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PubMed1992

Hoof and distal limb surface temperature in the normal pony under constant and changing ambient temperatures.

Forelimb surface temperatures were continuously monitored in four clinically normal ponies exposed to: (i) constant ambient temperature; (ii) a biphasic change in ambient temperature; and (iii) an incremental increase in ambient temperature. Limb surface temperatures were recorded at the hoof, metacarpus and forearm, and rectal temperature was also measured. Under constant ambient temperature, limb surface temperatures remained relatively constant. A pyrexic episode occurred in one pony under constant ambient temperature conditions and was characterised by an onset phase in which rectal temperature gradually increased while limb surface temperatures concurrently decreased; a plateau phase in which rectal temperature was elevated but essentially constant although limb surface temperatures rose dramatically; and a febrilytic phase in which limb surface temperatures remained elevated while rectal temperature gradually decreased. A biphasic change in ambient temperature produced corresponding changes in limb surface temperature, but limb surface temperatures were less stable at the lower ambient temperatures. Surface temperature responses to incremental increases in ambient temperature were dependent on the baseline ambient temperature (before increase), and dramatic, spontaneous increases in limb surface temperatures were observed. Rectal temperatures in the normal animals remained relatively constant under all three ambient temperature regimens. It was concluded that clinical interpretation of limb surface temperatures in ponies required an awareness of ambient temperature conditions. For evaluation of vasodilator agents, constant ambient temperatures of at least less than 18 degrees C are suggested, and constant ambient temperatures exceeding 20 degrees C are recommended for the evaluation of vasoconstrictor agents.

Animals↗
PubMed2003

[Bladder temperature versus tympanic membrane and forehead skin temperature].

INTRODUCTION: The purpose of the study was to compare three different methods of assessing the core temperature: by measuring the bladder temperature, the tympanic temperature, (Braun Thermoscan 3000) and the forehead skin temperature (Philips SensorTouch). Measuring of the bladder temperature and the tympanic temperature are wellknown methods whereas measuring of the forehead skin temperature by the use of Sensor Touch is a fairly new method by which the temperature at the warmest area of the forehead is measured. MATERIAL AND METHODS: Forty-two randomly chosen adult patients who all had a bladder catheter with a thermometer and a normal urine output. The patients were admitted to an intensive care unit and none were intubated nasally. Otoscopy was performed prior to temperature measurement. The temperatures were measured almost simultaneously. At the same time a white blood cell count and the C-reactive-protein value was recorded. RESULTS: There was a good linear coherence between the bladder temperature and the tympanic temperature (r = 0.97). The linear coherence between the bladder temperature and the forehead skin temperature was poor (r = 0.59). We found a mean deviation of 0.07 degree C and a standard deviation of 0.3 degree C of the difference between the bladder temperature and the tympanic temperature (p = 0.19). The mean of the difference between the bladder temperature and the forehead skin temperature was 0.5 degree C and a standard deviation of 0.8 degree C (p = 0.0003). Furthermore the forehead skin thermometer was not able to measure temperatures < 35.0 degrees C. We found no statistically significant coherence between the core temperature and the white blood cell count or C-reactive-protein. DISCUSSION: Tympanic temperature was well coherent with bladder temperature--forehead skin temperature was poorly coherent with bladder temperature. By evaluating the core temperature in intensive care patients the tympanic temperature is a reliable alternative to the bladder temperature.

Adult↗
PubMed2001

The relationship between intramuscular temperature, skin temperature, and adipose thickness during cryotherapy and rewarming.

