Thermal stress and physiological strain of children exposed to hot environments in a glass bangle factory

Summary A group of 19 male children (mean age 12.1 years SEM 1.6 years) occupationally exposed to an excessively hot environment for an average duration of 2.5 years SEM 1.7 years in the glass bangle factory in Firozabad, India, were studied to evaluate the physiological strain induced by the thermal radiation (mean radiant temperature 46.2° SEM 5.1° C) and high ambient temperature (38.2° SEM 3.4° C) prevailing in the factory. Over a work-shift the mean increase in oral temperature was 0.90° C in the exposed children, in comparison with the 0.40° C increase recorded in the control children (p<0.05). The maximum increase in oral temperature was recorded in ‘gulliwalas’ (0.90° C) and the minimum in ‘battiwalas’ (0.80° C). The mean peak value of oral temperature (37.5° C) was observed at 1600 hours. A significant increase in the pulse rate (25.9 beats·min⁻¹) during the work-shift was observed in the exposed children in comparison with a mean increase of 9.4 beats·min⁻¹ in the control group. Ventilatory studies showed pulmonary hyperventilation in the exposed workers. The increase in pulmonary ventilation was in the form of an increase in tidal volume and respiratory frequency induced by high environmental temperatures and thermal radiation. The cardio-respiratory responses showed physiological strain induced by the high ambient temperature and radiant heat prevailing in the glass bangle factory.     

Thermal stress and physiological strain in the glass bangle industry

Summary A preliminary survey of the few units of the small-scale glass bangle industry in Firozabad, Agra District, Uttar Pradesh, indicated that the workers were exposed to severe degrees of heat stress during various operations in the manufacturing processes. A more detailed study in eight glass bangle units was therefore undertaken to make quantitative estimates of heat stress on exposed workers in the summer season. The thermal data collected confirmed that the heat stress on the workers was severe but measurement of certain physiological indicators revealed relatively low levels of strain amongst the exposed workers. The findings could be attributable to high degrees of acclimatization, but further observations in the field supplemented by studies on simulated exposures of volunteers in a climatic chamber seem to be warranted.     

Time course and mechanisms of hemoconcentration in response to mental stress

Hemoconcentration with mental stress exposure may be involved in the triggering of acute cardiovascular events. In the present study, hematocrit was measured repeatedly at baseline, during a 4 min mental stress task and during 20 min of recovery. Blood was sampled every 1-2 min throughout. Blood pressure, heart rate and R-wave to pulse interval, a measure of cardiac contractility, were measured with the same periodicity. The stress task elicited a 1.3% increase in hematocrit, which was sustained with full return to baseline level occurring only after 16 min of recovery. Between-subject correlations between hematocrit and hemodynamic activity were low. Aggregate within-subject coefficients were more impressive; the temporal profile of hematocrit correlated significantly with all hemodynamic variables. Similar within-subject analyses indicated that whereas cardiac contractility was correlated with hematocrit both during stress-related increase and subsequent recovery, blood pressure was related to hematocrit only during the increase. This suggests that stress-induced hemoconcentration may driven by different mechanisms than those which underlie its recovery.     

Cardiac Awareness in Infarct Patients and Normals

It has been argued that many subjects may have low awareness of visceral sensations because such feedback is of little relevance and salience in normal activity. This experiment examines awareness of cardiac sensations (heartbeats) in a group of 13 subjects, aged 37–67 yrs, all of whom had myocardial infarcts within the preceding 6 yrs previous to the experiment. Cardiac awareness was contrasted with the performance of a gender and age matched noncardiac control group on 80 Whitehead type discrimination trials. It was hypothesized that since rehabilitated cardiac patients frequently profess extreme sensitivity to their heart's activity and often experience benign arrhythmias which cause them to focus attention on their heart rate, that this group would show greater awareness of heartbeats than controls. The results clearly show that cardiac patients are no better able to discriminate true from false trials than are normals. Only one of 26 subjects showed above chance levels of discrimination, which is much lower than the percentage usually reported for young adult subjects. Respiration rate and amplitude, finger pulse volume, and heart period showed no differences between groups. The results suggest that although cardiac patients may feel aware of cardiac activity, they show no higher awareness of heartbeats during normal sinus rhythm than noncardiac controls.     

