The relative influence of body characteristics on humid heat stress response

The present study was designed to determine the relative importance of individual characteristics such as maximal oxygen uptake ( O_2max), adiposity, DuBois body surface area (A _D), surface to mass ratio (A _D: mass) and body mass, for the individual's reaction to humid heat stress. For this purpose 27 subjects (19 men, 8 women), with heterogeneous characteristics ( O_2max 1.86–5.28 1 · min^–1; fat% 8.0%–31.9%; mass 49.8–102.1 kg; A _D 1.52–2.33 m²) first rested (30 min) and then exercised (60 W for 1 h) on a cycle ergometer in a warm humid climate (35°C, 80% relative humidity). Their physiological responses at the end of exercise were analysed to assess their relationship with individual characteristics using a stepwise multiple regression technique. Dependent variables (with ranges) included final values of rectal temperature (T _re 37.5–39.0°C), mean skin temperature (T _sk 35.7–37.5°C), body heat storage (S 3.2–8.1 J · g^–1), heart rate (HR 100–172 beat · min^–1), sweat loss (397–1403g), mean arterial blood pressure (BP_a, 68–96 mmHg), forearm blood flow (FBF, 10.1–33.9 ml · 100ml^–1 · min^–1) and forearm vascular conductance (FVC = FBF/BP_a, 0.11–0.49 ml · 100 ml^–1 · min^–1 · mmHg^–1). The T _re, T _sk and S were (34%–65%) determined in the: main by ( O_2max), or by exercise intensity expressed as a percent age of O_2max (% O_2max). For T _re, A _D: mass ratio also contributed to the variance explained, with about half the effect of ( O_2max), For T _sk, fat% contributed to the variance explained with about two-third the effect of O_2max. Total body sweat loss was highly dependent (50%) on body size (A _D or mass) with regular activity level having a quarter of the effect of body size on sweat loss. The HR, similar to T _re, was determined by O_2max (48%–51%), with less than half the effect of A _D or A _D :mass (20%). Other circulatory parameters (FBF, BP_a, FVC) showed little relationship with individual characteristics ( < 36% of variance explained). In general, the higher the ( O_2max), and/or the bigger the subject, the lower the heat strain observed. The widely accepted concept, that body core temperature is determined by exercise intensity expressed as % O_2max and sweat loss by absolute heat load, was only partially supported by the results. For both variables, other individual characteristics were also shown to contribute.     

Assessment of male anthropometric trends and the effects on simulated heat stress responses

Assessing temporal changes in anthropometrics and body composition of US Army soldiers is important because these changes may affect fitness, performance, and safety. This study investigated differences in body dimensions (height, weight, percent body fat (%BF)) of US Army male soldiers by comparing 2004 and 1988 databases. Anthropometric somatotypes were identified and physiological responses of the different somatotypes to simulated heat stress (35 degrees C/50%rh, approximately 550 W work rate, carrying 12 kg load including battle dress uniform and body armor, rest for 30 min and walk for 70 min) using a thermal regulatory model were evaluated. A significant increase in body weight (2.4 kg) was observed between the 2004 and 1988 data (P < 0.05, after Bonferroni correction). However, changes in height and circumference measurements for %BF were insignificant, with the magnitude of the changes not exceeding inter-observer errors. Multivariate analyses demonstrated that anthropometric distributions did not differ between the two databases and identified five primary somatotypes: "tall-fat", "tall-lean", "average", "short-lean", and "short-fat." Within each database, anthropometric values differed among the somatotypes. However, simulated physiological responses to heat stress in each somatotype were similar in the 2004 and 1988 populations. In conclusion, an increase in body weight was the primary change observed in this sample of US Army male soldiers. Temporal changes in somatotypes of soldiers over a 16-year period had minimal impact on simulated physiological response to heat stress using a thermal regulatory model.     