OBJECTIVE: To describe the relationships among muscle temperature, skin temperature, room temperature, body core temperature, time, and subcutaneous adipose thickness during cryotherapy and rewarming. DESIGN: A multiple linear regression with 5 independent variables (skin temperature, body core temperature, subcutaneous adipose thickness, room temperature, time) predicting intramuscular (IM) temperature. SETTING: A sports injury research laboratory. PARTICIPANTS: Fifteen volunteers with thigh skinfold measurements smaller than 40 mm. INTERVENTIONS: Thirty-minute cryotherapy treatment (ice bag) followed by a 120-minute rewarming period. MAIN OUTCOME MEASURES: The relationship between skin and IM temperature was described, and an equation predicting IM temperature by using room temperature, skin temperature, body core temperature, time, and adipose thickness was developed. RESULTS: Pearson's correlations between each predictor variable of IM temperature during cryotherapy were skin temperature, r = .46; skinfold, r = .37; time, r = -.59; core temperature, r =.21; and room temperature, r = -.47. During rewarming, the correlations were skin temperature, r = .71; skinfold, r = .27; time, r = .76; core temperature, r = - .05; and room temperature, r = - .21. A multiple regression equation (R(2) = .76) was developed to predict IM temperature during cryotherapy. A separate equation (R(2) =.81) was developed to predict muscle temperatures during rewarming. CONCLUSIONS: During and after ice application, no single predictor adequately explained the change in IM temperature. Skin surface temperature was a weak predictor of IM temperature during cryotherapy and should not be used as the sole dependent measure in cryotherapy efficacy studies.

Adult↗
PubMed2005

Heat stress from enclosed vehicles: moderate ambient temperatures cause significant temperature rise in enclosed vehicles.

OBJECTIVE: Each year, children die from heat stroke after being left unattended in motor vehicles. In 2003, the total was 42, up from a national average of 29 for the past 5 years. Previous studies found that on days when ambient temperatures exceeded 86 degrees F, the internal temperatures of the vehicle quickly reached 134 to 154 degrees F. We were interested to know whether similarly high temperatures occurred on clear sunny days with more moderate temperatures. The objective of this study was to evaluate the degree of temperature rise and rate of rise in similar and lower ambient temperatures. In addition, we evaluated the effect of having windows "cracked" open. METHODS: In this observational study, temperature rise was measured continuously over a 60-minute period in a dark sedan on 16 different clear sunny days with ambient temperatures ranging from 72 to 96 degrees F. On 2 of these days, additional measurements were made with the windows opened 1.5 inches. Analysis of variance was used to compare how quickly the internal vehicle temperature rose and to compare temperature rise when windows were cracked open 1.5 inches. RESULTS: Regardless of the outside ambient temperature, the rate of temperature rise inside the vehicle was not significantly different. The average mean increase was 3.2 degrees F per 5-minute interval, with 80% of the temperature rise occurring during the first 30 minutes. The final temperature of the vehicle depended on the starting ambient temperature, but even at the coolest ambient temperature, internal temperatures reached 117 degrees F. On average, there was an approximately 40 degrees F increase in internal temperature for ambient temperatures spanning 72 to 96 degrees F. Cracking windows open did not decrease the rate of temperature rise in the vehicle (closed: 3.4 degrees F per 5 minutes; opened: 3.1 degrees F per 5 minutes or the final maximum internal temperature. CONCLUSIONS: Even at relatively cool ambient temperatures, the temperature rise in vehicles is significant on clear, sunny days and puts infants at risk for hyperthermia. Vehicles heat up rapidly, with the majority of the temperature rise occurring within the first 15 to 30 minutes. Leaving the windows opened slightly does not significantly slow the heating process or decrease the maximum temperature attained. Increased public awareness and parental education of heat rise in motor vehicles may reduce the incidence of hyperthermia death and improve child passenger safety.

Automobiles↗
PubMed2000

Servo-control for maintaining abdominal skin temperature at 36C in low birth weight infants.

