Biomedical subjects

Yuval Heled

Publications and source records attributed to Yuval Heled.

At least 19 recordsLinked to original sources

PubMed2004

Metabolic rate monitoring and energy expenditure prediction using a novel actigraphy method.

BACKGROUND: A novel actigraphy method, the proportional integral mode, was used for monitoring metabolic rate and energy expenditure during different levels of exercise intensity. MATERIAL/METHODS: 13 young (24+/-3 yrs) male subjects, clothed in T-shirts, shorts and athletic shoes, ran/walked for 30 min on a level treadmill at different speeds (3, 5, 2, 6, 4, and 7 mph), 5 min at each speed. The following variables were continuously measured: Actigraphy (PCD, USA) data at three different modes (proportional integral mode, zero crossing, and time above threshold) from the wrist; oxygen consumption (Sensor Medics, USA), and heart rate (Polar, Finland). RESULTS: Analysis of the measured data revealed with low correlation between oxygen consumption and zero crossing or time above threshold (R=0.364 and 0.384, respectively), but with high correlation between oxygen consumption and proportional integral mode (R=0.843). CONCLUSIONS: The proportional integral mode, which is unlike the other modes, followed the oxygen consumption and the heart rate curves, showing a potential unique method to predict oxygen consumption and energy expenditure.

Adult↗

PubMed2004

Assessment of heat tolerance for post exertional heat stroke individuals.

BACKGROUND: The aim of this study was to evaluate the heat tolerance test, which was performed by individuals with high risk for heat injuries, for exposure duration and climatic conditions. MATERIAL/METHODS: Nineteen young (19+/-1 yr) post heat stroke males performed 2 separate tolerance tests consisting of identical treadmill walking (5km.h-1, 2% grade) for 120 min during hot (40 degrees C, 40%RH) and comfort (20 degrees C, 50%RH) climate conditions. Physiological monitoring included rectal temperature (Tre), heart rate (HR), skin temperature and sweat rate (msw). Concomitantly, strain evaluation was assessed by the physiological strain index (PSI) and the cumulative heat strain index (CHSI). RESULTS: 14 subjects were categorized as heat tolerant (HT) and 5 subjects as heat intolerant (HI). The comfort tolerance test was found as irrelevant for heat intolerance assessment. PSI after 60 min (PSI60) was unable to predict PSI after 120 min (PSI120) whereas there was not a high enough correlation between CHSI60 and CHSI120. CONCLUSIONS: It was concluded that tolerance to heat must be tested during heat stress and the test duration cannot be shorter than 120 min.

Adult↗

PubMed2004

Liver transplantation in exertional heat stroke: a medical dilemma.

BACKGROUND: Exertional heat stroke (EHS) is a life-threatening condition caused by an extreme elevation in core body temperature. Hepatic involvement is one of the hallmarks of heat stroke, affecting nearly all heat stroke patients. It is usually manifested by increased serum levels of liver enzymes, but acute liver failure has also been reported. Liver transplantation has been proposed as a potential treatment in cases of severe liver failure, but there are no unanimous criteria pointing to the right stage in which to conduct the transplantation. CASE PRESENTATION: We report a case of an 18-year old patient who suffered heat-induced liver failure. The patient was referred for orthotopic liver transplantation (OLT) but spontaneously recovered completely with conservative treatment. CONCLUSIONS: This case demonstrates the complexity of the decision for liver transplantation in EHS. The various prognostic criteria of acute hepatic failure and their relevance to EHS are critically reviewed, with an aim to assess their application for such a condition.

Adult↗

PubMed2004

Human ACE I/D polymorphism is associated with individual differences in exercise heat tolerance.

We hypothesized that there is an association between the angiotensin I-converting enzyme (ACE) insertion (I)/deletion (D) polymorphism with the variability in exercise heat tolerance in humans. Fifty-eight Caucasian men were exposed to a 2-h exercise heat-tolerance test. We analyzed the association between their heat-tolerance levels with the ACE DD (n = 25) and I+ (n = 33) genotypes and with various anthropometrical parameters and aerobic fitness. It was found that the relative changes in body core temperature, heat storage, and heart rate during the 120-min exposure to exercise heat stress was consistently lower in the I+ genotype group compared with the DD genotype group (0.8 +/- 0.2 vs. 1 +/- 0.1 degrees C, P < 0.05; 17.7 +/- 1.8 vs. 19.8 +/- 1.3 W/M(2), P < 0.05; and 33 +/- 7 vs. 44 +/- 5 beats/min, respectively, P = 0.06). No significant association was found between heat strain response and the anthropometrical measurements or aerobic fitness in the various genotype groups. We suggest that the ACE I+ polymorphism may be considered as a possible candidate marker for increased heat tolerance.

