Increase In Mean Body Temperature Research Articles

An evaluation of a healthy participant laboratory model of epidural hyperthermia: a physiological study

BackgroundHyperthermia complicates 21% of cases of intrapartum epidural analgesia, but the mechanism is unclear. One hypothesis is that blockade of cholinergic sympathetic nerves prevents active vasodilation and sweating, thus limiting heat loss. Because labour increases heat production, this could create a situation in which heat production exceeds loss, causing body temperature to rise. This physiological study tested a novel laboratory model of epidural-related hyperthermia, using exercise to simulate the increased heat production of labour and surface insulation to simulate the effect of epidural analgesia. MethodsTwelve healthy non-pregnant participants (six female) cycled an ergometer for two hours at 20 Watts (W) on two occasions: once with surface insulation (intervention) and once without (control). Core temperature, skin temperature (eight sites), and heat loss (eight sites) were recorded. Mean body temperature and heat production were calculated. Values are mean (SD). ResultsExercise increased heat production on both visits (intervention 38 (18) W; control 37 (31) W; P = 0.94). Total heat loss was less on the intervention visit (intervention 115 (19) W; control 129 (23) W; P = 0.002). Core temperature increased on both visits (intervention 0.21 (0.37)°C; control 0.19 (0.27)°C; P < 0.001). The increase in mean body temperature was greater on the intervention visit (intervention 0.47 (0.41)°C; control 0.25 (0.19)°C; P = 0.007). ConclusionsThis laboratory model predicts that labour epidural analgesia limits heat loss by >14 W. Once the model is validated, it could be used to test the efficacy of potential interventions to prevent and treat epidural-related maternal hyperthermia.

Autonomic thermoregulatory responses and subjective thermal perceptions upon the initiation of thermal behavior among resting humans in hot and humid environment

BackgroundWhile thermoregulatory behavior is critical for maintaining homeostasis, our knowledge of behavioral thermoeffectors in humid heat is limited compared to the control of autonomic thermoeffectors. The predictions that the frequency and duration of intensified humid heat events are expected to increase in the coming years underline this shortcoming. Therefore, this study aims to elucidate the activation of autonomic thermoregulatory responses and subjective thermal perceptions upon deciding to initiate thermal behavior in a hot and humid environment.MethodsTen young male adults participated in an experimental trial where local cooling was permitted at any time during the behavioral assessment during passive exposure to humid heat. The air temperature and relative humidity were kept at 33^{circ }C and 80%, respectively. Skin temperatures, core body temperature (T_{text {core}}), and skin blood flow (forearm, upper arm, and upper back) were obtained 120 s preceding thermal behavior. Local sweat rate (forearm and upper arm) and subjective thermal perceptions (neck and whole-body) upon thermal behavior initiation were also recorded.ResultsMean skin temperature ({overline{mathrm {T}}}_{text {sk}}) and T_{text {core}} increased prior to thermal behavior initiation (p= 0.002; p= 0.001). An increase in mean body temperature ({overline{mathrm {T}}}_{text {body}}) was also observed (p < 0.001). However, the initiation of thermal behavior is not preceded by an increase in skin blood flow (pge 0.154) and local sweat rate (pge 0.169). An increase in thermal discomfort and skin wetness perception was observed (ple 0.048; ple 0.048), while thermal sensation did not differ from the baseline (pge 0.357).ConclusionThese findings suggest that when given the opportunity to behaviorally thermoregulate in a hot and humid environment, changes in skin blood flow and sweat rate are not required for thermal behavior to be initiated in resting humans. Moreover, an increase in {overline{mathrm {T}}}_{text {sk}} and T_{text {core}}, which appears to cause an increase in thermal discomfort, precedes thermal behavior. In addition, an increase in {overline{mathrm {T}}}_{text {body}} leading up to thermal behavior initiation was observed, suggesting that changes in {overline{mathrm {T}}}_{text {body}} rather than {overline{mathrm {T}}}_{text {sk}} and T_{text {core}} alone mediate thermal behavior in humid heat. Collectively, the results of this study appear to support the hypothesis that the temporal recruitment of autonomic thermoeffectors follows an orderly manner based on their physiological cost.