The influence of heat stress on plasma volume and intravascular proteins in sedentary females

Summary 23 untrained female subjects underwent a standardised thermal dehydration. Plasma volume (PV), hematocrit (HCT), total intravascular protein concentration (TPC), albumin concentration (AC), total globulin concentration (TGC) were determined before, immediately, 90 min and 180 min after the heat stress. The intravascular protein masses (IPM) were calculated from PV and protein concentration. In comparison to men the loss of body weight and PV was smaller. Consequently the TPC does not increase to the same amount in men. A tendency for a diminution of IPM could be observed but this shift was not significant, compared to males. According to these findings the colloid osmotic capacity remained on a relatively high level. Opposite to men the IPM of globulins increased in females after thermal dehydration.This study was supported by the Bundesinstitut für Sportwissenschaft and the Deutsche Forschungsgemeinschaft     

The fine structure of broiler chicken blood cells, with particular reference to basophils, after severe heat stress

The fine structure of blood cells, with particular reference to basophils, was studied in broiler chickens before and after they had been subjected to heat stress. Granule counts in basophils after heat treatment showed a significant reduction in their total numbers compared with pre-heat treatment. This depletion of granules corresponded with evidence of degranulation seen at the ultrastructural level. Of the three types of basophilic granules described, only the type I electron-dense, homogeneous variety of granule was significantly reduced in number.After heat stress, there was a significant increase in heterophil lobulation. In several birds there was also evidence of cytoplasmic fragmentation in the form of portions of cells containing granules but no nuclei, lying free in the circulation. Damaged mitochondria, not seen before heat treatment, were frequently observed in the cells. Monocytes also showed significant increases in cytoplasmic lipid droplets after heat stress compared with pre-heat treatment, suggesting the onset of possibly early fatty degeneration. However, there was no evidence of increased pseudopodia or pinocytotic activity in these cells. With heat stress, there was a significant reduction in the numbers of electron-dense granules in the small lymphocytes. Despite there being a smaller proportion of circulating eosinophils after heat stress, which was considered to be the result of an immediate stress response, no significant differences were evident between pre- and post-heat treatment in the cells.The red cells and thrombocytes from post-heat-stressed broilers were significantly longer and thinner compared with pre-heat treatment due possibly to dehydration. The dimensional and ultrastructural changes identified in the cells after heat stress question their effective functional ability in raising an immune response under such circumstances.     

Combined effect of heat stress, dehydration and exercise on neuromuscular function in humans

This study examined the combined effect of exercise induced hyperthermia and dehydration on neuromuscular function in human subjects. Six trained male runners ran for 40 min on a treadmill at 65% of their maximal aerobic velocity while wearing a tracksuit covered with an impermeable jacket and pants to impair the evaporation of sweat. These stressful experimental running conditions led the runners to a physiological status close to exhaustion. On average, the 40 min run ended at a heart rate of 196 (SD 8) beats · min⁻¹, a tympanic temperature of 40 (SD 0.3) °C and with a loss of body mass of 2 (SD 0.5)%. Pre- and post-running strength tests included measurements of maximal knee extension and flexion torques in both isometric and isokinetic (at 60 and 240° · s⁻¹) conditions. A 20 s endurance test at 240° · s⁻¹ was also performed. Surface electromyographic (EMG) activity was recorded from six knee extensor and flexor muscles during the entire protocol. The treadmill run led to clear decrements in maximal extension torque and EMG activity both in isometric and at the slowest isokinetic velocity (60° · s⁻¹). However, no differences in these parameters were observed at 240° · s⁻¹. Furthermore, the EMG patterns of the major knee extensor and flexor muscles remained remarkably stable during the treadmill run. These results demonstrate that the exercise-induced hyperthermia and dehydration in the present experiments had only minor effects on the neuromuscular performance. However, it is also suggested that high internal body temperature per se could limit the production of high force levels. Accepted: 26 September 2000     

The influence of body posture,arm movement,and work stress on trapezius activity during computer work

The study aimed to determine the influence of arm posture and movement on trapezius activity of computer workers, considering the full workday. A second aim was to investigate if work periods perceived as stressful were associated with elevated or more sustained muscle activity pattern. Twenty-six computer workers performing call-center (n = 11), help desk (n = 7), or secretarial (n = 8) work tasks participated. Bilateral trapezius surface electromyographic (sEMG) activity and heart rate was recorded throughout the workday. Simultaneous inclinometer recordings from left thigh and upper arms identified periods with sitting, standing, and walking, as well as arm posture and movement. Perceived work stress and tension were recorded on visual analog scales (VAS) every hour. Trapezius sEMG activity was low in seated posture [group median 1.8 and 0.9% of activity at maximal voluntary contraction (%EMG_max) for dominant and non-dominant side] and was elevated in standing (3.0 and 2.5% EMG_max) and walking (3.9 and 3.4% EMG_max). In seated posture (mean duration 79% of workday) arm movement consistently influenced trapezius activity, accounting for ∼20% of intra-individual variation in trapezius activity. Arm elevation was on average not associated with trapezius activity when seated; however, considerable individual variation was observed. There was no indication of increase in trapezius activity or more sustained activity pattern, nor in heart rate, in high-stress versus low-stress periods, comparing periods with seated posture for the subjects reporting contrasts of at least two VAS units in stress (n = 16) or tension (n = 14) score.     

