Nasal heat exchange in a northern ungulate, the reindeer (Rangifer tarandus)

When reindeer were exposed to low ambient temperatures, heat and water were recovered from the exhaled air by a nasal counter-current heat exchanger. Measurements of respiratory frequency, minute volume, exhaled air temperature and metabolic rate were made over a range of ambient air temperatures extending from -5.5 degrees C to 27.2 degrees C. At ambient air temperatures less than 10 degrees C the exhaled air temperatures were an average of 21 degrees C less than body temperature. The reduction of the exhaled air temperature at the lowest ambient air temperatures used in this study resulted in the recovery of 75% of the heat added and 80% of the water added to the inspired air on its way to the lungs. The heat and water recovered by the nasal temporal counter-current heat exchanger in reindeer significantly reduced the metabolic cost of survival during cold exposure.     

Respiratory heat loss is not the sole stimulus for bronchoconstriction induced by isocapnic hyperpnea with dry air

It is uncertain if respiratory heat loss or respiratory water loss is the stimulus for bronchoconstriction induced by isocapnic hyperpnea or exercise with dry air in subjects with asthma. We partially separated these 2 stimuli by having 18 subjects with asthma breathe dry air (0 mg/L water content) at increasing ventilations by isocapnic hyperpnea while we measured the increase in specific airway resistance (SRaw). The study was divided into 2 phases. In Phase 1, we used an apparatus with a single respiratory valve and evaluated the subjects' responses at 3 different inspired temperatures (-8.4, 20.5, and 39.4 degrees C). Seven of the subjects had esophageal catheters with 2 thermocouples in place to measure retrocardiac and retrotracheal temperatures. In this phase, we found that there were no significant differences in the ventilation required to cause a 100% increase in SRaw among the 3 different inspired temperatures (48.4 L/min, cold; 47.5 L/min, room temperature; 44.2 L/min, hot), even though the retrotracheal temperature fell more when the subjects breathed cold air at 40 L/min (2.1 degrees C) than when they breathed hot air (1.2 degrees C), suggesting greater airway cooling with the cold air. In Phase 2, in order to accurately measure inspired and exhaled temperatures and exhaled water content, we used 2 separate systems for delivering the inspired air and collecting the exhaled air at 2 different inspired temperatures (-21.4 and 38.9 degrees C). Again, we found that there was no significant difference in the ventilation required to cause a 100% increase in SRaw between the 2 different inspired temperatures (28.3 L/min, cold; 33.6 L/min, hot). When the subjects inhaled cold air, exhaled temperature was warmer than previously reported.(ABSTRACT TRUNCATED AT 250 WORDS)     

Respiratory heat loss during work at various ambient temperatures

The purpose of this investigation was to establish the temperature and humidity of the expired air of subjects working at various metabolic rates at ambient temperatures between -40 degrees C and 20 degrees C in order to calculate respiratory heat loss. Measurements of the respired air temperature and water vapour content were made for five subjects while they either stood or walked on a treadmill. The results indicated that the maximum respired air temperature varied slightly with the ambient air temperature but changes in metabolic rate, respiration rate and breathing frequency had no apparent effect on the expired air temperature under the conditions studied. The relative humidity of the respired air was found to be close to saturation in the extreme-cold environments. Heat loss due to respiration was between 25 and 30% of the resting metabolic and between 15 and 20% of the working metabolic rate.     

Low indoor temperatures and morbidity in the elderly

Low ambient temperatures are particularly harmful to the elderly and in the winter in the UK temperatures in some dwellings may fall to 6 degrees C. The World Health Organization recommends a minimal indoor temperature of 18 degrees C and a 2-3 degrees C warmer minimal temperature for rooms occupied by sedentary elderly, young children and the handicapped. Below 16 degrees C, resistance to respiratory infections may be diminished. Both low and high relative humidities promote respiratory illnesses. At temperatures below 12 degrees C, cold extremities and slight lowering of core temperature can induce short-term increases in blood pressure. Raised blood pressure and increased blood viscosity in moderate cold may be important causal factors in the increased winter morbidity and mortality due to heart attacks and strokes. Deep body temperature does not usually fall until resting clothed elderly people are exposed for two or more hours to an ambient temperature of 9 degrees C or below. Statistics available for the UK population do not support the view that there are large numbers of elderly people suffering from clinical hypothermia, though there may be a larger number in whom hypothermia is undiagnosed when the condition occurs secondary to other disorders.     