Effect of massage therapy on preterm neonate's body temperature.

Low-cost care strategies can be implemented to avert the morbidity and mortality associated with hypothermia in preterm neonates. To determine the effect of massage therapy on body temperature of preterm neonates. A quasi-experimental design was conducted among 72 preterm neonates at a level II special care nursery in Western Kenya. Neonates were recruited on the third day of life and followed up for 10 days. Neonates in the intervention group were massaged three times a day for 15 minutes. Body temperature was monitored and recorded before, during and after each therapy session. Neonates in the control group received routine care: temperature monitoring three times a day, feeding and diaper change. Neonates who received massage had higher mean body temperature than the control group during therapy on day 6 (p = .019) and after therapy on day 6 (p = .017) and day 8 (p = .005). A comparison within massage group (before/during, during/after, before/after) showed an increase in mean body temperature during therapy compared to before therapy (p <.001) and after therapy compared to before therapy (p <.001). Massage therapy increases body temperature in preterm neonates.

Sex Difference in Regional Skin Blood Flow Perfusion and Sweat Rates during Exercise in Hot and Cool Conditions

BackgroundFemales are reported to have lower thermosenstivity for evaporative heat loss and skin blood flow (SKbF) response to an increase in mean body temperature during exercise compared to men. However, sweat rate (SR) and SkBF are typically examined only on the forearm. It is unclear if SR and SkBF differ between sex in various body regions during exercise hyperthermia when matched for exercise heat production.PurposeThis project tested the hypothesis that regional skin blood flow perfusion and sweat rates would differ between men and women exercising at matched exercise heat production.MethodsTwenty‐two healthy active (7 day activity: 8620±3008 steps/day; VO2max: 49±10 mL/kg/min) adults (11M/11F, 22.4±4.9y, 169±7.6cm, 68.3±13kg) exercised at similar metabolic heat production (M: 7.1±1.5 W/kg, F: 6.9±1.4 W/kg; P=0.32) for 60 min (cycle ergometer) in cool (24.0±0.0□C; 14.4±3.6%Rh) and hot (42.3±0.2□C; 27.9±5.5%Rh) conditions in random order separated by at least 7 days. The change for intestinal temperature (ΔTin) and heart rate (ΔHR) utilized a factorial two‐way repeated measure analysis of variance (RMANOVA) for interaction (In) and main effect (ME) for Sex and Condition. Local skin temperature (Tsk), SKbF, and SR were measured at the chest, stomach, forearm, and shoulder regions at rest and continuously during exercise and analyzed within each condition with a factorial two‐way RMANOVA for In and ME for Time and Sex.ResultsMales and females had a similar increase in hot compared to cool for ΔTin (Cool: Δ0.5±0.1□C, Hot: Δ1.5±0.6□C; ME: condition; P&lt;0.0001) and ΔHR (Cool: 58±15 b/min, Hot: 71±15 b/min; ME: Condition; P&lt;0.01). Tsk was hotter at each site in the hot compared to cool condition but not different between sex (ME: Condition, P≤.0001). SkbFchest increased during exercise in both sexes (ME: Time, P&lt;0.0001). SkbFstomach increased during exercise in both conditions, however in the hot increased greater in females compared to males (In: Time × Sex, P&lt;0.002). SkBFforearm increase during exercise in both sexes; however, was attenuated in females in the hot (In: Time × Sex, P&lt;0.002). SkBFshoulder increased during exercise and was greater in females compared to males in the hot (ME: Sex, P&lt;0.04) and more so in the cool (In: Time × Sex, P&lt;0.03). SRchest increased similar between sex in hot but was greater in cool for females (In: Time × Sex, P&lt;0.003). SRstomach increased less for females in the hot (ME: Sex, P&lt;0.04) but similar to males in cool (ME: Time, P&lt;0.0001). SRforearm increased less in females in the hot (In: Time × Sex, P&lt;0.0017). SRshoulder increased similar between sex in hot and cool conditions (ME: Time, P&lt;0.0001).ConclusionThese data indicate that sex differences exist for SkBF and SR in different body regions during exercise in hot and cool conditions. Females have elevated SkBF in the stomach and shoulder and similar in chest and forearm compared to males. SR in females are attenuated in stomach and forearm, but similar in the chest and shoulder regions compared to males.