Adult↗

PubMed2004

Physical exercise enhances hepatic insulin signaling and inhibits phosphoenolpyruvate carboxykinase activity in diabetes-prone Psammomys obesus.

We have shown that physical exercise enhances insulin sensitivity of skeletal muscle in diabetes-prone Psammomys-obesus. In this study, we examined the effect of physical exercise on the liver of these animals. Three groups of animals were exposed to a 4-week protocol; high-energy diet (CH), high-energy diet and exercising (EH), and low-energy diet (CL). Different groups were studied either in a fed state or after an overnight fast, 30 minutes after intraperitoneal (IP) injection of 1 U insulin. Hepatic phosphoenolpyruvate carboxykinase (PEPCK) and glucose-6-phosphatase (G6Pase) activity was measured. Insulin signaling response was examined after insulin injection in the fast state by analyzing tyrosine phosphorylation of insulin receptor (IR) and the association between insulin receptor substrate-1 (IRS-1) and IRS-2 with phosphatidylinositol 3 kinase (PI3-K). After 4 weeks, none of the EH animals became diabetic, whereas all the CH animals became diabetic. PEPCK activity in the fed state was higher in the CH group compared with the CL and EH groups (480 +/- 28 nmol/min/mg protein, 280 +/- 30 nmol/min/mg protein, and 208 +/- 13 nmol/min/mg protein, respectively) (P < .02). G6Pase activity was higher in the CH and EH groups compared with the CL group (261 +/- 54 nmol/min/mg protein, 251 +/- 34 nmol/min/mg protein, and 75 +/- 32 nmol/min/mg protein, respectively) (P < .01). After insulin administration in the fast state, tyrosine phosphorylation of IR and association of IRS-2 with PI3-K were higher in the EH and CL groups than in the CH group. We conclude that exercise improves in vivo hepatic insulin sensitivity in diabetes-prone Psammomys-obesus.

Animals↗

PubMed2004

Hydration status measurement by radio frequency absorptiometry in young athletes--a new method and preliminary results.

A new method for non-invasive measurement of the human state of hydration is presented. This method is based on frequency-dependent absorptiometry of radio-waves passing through tissues. A device utilizing this method was constructed and applied to 12 young (24 +/- 1) male volunteers, who were dehydrated for 1-2.5% of their weight by performance of a physical effort (two 30 min bouts of treadmill walking/running at 2, 3, 4, 5, 6 and 7 mph, 5 min at each speed, separated by 10 min rest), under moderate heat stress (40 degrees C, 40% RH). Hypohydration level was determined by body weight measurements taken before each session, after 30 min and at the end of each session. Concomitantly, measurements of radio frequency (RF) absorption were taken. Each volunteer underwent the heat stress exercise twice: one in which no drinking was permitted, and another with free drinking. A correlation (R2 = 0.734) between weight loss and a change in the radio-waves absorption pattern was observed in most of the volunteers, in both hypo and euhydration sessions. Further work to establish the reproducibility and validity of the RF methodology in larger and different populations, i.e., females, other age groups and different health conditions, is already being researched.

Adult↗

PubMed2004

Fatal exertional heat stroke: a case series.

BACKGROUND: Exertional heat stroke (EHS) is one of the most serious conditions that occur when excess heat, generated by muscular exercise, exceeds the body's heat-dissipation rate. The consequent elevated body core temperature causes damage to the body's tissues, resulting in a characteristic multiorgan syndrome, which is occasionally fatal. METHODS: We analyzed the fatal EHS cases that occurred in the Israeli Defence Forces during the last decade according to Minard's paradigm for evaluation of EHS predisposing factors, aiming to characterize the common features and unique circumstances leading to fatality. RESULTS: Accumulation of predisposing factors, particularly those concerning training regulations, coupled with inappropriate treatment at site, were found to be strong predictors of a grave prognosis. Analysis of the pathologic findings of the fatal EHS cases on autopsy revealed a possible association between the duration and length of exercise prior to EHS occurrence and the extent of pathologic findings. CONCLUSIONS: Strict adherence to existing training regulations may prevent further heat stroke fatalities.

Adolescent↗

PubMed2004

Heat stroke : a review of cooling methods.