Intracellular and extracellular NO differentially modulates the stress response and apoptosis in macrophages exposed to the influence of biological or physical factors

We studied the role of extracellular and intracellular NO in the regulation of the stress response and apoptosis in macrophages of proinflammatory and antiinflammatory phenotypes under the influence of S. aureus and heat shock. Blockade of extracellular nitric oxide synthesis in cells with antiinflammatory phenotype inhibited the stress response induced by S. aureus and heat shock. The decrease in extracellular nitric oxide concentration around antiinflammatory macrophages potentiated the stress response induced by S. aureus, but had no effect on the stress response induced by heat shock. Hence, intracellular NO mediates the stress response induced by S. aureus and heat shock, while extracellular NO inhibits the stress response induced by S. aureus, but has no effect on the stress response induced by heat shock. In cells with antiinflammatory phenotype, intracellular NO plays an antiapoptotic role. S. aureus and heat shock did not cause apoptosis in macrophages with proinflammatory phenotype, while intracellular NO did not play a role in antiapoptotic activity of the proinflammatory phenotype. Extracellular NO synthesized by macrophages protects these cells from apoptosis induced by S. aureus and heat shock. __________ Translated from Byulleten’ Eksperimental’noi Biologii i Meditsiny, Vol. 143, No. 6, pp. 614–618, June, 2007     

Pinealectomy in ground squirrels: effect on behavioral and physiological responses to heat stress

Richardson's ground squirrels, 1 year after pinealectomy, showed altered behavioral and physiological responses to heat stress when compared to an intact group. Pinealectomized squirrels bar-pressed more often for a cool temperature reward in a hot environment. When deprived of behavioral control of the hot environment, pinealectomized squirrels increased their oxygen consumption, had a higher body temperature, and displayed signs of greater thermal stress, including death, as compared to intact animals. When the intact group was pinealectomized and the experiments were repeated, the difference in behavioral and physiological responses to heat stress were not as great as with the 1 year pinealectomized group. A speculative explanation of the pineal gland's influence on central and peripheral control of evaporative water loss and peripheral blood circulation are offered. The pineal gland may exert a subtle influence on heat transfer mechanisms and adaptations to thermal stress.     

Responses of calves to acute stress: individual consistency and relations between behavioral and physiological measures

The present study examined the consistency over time of individual differences in behavioral and physiological responsiveness of calves to intuitively alarming test situations as well as the relationships between behavioral and physiological measures. Twenty Holstein Friesian heifer calves were individually subjected to the same series of two behavioral and two hypothalamo-pituitary-adrenocortical (HPA) axis reactivity tests at 3, 13 and 26 weeks of age. Novel environment (open field, OF) and novel object (NO) tests involved measurement of behavioral, plasma cortisol and heart rate responses. Plasma ACTH and/or cortisol response profiles were determined after administration of exogenous CRH and ACTH, respectively, in the HPA axis reactivity tests. Principal component analysis (PCA) was used to condense correlated measures within ages into principal components reflecting independent dimensions underlying the calves' reactivity. Cortisol responses to the OF and NO tests were positively associated with the latency to contact and negatively related to the time spent in contact with the NO. Individual differences in scores of a principal component summarizing this pattern of inter-correlations, as well as differences in separate measures of adrenocortical and behavioral reactivity in the OF and NO tests proved highly consistent over time. The cardiac response to confinement in a start box prior to the OF test was positively associated with the cortisol responses to the OF and NO tests at 26 weeks of age. HPA axis reactivity to ACTH or CRH was unrelated to adrenocortical and behavioral responses to novelty. These findings strongly suggest that the responsiveness of calves was mediated by stable individual characteristics. Correlated adrenocortical and behavioral responses to novelty may reflect underlying fearfulness, defining the individual's susceptibility to the elicitation of fear. Other independent characteristics mediating reactivity may include activity or coping style (related to locomotion) and underlying sociality (associated with vocalization).     