Older people's cardiac responses as indicators of stress in familiar and unfamiliar environments

Little is known about older people's physiological and emotional responses to environmental triggers. We examined this by estimating cardiac stress from heart rate variability (HRV). Thirty-eight participants were monitored while observing environmental scenarios at familiar and unfamiliar locations. Image scenarios included pedestrian and driving scenes in a random order. HRV indices including heart rate (HR), QT variability index (QTVI) and Total HRV Power (TP) were quantified. Familiar locations were associated with higher HR (p<.0005) and lower TP (p=.005) than unfamiliar locations, suggesting they were more stressful. HRV responses to pedestrian and driving scenarios indicated that stress was not influenced by either the type of image scenario or the order of image presentation. There were no gender-related differences in cardiac responses. HRV is a useful surrogate of cardiac stress when assessing older people's responses to their environments.     

微波辐照诱导内质网应激致心肌微血管内皮细胞损伤

目的探讨微波辐照致心肌微血管内皮细胞损伤与内质网应激之间的关系。方法取培养3~4代心肌微血管内皮细胞随机分为对照组和辐照各组。1.分别采用10mW/cm2,30mW/cm2、50mW/cm2微波辐射心肌微血管内皮细胞,辐照时间均为6min。于照射后24h收集细胞。2.细胞被暴露于30mW/cm2微波6 min,继续培养1 h、3 h或24 h之后,内皮细胞被收集,对照组于24 h结束实验。以膜联蛋白V-碘化丙啶双染法检测细胞凋亡;鬼笔环肽染色法观察微血管内皮细胞骨架的变化,评价微血管内皮细胞的损伤情况;免疫印迹法检测内质网应激分子钙网蛋白(CRT)、葡萄糖调节蛋白78(GRP78)和CCAAT/增强子结合蛋白同源蛋白(CHOP)的蛋白表达,评价微波辐照是否引起微血管内皮细胞内质网应激。结果内皮细胞凋亡率的量效研究发现,微波辐照之后,10mW/cm2、30mW/cm2、50mW/cm2照射组的细胞凋亡率分别为(2.34±0.15)%、(2.72±0.96)%、(2.62±0.34)%,与对照组(0.88±0.32)%比较差异显著(P0.05)。时效研究则发现,30mW/cm2照射后1h、3h和24h细胞凋亡率分别为(1.12±0.15)%,(1.49±0.54)%和(1.85±0.45)%。与对照组(1.10%±0.28)%比较,照射后1h组差异不显著(P0.05),照射后3h组和24h组差异显著(P0.05);内质网应激分子的检测发现,30mW组CRT、GRP78、CHOP的蛋白表达分别较对照组升高124%,76%,256%。50mW组CHOP的蛋白表达分别较对照组升高52%,189%。与对照组相比,30mW组CRT、GRP78、CHOP GRP78、及50mW组GRP78、CHOP表达差异显著(P0.05)。10mW组CRT、GRP78、CHOP及50mW组CRT蛋白表达与对照组相比差异无显著性(P0.05)。对照组内皮细胞表现出很少的肌动蛋白纤维。内皮细胞暴露于微波引起的丝状肌动蛋白应力纤维数量的急剧增加。最大应力纤维的形成发生在内皮细胞受到照射后3h或照射功率为30mW。结论微波辐照可诱导严重内质网应激反应,造成大鼠心肌微血管内皮细胞损伤。     

8-OH-DPAT prevents cardiac arrhythmias and attenuates tachycardia during social stress in rats

The aim of this study was to apply a behavioural stress paradigm for studying the neural mechanisms underlying stress-induced arrhythmias, and to test whether such arrhythmias could be suppressed by systemic administration of 8-OH-DPAT, a 5-HT1A agonist possessing central sympatholytic properties. The study was conducted on adult male rats instrumented for telemetric recordings of ECG, body temperature and locomotor activity. In the first experiment, rats were subjected to social defeat after either 8-OH-DPAT (100 µg/kg s.c.) or vehicle injection. In the second experiment, prior to vehicle/8-OH-DPAT administration, animals were pre-treated with zatebradine, a blocker of the pacemaker current. 8-OH-DPAT caused prolongation of basal RR interval, increase in locomotion and hypothermia. Subjecting vehicle-treated animals to social defeat caused shortening in RR interval, increase in locomotor activity and hyperthermia, and provoked the occurrence of premature ventricular and supraventricular beats; all these effects were substantially attenuated by 8-OH-DPAT. Zatebradine caused prolongation of RR interval. In zatebradine/vehicle-treated rats, the incidence of ventricular and supraventricular premature beats during defeat increased 2.5-fold and 3.5-fold, respectively. 8-OH-DPAT administered after zatebradine significantly reduced these stress-induced arrhythmias. We conclude that: i) pharmacologically induced prolongation of RR interval may contribute to an increased susceptibility to stress-induced cardiac arrhythmias, possibly due to the prolongation of the ventricular diastolic period with restored excitability; and ii) systemic administration of 8-OH-DPAT abolishes these arrhythmic events, likely by suppressing stress-induced cardiac sympathetic outflow.     