BACKGROUND: Randomized trials have shown that the neonatal mortality rate of low birth-weight babies can be reduced by keeping them warm. For low birth-weight babies nursed in incubators, warm conditions may be achieved either by heating the air to a desired temperature, or by servo-controlling the baby's body temperature at a desired set-point. OBJECTIVES: In low birth weight infants, to determine the effect on death and other important clinical outcomes of targeting body temperature rather than air temperature as the end-point of control of incubator heating. SEARCH STRATEGY: Standard search strategy of the Cochrane Neonatal Collaborative Review Group. SELECTION CRITERIA: Randomized or quasi-randomized trials which test the effects of having the heat output of the incubator servo-controlled from body temperature compared with setting a constant incubator air temperature. DATA COLLECTION AND ANALYSIS: Trial methodologic quality was systematically assessed. Outcome measures included death, timing of death, cause of death, and other clinical outcomes. Categorical outcomes were analyzed using relative risk and risk difference. Meta-analysis assumed a fixed effect model. MAIN RESULTS: Compared to setting a constant incubator air temperature of 31.8C, servo-control of abdominal skin temperature at 36C reduces the neonatal death rate among low birth weight infants: relative risk 0.72 (95% CI 0.54, 0.97); risk difference -12.7% (95% CI -1.6, -23.9). This effect is even greater among VLBW infants. REVIEWER'S CONCLUSIONS: During at least the first week after birth, low birth weight babies should be provided with a carefully regulated thermal environment that is near the thermoneutral point. For LBW babies in incubators, this can be achieved by adjusting incubator temperature to maintain an anterior abdominal skin temperature of at least 36C, using either servo-control or frequent manual adjustment of incubator air temperature.

Body Temperature Regulation↗
PubMed2000

"Deep-forehead" temperature correlates well with blood temperature.

PURPOSE: To evaluate the accuracy and precision of "deep-forehead" temperature with rectal, esophageal, and tympanic membrane temperatures, compared with blood temperature. METHODS: We studied 41 ASA physical status 1 or 2 patients undergoing abdominal and thoracic surgery scheduled to require at least three hours. "Deep-forehead" temperature was measured using a Coretemp thermometer (Terumo, Tokyo, Japan). Blood temperature was measured with a thermistor of a pulmonary artery. Rectal, tympanic membrane, and distal esophageal temperatures were measured with thermocouples. All temperatures were recorded at 20 min intervals after the induction of anesthesia. We considered blood temperature as the reference value. Temperatures at the other four sites were compared with blood temperature using correlation, regression, and Bland and Altman analyses. We determined accuracy (mean difference between reference and test temperatures) and precision (standard deviation of the difference) of 0.5 degrees C to be clinically acceptable. RESULTS: "Deep-forehead" temperature correlated well with blood temperature as well as other temperatures, the determination coefficients (r2) being 0.85 in each case. The bias for the "deep-forehead" temperature was 0.0 degrees C, which was the same as tympanic membrane temperature and was smaller than rectal and esophageal temperatures. The standard deviation of the differences for the "deep-forehead" temperature was 0.3 degrees C, which was the same as rectal temperature. CONCLUSIONS: We have demonstrated that the "deep-forehead" temperature has excellent accuracy and clinically sufficient precision as well as other three core temperatures, compared with blood temperature.

Aged↗
PubMed1994

Thermodilution right ventricular ejection fraction measurements: room temperature versus cold temperature injectate.