The effects of heat and massage application on autonomic nervous system

Purpose

The objective of this study is to evaluate the effects of heat and massage application on autonomic nervous system.

Materials and Methods

One hundred thirty-nine subjects volunteered and completed this study. Heat and massage was daily applied for 40 minutes, 5 days a week for 2 weeks. Primary-dependent measures included heart rate variability, sympathetic skin response, and serum cortisol and norepinephrine levels.

Results

Serum cortisol levels were significantly decreased at 2 weeks compared to baseline (p=0.003). Plasma norepinephrine levels at 4 weeks were significantly decreased compared to baseline (p=0.010). Heart rate, using the power spectra, increased significantly after 2 weeks compared to baseline. Of autonomic nerve conduction measures, latency was significantly increased at 2 and 4 weeks compared to baseline (p=0.023, 0.012), and amplitude was significantly decreased at 4 weeks compared to baseline (p=0.008). There were no serious adverse events such as burns or other major complications.

Conclusion

The results of this study suggest that heat and massage applications provide relaxation to the autonomic nervous system without serious adverse events.     

Behavioral response of the genetically obese (ob/ob) mouse to heat stress: effects of naloxone and prior exposure to immobilization stress

Genetically obese (ob/ob) mice, which possess abnormally elevated levels of pituitary β-endorphin and adrenocorticotropin exhibited less grooming, rearing and jumping during a five min exposure to different levels of heat stress compared to their lean littermate controls (ob/?). Naloxone had a diametrically opposite effect on rearing in these animals, particularly when exposed to low heat stress; it enhanced rearing in ob/ob mice and suppressed the rearing response in ob/? mice. Naloxone enhanced jumping in both the ob/ob mice and the ob/? mice. This effect was slightly, although not significantly, stronger in the obese mice. Finally, exposure to 10 min of immobilization stress before testing at 46°C, enhanced grooming and suppressed jumping in ob/ob and ob/? mice. Naloxone pretreatment reversed the effect of immobilization stress in ob/ob mice but not in their lean littermate controls. The data is discussed in terms of the differential involvement of pituitary endorphins in the behavioral response of ob/ob and ob/? mice to stress.     

热应激预适应对小鼠学习记忆的影响

目的观察热应激对脑缺血处理的小鼠空间学习记忆能力、海马CA1区神经元CREB的影响。方法采用Morris水迷宫筛选空间学习记忆能力正常的昆明小鼠60只,体重(40±5)g,雌雄不限。将实验动物分为4组:正常对照组(Normal)、热应激预处理后缺血再灌注组(HS/IR)、缺血再灌注组(IR)、单纯热应激组(HS);处理后存活时间分别为3h、24h、72h,每个时间点6只,动物处死前再作水迷宫检测。用免疫组织化学方法检测CREB的表达。常规尼氏染色法镜下计数海马CA1区存活神经元。结果水迷宫检测IR组小鼠潜伏期增加,其搜索策略以边缘式和限制式为主,与其它3组比较有显著的统计学意义(P<0.01)。尼氏染色证实IR组锥体细胞神经元减少;24h的HS/IR组的CREB的表达高于IR组。结论热应激预处理可以改善动物因脑缺血引起的学习记忆功能下降。其机制可能涉及到热应激对CREB表达的上调。     

The influence of morningness-eveningness on anxiety and cardiovascular responses to stress

The relationship between cardiovascular responses to stress and health outcomes is inconsistent. In this study, the effects of morningness-eveningness and time of day upon cardiovascular activity at rest and in response to stress were examined. Sixty morning-types and evening-types completed two testing sessions (one morning, one afternoon) that comprised a battery of three stress tasks and a measure of anxiety. The results failed to support a time of day effect upon cardiovascular activity, but there was evidence of an interaction between time of day and morningness-eveningness upon heart rate (HR) and rate pressure product (RPP; HRxSBP). Evening-types exhibited higher HR and RPP in the afternoon, both at rest and during stress. A time of day effect was shown for mood, with anxiety levels higher in the morning than the afternoon. These results are discussed in terms of their health and methodological implications.     

