Daniel S. Moran

A physiological strain index to evaluate heat stress

A physiological strain index (PSI), based on rectal temperature (Tre) and heart rate (HR), capable of indicating heat strain online and analyzing existing databases, has been developed. The index rates the physiological strain on a universal scale of 0-10. It was assumed that the maximal Tre and HR rise during exposure to exercise heat stress from normothermia to hyperthermia was 3 degrees C (36.5-39.5 degrees C) and 120 beats/min (60-180 beats/min), respectively. Tre and HR were assigned the same weight functions as follows: PSI = 5(Tret - Tre0) . (39.5 - Tre0)-1 + 5(HRt - HR0) . (180 - HR0)-1, where Tret and HRt are simultaneous measurements taken at any time during the exposure and Tre0 and HR0 are the initial measurements. PSI was applied to data obtained from 100 men performing exercise in the heat (40 degrees C, 40% relative humidity; 1.34 m/s at a 2% grade) for 120 min. A separate database representing seven men wearing protective clothing and exercising in hot-dry and hot-wet environmental conditions was applied to test the validity of the present index. PSI differentiated significantly (P < 0.05) between the two climates. This index has the potential to be widely accepted and to serve universally after extending its validity to women and other age groups.

Core Temperature Measurement Methods and Current Insights

AbstractClimatic injuries, including hypothermia, hyperthermia and heat stroke, are common in many sports activities. Body core temperature (Tc) measurement for the sportsperson can influence individual performance and may help to prevent injuries. Monitoring internal body Tc accurately requires invasive methods of measurement. The mercury thermometer, most commonly used to measure oral temperature (Toral), has been almost exclusively the only instrument for measuring Tc since the 18th century. Rectal (Tre) and oesophageal temperatures (Toes) have been the most preferred measurement sites employed in thermoregulatory investigations. However, these measurement sites (Tre, Toes, Toral), and the methods used to measure Tc at these sites, are not convenient. Toral measurements are not always possible or accurate. Toes is undesirable because of the difficulty of inserting the thermistor, irritation to nasal passages and general subject discomfort. Tre is not suitable under many circumstances as it is labour intensive and has a prolonged response time. However, Tre remains the most accurately available method for monitoring Tc in thermal illness that occurs during sports activities. In addition, Tre and Toes require wire connections between the thermistor and the monitoring device. The purpose of this paper is to review the various existing methods of Tc measurements in order to focus on the breakthrough needed for a simple, noninvasive, universally used device for Tc measurement which is essential for preventing climatic injuries during sports events.

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 bodys 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.

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.

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°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°C) or evaporative cooling.

An Environmental Stress Index (ESI) as a Substitute for the Wet Bulb Globe Temperature (WBGT)

Abstract The purpose of this study was to develop a new environmental stress index (ESI) based on different parameters relating to heat stress. Meteorological measurements were taken in three climatic zones (hot/wet, hot/dry, and extremely hot/dry) for 60 days, and a new stress index based on these databases was developed as follows: ESI=0.63 T a − 0.03RH+0.002SR+0.0054( T a · RH) − 0.073(0.1+SR) −1 , where Ta is the ambient temperature (°C), RH the relative humidity (%), and SR the solar radiation (W·m−1). The correlation coefficients between ESI and wet bulb globe temperature (WBGT) were very high (R2>0.981). Therefore, we conclude that ESI, based on fast response and the more commonly used accurate climatic microsensors (Ta, RH, SR) which can be combined in a small portable device, has the potential to be a practical alternative to the WBGT.