OBJECTIVE: To compare thermodilution right ventricular ejection fraction measurements using 10 mL room temperature injectate vs. 10 mL cold temperature injectate. DESIGN: Prospective, clinical study. SETTING: Adult surgical intensive care unit (ICU) in a university hospital. PATIENTS: Sixty adult surgical ICU patients requiring hemodynamic monitoring by a pulmonary artery catheter. INTERVENTIONS: Patients were in a supine position with the bed flat during thermodilution measurements. Four 10 mL room temperature injections were alternated with four 10 mL cold temperature injections. MEASUREMENTS AND MAIN RESULTS: One hundred eleven paired thermodilution right ventricular ejection fraction measurements were made in patients during a "steady state." There were no restrictions regarding body temperature, cardiac index, heart rate or rhythm. Injectate temperature was measured by an in-line temperature probe. Injections were synchronized with end-expiration of mechanical ventilator breaths. The first injection was deleted from each temperature group. Reproducibility of individual right ventricular ejection fraction measurements was assessed by calculating the mean variation of triplicate measurements in each temperature group. Mean values of room temperature measurements were compared with cold temperature measurements by Student's t-test. Linear regression analysis, bias, and precision were also calculated. There was no significant difference (p = .752) between mean right ventricular ejection fraction measurements determined with room temperature (23.9 +/- 1 degrees C) vs. cold temperature (8.0 +/- 1.1 degrees C) injectate. There was a high degree of correlation between measurements (r2 = .876, p < .001). The bias of room temperature measurements compared with cold temperature was -0.39% and the precision was +/- 3.3%. The mean variation between individual measurements in all room temperature and cold temperature right ventricular ejection fraction measurements was 9.7% and 8.0%, respectively. There was no significant difference and there was a high degree of correlation in mean right ventricular ejection fraction measurements when data were grouped according to body temperature, heart rate, cardiac index, right ventricular ejection fraction, central venous pressure, pulmonary vascular resistance index, right ventricular end-diastolic volume index, or right ventricular stroke work index. CONCLUSIONS: The results suggest that room temperature injectate may be used for right ventricular ejection fraction measurements in critically ill adult surgical patients. Utilizing room temperature injectate for right ventricular ejection fraction measurements may save time and costs in the critical care unit.

Adult↗
PubMed1995

Comparison of in vivo tissue temperature profile and lesion geometry for radiofrequency ablation with a saline-irrigated electrode versus temperature control in a canine thigh muscle preparation.

BACKGROUND: It is thought that only a thin layer of tissue adjacent to the electrode is heated directly by electrical current (resistive heating) during radiofrequency ablation. Most of the thermal injury is thought to result from conduction of heat from the surface layer. The purpose of this study was to determine whether lesion depth could be increased by producing direct resistive heating deeper in the tissue with higher radiofrequency power, allowed by cooling the ablation electrode with saline irrigation to prevent the rise in impedance that occurs when the electrode-tissue interface temperature reaches 100 degrees C. METHODS AND RESULTS: In 11 anesthetized dogs, the thigh muscle was exposed and bathed with heparinized canine blood (36 degrees C to 37 degrees C). A 7F catheter, with a central lumen, a 5-mm tip electrode with six irrigation holes, and an internal thermistor, was positioned perpendicular to the thigh muscle and held at a constant contact weight of 10 g. Radiofrequency current was delivered to 145 sites (1) at high constant voltage (66 V) without irrigation (CV group, n = 31), (2) at variable voltage (20 to 66 V) to maintain tip-electrode temperature at 80 degrees C to 90 degrees C without irrigation (temperature-control group, n = 39), and (3) at high CV (66 V) with saline irrigation through the catheter lumen and ablation electrode at 20 mL/min (CV irrigation group, n = 75). Radiofrequency current was applied for 60 seconds but was terminated immediately in the event of an impedance rise > or = 10 omega. Tip-electrode temperature and tissue temperature at depths of 3.5 and 7.0 mm were measured in all three groups (n = 145). In 33 CV irrigation group applications, temperature was also measured with a separate probe at the center (n = 18) or edge (n = 15) of the electrode-tissue interface. In all 31 CV group applications, radiofrequency energy delivery was terminated prematurely (at 11.6 +/- 4.8 seconds) owing to an impedance rise associated with an electrode temperature of 98.8 +/- 2.1 degrees C. All 39 temperature-control applications were delivered for 60 seconds without an impedance rise, but voltage had to be reduced to 38.4 +/- 6.1 V to avoid temperatures > 90 degrees C (mean tip-electrode temperature, 84.5 +/- 1.4 degrees C). In CV irrigation applications, the tip-electrode temperature was not > 48 degrees C (mean, 38.4 +/- 5.1 degrees C) and the electrode-tissue interface temperature was not > 80 degrees C (mean, 69.4 +/- 5.7 degrees C). An abrupt impedance rise with an audible pop and without coagulum occurred in 6 of 75 CV irrigation group applications at 30 to 51 seconds, probably owing to release of steam from below the surface. In the CV and temperature-control group applications, the temperatures at depths of 3.5 (62.1 +/- 15.1 degrees C and 67.9 +/- 7.5 degrees C) and 7.0 mm (40.3 +/- 5.3 degrees C and 48.3 +/- 4.8 degrees C) were always lower than the electrode temperature. Conversely, in CV irrigation group applications, electrode and electrode-tissue interface temperatures were consistently exceeded by the tissue temperature at depths of 3.5 mm (94.7 +/- 9.1 degrees C) and occasionally 7.0 mm (65.1 +/- 9.7 degrees C). Lesion dimensions were smallest in CV group applications (depth, 4.7 +/- 0.6 mm; maximal diameter, 9.8 +/- 0.8 mm; volume, 135 +/- 33 mm3), intermediate in temperature-control group applications (depth, 6.1 +/- 0.5 mm; maximal diameter, 11.3 +/- 0.9 mm; volume, 275 +/- 55 mm3), and largest in CV irrigation group applications (depth, 9.9 +/- 1.1 mm; maximal diameter, 14.3 +/- 1.5 mm; volume, 700 +/- 217 mm3; P < .01, respectively). CONCLUSIONS: Saline irrigation maintains a low electrode-tissue interface temperature during radiofrequency application at high power, which prevents an impedance rise and produces deeper and larger lesions. A higher temperature in the tissue (3.5 mm deep) than at the electrode-tissue interface indicates that direct resistive heating occurred deeper