Body temperature, cutaneous heat loss and skin blood flow during epidural anaesthesia for emergency caesarean section.

It is not clear how converting epidural analgesia for labour to epidural anaesthesia for emergency caesarean section affects either cutaneous vasomotor tone or mean body temperature. We hypothesised that topping up a labour epidural blocks active cutaneous vasodilation (cutaneous heat loss and skin blood flow decrease), and that as a result mean body temperature increases. Twenty women in established labour had body temperature, cutaneous heat loss and skin blood flow recorded before and after epidural top-up for emergency caesarean section. Changes over time were analysed with repeated measures ANOVA. Mean (SD) mean body temperature was 36.8 (0.5)°C at epidural top-up and 36.9 (0.6)°C at delivery. Between epidural top-up and delivery, the mean (SD) rate of increase in mean body temperature was 0.5 (0.5) °C.h-1 . Following epidural top-up, chest (p < 0.001) and forearm (p = 0.004) heat loss decreased, but head (p = 0.05), thigh (p = 0.79) and calf (p = 1.00) heat loss did not change. The mean (SD) decrease in heat loss was 15 (19) % (p < 0.001). Neither arm (p = 0.06) nor thigh (p = 0.10) skin blood flow changed following epidural top-up. Despite the lack of change in skin blood flow, the most plausible explanation for the reduction in heat loss and the increase in mean body temperature is blockade of active cutaneous vasodilation. It is possible that a similar mechanism is responsible for the hyperthermia associated with labour epidural analgesia.

Personalized Hydration Strategy Attenuates the Rise in Heart Rate and in Skin Temperature Without Altering Cycling Capacity in the Heat.

The optimal hydration plan [i.e., drink to thirst, ad libitum (ADL), or personalized plan] to be adopted during exercise in recreational athletes has recently been a matter of debate and, due to conflicting results, consensus does not exist. In the present investigation, we tested whether a personalized hydration strategy based on sweat rate would affect cardiovascular and thermoregulatory responses and exercise capacity in the heat. Eleven recreational male cyclists underwent two familiarization cycling sessions in the heat (34°C, 40% RH) where sweat rate was also determined. A fan was used to enhance sweat evaporation. Participants then performed three randomized time-to-exhaustion (TTE) trials in the heat with different hydration strategies: personalized volume (PVO), where water was consumed, based on individual sweat rate, every 10 min; ADL, where free access to water was allowed; and a control (CON) trial with no fluids. Blood osmolality and urine-specific gravity were measured before each trial. Heart rate (HR), rectal, and skin temperatures were monitored throughout trials. Time to exhaustion at 70% of maximal workload was used to define exercise capacity in the heat, which was similar in all trials (p = 0.801). Body mass decreased after ADL (p = 0.008) and CON (p < 0.001) and was maintained in PVO trials (p = 0.171). Participants consumed 0 ml in CON, 166 ± 167 ml in ADL, and 1,080 ± 166 ml in PVO trials. The increase in mean body temperature was similar among trials despite a lower increase in skin temperature during PVO trial in comparison with CON (2.1 ± 0.6 vs. 2.9 ± 0.5°C, p = 0.0038). HR was lower toward the end of TTE in PVO (162 ± 8 bpm) in comparison with ADL (168 ± 12 bpm) and CON (167 ± 10 bpm), p < 0.001. In conclusion, a personalized hydration strategy can reduce HR during a moderate to high intensity exercise session in the heat and halt the increase in skin temperature. Despite these advantages, cycling capacity in the heat remained unchanged.

Afferent thermosensory function in relapsing-remitting multiple sclerosis following exercise-induced increases in body temperature.