The prognosis of heat stroke in patients is directly related to the degree of hyperthermia and its duration. Therefore, the most important feature in the treatment of heat stroke is rapid cooling. Several cooling methods have been presented in the literature including immersion in water at different temperatures, evaporative cooling, ice pack application, pharmacological treatment and invasive techniques. This article describes the various cooling techniques in terms of efficacy, availability, adverse effects and mortality rate. Data suggest that cooling should be initiated immediately at time of collapse and should be based on feasible field measures including ice or tepid water (1-16 degrees C), which are readily available. In the emergency department, management should be matched to the patient's age and medical background and include immersion in ice water (1-5 degrees C) or evaporative cooling.

Animals↗

PubMed2004

Evaluation of CO2 accumulation in respiratory protective devices.

A simple mathematical model was developed to grade the results of the fraction of inspiratory CO2 levels in respiratory protective devices (RPDs). Using this model, the level of FiCO2 of two chemical warfare RPDs was monitored during the examination of 54 young male volunteers at rest and exercise. No set of results distributed in a normal Gaussian mode; therefore, parametric statistics could not be used to analyze the group's results. Yet the model allowed simple and insightful evaluation of the results, stressing differences between the similar RPDs. We suggest continued use of the analysis model as a tool for quantitative evaluation of results and further understanding of the respiratory patterns of RPDs.

Adult↗

PubMed2004

The "golden hour" for heatstroke treatment.

Exertional heatstroke is a life-threatening event. It occurs mainly among the young healthy populations of athletes and soldiers. The severity of exertional heatstroke is directly correlated to the area under the temperature duration curve. Therefore, rapid cooling in the field has an enormous effect on prognosis. Four cases of exertional heatstroke are presented which differ in their outcome. We argue that there is a "window time period" within which simple and effective cooling techniques can determine prognosis.

Adult↗

PubMed2004

Cold injuries among Israeli soldiers operating and training in a semiarid zone: a 10-year review.

Cold weather injuries (CIs) in 242 incidences among Israeli soldiers, who were operating and training in a relatively warm country, were reviewed. Peripheral CIs accounted for 55% of all CIs, whereas hypothermia accounted for 45%. A significant relationship was found between peripheral CIs and continuous operations, characterized by prolonged static exposures to a relatively high environmental cold stress. A significant relationship was also found between hypothermia cases and training activities, characterized by relatively short exposures to a low environmental cold stress in the absence of adequate protective clothing for the cold. Static exposure to a cold environment while wearing wet clothing was found to be the leading cause of both CI types. Peripheral CI prevention requires the improvement of protective clothing for the cold, with special emphasis on protective gear for the extremities. Hypothermia prevention requires increased awareness of military regulations regarding cold weather behavior, especially the importance of changing wet clothing during static periods of the training program.

Adult↗

PubMed2004

Heat strain attenuation while wearing NBC clothing: dry-ice vest compared to water spray.

BACKGROUND: While wearing impermeable nuclear, biological, and chemical (NBC) clothing, reduction of thermal stress is of primary importance. We compared the effect between two cooling methods on the attenuation of heat strain. METHODS: There were six male subjects who were divided into two groups of three and exposed on two consecutive days to 125 min of exercise in a high heat load (40 degrees C, 40% RH) wearing NBC clothing. They were cooled by one of two different cooling methods: an active cooling vest (CV) based on the sublimation of dry ice, or tap water spraying (TP). RESULTS: After 2 h, rectal temperature (Tre) was significantly higher for the CV compared with the TP (38.1 +/- 0.04 degrees C vs. 37.7 +/- 0.10 degrees C, respectively). Skin temperature (Tsk) was significantly higher for the CV compared with the TP (36.60 +/- 0.54 degrees C vs. 34.90 +/- 0.35 degrees C, respectively). In the second hour, heart rate (HR) was significantly higher for CV compared with TP (118 +/- 13 bpm vs. 104 +/- 64 bpm, respectively). Heat storage was significantly higher after the first and second hours for the CV compared with the TP. The physiological strain index (PSI) was higher for CV compared with TP in the second hour. Sweat rate (msw) was significantly higher for CV compared with TP (560 +/- 45 g x h(-1) vs. 409 +/- 84 g x h(-1), respectively). Subjective thermal comfort was not significantly different. CONCLUSIONS: TP was more effective than the CV in reducing heat strain under the conditions used in the study. Until a significant breakthrough in reducing heat strain while wearing NBC clothing in field conditions can be found, TP appears to be an effective and recommended cooling method.

