully recumbent position. The EST decreased with decreasing room temperature, and the range in the EST's at the three set point temperatures was larger during day than night (4 °C versus 2 °C). The results indicate that pigs adjust their behaviour to a higher EST when resting than when they are active, and they use behavioural adjustment (e.g. increased/decreased contact to pen mates) to bring their skin temperature into a preferred interval.