Fever and survival in aged mice after endotoxin challenge

Male C57BL/6 mice of 12, 19, and 24 months of age received injections of low (25 micrograms 100 g-1 body weight) or high (50 micrograms 100 g-1 body weight) doses of Salmonella typhosa endotoxin and were exposed to ambient temperatures below (24 degrees C) or within (30 degrees C) the thermoneutral zone. Old mice (19 and 24 months) developed initial fevers followed by hypothermia in response to endotoxin challenge at 24 degrees C, irrespective of dose; 12-month-old-mice became hypothermic at 24 degrees C following injection of the high dose of endotoxin only. At 30 degrees C, 12- and 19-month-old mice developed and maintained fever over 4 hr in response to endotoxin compared with the 24-month-old mice who were unable to maintain fevers. Logistic regression analysis showed that age, ambient temperature, and body temperature responses were significant predictors of survival outcome in endotoxin-treated mice; of these, age and ambient temperature had the strongest effects.     

Metabolic, respiratory and cardiac activity in the shrew Crocidura russula

Oxygen consumption, respiratory rate, heart rate and body temperature of resting common white-toothed shrews (Crocidura russula, mean = 11.4 g), have been determined at ambient temperatures (Ta) between 0 and 37 degrees C. Mean basal oxygen consumption (Ta = 30 degrees C, Tb = 35.4 degrees C) was 2.3 ml.g-1.h-1 and was about 12% above the value expected on the basis of the allometric relationship applying for mammals. At 0 degree C oxygen consumption was 4.2 times that in the thermal neutral zone (TNZ) which is located at Ta of about 30 degrees C. The mean basal respiratory rate was 103 min-1 (Ta = 30 degrees C), fully 40% below the predicted value. The respiratory rate increased at 0 degree C to 3.8 times that in TNZ. The amount of oxygen consumed per breath was rather constant, increasing from a mean of 4.3 microliters (Ta = 30 degrees C) to 4.9 microliters (Ta = 0 degree C) which was only 15% above the basal value. Comparing the great changes of respiratory rate with the small alterations of oxygen consumed per breath, a dominant influence of respiratory rate in the regulation of respiration is shown. Basal heart rate was 444 min-1 (Ta = 30 degrees C), in agreement with the expected value. Heart rate increased only 1.75-fold at an ambient temperature of 0 degree C. Oxygen pulses depend very strongly on ambient temperature, increasing from 0.98 microliters (Ta = 30 degrees C) to 2.5 microliters at 0 degree C. Beat frequency and stroke volume regulation are salient features of heart function.     

Effects of immersion in cool water on lung-exhaled nitric oxide at rest and during exercise.

Lung nitric oxide (NO) has been postulated to relax airway and vascular smooth muscle at rest and during exercise. As a cold environment is a common cause of respiratory distress, lung exhaled NO was measured during skin and core body cooling at rest and during a progressive cycle exercise. Ten healthy male subjects were immersed in water at a water temperature (Tw) which was thermal neutral (35 degrees C) at 30 degrees C Tw, at which only skin temperature is decreased; and at 20 degrees C Tw, at which the core temperature is decreased (0.05 degrees C). At rest, V(O), and V(E) increased while exhaled NO concentration [NO] and the rate of expiration of NO (V(NO)) decreased with decreased Tw. V(O2) and ventilation (V(E)) increased with workload (W) and the values at all Tw were not different, whereas, [NO] decreased with W and the values during exercise were progressively less at all Ws as Tw declined. These results indicate that lung NO output is reduced in a graded fashion during body cooling at rest and during exercise. This suggests that lower lung NO may contribute to airway obstruction in cold environments and NO may contribute to regulation of lung heat and water exchange.     

Observations on the sites of respiratory evaporation in the fowl during thermal panting.