Adult↗

PubMed2004

[Exercise induced hyponatremia].

A normal water-electrolyte balance is essential for normal function of body systems during physical activity. During recent years, awareness of the importance of drinking amongst athletes and Israeli Defense Force (IDF) soldiers, in particular, has been highlighted. A large number of athletes tend to drink prior to, during and after their exercise in order to enhance physical abilities and to prevent heat casualties and dehydration. However, excessive water consumption combined with sweat induced electrolytes loss during physical activity, may cause hyponatremia in extreme cases. Recently, several cases of exercise induced hyponatremia were reported in the IDF, resulting from improper water consumption. In this article, we describe a clinical case of exercise-induced hyponatremia in a soldier and a review of the literature, including the etiology, clinical characterization and recommended treatment. Moreover, water consumption recommendations with regard to physical activity are presented. The application of such recommendations may prevent future events of exercise-induced hyponatremia.

Adult↗

PubMed2003

Plasma antioxidant status and cell injury after severe physical exercise.

Strenuous exercise leads to an increase in metabolic rate, increased production of reactive oxygen species, and compromised antioxidant defense systems. To study the effects of oxidative stress during strenuous exercise, a homogeneous group of 31 male subjects participated in a 6-month, 5 days/week training schedule involving two extreme marches of 50 km and 80 km at sea level, separated by 2 weeks of regular training. Each participant carried 35 kg of extra weight. Blood samples were drawn immediately before and after each march. Twenty-nine subjects completed the 50-km march, and only 16 completed the 80-km march. Plasma levels of reduced ascorbic acid, total ascorbate, and dehydroascorbate did not undergo significant changes during either march. However, the 50- and 80-km marches led to 25% and 37% increases, respectively, in plasma levels of uric acid; due presumably to increases in the metabolic rate and consequent pyrimidine nucleotide metabolism. Both marches led to an approximately 10-fold increase leakage of creatine phosphokinase into the plasma. Likewise, plasma levels of aspartate transaminase, a characteristic marker of liver injury, increased approximately 4-fold. Plasma levels of bilirubin, creatine, urea, and glucose also increased. Plasma protein carbonyl content, a marker of protein oxidative damage, decreased significantly during each march. These results are discussed with respect to the consideration that elevation of the respiration rate during exercise leads to production of more reactive oxygen species than the antioxidant systems can scavenge. Plausible explanations for leakage of molecules into the plasma are discussed.

Aged↗

PubMed2003

Physical exercise enhances protein kinase C delta activity and insulin receptor tyrosine phosphorylation in diabetes-prone psammomys obesus.

We recently reported that physical exercise prevents the progression of type 2 diabetes mellitus in Psammomys obesus, an animal model of nutritionally induced type 2 diabetes mellitus. In the present study we characterized the effect of physical exercise on protein kinase C delta (PKC delta) activity, as a mediator of the insulin-signaling cascade in vivo. Three groups of Psammomys obesus were exposed to a 4-week protocol: high-energy diet (HE/C), high-energy diet and exercise (HE/EX), or low-energy diet (LE/C). None of the animals in the HE/EX group became diabetic, whereas all the animals in the HE/C group became diabetic. After overnight fast, intraperitoneal (IP) insulin (1U) caused a greater reduction in blood glucose levels in the HE/EX and LE/C groups compared to the HE/C group. Tyrosine phosphorylation of insulin receptor (IR), insulin receptor substrate-1 (IRS-1), and phosphatidylinositol 3 kinase (PI3 kinase) was significantly higher in the HE/EX and LE/C groups compared with the HE/C group. Finally, IR-associated PKC delta was higher in the HE/EX and LE/C groups compared to the HE/C group. Coprecipitation of PKC delta with IR was higher in the HE/EX and LE/C groups compared to the HE/C group. Thus, we suggest that 4 weeks of physical exercise results in improved insulin-signaling response in Psammomys obesus accompanied by a direct connection between PKC delta and IR. We conclude that this mechanism may be involved in the preventive effect of exercise on type 2 diabetes mellitus in Psammomys obesus.

Animals↗

PubMed2003

Combined environmental stress and physiological strain indices for physical training guidelines.