What is the central question of this study? Between 60 and 80% of multiple sclerosis (MS) patients experience transient worsening of symptoms with increased body temperature (heat sensitivity). As sensory abnormalities are common in MS, we asked whether afferent thermosensory function is altered in MS following exercise-induced increases in body temperature. What is the main finding and its importance? Increases in body temperature of as little as ∼0.4°C were sufficient to decrease cold, but not warm, skin thermosensitivity (∼10%) in MS, across a wider temperature range than in age-matched healthy individuals. These findings provide new evidence on the impact of heat sensitivity on afferent function in MS, which could be useful for clinical evaluation of this neurological disease. In multiple sclerosis (MS), increases in body temperature result in transient worsening of clinical symptoms (heat sensitivity or Uhthoff's phenomenon). Although the impact of heat sensitivity on efferent physiological function has been investigated, the effects of heat stress on afferent sensory function in MS are unknown. Hence, we quantified afferent thermosensory function in MS following exercise-induced increases in body temperature with a new quantitative sensory test. Eight relapsing-remitting MS patients (three men and five women; 51.4±9.1years of age; Expanded Disability Status Scale score 2.8±1.1) and eight age-matched control (CTR) subjects (five men and three women; 47.4±9.1years of age) rated the perceived magnitude of two cold (26 and 22°C) and two warm stimuli (34 and 38°C) applied to the dorsum of the hand before and after 30min cycling in the heat (30°C air; 30% relative humidity). Exercise produced similar increases in mean body temperature in MS [+0.39°C (95% CI: +0.21, +0.53) P=0.001] and CTR subjects [+0.41°C (95% CI: +0.25, +0.58) P=0.001]. These changes were sufficient to decrease thermosensitivity significantly to all cold [26°C stimulus, -9.1% (95% CI: -17.0, -1.5), P=0.006; 22°C stimulus, -10.6% (95% CI: -17.3, -3.7), P=0.027], but not warm, stimuli in MS. Contrariwise, CTR subjects showed sensitivity reductions to colder stimuli only [22°C stimulus, -9.7% (95% CI: -16.4, -3.1), P=0.011]. The observation that reductions in thermal sensitivity in MS were confined to the myelinated cold-sensitive pathway and extended across a wider (including milder and colder) temperature range than what is observed in CTR subjects provides new evidence on the impact of rising body temperature on afferent neural function in MS. Also, our findings support the use of our new approach to investigate afferent sensory function in MS during heat stress.

Sex differences in postsynaptic sweating and cutaneous vasodilation

The current study aimed to determine whether a peripheral modulation of sweating contributes to the lower sudomotor thermosensitivity previously observed in females during exercise. We examined dose-response relationships in 12 males and 12 females to incremental doses of acetylcholine (ACh) and methylcholine (MCh) for sweating (ventilated capsule), as well as to ACh and sodium nitroprusside (SNP) for cutaneous vasodilation (laser-Doppler). All drugs were infused using intradermal microdialysis. On a separate day, potential sex differences in the onset threshold and/or thermosensitivity of heat loss responses were assessed during progressive increases in mean body temperature elicited by passive heating. Increases in sweating as a function of increasing concentration of ACh (P = 0.008) and MCh (P = 0.046) significantly differed between males and females. Although the concentration eliciting 50% of the maximal sweating response did not differ between sexes for either agonist (P > 0.1), maximum values were lower in females in response to ACh (0.34 ± 0.12 vs. 0.59 ± 0.19 mg·min(-1)·cm(-2), P = 0.04) and MCh (0.48 ± 0.12 vs. 0.78 ± 0.26 mg·min(-1)·cm(-2), P = 0.05). This observation was paralleled by a lower thermosensitivity of sudomotor activity in females during passive heating (1.29 ± 0.34 vs. 1.83 ± 0.33 mg·min(-1)·cm(-2)·°C(-1), P = 0.03), with no significant differences in the change in mean body temperature at which onset of sweating occurred (0.85 ± 0.19 vs. 0.67 ± 0.13°C, P = 0.10). No sex differences in cutaneous vasodilation were observed in response to ACh and SNP, as well as during passive heating (all P > 0.1). These findings provide direct evidence for a peripheral modulation of sudomotor activity in females. In contrast, sex does not modulate cutaneous vasodilation.