Animals↗
PubMed2006

Evaluation of manometric temperature measurement, a process analytical technology tool for freeze-drying: part I, product temperature measurement.

This study examines the factors that may cause systematic errors in the manometric temperature measurement (MTM) procedure used to evaluate product temperature during primary drying. MTM was conducted during primary drying using different vial loads, and the MTM product temperatures were compared with temperatures directly measured by thermocouples. To clarify the impact of freeze-drying load on MTM product temperature, simulation of the MTM vapor pressure rise was performed, and the results were compared with the experimental results. The effect of product temperature heterogeneity in MTM product temperature determination was investigated by comparing the MTM product temperatures with directly measured thermocouple product temperatures in systems differing in temperature heterogeneity. Both the simulated and experimental results showed that at least 50 vials (5 mL) were needed to give sufficiently rapid pressure rise during the MTM data collection period (25 seconds) in the freeze dryer, to allow accurate determination of the product temperature. The product temperature is location dependent, with higher temperature for vials on the edge of the array and lower temperature for the vials in the center of the array. The product temperature heterogeneity is also dependent upon the freeze-drying conditions. In product temperature heterogeneous systems, MTM measures a temperature close to the coldest product temperature, even if only a small fraction of the samples have the coldest product temperature. The MTM method is valid even at very low product temperature (-45 degrees C).

Freeze Drying↗
PubMed2004

Changes in gene expression associated with acclimation to constant temperatures and fluctuating daily temperatures in an annual killifish Austrofundulus limnaeus.

