Thermal gradients in the oesophagus of man during exercise and passive warming

1. 1.|Oesophageal temperature (T_es) has been recorded at four vertical levels in the oesophagus of human subjects during exercise and during passive body heating.

2. 2.|The temperature increased with depth.

3. 3.|The rate of increase in T_es during exercise was greatest at the level of the diaphragm.

4. 4.|During passive heating of the body T_es increased most rapidly, and with shortest latency time, at the level adjacent to the left atrium of the heart.

5. 5.|During exercise, when breathing is deeper than at rest, T_es should be measured at a deeper level than that which is used during passive heating.

Diurnal activity, temperature responses and endothermy in three South American cicadas (Homoptera: Cicadidae: Dorisiana bonaerensis, Quesada gigas and Fidicina mannifera)

1. 1. Measurements of body temperature (T_b) in the field demonstrated that endothermic cicadas regulate T_b by behavioral mechanisms as well as by endogenous heat production.

2. 2. The T_b of endothermically active cicadas without access to exogenous heat is approximately the same as the T_b of basking cicadas.

3. 3. Dorisiana bonaerensis (Berg) and Quesada gigas (Olivier) raise T_b in the field with the heat produced in flight.

4. 4. The thermal responses of a particular species are related to its activity patterns and habitat.

5. 5. Endothermy in cicadas may serve to uncouple reproductive behavior from environmental constraints; to circumvent possible thermoregulatory problems; to permit the utilization of habitats unavailable to strictly ectothermic cicadas; to reduce predation; and to optimize broadcast coverage and sound transmission.

     

Intramuscular temperatures during exercise in the heat following pre-cooling and pre-heating

Pre-cooling improves heat tolerance and time to exhaustion in the heat. We tested the possibility that reduced tissue temperatures may explain this phenomenon, using three whole-body treatments: pre-cooling, thermoneutral (control) and pre-heating. Pre-cooling reduced muscle temperature (T_m) by 6.3 °C while pre-heating increased T_m 3.4 °C, relative to control. Despite this offset, T_m climbed towards a common asymptote, with pre-cooling offering no thermal protection beyond 40 min. Following pre-cooling, exercising oesophageal temperature (T_es) initially increased at 0.09 °C min⁻¹, being significantly faster than control (0.05 °C min⁻¹) and pre-heated conditions (0.03 °C min⁻¹). Pre-cooling lowered the sweat threshold and also resulted in a reduced cardiac frequency across the exercise-heat exposure. Our observations do not support the hypothesis that pre-cooling reduces T_m at the end of an exercise-heat exposure, thereby delaying the development of fatigue.     

Infra-red irradiance and set point temperatures in behaviourally thermoregulating lacertid lizards

1. 1. Set point temperatures at which Podarcis muralis and Lacerta vivipara ceased basking (T_move; upper set point) and commenced basking (T_bask; lower set point) increased incrementally with increasing i.r. irradiance; values for all set point temperatures were higher in the former species.

2. 2. Changing the i.r. irradiance during a bask resulted in a shift in the upper set point temperature to a level intermediate between the values expected at constant previous and new irradiances (experiment with L. vivipara only).

3. 3. The changes in set-point temperatures following changes in i.r. irradiance were not due to changes in light intensity.

4. 4. The ability to respond to immediate changes in i.r. irradiance is adaptive for lizards in areas in which rapid changes in amounts of sunshine are a feature of the climate.

     

The effect of shielding the parietal eye of Podarcis muralis on behavioral thermoregulation

1. 1. Body temperatures (T_bs) and thermoregulatory precision of 7 sham shielded and 7 parietal eye shielded Podarcis muralis were measured in a linear thigmothermal gradient over a 24 h period.

2. 2. Shielding the parietal eye did not alter the mean T_b selected over the 24 h period.

3. 3. Both groups selected T_bs that did not differ between photophase and scotophase.

4. 4. Shielding the parietal eye did not influence thermoregulatory precision when measured over the 12 h of photophase, but from 0600–1200 h EST parietal eye shielded lizards thermoregulated more precisely than sham shielded lizards.

