Temperature and surgical wound heat loss during orthopedic surgery: computer simulations and measurements

No Abstrac

Human Skeletal Muscle Mitochondrial Uncoupling Is Associated with Cold Induced Adaptive Thermogenesis

Background: Mild cold exposure and overfeeding are known to elevate energy expenditure in mammals, including humans. This process is called adaptive thermogenesis. In small animals, adaptive thermogenesis is mainly caused by mitochondrial uncoupling in brown adipose tissue and regulated via the sympathetic nervous system. In humans, skeletal muscle is a candidate tissue, known to account for a large part of the epinephrine-induced increase in energy expenditure. However, mitochondrial uncoupling in skeletal muscle has not extensively been studied in relation to adaptive thermogenesis in humans. Therefore we hypothesized that cold-induced adaptive thermogenesis in humans is accompanied by an increase in mitochondrial uncoupling in skeletal muscle. Methodology/Principal Findings: The metabolic response to mild cold exposure in 11 lean, male subjects was measured in a respiration chamber at baseline and mild cold exposure. Skeletal muscle mitochondrial uncoupling (state 4) was measured in muscle biopsies taken at the end of the respiration chamber stays. Mild cold exposure caused a significant increase in 24h energy expenditure of 2.8 % (0.32 MJ/day, range of 20.21 to 1.66 MJ/day, p,0.05). The individual increases in energy expenditure correlated to state 4 respiration (p,0.02, R 2 = 0.50). Conclusions/Significance: This study for the first time shows that in humans, skeletal muscle has the intrinsic capacity for cold induced adaptive thermogenesis via mitochondrial uncoupling under physiological conditions. This opens possibilitie

Individual variation in the relation between body temperature and energy expenditure in response to elevated ambient temperature

The question we address here is whether a mild increase in environmental temperature affects body temperature and energy expenditure, focusing on the individual variation in the relation between energy expenditure and body temperature. We studied eight normal weight healthy females, 48 h at an ambient temperature of 22°C, and 48 h at 27°C. Energy expenditure (EE) was measured in a respiration chamber. Subjects' skin temperature was measured continuously from 8:00 a.m. until 12:00 p.m.: forehead, infraclavicular zone, thigh, hand, and foot. Core temperature was determined tympanically. Body composition was determined by under water weighing. Exposure to 27°C caused a significant increase in body temperature (both skin and core), a decrease in temperature gradients, and a decrease in energy expenditure. At 27°C 24 h EE, adjusted for body composition, was significantly related to body tympanic temperature. The decrease in 24 h EE, at 27°C ambient temperature, was significantly, negatively related to the increase in Ttym, indicating individual responses in adaptation to elevated ambient temperature. Changes in temperature gradient (comparing 27°C with 22°C) were negatively related to changes in EE. This shows that individuals differ in their response to an increase in environmental temperature regarding the relative contribution of insulative or metabolic adjustments

Early evening light mitigates sleep compromising physiological and alerting responses to subsequent late evening light

\u3cp\u3eThe widespread use of electric light and electronic devices has resulted in an excessive exposure to light during the late-evening and at night. This late light exposure acutely suppresses melatonin and sleepiness and delays the circadian clock. Here we investigate whether the acute effects of late-evening light exposure on our physiology and sleepiness are reduced when this light exposure is preceded by early evening bright light. Twelve healthy young females were included in a randomised crossover study. All participants underwent three evening (18:30-00:30) sessions during which melatonin, subjective sleepiness, body temperature and skin blood flow were measured under different light conditions: (A) dim light, (B) dim light with a late-evening (22:30-23:30) light exposure of 750 lx, 4000 K, and (C) the same late-evening light exposure, but now preceded by early-evening bright light exposure (18.30-21.00; 1200 lx, 4000 K). Late-evening light exposure reduced melatonin levels and subjective sleepiness and resulted in larger skin temperature gradients as compared to dim. Interestingly, these effects were reduced when the late-evening light was preceded by an early evening 2.5-hour bright light exposure. Thus daytime and early-evening exposure to bright light can mitigate some of the sleep-disruptive consequences of light exposure in the later evening.\u3c/p\u3

Body mass index and daily physical activity in anorexia nervosa

The level of daily physical activity in 11 non-hospitalized women with anorexia (age: 21-48 yr, body mass index (BMI): 12.518.3 kg [middle dot] m-2), compared with 13 normal-weight women (age: 20-35 yr, BMI 19.2-26.7 kg [middle dot] m-2), was studied in relation to BMI. Daily physical activity over a 7-d period was determined from movement registration and by combining measurements of average daily metabolic rate (using the doubly labeled water method) and sleeping metabolic rate (measured in a respiration chamber). Group averages of daily physical activity were similar for subjects with anorexia and control subjects. However, women with anorexia had either a low or a high level of daily physical activity, whereas most control subjects had a moderate level of daily physical activity. In the women with anorexia, daily physical activity was significantly related to BMI (r =0.84). Subjects with a BMI -2 were equally or more active compared with control subjects, while subjects with a BMI -2 were equally or less active compared with control subjects. The increased physical activity at BMI -2 is considered to be facilitated by an improving physical capacity combined with the advantages of a low body mass during weight-bearing activities. At lower BMI, undereating and declining physical capacity may have caused the observed decrease in daily physical activity