The influence of fatigue-induced increase in relative work rate on temperature regulation during exercise

Heat-loss responses during steady-load exercise are affected by an increase in relative work rate induced by muscle ischaemia or hypoxaemia. The present study investigated whether progressive increases in perception of exertion and relative oxygen uptake %VO2peak which occur during prolonged steady-load exercise as a result of progressively increased peripheral fatigue, might also affect the regulation of heat loss responses and hence the exercise-induced increase in mean body temperature. Ten male subjects first performed a ramp-test to exhaustion on a cycle ergometer to evaluate their initial peak oxygen uptake (Control VO2peak). On a separate day, 120 min of cycling at constant power output corresponding to 60% of Control VO2peak was performed in thermoneutral environment (Ta = 23 degrees C, RH = 50%, wind speed = 5 m s(-1)). This was immediately followed by another maximal performance test (Fatigue VO2peak). During prolonged exercise, median (range) rating of perceived exertion for whole-body (RPEwb) increased (P < 0.01) from initial 3.5 (1-5) to 5.5 (5-9) at the end of exercise. Fatigue VO2peak and peak power output were 9 (5) and 10 (5)% lower (P < 0.01) when compared to control values. At the onset of exercise, heat production, mechanical efficiency, heat loss and mean body temperature increased towards asymptotic values, thereafter remained constant throughout the 120 min exercise, despite the concomitant progressive increase in relative work rate, as reflected in increased RPEwb and relative oxygen uptake. It is thus concluded that the increase in relative work rate induced predominantly by peripheral muscle fatigue affects neither the level of increase in mean body temperature nor the regulation of heat loss responses during prolonged steady-load exercise.

Decreased energy expenditure during prolonged sub-maximal exercise in a warm environment

The purpose of this study was to investigate the influence of a warm environment on thermoregulation and energy expenditure during sub-maximal prolonged exercise in humans. Six healthy male subjects cycled for 120 min at an intensity of 60% maximal oxygen uptake (Vo2max) at three environmental temperatures (10°C, CT; 20°C, MT; and 30°C, WT). Although oxygen uptake at WT showed a significantly lower value compared to those at MT and CT, no significant differences of respiratory exchange ratio were observed among the three environmental trials. A remarkable decrease in total energy expenditure during the 120-min exercise at WT was observed in comparison with those at MT and CT (p<0.05). Changes in rectal temperature, mean skin temperature, and mean body temperature at WT were significantly higher than those at both MT and CT. Although increases in mean body temperature from rest every five minutes during exercise were not different among three environmental temperatures, mean energy expenditures every five minutes at WT were lower compared with those at MT and CT (p<0.05). These results suggest that the increase in energy expenditure for physical exertion is substantially reduced during prolonged sub-maximal exercise in a warm environment. This acute alteration in the energy metabolism may contribute to inhibition of excess heat production and enable prolonged exercise in a warm environment.

A new device for measuring intrauterine temperature

Objective: We evaluated a new device that uses the intrauterine pressure catheter to measure the maternal temperature in patients who are in labor. Study Design: The study was conducted at two medical centers, Christiana Hospital in Newark, Delaware, and Saint Louis University/St Mary’s Health Center in St Louis, Missouri, from September 1, 1997, to May 2, 1998. An intrauterine pressure catheter with a thermistor sensor in the tip was placed into the uterus after spontaneous rupture of membranes. The intrauterine, oral, and tympanic temperatures were simultaneously obtained immediately after insertion of the intrauterine pressure catheter and then hourly until delivery or the initiation of amnioinfusion. Results: The study comprised 97 patients and 404 temperature readings with a temperature range of 34.7°C to 40.7°C. The normal mean ± SD for the oral, tympanic, and intrauterine temperatures was 36.7°C ± 0.5°C, 36.8°C ± 0.5°C, and 37.3°C ± 0.4°C, respectively. There was a linear relationship among the oral, tympanic, and intrauterine temperatures. All three methods showed a significant increase in mean body temperature after epidural anesthesia. Conclusion: The new device, the intrauterine pressure-temperature catheter, provides a convenient and accurate means of continuously measuring uterine temperature in patients who are in labor and require intrauterine monitoring. (Am J Obstet Gynecol 2001;184:1431-5.)