Evaluation of different levels of hydration using a new physiological strain index

A physiological strain index (PSI), based on rectal temperature (Tre) and heart rate (HR), was recently suggested for evaluating heat stress. The purpose of this study was to evaluate the PSI for different combinations of hydration level and exercise intensity. This index was applied to two databases. The first database was obtained from eight endurance-trained men dehydrated to four different levels (1.1, 2.3, 3.4, and 4.2% of body wt) during 120 min of cycling at a power output of 62-67% maximum O2 consumption (V˙o 2 max) in the heat [33°C and 50% relative humidity (RH)]. The second database was obtained from nine men performing exercise in the heat (30°C and 50% RH) for 50 min. These subjects completed a matrix of nine trials of exercise on a treadmill at three exercise intensities (25, 45, and 65%V˙o 2 max) and three hydration levels (euhydration and hypohydration at 3 and 5% of body wt). Tre, HR, esophageal temperature (Tes), and local sweating rate were measured. PSI (obtained from either Tre or Tes) significantly ( P < 0.05) differentiated among all exposures in both databases categorized by exercise intensity and hydration level, and we assessed the strain on a scale ranging from 0 to 10. Therefore, PSI applicability was extended for heat strain associated with hypohydration and continues to provide the potential to be universally accepted.

Effects of a 4-Month Recruit Training Program on Markers of Bone Metabolism

UNLABELLED Stress fracture susceptibility results from accelerated bone remodeling after onset of novel exercise and may be reflected in bone turnover changes. It is unknown if the bone turnover response to exercise is different between sexes. PURPOSE To assess disparity between sexes in bone metabolism markers during military recruit training and to evaluate relationships between bone turnover markers and factors that may affect bone metabolism. METHODS Volunteers were age-matched men (n = 58) and women (n = 199), 19 yr old, entering gender-integrated combat training. Blood was collected at 0, 2, and 4 months and anthropometric and fitness measures at 0 and 4 months. Serum was analyzed for biomarkers reflecting bone formation (bone alkaline phosphatase and procollagen I N-terminal peptide), bone resorption (C-telopeptide cross-links of type I collagen and tartrate-resistant acid phosphatase), endocrine regulation (parathyroid hormone, calcium, and 25(OH)D), and inflammation (interleukin 1B, interleukin 6, and tumor necrosis factor alpha). Data were analyzed using ANOVA, correlation, and regression analyses. RESULTS Bone turnover markers were higher in men (P < 0.01) and increased similarly for both sexes from 0 to 2 months (P < 0.01). Independent of gender, VO2max (R = 0.477) and serum calcium (R = 0.252) predicted bone formation activity (bone alkaline phosphatase) at baseline (P < 0.01). Serum calcium and parathyroid hormone decreased (2.0 and 6.4%, respectively) from 0 to 2 months (P < 0.001), returning to baseline at 4 months for both sexes. Men exhibited a decrease in 25(OH)D from 0 to 4 months (P = 0.007). Changes in endocrine regulators were significantly correlated with changes in bone turnover markers. Inflammatory markers did not differ between sexes and did not increase. CONCLUSION Military training increased bone formation and resorption markers in 2 months, suggesting rapid onset of strenuous exercise accelerates bone turnover similarly in men and women. Although bone turnover markers were higher in men than women, bone formation status may be related to aerobic fitness and serum calcium independent of gender and may be affected by small changes in endocrine regulators related to nutrition.