Changes in Cardiac Refractory Period During Signalled Shock Avoidance in Dogs

The effect of training during an aversive conditioning schedule on the ventricular effective refractory period (ERP) and the occurrence of repetitive extrasystoles (RE) was investigated in 11 dogs. The ERP was decreased significantly at avoidance onset during the first 5 days of the experiment. but remained unaltered during the second 5 days of testing. The changes in ERP were most pronounced on the first day. REs were observed most during avoidance in the animal with the greatest decrease in ERP but inconsistently in other animals. The potential use of aversive Training procedures to study the role of neural factors in cardiac arrhythmias is discussed.     

Psychophysiological Reactivity in Cardiac Transplant Recipients

To assess the contribution of the heart's autonomic innervation to reactivity to psychological stressors, hemodynamic responsiveness of the denervated human heart was examined in two studies. In Study 1, cardiac output measured by thermodilution. heart rate, and systolic and diastolic blood pressure responses to a 4-min mental arithmetic task were studied in 7 cardiac transplant patients during routine post-transplant cardiac catheterization. In Study II, 6 cardiac transplant patients, 5 normal controls, and 5 renal transplant patients participated in a 78-min psychophysiological stress protocol during which heart rate, systolic and diastolic pressure, and cardiac output (measured noninvasively by impedance cardiography) as well as serum epinephrine and norepinephrine were measured at baseline and while subjects performed mental arithmetic and reaction time tasks. In Study I, transplant patients showed significant increases, relative to baseline, in heart rate, systolic blood pressure, and cardiac output in response to mental arithmetic. The diastolic blood pressure response was marginally significant. In Study II, mental arithmetic produced significant reactivity in systolic blood pressure and marginally significant increases in heart rate and diastolic blood pressure in cardiac transplant patients. Reaction time produced only marginally significant diastolic blood pressure reactivity. Hemodynamic reactivity of the cardiac transplant group generally was lower than that of the two innervated groups, which generally were similar to each other. Although the small number of subjects makes conclusions tentative, these data suggest that: 1) Cardiac transplant patients are capable of significant reactivity to psychological stressors despite the absence of innervation of the heart, and 2) reactivity to these stressors is diminished relative to innervated control subjects. In the absence of cardiac innervation, reactivity is due to the vascular system and cardiac effects mediated by humoral factors.     

Myocardial Degeneration and Cardiac Arrest in Squirrel Monkey: Physiological and Psychological Correlates

Behavioral factors and cardiovascular changes associated with myocardial degeneration and cardiac arrest induced by shock avoidance stress were studied. Pairs of avoidance and yoked squirrel monkeys were exposed to a 24-hr session. Myocardial degeneration and cardiac arrest were more readily induced in avoidance than yoked monkeys. The cardiac lesions were not related to body weight, aggressive behavior, or number of shocks received during stress, but an increased heart rate without hypertension during the first stress hour was more evident in avoidance than yoked monkeys. These cardiac changes were attributed to an autonomic disturbance associated with the response contingencies of the avoidance situation. An autonomic effect also appeared to be involved with stress-induced death. These deaths were characterized by a sudden, severe bradycardia without initial hypotension and cardiac arrest which was attributed to either parasympathetic activation or sympathetic inhibition. While heart rate decreased in all monkeys, stress-induced death followed only in monkeys which gave up and stopped contending with the stress. Thus, stress-induced myocardial changes and death were related to autonomic disturbances precipitated by psychological stress.     