     

A test of the accuracy of operative temperature thermometers for studies of small ectotherms

1. 1. Various devices have been used to estimate the equilibrium body temperature of ectotherms occupying natural environments. We tested the accuracy of such devices under a range of conditions.

2. 2. We measured body temperatures of lizards (Sceloporus magister) exposed to short-wave radiation under varying convective conditions and compared these to temperatures of hollow metal casts duplicating the animal's shape and reflectivity, as well as to the temperatures of cylinders similar to those used by other workers.

3. 3. Casts equilibrated within 2–3°C of live animals, yielding errors of 14–37% of the radiation-produced elevation of body temperature.

4. 4. Various cylinders differed from animal body temperature more than lizard casts did, producing errors equally 33–53% of the radiation-produced elevation.

5. 5. It is imperative that workers using operative-temperature thermometers experimentally confirm the adequacy of the devices they use for the range of conditions encountered within a specific analysis.

     

Thermoregulatory responses to manipulations of photoperiod in wood mice Apodemus sylvaticus from high latitudes (57°N)

1. 1. The thermoregulatory responses to manipulations of photoperiod in wood mice (Apodemus sylvaticus), which were drawn from a population living at a high latitude (57°N) were studied.

2. 2. Mice captured in spring were acclimated to two different photoperiod regimes 16L:8D and 8L:16D at a constant ambient temperature of 24°C, for 3 weeks.

3. 3. Daily rhythms of body temperature, oxygen consumption and body temperature at various ambient temperatures, nonshivering thermogenesis (the response to a noradrenaline injection) and body mass were measured. Minimal overall thermal conductance was calculated for both groups.

4. 4. Acclimation to long photophase increased the thermoregulatory abilities at relatively high ambient temperatures while that of long-scotophase increased thermoregulatory abilities at low ambient temperatures.

5. 5. Changes in photoperiod may therefore be used as cues for seasonal acclimatization of thermoregulatory mechanisms in this population of wood mice.

     

Development of autonomic and behavioural thermoregulation in turkeys (Meleagris gallopavo)

1. 1.|Heat production (HP) and body temperature (T_b) measurements were conducted at ambient temperatures (T_a) between 10 and 40°C. In addition preference temperatures (PT) were determined in a temperature channel and T_b was measured at preferred T_a

2. 2.|The influence of age on T_b at constant, as well as at PT, was proved. Increasing age was accompanied by an elevation of T_b whereas HP remained constant in the mid-range of T_a

3. 3.|The lower T_b in the first days of life is suggested to result from a lower thermoregulatory set point during the postnatal period.

4. 4.|The PT were different for the observed types of behaviour. The PT at rest was higher than the PT during locomotion, food intake and drinking.

The effects of temperature and season on the O2 consumption of third-instar larvae of the goldenrod gall fly (Eurosta solidaginis)

Abstract. Third-instar larvae of the goldenrod gall fly ( Eurosta solidaginis Fitch) live inside ball galls on goldenrod plants from summer to the following spring.Because galls are highly exposed to the weather, larvae experience substantial variations in body temperature.This study documents the oxygen consumption of gall fly larvae with regard to the effects of ambient temperature, seasonal conditioning, and prior exposure to subzero temperature.The body mass of larvae doubles between the late summer and the autumn; it subsequently undergoes a modest decline by early winter.The O₂, consumption of field-acclimatized larvae increases with ambient temperature, especially between 0 and 10°C (Q₁₀= 2.6-3.4).The thermal sensitivity of metabolism declines at higher ambient temperatures, most notably during the autumn/early winter.After exposure to 15°C for 1 week, autumn and early winter larvae maintain much lower rates of O₂ consumption than do late summer specimens.Prior exposure to -5°C for 24 h did not influence the O₂ consumption of larvae.Low thermal sensitivity of O₂ consumption, especially at higher ambient temperatures, is an energy-sparing mechanism during seasonal inactivity.Indeed, the persistence of this metabolic pattern in larvae exposed to 15°C suggests that they have entered a state of diapause.     