Imaging of Lower Extremity Stress Fracture Injuries

Stress reactions and stress fractures in the lower extremities occur frequently in military and athletic populations. As the clinical symptoms of stress fracture may mimic other less severe musculoskeletal injuries, the diagnosis of stress fracture can often be delayed. The following article reviews the characteristics, advantages and disadvantages of the various imaging tools available to detect stress fracture of the lower limbs in order to clarify their utility when diagnosing this condition. Plain radiography, the primary imaging tool for diagnosing suspected stress injuries, may not detect stress fracture injury until fracture healing is well underway. In some cases of suspected stress fracture, this delay in diagnosis can lead to catastrophic fracture and surgical intervention. Bone scintigraphy has long been recommended for the diagnosis of stress fracture, claiming that skeletal scintigraphy is 100% sensitive for the detection of stress fracture. However, there is a potential for a false negative examination and findings might be nonspecific as tumours or infections may mimic stress injury. In addition, bone scintigraphy involves ionizing radiation and it should not be used whenever there is an alternative. Computed tomography (CT) provides exquisitely fine osseous detail, but should be reserved only for specific indications because it also involves ionizing radiation. Magnetic resonance (MR) imaging, which is noninvasive, has no ionizing radiation, is more rapidly performed than bone scintigraphy, and should be the method of choice for stress fracture diagnosis whenever it is available. However, using MR imaging demands an experienced diagnostician in order to decrease reported false-positive injuries. The ultrasonography technique, which is being used increasingly in the evaluation of the musculoskeletal system has recently been shown to have some potential in the diagnosis of stress fracture; however, currently the imaging modalities are insufficient. The peripheral quantitative CT (pQCT) device, which has been developed to specifically assess skeletal status of the extremities, provides data on bone geometry, strength and density. However, the pQCT needs further evaluation prior to being considered for use in diagnosis stress changes in bone. This article reviews the utility of each of the imaging modalities currently available to detect stress fracture injuries of the lower extremities, as well as other utilization factors, which include exposure to ionizing radiation, the ability to detect early- and late-stage reactions in the bone and surrounding soft tissues, and the ability to differentiate between different types of bone lesions.

Can gender differences during exercise-heat stress be assessed by the physiological strain index?

A physiological strain index (PSI) based on rectal temperature (Tre) and heart rate (HR) was recently suggested to evaluate exercise-heat stress. The purpose of this study was to evaluate PSI for gender differences under various combinations of exercise intensity and climate. Two groups of eight men each were formed according to maximal rate of O2 consumption (VO2 max). The first group of men (M) was matched to a group of nine women (W) with similar (P > 0.001) VO2 max (46.1 +/- 2.0 and 43.6 +/- 2.9 ml. kg-1. min-1, respectively). The second group of men (MF) was significantly (P < 0. 001) more fit than M or W with VO2 max of 59.1 +/- 1.8 ml. kg-1. min-1. Subjects completed a matrix of nine experimental combinations consisting of three different exercise intensities for 60 min [low, moderate, and high (300, 500, and 650 W, respectively)] each at three climates (comfortable, hot wet, and hot dry [20 degrees C 50% relative humidity (RH), 35 degrees C 70% RH, and 40 degrees C 35% RH, respectively]). No significant differences (P > 0.05) were found between matched genders (M and W) at the same exposure for sweat rate, relative VO2 max (%VO2 max), and PSI. However, MF had significantly (P < 0.05) lower strain than M and W as reflected by %VO2 max and PSI. In summary, PSI applicability was extended for exercise-heat stress and gender. This index continues to show potential for wide acceptance and application.A physiological strain index (PSI) based on rectal temperature (Tre) and heart rate (HR) was recently suggested to evaluate exercise-heat stress. The purpose of this study was to evaluate PSI for gender differences under various combinations of exercise intensity and climate. Two groups of eight men each were formed according to maximal rate of O2 consumption (V˙o 2 max). The first group of men (M) was matched to a group of nine women (W) with similar ( P > 0.001)V˙o 2 max (46.1 ± 2.0 and 43.6 ± 2.9 ml ⋅ kg-1 ⋅ min-1, respectively). The second group of men (MF) was significantly ( P < 0.001) more fit than M or W with V˙o 2 max of 59.1 ± 1.8 ml ⋅ kg-1 ⋅ min-1. Subjects completed a matrix of nine experimental combinations consisting of three different exercise intensities for 60 min [low, moderate, and high (300, 500, and 650 W, respectively)] each at three climates {comfortable, hot wet, and hot dry [20°C 50% relative humidity (RH), 35°C 70% RH, and 40°C 35% RH, respectively]}. No significant differences ( P > 0.05) were found between matched genders (M and W) at the same exposure for sweat rate, relativeV˙o 2 max(%V˙o 2 max), and PSI. However, MF had significantly ( P < 0.05) lower strain than M and W as reflected by %V˙o 2 max and PSI. In summary, PSI applicability was extended for exercise-heat stress and gender. This index continues to show potential for wide acceptance and application.