National Critical Care and Trauma Response Center

Darwin, Australia

National Critical Care and Trauma Response Center

Darwin, Australia

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Walker A.,University of Canberra | Rattray B.,University of Canberra | Brearley M.,National Critical Care and Trauma Response Center
Journal of Occupational and Environmental Hygiene | Year: 2017

Accurately assessing the physiological status of firefighters during work in the heat is critical to ensuring their safety. Evaluating core temperatures (Tc) in the field is problematic due to cost and limitations in technology and accuracy. As such, fire services rely on individual perceptions of wellbeing. The present study aimed to establish whether perceptual responses measured using the perceptual strain index (PeSI), calculated from rate of perceived exertion (RPE) and thermal sensation (TS), could reliably predict the physiological strain (PSI) encountered by experienced firefighters working in a hot environment. We conducted two firefighting simulations (set-pace and self-paced) in a purposefully built heat chamber (100 ± 5°C) comprised of two 20-min periods separated by a 10-min recovery outside the chamber. Physiological strain was measured via heart rate (HR) and gastrointestinal temperature (Tgi) and compared with PeSI at 5-min intervals. To evaluate the predictive ability of the PeSI for PSI, mean differences and the 95% limits of agreement (LOA) were established, along with correlation coefficients at each 5-min interval. Moderately significant correlations occurred in the second work bout of the self-paced trial only (10 min: r = 0.335, 15 min: r = 0.498, 20 min r = 0.439) with no other correlations observed at any other time during either trial or during the rest periods. Bland-Altman analysis revealed mean differences of −0.74 ± 2.70 (self-paced) and +0.04 ± 2.04 (set-paced) between PeSI and PSI with the 95% LOA being −4.77 to 3.28 (self-paced) and −4.01 to 2.01 (set-paced). The wide LOA and lack of correlations observed between perceptual and physiological strain in both self-paced and set-paced work trials indicate that PeSI is not sufficiently reliable as a sole measure of wellbeing for firefighters working in the heat. Hence, we recommend that fire services prioritise the development of reliable and effective monitoring tools for use in the field. © 2017 JOEH, LLC.


Elgendi M.,University of Alberta | Norton I.,National Critical Care and Trauma Response Center | Brearley M.,National Critical Care and Trauma Response Center | Abbott D.,University of Adelaide | Schuurmans D.,University of Alberta
BioMedical Engineering Online | Year: 2014

Background: Analyzing acceleration photoplethysmogram (APG) signals measured after exercise is challenging. In this paper, a novel algorithm that can detect a waves and consequently b waves under these conditions is proposed. Accurate a and b wave detection is an important first step for the assessment of arterial stiffness and other cardiovascular parameters.Methods: Nine algorithms based on fixed thresholding are compared, and a new algorithm is introduced to improve the detection rate using a testing set of heat stressed APG signals containing a total of 1,540 heart beats. Results: The new a detection algorithm demonstrates the highest overall detection accuracy-99.78% sensitivity, 100% positive predictivity-over signals that suffer from 1) non-stationary effects, 2) irregular heartbeats, and 3) low amplitude waves. In addition, the proposed b detection algorithm achieved an overall sensitivity of 99.78% and a positive predictivity of 99.95%. Conclusions: The proposed algorithm presents an advantage for real-time applications by avoiding human intervention in threshold determination. © 2014 Elgendi et al.; licensee BioMed Central Ltd.


Elgendi M.,University of Alberta | Norton I.,National Critical Care and Trauma Response Center | Brearley M.,National Critical Care and Trauma Response Center | Abbott D.,University of Adelaide | Schuurmans D.,University of Alberta
PLoS ONE | Year: 2013