Thermal interaction between animal and microclimate: a comprehensive model

An equation based on heat transfer theory is developed to predict the rate of heat loss from a homeothermic vertebrate to the environment, specified by the air temperature, humidity, windspeed and radiation receipt. The analysis incorporates the animal's thermoregulatory responses--sweating ability, vasomotor action, and regulation of body-core temperature, metabolic and respiratory rate. The loss of heat and water vapour from cattle is used as an illustration, and particular attention is given to their heat balance in hot environments. The predicted rates of heat loss from cattle indoors at various air temperatures and humidities are consistent with experiments. Outdoors, intercepted solar radiation can reduce substantially heat loss through the body tissue when the air temperature is low. In contrast, at high air temperatures the heat dissipation may not be sensitive to the radiation load, although body-core temperature is. Increased rates of air movement can aggravate strain at low air temperatures, but mitigate strain in a hot environment.     

Control of body temperature in shuttling ectotherms

During the daily increase of ambient temperatures (T_a), a thermoregulating ectothermic animal enters three successive phases: a basking-foraging phase, a proportional control phase and a sun-shade shuttling phase. The first and third phase consist of shuttling between two different microclimates, and a model is developed describing the relation between mean body temperature (T_b) and the lower operative environmental temperature. It is shown to be a curvilinear function, not a linear one as often has been assumed. The conditions for relating T_bs of ectothermic animals to T_as in a meaningful way is discussed, and the daily course of T_bs in shuttling animals is described. The model provides a reasonable fit to empirical values of T_bs in the tiger beetle Cicindela hybrida L.     

Skin temperatures, thermosensory and pleasantness estimates in case of heterogeneity in the thermal environment

1. 1. Seven thermal conditions were imposed on male sitting subjects (slightly clothed: 0.6 clo).

2. 2. A thermal mannikin was also used to determine the exact operative temperature, T₀.

3. 3. Conditions were: uniform (UN: all parameters at 24.5°C, air velocity at 0.15 ms⁻¹), heated ceiling (HC at 45°C), heated floor (HF at 34°C), cold floor (CF at 14°C), two conditions of one cold wall at 6°C (CW1 and CW2 respectively with and without air temperature compensation) and increased air velocity (AV at 0.4 ms⁻¹).

4. 4. Local skin temperatures and answers to questionnaires were obtained.

5. 5. Skin temperature variations were affected by conditions and slight T₀ changes.

6. 6. Comfort judgments were fairly well related to T₀, especially when expressed as differences between actual non-uniform environment and the uniform one.

7. 7. It is concluded that, in case of non-uniform environments close to thermoneutral zone, thermal comfort or discomfort reflects the climate alterations better than the thermal sensation does.

Thermal parameters of four species of Gerbillurus

1. 1.Thermal parameter of the four Gerbillurus species measured in the laboratory were examined in relation to their micro-environments in a xeric habitat.

2. 2.Basal metabolic rates (BMR) were lower than predicted, while thermoneutral zonds (TNZ) were narrow and exceeded burrow temperatures.

3. 3.Body temperatures (T_b) were regulated over a range of ambient temperatures (T_a). Evaporative water loss was used as a short-term cooling mechanism to reduce hyperthermia above the TNZ.

4. 4.Conductance was low below the TNZ to reduce heat loss.

5. 5.Adaptation to low temperatures is important for gerbils when active at night.

6. 6.The adaptive significance of the thermal biology of Gerbillurus is discussed in relation to phylogeny, distribution, food availability and nocturnal activity.

Polar bear thermoregulation: Effect of oil on the insulative properties of fur

1. 1.|Oil caused a substantial decrease in the insulative value of polar bear (Ursus maritimus) pelts measured in vitro.

2. 2.|Following oil contamination the calm air heat transfer coefficient increased by a factor of 2 to 5: the wind coefficient averaged 290% greater and the solar utilization increased by 55%.

3. 3.|Conductance through oil-covered furs remained high at winter temperatures (T_a = 0.6°C) but decreased with time at summer temperatures (T_a = 24.7°C).