The rate of respiratory water loss (RWL) was investigated in domestic fowls by the open-flow method, and the relative importance of the surfaces of the upper and lower respiratory tract was assessed by cannulating the trachea and by recording the temperatures at the potential evaporating sites. Birds were exposed to Ta from 20 to 40 degrees C and RWL examined at rectal temperatures (Tre) from 41 to 44 degrees C. Overall, the increase in RWL from the whole tract, and from the upper and lower divisions, was by about 1.1, 1.0 and 0.3 mg (g-hr. degrees C)-1, respectively. There was a rapid increase in V and in RWL from the whole and from the upper tract at Tre 41.5-42.5 degrees C, but no comparable change from the lower tract. Temperatures significantly below Ta and Tre (both 43 degrees C) were detected in the trachea and in the nasal and buccal cavities, but not in the air sacs. It was concluded that respiratory evaporation occurs mainly from the upper tract during panting and that the air sacs are unlikely to be involved.     

Ventilation, gas exchange and blood gases in the snake, Pituophis melanoleucus

Oxygen consumption of Pituophis melanoleucus was about 30-50% of values predicted for snakes of similar body mass. Following a rise in body temperature there were transient increases in CO2 elimination and the respiratory exchange ratio for about 6 hours. Lowering body temperature produced transient decreases in CO2 elimination and the respiratory exchange ratio for about 24 hours. Respiratory exchange ratios measured up to 6 days following these transients were found to be significantly higher at higher temperatures. From 20 to 30 degrees C arterial pH declined 0.157 unit, and there was a significant decline in blood CO2 of 1.3 mM which is consistent with the direction of the transients in CO2 elimination. This fall in CO2 at higher temperatures probably results from increased levels of plasma fixed acid (e.g., lactate). Minute ventilation and breathing frequency increased with body temperature while tidal volume remained nearly constant at 29 ml/kg. Breathing was regular, with each breath followed by an inspiratory pause. Air convection requirement declined from about 61 ml air/ml O2 at 15 degrees C to 36 ml air/ml O2 at 30 degrees C. Blood convection requirement remained constant at about 44.6 ml blood/ml O2 at 20 degrees C and 30 degrees C with the result that ventilation/perfusion declined from approximately 1.13 to 0.76. In Pituophis, mechanisms of acid-base regulation and adjustments in gas transfer with temperature do not differ fundamentally from those of other air-breathing ectotherms. However, snakes utilize tidal volumes which are 2 to 2.5 times larger than other reptiles and have air convection requirements which exceed other reptiles by about 50%.     

Energy turnover and heat exchange in mature lean and obese Zucker rats acutely exposed to three environmental temperatures for 24 hours

Differences between lean (FA/?, n = 6) and obese (fa/fa, n = 6) mature male Zucker rats' energy turnover and heat storage were compared during a 24-h period when the animals were exposed to ambient temperatures of 30, 15 or 5 degrees C. Energy turnover was examined through measurements of heat production rates via indirect calorimetry and heat loss rates via direct calorimetry. Heat storage rates were calculated as the difference between heat production and heat loss rates. Predicted heat storage rates were also calculated as the product of the change in core temperature and the calculated specific heat of the animal based on body composition (carcass) analysis. A minimal heat loss rate was determined for each animal representing a period of least activity. Various comparisons were made: between groups (lean/obese), temperature (30, 15, 5 degrees C), calorimetry method (indirect/direct), period (light/dark), heat storage (experimental/predicted), and minimal heat loss. Immediately before a test, pretest weight and colonic temperature were obtained. Then, the animal was placed into the calorimeter chamber and remained there unrestrained for 24 h. Normal light/dark periods were maintained. On removal from the calorimeter, core temperature and body weight measurements were again obtained. Upon completion of all tests, body composition was analyzed and surface area determined. Energy turnover, i.e. both heat production and heat loss in the lean and obese animals differed among the 30, 15 and 5 degrees C exposures. The obese animals had relatively greater heat production rate and heat loss rate (kcal/day or kcal/kg (FFM)/day than the lean animals at 30, 15 and 5 degrees C. But, on a relative basis, the increments in heat production in the cold environments were greater for the lean animals. Both the lean and obese animals tended to be more active during the dark period when at 30 degrees C, but the difference was less at 15 degrees C and even less at 5 degrees C. Experimental heat storage rates did not differ significantly from predicted values at any of the temperatures with the possible exception of the animals at 5 degrees C. It was concluded that the mature obese Zucker rats had no major discernible defect in thermoregulation as revealed by rates of heat production and loss, although three of the obese rats did elicit a drop in colonic temperature during exposure to 5 degrees C, i.e. their excessive subcutaneous adiposity and thermal insulation did not prevent a fall in colonic temperature.(ABSTRACT TRUNCATED AT 400 WORDS)     