Eurythermal ectotherms commonly thrive in environments that expose them to large variations in temperature on daily and seasonal bases. The roles played by alterations in gene expression in enabling eurytherms to adjust to these two temporally distinct patterns of thermal stress are poorly understood. We used cDNA microarray analysis to examine changes in gene expression in a eurythermal fish, Austrofundulus limnaeus, subjected to long-term acclimation to constant temperatures of 20, 26 and 37 degrees C and to environmentally realistic daily fluctuations in temperature between 20 degrees C and 37 degrees C. Our data reveal major differences between the transcriptional responses in the liver made during acclimation to constant temperatures and in response to daily temperature fluctuations. Control of cell growth and proliferation appears to be an important part of the response to change in temperature, based on large-scale changes in mRNA transcript levels for several key regulators of these pathways. However, cell growth and proliferation appear to be regulated by different genes in constant versus fluctuating temperature regimes. The gene expression response of molecular chaperones is also different between constant and fluctuating temperatures. Small heat shock proteins appear to play an important role in response to fluctuating temperatures whereas larger molecular mass chaperones such as Hsp70 and Hsp90 respond more strongly to chronic high temperatures. A number of transcripts that encode for enzymes involved in the biosynthesis of nitrogen-containing organic osmolytes have gene expression patterns that indicate a possible role for these 'chemical chaperones' during acclimation to chronic high temperatures and daily temperature cycling. Genes important for the maintenance of membrane integrity are highly responsive to temperature change. Changes in fatty acid saturation may be important in long-term acclimation and in response to fluctuating temperatures; however cholesterol metabolism may be most critical for short-term acclimation to fluctuating temperatures. The variable effect of temperature on the expression of genes with daily rhythms of expression indicates that there is a complex interaction between the temperature cycle and daily rhythmicity in gene expression. A number of new hypotheses concerning temperature acclimation in fish have been generated as a result of this study. The most notable of these hypotheses is the possibility that the high mobility group b1 (HMGB1) protein, which plays key roles in the assembly of transcription initiation and enhanceosome complexes, may act as a compensatory modulator of transcription in response to temperature, and thus as a global gene expression temperature sensor. This study illustrates the utility of cDNA microarray approaches in both hypothesis-driven and 'discovery-based' investigations of environmental effects on organisms.

Acclimatization↗
PubMed2004

Body temperature regulation during hemodialysis in long-term patients: is it time to change dialysate temperature prescription?

During hemodialysis procedures, changes in the dialysate temperature can raise or lower body temperature because the blood is returned to the patient in thermal equilibrium with the dialysate. Even a dialysate temperature equal to the patient's body temperature as measured from the tympanic membrane, oral cavity, or axilla can result in an increase in the patient's body temperature, leading to cutaneous vasodilation and the potential for cardiovascular instability and hypotension. This deleterious cycle of events can be prevented by suitably adjusting the dialysate temperature. Lowering the dialysate temperature from 37 degrees C to 34-35.5 degrees C has improved the cardiovascular stability of many hemodialysis patients. Continuous monitoring of blood temperature allows the practitioner to make preemptive changes in dialysate temperature because a small change in body temperature can have enormous cardiovascular implications. For example, only 0.3 degrees C to 0.8 degrees C separates the thresholds for skin vasodilation from that for shivering. A suggested improvement in the hemodialysis procedure is to use devices that allow continuous monitoring of arterial and venous blood temperatures and adjust the dialysate temperature automatically, keeping the patient, not the dialysate, isothermic. Less optimal solutions appear to be (1) to monitor arterial and venous temperatures while manually adjusting the dialysate temperature to maintain arterial (and hence body) temperature stability; (2) to monitor peripheral temperatures (oral, tympanic) at regular intervals and adjust dialysate temperature to maintain the body temperature constant; (3) routinely use a dialysate temperature <37.0 degrees C in all patients unless contraindicated.

Adult↗
PubMed2002

A comparison of the suitabilities of rectal, gut, and insulated axilla temperatures for measurement of the circadian rhythm of core temperature in field studies.