4. 4.|The most viscous of the three oils tested had a more consistently negative effect on insulation.

Comparative aspects of the thermal biology of the short-tailed gerbil, Desmodillus auricularis, and the bushveld gerbil, Tatera leucogaster

1. 1. The response of oxygen consumption (VO₂), thermal conductance (C_d and C_min, body temperature (T_b), and evaporative water loss (EWL) of Tatera leucogaster and Desmodillus auricularis were measured over the range of ambient temperatures (T_a) from 5–35°C.

2. 2. Basal metabolic rate (BMR) of T. leucogaster was 0.841 ± 0.049 ml O₂ g⁻¹ h⁻¹ and lower than predicted, while that of D. auricularis was similar to the expected value (1.220 ± 0.058 ml O₂ g⁻¹ h⁻¹). D. auricularis had a high, narrow thermoneutral zone (TNZ) typical of nocturnal, xerophilic, burrowing rodents.

3. 3. D. auricularis and T. leucogaster regulated T_b over the range T_a = 5–35°C and kept EWL and dry thermal conductance at a minimum below the TNZ. However, the EWL of T. leucogaster increased rapidly above T_a = 30°C.

4. 4. After comparison with data from other species, it was concluded that there is an optimum size for xeric, nocturnal, burrowing rodents.

Shifts in thermoregulatory patterns with pregnancy in the poikilothermic mammal—The naked mole-rat (Heterocephalus glaber)

1. 1. The naked mole-rat (Heterocephalus glaber) is a poikilothermic mammal. During gestation metabolic shifts that differ from both mammalian and reptilian thermoregulatory patterns occurred.

2. 2. Body temperature was directly dependent on ambient temperature. At low ambient temperatures the temperature differential (T_b − T_a) was approximately 3°C, whereas at higher ambient temperatures the temperature differential diminished.

3. 3. In early pregnancy (prior to week 3) oxygen consumption at low ambient temperatures was greater than that of non-reproductive animals. A maximal metabolic rate (3.2 ± 1.0 ml O₂ . g⁻¹ . h⁻¹) occurred at an ambient temperature of 27°C. Thereafter the endothermic pattern of metabolism with increasing ambient temperatures was evident. Oxygen consumption decreased with increasing ambient temperature to minimal rates of 1.2 ± 0.1 ml O₂ . g⁻¹ . h⁻¹ over the ambient temperature range of 31–34°C.

4. 4. Oxygen consumption in late pregnancy (1.8 ± 0.1 ml O₂ . g⁻¹ . h⁻¹) was not correlated with ambient temperature over the entire ambient temperature range measured (24–36°C).

5. 5. Differences in thermoregulation in early and late pregnancy may be attributed to different rates of heat loss as a consequence of (a) changes in surface area and body mass or (b) vascular changes. Furthermore the thermoregulatory changes in late pregnancy may indicate that maximal overall metabolic capacity had been reached, for peak resting metabolism (expressed per animal rather than per gram body mass) in early pregnancy was similar to observed metabolism in late pregnancy.

6. 6. The dissociation of metabolism from both ambient temperature and body temperature in late pregnancy could confer an energetic advantage to this arid dwelling underground inhabitant; for it may enable the breeding female to partition a greater portion of available energy into reproduction.