Variation in the sensitivity of organismal body temperature to climate change over local and geographic scales

Global climate change is expected to have broad ecological consequences for species and communities. Attempts to forecast these consequences usually assume that changes in air or water temperature will translate into equivalent changes in a species' organismal body temperature. This simple change is unlikely because an organism's body temperature is determined by a complex series of interactions between the organism and its environment. Using a biophysical model, validated with 5 years of field observations, we examined the relationship between environmental temperature change and body temperature of the intertidal mussel Mytilus californianus over 1,600 km of its geographic distribution. We found that at all locations examined simulated changes in air or water temperature always produced less than equivalent changes in the daily maximum mussel body temperature. Moreover, the magnitude of body temperature change was highly variable, both within and among locations. A simulated 1 degrees C increase in air or water temperature raised the maximum monthly average of daily body temperature maxima by 0.07-0.92 degrees C, depending on the geographic location, vertical position, and temperature variable. We combined these sensitivities with predicted climate change for 2100 and calculated increases in monthly average maximum body temperature of 0.97-4.12 degrees C, depending on location and climate change scenario. Thus geographic variation in body temperature sensitivity can modulate species' experiences of climate change and must be considered when predicting the biological consequences of climate change.     

Ventilatory response to hypoxia and hypercapnia in the torpid bat, Eptesicus fuscus.

Ventilatory pattern and ventilatory responses to hypercapnia and hypoxia were investigated in torpid big brown bats at body temperatures of 5, 10, 20, 30 and 37 degrees C. The pattern of breathing at temperatures below 30 degrees C was intermittent, consisting of rhythmic breathing bouts separated by apneic periods with occasional sporadic, non-rhythmic breathing episodes. Overall ventilation (Ve) was matched consistently to overall oxygen consumption (MO2) over the entire range of temperatures with a mean air convection requirement (Ve/MO2) of 1.28 L/mmol. However, calculating the air convection requirement using only oxygen uptake acquired during ventilation yielded an ectotherm-like temperature relationship. Ventilation was stimulated at all temperatures by either increased inspired CO2 or decreased inspired O2. At 20 degrees C, graded hypercapnic stimulation increased the duration of the rhythmic bouts and decreased the duration of apneas until at high CO2 (greater than 3%) breathing was continuous. Hypoxic stimulation below about 7% O2 increased ventilation by selectively increasing the non-rhythmic ventilations and decreasing rhythmic bouts.     

Airway cooling. Stimulus for exercise-induced asthma.

Five patients were studied using a randomly assigned sequence of four inspired-air conditions during strenuous treadmill exercise for 10 min. The four inspired-air conditions were: (1) Cool, dry room air (CDA) at 23 degrees C with 3 mg of water and 7.3 cal of heat content/l, (2) over-saturated air (OSA) at room temperature containing 43 mg water and 16.3 cal/l, (3) hot, dry air (HDA) at 120 degrees C having 3 mg water and 24.4 cal/l, and (4) warm, humidified air (WHA) at 37 degrees C with 43 mg water and 34.7 cal/l. Using inspired-air CDA and OSA, all patients manifested exercise-induced asthma (EIA) while forced expiratory volume in 1 sec (FEV1) and maximal mid-expiratory flow (MMEF) decreased to an average of 81% and 63% of the baseline when breathing CDA and to 83% and 71% of the baseline when breathing OSA. With WHA, EIA was clearly prevented while the post-exercise FEV1 and MMEF were 101% and 103% of baseline, respectively. With HDA, the post-exercise FEV1 and MMEF were 95% and 86% of baseline, respectively. Analysis of variance revealed that the post-exercise pulmonary function changes had resulted solely from respiratory heat loss and not from water loss or from interaction of heat and water losses. These results indicate that exercise-induced asthma is associated with airway cooling incurred during exercise rather than airway dehydration.     