Eight healthy males were studied for a total of 13 subject-days to assess if gut (from an ingested pill) and axilla (from a thermally insulated skin probe) temperatures would act as a substitute for rectal temperature in field studies of the circadian rhythm of core temperature. Subjects slept and went about their activities, indoors and outdoors, normally. Regular recordings (at 6 min intervals) were made of temperatures from the three sites. In addition, activity was measured (by a sensor on the nondominant wrist) so that the raw temperature data could be "purified," that is, corrected for the direct effects of sleep and activity. Inspection of the raw data indicated that there was a close parallelism between rectal and gut temperatures, but that the parallelism between rectal and insulated axilla temperatures was less reliable. This parallelism was supported by initial calculations of the correlations between rectal and gut temperatures (high and positive) and between rectal and insulated axilla (lower, though still positive) temperatures. Calculation of the limits of agreement between the parameters of the cosine curves fitted to the raw data confirmed that the rectal and gut temperatures were far closer with regard to acrophase and amplitude than were rectal and insulated axilla temperatures (-0.31 +/- 0.89 vs. +0.75 +/- 6.03 h and +0.002 +/- 0.116 vs. +0.083 +/- 0.625 degrees C, respectively). After purification of the temperature data, the limits of agreement for the cosine parameters acrophase and amplitude still indicated that there was a closer agreement between rectal and gut temperatures than between rectal and insulated axilla temperatures (-0.30 +/- 1.12 vs. +0.58 +/- 6.69 h, and +0.007 +/- 0.116 vs. +0.104 +/- 0.620 degrees C, respectively). Part of the explanation of this difference was the unreliable relationships between temperature changes in insulated axilla temperature and bursts of activity and going to bed. It is concluded that, whereas gut temperature is a viable alternativ to rectal temperature (from the viewpoints of both user acceptability and the reliability of data obtained), insulated axilla temperature, though acceptable to subjects, is unreliable from an experimental viewpoint.

Adult↗
PubMed2000

Effect of different daytime and night-time temperature regimes on the foliar respiration of Pinus taeda: predicting the effect of variable temperature on acclimation.

The objectives of this study were to determine the acclimation of loblolly pine (Pinus taeda L.) foliar respiration to different night-time low temperatures, daytime high temperatures, and daily mean temperatures, and then to use the responses of temperature acclimation to various temperature regimes to predict acclimation under fluctuating temperatures. Experiments were conducted on two-year-old seedlings in growth chambers using different combinations of day and night-time temperatures. The first experiment exposed trees to 22/22, 29/22, 22/15, and 29/15 degrees C day/night (d/n). When measured at a common temperature (15, 22 or 29 degrees C), respiration rates were lower for trees exposed to higher treatment temperatures and acclimation was influenced by both day and night-time temperature. However, the extent of acclimation did not relate to mean temperature, i.e. respiration rates measured at a common temperature ranked as follows for seedlings exposed to different temperature regimes, 22/15>22/22>29/15 congruent with29/22 degrees C d/n. Rather, acclimation of foliar respiration was linearly related to mean daily respiration rate, where mean daily respiration rate is the average of the respiration rates measured at the day and night-time treatment temperatures. The discrepancy between mean daily respiration rate and mean daily temperature occurred because respiration increased exponentially with increasing temperature. In a second experiment, the same seedlings were exposed to 22/22, 15/15, 25.5/18.5, and 25.5/15 degrees C d/n to test the relationship between mean daily respiration rate and acclimation. As in the first experiment, acclimation was linearly related to mean daily respiration rate. The concept of effective acclimation temperature, which is the temperature at which the mean daily respiration rate occurs, was derived from these results as a means to predict the extent that foliar respiration acclimates to treatment temperature.

Adaptation, Physiological↗
PubMed1997

Influence of thermoregulatory vasomotion and ambient temperature variation on the accuracy of core-temperature estimates by cutaneous liquid-crystal thermometers.