六盘山南侧华北落叶松人工林冠层蒸腾及其影响因子的坡位差异

2014年5—10月,在宁夏六盘山香水河小流域选择了一个东南坡向的典型华北落叶松人工林坡面,设立上、中上、中、中下、下5个坡位的样地(P_1、P_2、P_3、P_4、P_5),利用热扩散探针法监测树干液流,并同步监测气象、土壤水势等环境因子.结果表明:研究期间林分日蒸腾(T_r,mm·d^-1)存在显著的坡位差异,不同坡位T_r为:P_2(0.975)>P_4(0.876)>P_3(0.726)>P_1(0.653)>P_5(0.628).T_r与日最高气温(T_max)、日均太阳辐射强度(SR)、日均饱和水汽压差(VPD)、日潜在蒸散(PET)、日均土壤水势(Ψ)呈显著正相关,与日均大气相对湿度(RH)、日降水量(P)、日最低气温(T_min)呈显著负相关.基于边界线的斜率绝对值分析表明,从坡上到坡下,T_r对日均气温(T)、RH、VPD、PET和Ψ的响应呈现逐渐减小的趋势,而对SR、土壤体积含水量(VSM)的响应程度则逐渐增大.进一步回归分析和偏相关分析表明,VPD、PET和RH对不同坡位T_r的影响均占主导地位,Ψ和T对上坡样地T_r影响较大,而下坡样地T_r受SR、T_min和VSM的影响较大.总体来看,T_r的坡位差异是土壤水分和气象条件共同作用的结果,在利用特定观测样地的液流速率尺度外推计算坡面T_r时,需同时考虑土壤水分和气象因子随坡位的变化.     

Thermoregulatory responses of old men to gradual changes in ambient temperature

1. 1. Thermoregulatory respones to gradual rise and fall in the ambient temperature (T_a) were compared between 8 old (68–78 years) and 8 younger (20–25 years) male subjects.

2. 2. Starting at T_a of 31.5°C (r.h. 40%), T_a was raised to 39.5°C, then lowered to 21.5°C, and raised back to 31.5°C at a constant rate of 0.3°C/min.

3. 3. Noticeable differences in responses between the age groups were as follows: decline of sweating rate and reduction of acral blood flow during room cooling were retarded in the aged group, with wider variations among individuals, compared with those in the younger group; the tympanic and oesophageal temperatures fell considerably during cooling in the elderly group, failing to return to the level at start during the rewarming of the room, in contrast to the younger group.

4. 4. Such sluggish responses may be attributed largely to reduced cutaneous thermal perception with advancing age.

Behavioural and autonomic thermoregulation in hamsters during microwave-induced heat exposure

1. 1.|Preferred ambient temperature (T_a) and ventilatory frequency were measured in free-moving hamsters exposed to 2450 MHz microwaves. A waveguide exposure system which permits continuous monitoring of the absorbed heat load accrued from microwave exposure was imposed with a longitudinal temperature gradient which allowed hamsters to select their preferred T_a. Ventillatory frequency was monitored remotely by analysing the rhythmic shifts in unabsorbed microwave energy passing down the waveguide.

2. 2.|Without microwave exposure hamsters selected an average T_a of 30.2°C. This preferred T_a did not change until the rate of heat absorption (SAR) from microwave exposure exceeded approx. 2 W kg⁻¹. In a separate experiment, a SAR of 2.0 W kg⁻¹ at a T_a of 30°C was shown to promote an average 0.5°C increase in colonic temperature. Hamsters maintained their ventilatory frequency at baseline levels by selecting a cooler T_a during microwave exposure. In contrast, hamsters maintained at a T_a of 30°C (without a temperature gradient) underwent a sharp increase in ventilatory frequency compared to animals allowed to select their own T_a.

3. 3.|These data support previous studies suggesting that during thermal stress behavioural thermoregulation (i.e. preferred T_a) takes prescedence over autonomic thermoregulation (i.e. ventilatory frequency). It is apparent that selecting a cooler T_a is a more efficient and/or effective than autonomic thermoregulation for dissipating a heat load accrued from microwave exposure.

Estimating outdoor thermal comfort using a cylindrical radiation thermometer and an energy budget model

A mathematical model to estimate outdoor thermal comfort for humans from micrometeorological data has been formulated using the energy balance concept and the simultaneous satisfaction of four criteria for comfort from the literature: (a) a comfortable perspiration rate, (b) a comfortable core body temperature, (c) a comfortable skin temperature, and (d) a near-zero energy budget. A cylindrical modification of the globe thermometer is proposed as a simple monitor of outdoor radiation absorption for a person, and the effect of windspeed on the thermal resistance of clothing is considered. Results show a correlation coefficient of 0.91 between model output and subjective comfort ratings of 59 different situations with a variety of temperatures, insolations and windspeeds.