Effects of propofol on damage of rat intestinal epithelial cells induced by heat stress and lipopolysaccharides

Gut-derived endotoxin and pathogenic bacteria have been proposed as important causative factors of morbidity and death during heat stroke. However, it is still unclear what kind of damage is induced by heat stress. In this study, the rat intestinal epithelial cell line (IEC-6) was treated with heat stress or a combination of heat stress and lipopolysaccharide (LPS). In addition, propofol, which plays an important role in anti-inflammation and organ protection, was applied to study its effects on cellular viability and apoptosis. Heat stress, LPS, or heat stress combined with LPS stimulation can all cause intestinal epithelial cell damage, including early apoptosis and subsequent necrosis. However, propofol can alleviate injuries caused by heat stress, LPS, or the combination of heat stress and LPS. Interestingly, propofol can only mitigate LPS-induced intestinal epithelial cell apoptosis, and has no protective role in heat-stress-induced apoptosis. This study developed a model that can mimic the intestinal heat stress environment. It demonstrates the effects on intestinal epithelial cell damage, and indicated that propofol could be used as a therapeutic drug for the treatment of heat-stress-induced intestinal injuries.     

Effects of individual housing on behavior and resistance to Ehrlich tumor growth in mice

This study analyzed in Balb/C mice the effects of individual housing on behavior, serum corticosterone and resistance to Ehrlich tumor growth. Mice (60 days old) were individually (IH) or grouped housed (G) (10-12 animals/cage) for 14-21 days. The 1st day of the housing condition was considered experimental day 1 (ED1). Results showed that on ED21, IH mice, when compared to G mice, presented no differences on corticosterone serum levels when kept undisturbed; however, an increased level of this hormone was observed in IH mice after an immobilization stress challenge. An increased time spent in the plus-maze closed arms and a decreased time in the open arms were also observed in IH mice. When compared to G animals, after inoculation with 10⁵ Ehrlich tumor cells on ED1, IH mice presented an increase in volume of ascitic fluid and number of tumor cells. The survival time of IH mice was also shorter than that measured in G animals. Furthermore, IH mice injected with a different number of tumor cells on ED1 always presented increased Ehrlich tumor cells than G group. Interestingly, these effects were not observed when the tumor cells injection was done on ED4. These results suggest that individual-housing conditions induce an altered immune-endocrine response and, at the same time, decrease animals' resistance to Ehrlich tumor growth. It is proposed that the neural link between the behavioral and immunological changes observed after the stress of individual housing might involve the activation of the HPA axis.     

The Effects of Attention, Stimulus Intensity, and Individual Differences on the Average Evoked Response

The effects of shifting attention toward or away from visual or auditory stimuli of varying intensities were studied using average evoked responses (AERs) in 24 normal human volunteers. Ss were asked to attend to visual or auditory stimuli of four intensities (randomly presented) or to ignore the lights and tones and do mental arithmetic. For visual stimuli, attentional effects were largest at low intensities whereas for auditory stimuli equal effects were shown across intensities. Similar individual rates of increase of AER amplitude with increasing intensity were observed for both visual and auditory stimuli when attentional conditions were controlled. These results suggest that some general intensity processing response is reflected in the AER and that it is important to control attention in AER experiments.     

The influence of the initial state of hydration on endocrine responses to exercise in the heat

Summary This study examines the effect of the initial state of hydration on hormone responses to prolonged exercise in the heat. Five subjects at two initial hydration levels (hypohydrated and hyperhydrated) were exposed to a 36°C environment for 3 h of intermittent exercise. During exercise, the subjects were either fluid-deprived, or rehydrated with water or an isotonic electrolyte sucrose solution (ISO). Both the stress hormones, adrenocorticotropic hormone and cortisol, and the main fluid regulatory hormones, aldosterone, renin activity (PRA) and arginine vasopressin (AVP), were measured in blood samples taken every hour. Prior hyperhydration significantly reduced initial AVP, aldosterone and PRA levels. However, except for AVP, which responded to exercise significantly less in previously hyperhydrated subjects (p<0.05), the initial hydration state did not influence the subsequent vascular and hormonal responses when the subjects were fluid-deprived while exercising. Concurrent rehydration, either with water or with ISO, reduced or even abolished the hormonal responses. There were no significant differences according to the initial hydration state, except for PRA responses, which were significantly lower (p<0.01) in previously hyperhydrated subjects who also received water during exercise. These results indicate that prior hydration levels influence only slightly the hormonal responses to prolonged exercise in the heat. Progressive rehydration during exercise, especially when extra electrolytes are given, is more efficient in maintaining plasma volume and osmolarity and in reducing the hormonal responses.