Influence of ambient and ventilator output temperatures on performance of heated-wire humidifiers

Although heated humidifiers are considered the most efficient humidification devices for mechanical ventilation, endotracheal tube occlusion caused by dry secretions has been reported with heated-wire humidifiers. We tested the hypothesis that inlet chamber temperature, influenced by ambient air and ventilator output temperatures, may affect humidifier performance, as assessed by hygrometry. Hygrometry was measured with three different humidifiers under several conditions, varying ambient air temperatures (high, 28-30 degrees C; and normal, 22-24 degrees C), ventilators with different gas temperatures, and two VE levels. Clinical measurements were performed to confirm bench measurements. Humidifier performance was strongly correlated with inlet chamber temperature in both the bench (p < 0.0001, r2 = 0.93) and the clinical study. With unfavorable conditions, absolute humidity of inspired gas was much lower than recommended (approximately 20 mg H2O/L). Performance was improved by specific settings or new compensatory algorithms. Hygrometry could be evaluated from condensation on the wall chamber only when ambient air temperature was normal but not with high air temperature. An increase in inlet chamber temperature induced by high ambient temperature markedly reduces the performance of heated-wire humidifiers, leading to a risk of endotracheal tube occlusion. Such systems should be avoided in these conditions unless automatic compensation algorithms are used.     

Thermally induced asthma and airway drying.

The purpose of this study was to determine whether mucosal dehydration causes thermally induced asthma. To provide data on this point, we studied the effects on lung function of progressive water loss (WL) from the respiratory tract by having eight subjects perform isocapnic hyperventilation for 1, 2, 4, and 8 min at a constant level (V E = 57.5 +/- 6.3 L/min [mean +/- SEM]) while they breathed dry air at frigid (TI = -12.5 +/- 2.7 degrees C) (cold trial) and ambient (24.3 +/- 0.7 degrees C) (warm trial) temperatures. Expired temperatures (TE) were continuously monitored, and WL from the intrathoracic airways was calculated from published relationships. FEV1 was measured before and after each challenge. Each inspirate produced stimulus-response decrements in FEV1, but the effect of cold air was greater (% Delta cold8min = 30.0 +/- 4.7%, warm = 16.0 +/- 4.4%; p = 0.01). Water loss, however, was significantly less in the cold experiment because TE was lower (WL cold8min = 4.8 +/- 0.4 g, warm = 7.1 +/- 0.7 g; p = 0.001; TE cold8min = 22.8 +/- 2.3 degrees C, warm 30.9 +/- 1.5 degrees C; p = 0.003). The FEV1 decreased as WL rose, but the largest intrathoracic losses were associated with the smallest obstructive response (% DeltaFEV1 cold8min = 30%, WL = 4.7 mg; % DeltaFEV1 warm8min = 16%, WL = 7.1 mg; p = 0.002). These data show that removal of water from the lower respiratory tract, and by inference the development of a hyperosmolar periciliary fluid, do not appear to be the primary causes of thermally induced asthma.     

Effects of PCO2 on respiratory pattern during thermal and exercise hyperventilation in domestic fowl

The relationship between respiratory pattern and arterial PCO2 was investigated during hyperventilation induced by graded exercise and hyperthermia. Treadmill exercise was performed both in isothermic and hyperthermic conditions. Isothermic exercise was induced by spraying the birds with water before exercise at environmental temperatures of 18 +/- 2 degrees C. Hyperthermic exercise was performed in unsprayed birds at temperatures of 18 +/- 2 degrees C and 30 +/- 2 degrees C. During isothermic exercise there was no significant change in arterial PCO2 at moderate work loads and only a small drop in PCO2 at the heaviest work loads; ventilation was increased by coupled increases in tidal volume and respiratory frequency. During exercise in unsprayed birds rectal temperature rose progressively and arterial PCO2 fell progressively with work load. At each work load ventilation was higher and breathing was more rapid and shallow than during isothermic exercise. These effects were more pronounced during exercise at 30 +/- 2 degrees C than at 18 +/- 2 degrees C. When normal PCO2 was maintained during hyperthermic exercise, as a result of the administration of CO2-enriched air, polypnea was suppressed and the tidal volume-respiratory frequency relationship became identical to that observed during graded isothermic exercise. Maintenance of normal PCO2 in resting birds subjected to a gradual increase in environmental temperature also resulted in changes in respiratory pattern identical to those obtained during eucapnic exercise. It is concluded that, provided arterial PCO2 is held constant, the pattern of breathing is the same for hyperventilation induced by exercise or by body temperature increases.     