BACKGROUND: Recently, liquid crystal skin-surface thermometers have become popular for intraoperative temperature monitoring. Three situations during which cutaneous liquid-crystal thermometry may poorly estimate core temperature were monitored: (1) anesthetic induction with consequent core-to-peripheral redistribution of body heat, (2) thermoregulatory vasomotion associated with sweating (precapillary dilation) and shivering (minimal capillary flow), and (3) ambient temperature variation over the clinical range from 18-26 degrees C. METHODS: The core-to-forehead and core-to-neck temperature difference was measured using liquid-crystal thermometers having an approximately 2 degrees C offset. Differences exceeding 0.5 degree C (a 1 degree C) temperature range) were a priori deemed potentially clinically important. Seven volunteers participated in each protocol. First, core-to-peripheral redistribution of body heat was produced by inducing propofol/desflurane anesthesia; anesthesia was then maintained for 1 h with desflurane. Second, vasodilation was produced by warming unanesthetized volunteers sufficiently to produce sweating; intense vasoconstriction was similarly produced by cooling the volunteers sufficiently to produce shivering. Third, a canopy was positioned to enclose the head, neck, and upper chest of unanesthetized volunteers. Air within the canopy was randomly set to 18, 20, 22, 24, and 26 degrees C. RESULTS: Redistribution of body heat accompanying induction of anesthesia had little effect on the core-to-forehead skin temperature difference. However, the core-to-neck skin temperature gradient decreased approximately 0.6 degree C in the hour after induction of anesthesia. Vasomotion associated with shivering and mild sweating altered the core-to-skin temperature difference only a few tenths of a degree centigrade. The absolute value of the core-to-forehead temperature difference exceeded 0.5 degree C during approximately 35% of the measurements, but the difference rarely exceeded 1 degree C. The core-to-neck temperature difference typically exceeded 0.5 degree C and frequently exceeded 1 degree C. Each 1 degree C increase in ambient temperature decreased the core-to-fore-head and core-to-neck skin temperature differences by less than 0.2 degree C. CONCLUSIONS: Forehead skin temperatures were better than neck skin temperature at estimating core temperature. Core-to-neck temperature differences frequently exceeded 1 degree C (a 2 degrees C range), whereas two thirds of the core-to-forehead differences were within 0.5 degree C. The core-to-skin temperature differences were, however, only slightly altered by inducing anesthesia, vasomotor action, and typical intraoperative changes in ambient temperature.

Adult↗
PubMedDate not supplied

Core temperature response to immersed bicycle ergometer exercise at water temperatures of 21 degrees, 25 degrees, and 29 degrees C.

A bicycle ergometer modified for aquatic exercise was used to determine the effects of immersion on core temperature during submaximal exercise at different water temperatures. An exercise intensity (60% of maximal oxygen consumption) and duration (30 minutes) considered appropriate for cardiovascular conditioning were used. These data will be useful in cardiovascular and leg-strengthening hydrotherapy programs. Rectal temperature, skin temperature, and a rating of thermal comfort were studied in five normal men (14.8% +/- 5.6% fat) during headout immersion at water temperatures of 21.1 degrees, 25.3 degrees, and 29.4 degrees C and exercise in air of 21.1 degrees C. Subjects were immersed for 30 minutes during static and exercise (63% +/- 0.6% maximal oxygen consumption) conditions. Data were collected every 5 minutes and analyzed by repeated measured analysis of variance. At water temperatures, rectal temperature fell from control during static immersion (p less than or equal to 0.05) and was lower than control at the end of the 30-minute recovery period (p less than or equal to 0.05). During exercise there was no change in rectal temperature at water temperatures of 21.1 degrees and 25.3 degrees C; however, rectal temperature rose at water temperatures of 29.4 degrees (p less than or equal to 0.05) and air 21.1 degrees C (p less than or equal to 0.05). At the end of recovery rectal temperature was lower than control at water temperatures 21.1 degrees C (p less than or equal to 0.05) and greater than control at water temperatures 29.4 degrees C (p less than or equal to 0.05). There was no change from control in rectal temperatures at water temperatures 25.3 degrees C and air at 21.1 degrees C. These results indicate that immersion in 25.3 degrees and 21.1 degrees C water effectively attenuates the rise in rectal temperature during exercise at 63% of maximal oxygen consumption, whereas immersion in 29.4 degrees C water does not. In addition, both skin and rectal temperatures affect perception of thermal state but do not give the subjects an accurate estimation of thermal balance.

Adult↗