Physiological coherence in healthy volunteers during laboratory‐induced stress and controlled breathing

Physiological coherence has been related with a general sense of well‐being and improvements in health and physical, social, and cognitive performance. The aim of this study was to evaluate the relationship between acute stress, controlled breathing, and physiological coherence, and the degree of body systems synchronization during a coherence‐generation exercise. Thirty‐four university employees were evaluated during a 20‐min test consisting of four stages of 5‐min duration each, during which basal measurements were obtained (Stage 1), acute stress was induced using validated mental stressors (Stroop test and mental arithmetic task, during Stage 2 and 3, respectively), and coherence states were generated using a controlled breathing technique (Stage 4). Physiological coherence and cardiorespiratory synchronization were assessed during each stage from heart rate variability, pulse transit time, and respiration. Coherence measurements derived from the three analyzed variables increased during controlled respiration. Moreover, signals synchronized during the controlled breathing stage, implying a cardiorespiratory synchronization was achieved by most participants. Hence, physiological coherence and cardiopulmonary synchronization, which could lead to improvements in health and better life quality, can be achieved using slow, controlled breathing exercises. Meanwhile, coherence measured during basal state and stressful situations did not show relevant differences using heart rate variability and pulse transit time. More studies are needed to evaluate the ability of coherence ratio to reflect acute stress.     

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.     

Metabolically exaggerated cardiac reactions to acute psychological stress revisited

The reactivity hypothesis postulates that large magnitude cardiovascular reactions to psychological stress contribute to the development of pathology. A key but little tested assumption is that such reactions are metabolically exaggerated. Cardiac activity, using Doppler echocardiography, and oxygen consumption, using mass spectrometry, were measured at rest and during and after a mental stress task and during graded submaximal cycling exercise. Cardiac activity and oxygen consumption showed the expected orderly association during exercise. However, during stress, large increases in cardiac activity were observed in the context of modest rises in energy expenditure; observed cardiac activity during stress substantially exceeded that predicted on the basis of contemporary levels of oxygen consumption. Thus, psychological stress can provoke increases in cardiac activity difficult to account for in terms of the metabolic demands of the stress task.     

Plasma oxytocin is related to lower cardiovascular and sympathetic reactivity to stress

In addition to known reproductive and social affiliation functions, oxytocin (OT) has been identified as a cardiovascular hormone. OT synthesis and receptors are found in cardiac and vascular tissue. Animal studies suggest that OT activates an ‘anti-stress’ response that reduces cardiovascular and neuroendocrine stress reactivity. We tested 28 early postpartum mothers, obtaining multiple blood samples for OT, the sympathetic marker, norepinephrine (NE), and the lactation hormone, prolactin, while monitoring their cardiovascular responses to two stressors: public speaking and forehead cold pressor. Although plasma OT did not increase reliably from pre-stress levels during stressors, greater overall OT level was related to greater vasodilation and cardiac stroke volume responses to both tasks, to reduction in heart rate to the cold pressor, as well as to lower plasma NE and higher prolactin levels. In contrast, higher NE was linked to increases in heart rate and decreases in stroke volume. These data support a cardioprotective role for OT, which may influence the magnitude and hemodynamic determinants of cardiovascular stress responses.     

Ratings of perceived exertion and affect in hot and cool environments

Summary The effects of hot and cool environments on perceptual and physiological responses during steady-state exercise were examined in men (n = 14) performing 30 min of constant exercise (cycle ergometry) at a perceived exertion of somewhat hard. Subjects exercised at the same absolute exercise intensity in hot (40°C), neutral (24°C), and cool (8°C) conditions. Data were collected for differential ratings of perceived exertion (RPE), affect, thermal sensation, mean skin ( ) (and rectal temperatures (T _re), and cardiac frequency (f_c). The subjects completed the hot exposure with an average {ei174-2}_sk of 37.5°C (SEM 0.11), while the neutral and cool conditions produced values of 33.8 (SEM 0.09) and 28.2°C (SEM 0.30), respectively. The was significantly higher in the hot than the neutral and cool conditions throughout exercise (P < 0.05). The f_c was significantly lower in the cool than in the other conditions (P < 0.05), and the subjects completed the hot exposure with a mean f_c more than 20 beats · min^–1 greater than observed in the other conditions. The subjects felt worse (lower affect) in the heat throughout exercise (P < 0.05). Overall RPE was significantly lower in the cool than in the heat, while chest RPE scores for the cool and hot conditions were displaced vertically by approximately two points. Subjects perceived work to be harder, felt worse, and experienced greater thermal sensation in the hot condition, compared with the neutral and cool conditions. Changes in cutaneous vasomotor tone and heat-induced influences on the chest may have accounted for the RPE changes observed in the heat.     