Seasonal patterns of body temperature and activity in free-ranging beaver (Castor canadensis)

Daily activity and body temperature patterns of beavers (Castor canadensis) were monitored in the field with an automated radiotelemetry system from June 1988 through March 1989. Body temperatures of kits and adults averaged close to 37 °C throughout the year, with no evidence of seasonal hypothermia. The greatest temperature changes accompanied episodes of aquatic activity. Body temperature typically dropped 1.0–1.5 °C during periods when beavers were absent from the lodge, then recovered when animals returned to the house. Throughout the open-water season (20 June – 1 November), both age groups demonstrated a daily rhythm in body temperature characterized by a gradual rise between 06:00 and 18:00 followed by a general decline during the nocturnal active period. During the ice-bound season (2 November – 15 March), there was little evidence of a distinct daily rhythm in activity or body temperature, especially in adults. Both age groups exhibited a 0.22–0.64 °C increase in mean body temperature during the 3-h period preceding the first trip in each sequence of excursions away from the lodge. We propose that this predeparture rise in temperature may contribute to the avoidance of immersion hypothermia in foraging beavers.

Body temperature fluctuations in the periparturient horse mare

The objective of this study was to determine the pattern of mare deep body temperature fluctuations associated with parturition using biotelemetry. A radio transmitter was implanted in one flank in each of six mares. Telemetered data were received by a pair of antennae placed at right angles in a 3.3 × 6.6-m stall and stored on a computer hard disk. Hourly temperature data were recorded for the period of −168 through 168 hours post partum. A decrease of 0.76°C in body temperature began at 4 hours prior to parturition (P < 0.1) then decreased rapidly between the 3 hours prior to and the time of parturition (Time 0). The lowest mean body temperature recorded was at the time of parturition (36.58 ± 0.16°C; P < 0.001). A supranormal increase in mean body temperature began one hour post partum, peaked at 38.02 ± 0.08 °C and remained elevated for 48 hours post partum until gradually decreasing to the level of the prepartum mean by 106 hours.

Some aspects of body temperature regulation in sheep

SummarySkin temperatures, deep body temperatures and respiratory rates have been measured in Southdown and Merino sheep following feeding, and during infra-red irradiation, rumen infusions of hot and cold water, and cold exposure induced by shearing. The increases in respiratory rate and skin temperatures induced by infra-red heating and the heat increment of feeding were reversed by addition of iced water to the rumen and were suppressed by shearing. These responses could not be systematically related to particular body temperatures in the sheep and appeared to be continuously variable rather than ‘all-or-none’ phenomena. Considerable overlap was observed between respiratory and vasomotor mechanisms of thermoregulation. Measurements of the surface area and weight of ears and legs showed that these regions contribute approximately 23% of the surface area and 8% of the body weight in Merino sheep. Calculations suggested that up to 70% of the additional heat produced in the 2 h after feeding in sheep may be stored in the tissues through increase in mean body temperature. Sheep kept in short wool throughout the winter appeared to establish a new thermoregulatory ‘set-point’ associated with lower rectal temperatures than those in sheep with a full fleece.

Thermal influence of sunshine and clothing on men walking in humid heat.

For two men walking on a treadmill and wearing two layers of permeable clothing, the same physiological strain measured by the rate of increase in mean body temperature could be produced a) next to a building outdoors in the sunshine with an average air temperature of 85 F and humidity of 20 mm Hg and b) indoors with the same humidity and an air temperature 10 F higher. Under these conditions, the underwear was mainly wet with sweat and the outer layer was mainly dry. In comparable indoor tests on a third subject, the temperature of the underwear approached equilibrium 1 or 2 F lower than the temperature of the skin at air temperatures of 85 and 115 F. The error in calculating clothing insulation introduced by assuming the clothing to be dry is determined by the size and direction of the temperature gradient between skin and air. Adding 10 F to the indoor air temperature does not duplicate all the effects of sunshine. Submitted on September 15, 1961