The influence of light on thermal responses

\u3cp\u3eLight is essential for vision and plays an important role in non-visual responses, thus affecting alertness, mood and circadian rhythms. Furthermore, light influences physiological processes, such as thermoregulation, and therefore may be expected to play a role in thermal comfort (TC) as well. A systematic literature search was performed for human studies exploring the relation between ocular light exposure, thermophysiology and TC. Experimental results show that light in the evening can reduce melatonin secretion, delay the natural decline in core body temperature (CBT) and slow down the increase in distal skin temperature. In the morning though, bright light can result in a faster decline in melatonin levels, thus enabling a faster increase in CBT. Moreover, the colour of light can affect temperature perception of the environment. Light with colour tones towards the red end of the visual spectrum leads to a warmer perception compared to more bluish light tones. It should be noted, however, that many results of light on thermal responses are inconclusive, and a theoretical framework is largely lacking. In conclusion, light is capable of evoking thermophysiological responses and visual input can alter perception of the thermal environment. Therefore, lighting conditions should be taken into consideration during thermophysiological research and in the design of indoor climates.\u3c/p\u3

Effect of local skin blood flow during light and medium activities on local skin temperature predictions

\u3cp\u3eThe quality of local skin temperature prediction by thermophysiological models depends on the local skin blood flow (SBF) control functions. These equations were derived for low activity levels (0.8−1met) and mostly in sitting or supine position. This study validates and discusses the prediction of foot SBF during activities of 1−3met in male and females, and the effect on the foot skin temperature prediction (ΔT\u3csub\u3eskin,foot\u3c/sub\u3e) using the thermophysiological simulation model ThermoSEM. The SBF at the foot was measured for ten male and ten female human subjects at baseline and during three activities (sitting, walking at 1km/h, preferred walking around 3km/h). Additional measurements included the energy expenditure, local skin temperatures (T\u3csub\u3eskin,loc\u3c/sub\u3e), environmental conditions and body composition. Measured, normalized foot SBF is 2-8 times higher than the simulated SBF during walking sessions. Also, SBF increases are significantly higher in females vs. males (preferred walking: 4.8±1.5 versus 2.7±1.4, P < 0.05). The quality of ΔT\u3csub\u3eskin,foot\u3c/sub\u3e using the simulated foot SBF is poor (median deviation is −4.8°C, maximumumdeviationis−6°C). Using the measured SBF in ThermoSEM results in an improved local skin temperature prediction (new maximum deviation is −3.3°C). From these data a new SBF model was developed that includes the walking activity level and gender, and improves SBF prediction and ΔT\u3csub\u3eskin,foot\u3c/sub\u3e of the thermophysiological model. Accurate SBF and local skin temperature predictions are beneficial in optimizing thermal comfort simulations in the built environment, and might also be applied in sport science or patient's temperature management.\u3c/p\u3

Thermal sensation : a mathematical model based on neurophysiology

Thermal sensation has a large influence on thermal comfort, which is an important parameter for building performance. Understanding of thermal sensation may benefit from incorporating the physiology of thermal reception. The main issue is that humans do not sense temperature directly; the information is coded into neural discharge rates. This manuscript describes the development of a mathematical model of thermal sensation based on the neurophysiology of thermal reception. Experimental data from two independent studies were used to develop and validate the model. In both studies, skin and core temperature were measured. Thermal sensation votes were asked on the seven-point ASHRAE thermal sensation scale. For the development dataset, young adult males (n = 12, 0.04Clo) were exposed to transient conditions; Tair 30-20-35-30°C. For validation, young adult males (n = 8, 1.0Clo) were exposed to transient conditions; Tair: 17-25-17°C. The neurophysiological model significantly predicted thermal sensation for the development dataset (r2 = 0.89, P <0.001). Only information from warm-sensitive skin and core thermoreceptors was required. Validation revealed that the model predicted thermal sensation within acceptable range (root mean squared residual = 0.38). The neurophysiological model captured the dynamics of thermal sensation. Therefore, the neurophysiological model of thermal sensation can be of great value in the design of high-performance buildings

The influence of different cooling techniques and gender on thermal perception.

The use of low exergy cooling concepts in the built environment can reduce the reliance upon high-quality energy sources. However, the application of such cooling systems can result in whole-body and local discomfort of the occupants. The differences in thermal perception between genders are studied to understand how convective and radiant cooling may impact upon comfort. Physiological and thermal sensation data indicate significant differences between the different experimental cases for each gender. For the prediction of thermal sensation and thermal comfort under non-uniform conditions, the operative temperature only is not sufficient. Combined local factors play an important role in the comfort assessment. For females, the local sensations and skin temperatures of the extremities have a significant influence on whole-body thermal sensation and are therefore important to consider under non-uniform environmental conditions. The results show that existing thermal comfort standards are not suitable for application under non-uniform thermal environments for the assessment of thermal comfort. Local effects, as local skin temperatures, play an important role in the whole-body thermal assessment. Therefore, the operative temperature alone is insufficient for the assessment of thermal comfort