九种心脏起搏器临床应用结果分析

本文报告我院1974年至1986年7月使用九种心脏起搏器于70例病人进行150次人工心脏起搏的情况,重点是分析117个国产埋藏式起搏器的质量与临床应用结果。 已使用完毕的67个埋藏式起搏器的平均使用寿命为18.06±10.65个月。其中66个为国产起搏器,其使用寿命以YCP—Ⅱ型最长(19.17±12.35个月),但YCP—Ⅱ、YCP—Ⅰ、GXB—2M及AXB—3型共四种国产起搏器间的平均使用寿命无显著差别(p>0.05)。起搏器失效率为53.7％,其中以YCP—Ⅰ型最高,但无统计学意义(x~2值=4.256,p>0.05)。全组共发生30次起搏器故障,占20.4％(不含电源提前耗竭)。 经分析发现,目前国产埋藏式起搏器存在的主要问题是使用寿命短(平均约18个月)、体积大、重而厚、并发症多、故障率高。其原因关键是能源电池问题。因此,在讨论中强调指出:改进电池性能,研先和采用可靠性高、使用寿命长、体积小的锂碘电池或微型锂电池,不仅是起搏器临床应用的当务之急,而且是生物医学工程学工作者面临的重要课题。     

Phasic Cardiac Reactivity to Psychological Stress as a Function of Aerobic Fitness Level

Cardiovascular adjustments to physical exertion are known to be affected by aerobic fitness level. This raises the possibility that the cardiovascular responses associated with psychological stress may also be related to aerobic fitness. This study was undertaken to determine if phasic cardiac reactivity to stress would be affected by aerobic fitness level, and to make inferences regarding the autonomic mechanisms which might mediate such an effect. Twenty-four males were given a standard physical fitness test and then divided into high and low aerobic fitness level groups. Within two weeks of this assessment, the heart rate and electrocardiographic T-wave amplitude responses of these subjects were monitored during the performance of hard and easy versions of a mental arithmetic task. Analysis of the heart rate data revealed no aerobic fitness level effect. There was, however, greater T-wave amplitude attenuation in the low as compared to the high aerobic fitness level group on hard trials. This pattern of results suggests that psychologically-elicited sympathetic cardiac reactivity is reduced by enhanced aerobic fitness level.     

Cardiac vagal tone and sustained attention in school-age children

Three hypotheses tested relationships between cardiac responses mediated via the vagus and sustained attention in a population of normal school-age children. These hypotheses addressed the theoretical relationships among resting cardiac vagal tone (using the Porges estimate of respiratory sinus arrhythmia, V), performance measures of sustained attention, and cardiac reactivity during sustained attention. Thirty-two fourth and fifth grade children performed a continuous performance task while their electrocardiograms were monitored. Children with higher resting levels of V performed better on the first 3-min block of the continuous performance task. Additionally, levels of V were significantly reduced across the blocks of the 9-min task for all children. No relationships were found between resting levels of V and change in either V or heart period during task performance. These findings support two of the three hypotheses proposed by Porges regarding individual differences in cardiac vagal tone and sustained attention.     

Oxygen radical absorbance capacity (ORAC) and exercise-induced oxidative stress in trotters

Strenuous exercise is a potent inducer of oxidative stress, which has been suggested to be associated with disturbances in muscle homeostasis, fatigue and injury. There is no comprehensive or uniform view of the antioxidant status in horses. We have previously shown that moderate exercise induces protein oxidation in trotters. The aim of this study was to measure the antioxidative capacity of the horse in relation to different antioxidant components and oxidative stress markers after a single bout of moderate exercise to elucidate the mechanisms of antioxidant protection in horses. Eight clinically normal and regularly trained standard-bred trotters were treadmill-exercised for 53 min at moderate intensity. Blood samples were collected prior to and immediately after exercise and at 4 and 24 h of recovery. Muscle biopsies from the middle gluteal muscle were taken before exercise and after 4 h of recovery. Acute induction of oxygen radical absorbance capacity (ORAC) did not prevent exercise-induced oxidative stress, which was demonstrated by increased lipid hydroperoxides (LPO). Pre-exercise ORAC levels were, however, a determinant of total glutathione content of the blood after 4 and 24 h of recovery. Furthermore, baseline ORAC level correlated negatively with 4-h recovery LPO levels. Our results imply that horses are susceptible to oxidative stress, but a stronger antioxidant capacity may improve coping with exercise-induced oxidative stress.