Scientific ethics.
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Ethics, Professional↗
Biomedical subjects
Y Epstein
Publications and source records attributed to Y Epstein.
The cumulative heat strain index--a novel approach to assess the physiological strain induced by exercise-heat stress.
The cumulative heat strain index (CHSI) is a new approach for assessing the total physiological strain experienced by subjects exposed to an exercise-heat stress. The index is based on inherent physiological logic that combines the thermoregulatory strain, which is described by the area under the hyperthermic curve, and the circulatory strain, which is characterized by heart-beat count. According to this model, the index reflects the dynamics of changes in the thermoregulatory and cardiovascular components and accounts for the complementary nature of the interaction between them. Mathematically, the index is calculated as follows: CHSI =[ sigma(0-t) hb-fc(0) x t] x l0(-3) x [ integral (0-t) Tre x dt-Tre(0) x t] (units) Where: hb=heart beats, fc(0)=initial lowest heart rate (bpm), Tre = rectal temperature (Tre(0) = baseline Tre) (degrees C) and t = time (min) from the onset of measurements. Four sets of data, from various former studies, have been used to demonstrate the index's applicability and its sensitivity to differentiate between levels of stain under various stressful conditions (e.g. clothing insulation, acclimation to heat and levels of tolerance to heat). In all cases, the index was found to be a sensitive tool for assessing the level of strain. Furthermore, the CHSI can be used to predict potential strain. The index's high sensitivity arises from its nature, which reflects miniature differences in the pattern of changes in the dynamics of physiological responses and therefore is a powerful and practical tool for evaluating even minor changes in strain.
Adolescent↗
Abnormal thermoregulation in drug-free male schizophrenia patients.
Schizophrenia patients may develop various thermoregulatory disturbances. We hypothesized that a standardized exercise-heat tolerance test [two 50-min bouts of walking a motor-driven treadmill at 40 degrees C (relative humidity=40%)] would reveal abnormal thermoregulation in drug-free schizophrenia patients. Six drug-free schizophrenia outpatients and seven healthy comparison subjects participated in this study. The schizophrenia patients exhibited significantly higher baseline and exertion-related rectal temperature. The relevance of these findings to the pathophysiology of schizophrenia-related thermoregulatory disorders is as yet unclear.
Adult↗
Changes in heart rate variability following acclimation to heat.
We studied the sympatho-vagal balance during acclimation to heat in eight healthy individuals. The subjects, dressed in shorts and tennis shoes, underwent a 10 d procedure of acclimation. Daily exposure lasted 115 min--5 min rest followed by 2 bouts of 50 min exercise (walking on a treadmill at a work load of approximately 350 watt) separated by 10 min rest-at 40 degrees C and 40% relative humidity. We analyzed the time and frequency domains of 256 R-R intervals, toward the end of the second bout of exercise, on the first and tenth days of acclimation. Typical changes for heat acclimation (a reduction in rectal temperature and heart rate, an increase in sweat rate) were observed. Concomitant to a decrease in the final heart rate on the tenth day, sympathetic tone increased. We suggest that, except for the chronotropic response, changes in the sympatho-vagal balance may reflect several adaptive mechanisms of the cardiovascular system. Peripheral factors rather than intrinsic cardiac factors are of relatively greater importance in the direct control of cardiac function.
Acclimatization↗
[Thermoregulation in rest and exercise--gender differences].
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Body Composition↗
Exertional heat illness.
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Health Education↗
[Prediction of physiological response from mathematical models].
The ability to predict the physiological responses of workers exposed to extreme environmental conditions, has been a challenge to environmental physiologists for more than 3 decades. Therefore, mathematical models have been developed to predict metabolic rate under various levels of work intensity and dynamic changes in body temperature and heart rate. Based on the effect of exercise on the cardiovascular system, a model was developed to predict mean arterial blood pressure as a function of heart rate. Physiological strain could also be estimated on the basis of thermoregulatory and cardiovascular strains. This paper summarizes knowledge accumulated during 25 years of studies in the field of mathematical modeling of physiological parameters. Besides analyzing the logic underlying each model, it explains the scientific approach in developing a model from its early concept to the model's application in the field.