The purpose of this study was to develop guidelines based on the previously described environmental stress index (ESI) and physiological strain index (PSI) for work-rest cycles (WRC) during training, especially in the military. The ESI was introduced as a potential substitute for the Wet Bulb Globe Temperature Index because of the very high correlation coefficients between them. The ESI is constructed from the fast-reading meteorological response sensors ambient temperature (Ta), relative humidity (RH), and global radiation (GR), which require only a few seconds to reach equilibrium. The ESI, the first stress index using direct measurements of solar radiation (SR), is calculated as follows: ESI = 0.63Ta - 0.03RH + 0.002SR + 0.0054 (Ta x RH) - 0.073(0.1 + SR)(-1). The PSI is based on heart rate (HR) and rectal temperature (Tre) and can indicate heat strain online and analyze databases. The PSI is constructed as follows: PSI = 5(Tret - Tre0) x (39.5 - Tre0)(-1) + 5(HRt - HR0) x (180 - HR0)(-1), where Tre0 and HR0 are the initial Tre and HR, and Tret and HRt are simultaneous measurements taken at any time. The PSI is scaled from 0 to 10, whereby the respective variables, PSIHR and PSITre, representing the cardiovascular and thermoregulation systems, can contribute up to five units to the overall strain assessment. To integrate the PSI and ESI, we decided to use only the PSIHR component, which represents the metabolic rate and the strain reflected by the cardiovascular system. Furthermore, PSIHR is easier to measure, is easier to implement, and simplifies the integration with ESI. Concomitantly, PSIHR categorizes the strain between 0 and 5, the higher the value, the higher the strain. We believe that the use of the PSI WRC values will help in decreasing the risk of future heat injuries.

Algorithms↗

PubMed2003

Hypothermia and local cold injuries in combat and non-combat situations--the Israeli experience.

INTRODUCTION: Cold weather has been recognized in the Israel Defense Forces (IDF) as a potential medical and operational threat to the soldier. Although regulations have been issued to cope with this situation, every year about 20 cases of hypothermia (T(core) < 35 degrees C) and peripheral cold injuries are reported. METHODS: This study was aimed at following cold weather injuries (CI) in the IDF in the period 1994-2001. 136 cases were reported to our institute during this period. All patients were from the general population of young (20 +/- 2 yr), male soldiers in the IDF. All were classified a priori as healthy, active subjects. RESULTS: Of these patients, 51% were diagnosed with mild hypothermia and 49% with peripheral CI. Among those soldiers who suffered from peripheral CI, less than 5% were diagnosed with frostbite. Most of the cases (76%) occurred in the winter months; however, 10% occurred in the spring, 13% in autumn, and 2 cases (1%) were reported in the summer. The majority of all CI cases occurred during routine scheduled training (51%), and 15% occurred during routine duties. Of the cases, 34% occurred during combat operations (mainly ambushing and surveillance). DISCUSSION: The present study provides data on CI cases in an army where the awareness of the hazards involved in hostile environments is extensive, and in which detailed regulations aimed to prevent these injuries are common practice. The Israeli experience indicates that CI is preventable in most instances by following a few simple regulations and providing proper education to the soldiers and their commanding officers.

Adolescent↗

PubMed2003

[Pre-hospital rewarming methods for hypothermia casualties].

Various methods exist for rewarming hypothermia casualties. Most of these methods necessitate sophisticated medical equipment or vigorous hemodynamic and electrolytic monitoring. Therefore, only a few methods remain suitable for pre-hospital scenarios. The current work reviews the literature regarding these pre-hospital rewarming methods, focusing on their efficacy and compatibility to the cold pre-hospital environment with its limited resources. By relying on endogenous heat producing mechanisms and by isolating the victim, one can achieve fairly efficient rewarming for mild hypothermia (rectal temperature of 32 degrees C-35 degrees C) casualties. Many consider this as an independent rewarming method (passive or endogeneous rewarming method), advisable for mild hypothermia cases. There are also many active rewarming methods, suitable for pre-hospital treatment. These methods, however, suppress the endogenous heat producing mechanisms, and therefore are not more efficient than passive rewarming for mild hypothermia cases. In moderate or severe hypothermia casualties, hypothermia (rectal temperature below 32 degrees C) however, is characterized by suppressed or deficient endogenous heat producing mechanisms. Passive rewarming is not enough in these cases, necessitating the addition of active, central or peripheral rewarming methods. Studies regarding the use of various active rewarming methods in severe hypothermia casualties revealed low rewarming efficacy for the low heat capacity methods, such as warm air inhalation, and a high rewarming efficacy for the high heat capacity methods, such as forced air methods.

Accidents↗