Temperature effects on metabolism, ventilation, and oxygen extraction in a Neotropical bat

We examined the relationship between ambient temperature (Ta), body temperature (Tb), oxygen consumption (VO2), carbon dioxide production (VCO2), evaporative water loss (mH2O), respiratory frequency (f), tidal volume (VT), minute volume (VI), and oxygen extraction (EO2) in the Neotropical bat Noctilio albiventris (mean mass 40 g). The factorial aerobic scope was 7.2 between Ta of 1-35 degrees C (VO2 = 0.119 and 0.0165 ml/(g.min), respectively). The respiratory exchange ratio (VCO2/VO2) did not change with Ta and mH2O was constant between Ta of 10-35 degrees C. Thermal conductance was minimal at 30 degrees C and constant and low at Ta less than 30 degrees C. Between 10 and 35 degrees C, Noctilio accommodated changing VO2 with parallel and roughly equivalent changes in f, VT, and EO2. The change in VO2 between 10 and 1 degrees C was accommodated mainly through changing f. Ventilation parameters in resting thermoneutral Noctilio are intermediate between allometric values for birds and mammals. Maximal EO2 in Noctilio (35-40%) is higher than for other mammals but considerably less than maximal EO2 in some birds.     

Brain cooling and respiratory heat exchange in camels during rest and exercise

Respiration in relation to brain temperature (Tb) and body temperature (Tc) were investigated in two camels at rest and one during exercise (running at 10 km/h). The animals were subjected to natural ambient conditions (day: 25-30 degrees C, relative humidity (RH) about 65%; night: 15-20 degrees C, RH approx. 90%). They were studied when fully hydrated and during progressive dehydration by up to 15% of initial weight. At low Tc (less than 38 degrees C) Tb greater than Tc by approximately 0.2 degrees C, at higher Tc significant brain cooling was observed by as much as 1.5 degrees C during exercise. Minute ventilation (VE) and respiratory rate (f) increased with Tc such that tidal volume was constant and similar at rest and during exercise (Tc-Tb) increased linearly with f and hence VE. The cooling, dependent on turbinate heat exchange was related to certain features of the air flow pattern and f which have also been described in other large mammals.     

Office spirometry: temperature conversion of volumes measured by the Vitalograph-R bellows spirometer is not necessary

The aim of the present study was to investigate the relevance of BTPS (gas at body temperature, atmospheric pressure and saturated with water vapour) conversion of volumes measured with the Vitalograph bellows spirometer. The Vitalograph bellows were tested against a MicroMedical turbine spirometer in extreme temperatures (0-37 degrees C) using a biological control to deliver expired gas at BTPS. Before testing, it was shown that the accuracy of the DairyCard turbine was stable in the relevant temperature range. In a clinical trial six patients with emphysema performed home spirometry b.i.d for 1 month using both the Vitalograph and the turbine. Both the DairyCard and the Vitalograph showed stable accuracy at extreme temperatures when results were reported without any BTPS conversion. These findings were supported by the clinical trial but the conclusions from the clinical setting were weakened by the surprising fact that domiciliary temperatures showed almost no variation. We conclude that the Vitalograph bellows, during dynamic spirometry, measures expired volume at conditions closer to BTPS (than to ATPS) gas at ambient temperature, atmospheric pressure and saturated with water vapour). The use of the BTPS correction based on ambient temperature seems unjustified at office temperatures close to 23 degrees C and at extreme temperatures the conversion of volume will introduce significant over or underestimation.     

Temperature preference in Rhodnius prolixus, effects and possible consequences

The present work examines the thermal preference of adult Rhodnius prolixus along a temperature gradient. The mean preferred temperature differed slightly between sexes: 25.0 degrees C for males versus 25.4 degrees C for females. This preference was not constant, but varied daily by about 0.2 degrees C for both sexes, and reached its highest value at the onset of the dark phase and was lowest during the light phase. A change in the preferred temperature with the level of starvation was also observed (about 1 degrees C lower after 20 days of starvation). Changes in environmental temperature strongly affected the rate of weight loss for both sexes. When insects were maintained for 20 days in a chamber at 32 degrees C, they lost significantly more weight than when kept at 24 degrees C; both water loss and nutrient conversion processes are involved. This increase in weight loss rate with increasing temperature would cause a higher biting rate and consequently higher probability of Chagas' disease transmission. Females oviposit across a range of temperatures from 22 to 33 degrees C with a peak at 25-26 degrees C. These results are compared with patterns of thermopreference in other species of triatomine, as related to differences in their distribution and tolerance to starvation.