Blood Pressure↗
[Man in a hot climate--early studies of the Institute of Military Physiology].
In the 1950's many IDF soldiers were hospitalized for heat stroke--about 25% of whom died. Analyzing these cases revealed that commanders misinterpreted human ability to perform in the heat and ignored basic concepts of fluid and electrolyte balance and heat load. In the early 1960's a series of studies was conducted with regard to soldiers' performance in the heat. The first study (1959), which later became a classic, was conducted during a 21-day march from Eilat to Metula, crossing all climatic zones of Israel. The study was followed by other investigations which approached the issues of voluntary dehydration, fluid consumption vs sweat loss, salt additives, and the effect of heat load on performance. Based on these early studies, proper regulations were issued to field officers. Over the years, the lessons learned from these studies saved many lives. The number of cases of heat stroke and of other climate-related injuries was dramatically reduced, and performance was enhanced.
Acclimatization↗
[External heat stroke--is it preventable in military settings?].
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Heat Stroke↗
Heat intolerance in patients with chronic schizophrenia maintained with antipsychotic drugs.
OBJECTIVE: Schizophrenia may be associated with hyperthermic syndromes such as febrile catatonia, neuroleptic malignant syndrome, and heatstroke. The authors hypothesized that an exercise-heat tolerance test would disclose abnormal thermoregulation in schizophrenic patients. METHOD: Seven male schizophrenic outpatients in remission maintained on depot antipsychotic treatment and eight healthy comparison subjects completed a heat tolerance test that consisted of two 50-minute bouts of walking a motor-driven treadmill at 40xC (relative humidity=40%). RESULTS: A significantly higher rise in rectal and skin temperatures was observed in the patient group. No differences in heart rate, blood pressure, or perspiration were detected. CONCLUSIONS: Schizophrenic patients maintained on antipsychotic drugs exhibit impaired heat tolerance. Possible explanations are a reduced ability to convey heat from the body's core to the periphery with or without excessive heat production. The hyperthermic response to the heat tolerance test may reflect a dysfunction associated with schizophrenia, a neuroleptic-induced side effect, or both.
Adult↗
Exertional heat stroke--the prevention of a medical emergency.
In most cases, exertional heat stroke (EHS) can be prevented in the military setting. The actions taken by the Israel Defense Forces (IDF) and their outcome prove this well. Unfortunately, despite the available information, there are still incidents of failure of command in conducting physical exercise, leading to EHS. In our experience, most incidences are a consequence of disregarding safety regulations. The application of simple and reasonable measures will not only prevent accidents from happening, but will also result in better trained soldiers.
Adult↗
[Physiological aspects of women in combat].
Since military service is physically demanding, soldiers must maintain high levels of physical fitness for optimal performance of their duties. Women are at a physiological disadvantage when competing against men: they have a smaller muscle mass, more body fat, lower red blood cell counts, lower hemoglobin levels and smaller cardiac outputs. Women are slower and weaker than men and more prone to exercise-induced skeletal injuries. Fewer women than men meet the standards of physically demanding jobs. Therefore integrating women into physically demanding military-oriented jobs requires redesigning or modifying the tasks (different pace, mechanical aids, teamwork). While physical training can increase the physical capacity of women, training cannot completely eliminate gender differences. Thus the data presented do not imply that women cannot be integrated into combat units, but highlight gender-related differences which might have an effect on the ability of women to compete equally with men at the same task.
Body Composition↗
Exertional heat stroke: a case series.
UNLABELLED: Exertional heat stroke (EHS) is a state of extreme hyperthermia that occurs when excess heat that is generated by muscular exercise exceeds the body's ability to dissipate it at the same rate. EHS is thought to coincide with previously healthy, highly motivated, and relatively untrained individuals exerting in hot environments for long periods. PURPOSE: To establish this notion, the present study was aimed to follow the trends in the incidence of EHS in the period 1988-1996. METHODS: During these years, 150 cases of male soldiers (age = 20+/-3 yr) were reported to our institute as suffering from heat illnesses. According to the files, 82 cases were definitely diagnosed as EHS. RESULTS: More than 50% of the cases occurred during the first 6 months in service. Most of the cases occurred during the summer season (June-September), but 30% of the cases occurred during the spring. EHS was not related to time in the day. Many cases occurred during the night or early morning, even under mild heat load. Forty percent of the cases occurred during very short activities, and about 60% occurred already during the first 2 h of exercise. The results were discussed in view of the regulations which prevail in the Israeli army. CONCLUSIONS: It seems that almost all EHS cases occurred when regulations were not strictly followed.
Heat Stroke↗
Fluid-electrolyte balance during labor and exercise: concepts and misconceptions.
Body water and electrolyte balance are essential to optimal physiological function and health. During exercise, work, or high temperatures, a significant level of dehydration can develop, and the ratio of extracellular to intracellular fluid can change, despite an ample supply of water. Physical and cognitive performance are impaired at 1-2% dehydration, and the body can collapse when water loss approaches 7%. Because fluid needs and intakes vary, formulating one general guideline for fluid replacement is difficult. Knowing the amount of water lost in sweat may enable predicting fluid needs via mathematical models for industrial, athletic, and military scenarios. Sodium imbalance might result from excessive Na+ loss or from gross overhydration. In most work or exercise lasting < 3-4 hr, the major concern is that fluid be available to prevent heat-related illnesses, which can be prevented if fluid and electrolyte losses are balanced with intake, using the recommendations presented.
Adult↗
Dantrolene and recovery from heat stroke.
Several authors have shown that dantrolene may be effective in the treatment of heat stroke patients. However, the scant data available are still controversial. The aim of this investigation was to establish an animal experimental model for studying the efficacy of this drug both as a prophylactic agent and as a means of hastening the cooling process after heat stroke. Male albino rats were divided into five groups: Sedentary controls (SC), Sedentary+dantrolene (S+D), Exercise controls (EC), and Exercise+dantrolene (E+D, E+D1). The drug (140 mg x kg(-1) body weight) was administered i.v. either prior to subjection to heat stress (40 degrees C) (S+D, E+D) or upon development of heat stroke syndrome (E+D1). In the S+D group, dantrolene administered prior to heat stress (HS) delayed the development of heat stroke by 70%, although colonic temperature (Tc) at the onset of heat stroke was similar to that in group SC (43.0 +/- 0.1 degrees C and 43.2 +/- 0.4 degrees C for S+D and SC, respectively). In E+D animals, dantrolene shortened exercise endurance in the heat by 17.5%, but concomitantly hindered severe Tc rise (40.9 +/- 0.2 degrees C and 40.0 +/- 0.2 degrees C for EC and E+D, respectively). Administration of dantrolene on the development of heat stroke appeared to improve cooling in the exercise group (0.25 degrees C x min(-1) and 0.18 degrees C x min(-1), for the first 1 5 min of cooling, for E+D1 and EC, respectively). The results suggest that dantrolene is effective as a prophylactic agent in sedentary animals only. It also might have application on development of heat stroke. It is hypothesized that the observed rapid cooling is associated with dantrolene's effect on muscle contraction, thus leading to attenuated heat production and peripheral vascular relaxation.
Analysis of Variance↗
Acclimatization strategies--preparing for exercise in the heat.
More than 200 years ago, in 1768, Lind in his monograph: "An assay on diseases incidental to Europeans in hot climate" pointed out that habituation to hot climates reduced the danger to health. Two centuries later, Lind and Bass in a classical study which was carried out under hot/dry climatic conditions (49 degrees C and 20% rh) demonstrated that the adaptation to heat may be described as the series of physiological adjustments that occur when a person who is accustomed of living in a cool environment is transferred to a hot climate. This adaptation is a process which is fully achieved after 10 to 14 days of exposure to heat, but two thirds or even 75% of the adaptation is obtained already within 5 days (1). According to this study improved tolerance to heat is related to typical physiological changes: heightened sweating response, lowered heart rate, and lowered rectal temperature during exercise in the heat.
Acclimatization↗
Predominance of type II fibres in exertional heat stroke.
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Acidosis, Lactic↗
[Heat intolerance].
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Heat Stress Disorders↗