Photoplethysmogram (PPG) monitoring is not only essential for critically ill patients in hospitals or at home, but also for those undergoing exercise testing. However, processing PPG signals measured after exercise is challenging, especially if the environment is hot and humid. In this paper, we propose a novel algorithm that can detect systolic peaks under challenging conditions, as in the case of emergency responders in tropical conditions. Accurate systolic-peak detection is an important first step for the analysis of heart rate variability. Algorithms based on local maxima-minima, first-derivative, and slope sum are evaluated, and a new algorithm is introduced to improve the detection rate. With 40 healthy subjects, the new algorithm demonstrates the highest overall detection accuracy (99.84% sensitivity, 99.89% positive predictivity). Existing algorithms, such as Billauer's, Li's and Zong's, have comparable although lower accuracy. However, the proposed algorithm presents an advantage for real-time applications by avoiding human intervention in threshold determination. For best performance, we show that a combination of two event-related moving averages with an offset threshold has an advantage in detecting systolic peaks, even in heat-stressed PPG signals. © 2013 Elgendi et al.


Brearley M.B.,National Critical Care and Trauma Response Center | Heaney M.F.,Royal Darwin Hospital | Norton I.N.,National Critical Care and Trauma Response Center | Norton I.N.,Royal Darwin Hospital
Prehospital and Disaster Medicine | Year: 2013

Introduction Responses to physical activity while wearing personal protective equipment in hot laboratory conditions are well documented. However less is known of medical professionals responding to an emergency in hot field conditions in standard attire. Therefore, the purpose of this study was to assess the physiological responses of medical responders to a simulated field emergency in tropical conditions. Methods Ten subjects, all of whom were chronically heat-acclimatized health care workers, volunteered to participate in this investigation. Participants were the medical response team of a simulated field emergency conducted at the Northern Territory Emergency Services training grounds, Yarrawonga, NT, Australia. The exercise consisted of setting up a field hospital, transporting patients by stretcher to the hospital, triaging and treating the patients while dressed in standard medical response uniforms in field conditions (mean ambient temperature of 29.3°C and relative humidity of 50.3%, apparent temperature of 27.9°C) for a duration of 150 minutes. Gastrointestinal temperature was transmitted from an ingestible sensor and used as the index of core temperature. An integrated physiological monitoring device worn by each participant measured and logged heart rate, chest temperature and gastrointestinal temperature throughout the exercise. Hydration status was assessed by monitoring the change between pre- and post-exercise body mass and urine specific gravity (USG). Results Mean core body temperature rose from 37.5°C at the commencement of the exercise to peak at 37.8°C after 75 minutes. The individual peak core body temperature was 38.5°C, with three subjects exceeding 38.0°C. Subjects sweated 0.54 L per hour and consumed 0.36 L of fluid per hour, resulting in overall dehydration of 0.7% of body mass at the cessation of exercise. Physiological strain index was indicative of little to low strain. Conclusions The combination of the unseasonably mild environmental conditions and moderate work rates resulted in minimal heat storage during the simulated exercise. As a result, low sweat rates manifested in minimal dehydration. When provided with access to fluids in mild environmental conditions, chronically heat-acclimatized medical responders can meet their hydration requirements through ad libitum fluid consumption. Whether such an observation is replicated under a harsher thermal load remains to be investigated. Copyright © World Association for Disaster and Emergency Medicine 2013 2013 World Association for Disaster and Emergency Medicine.


Elgendi M.,University of British Columbia | Elgendi M.,University of Alberta | Fletcher R.R.,Massachusetts Institute of Technology | Norton I.,National Critical Care and Trauma Response Center | And 4 more authors.
Computer Methods and Programs in Biomedicine | Year: 2015

There are a limited number of studies on heat stress dynamics during exercise using thephotoplethysmogram (PPG). We investigate the PPG signal and its derivatives for heat stressassessment using Welch (non-parametric) and autoregressive (parametric) spectral estima-tion methods. The preliminary results of this study indicate that applying the first andsecond derivatives to PPG waveforms is useful for determining heat stress level using 20-srecordings. Interestingly, Welch's and Yule-Walker's methods in agreement that the secondderivative is an improved detector for heat stress. In fact, both spectral estimation meth-ods showed a clear separation in the frequency domain between measurements before andafter simulated heat-stress induction when the second derivative is applied. Moreover, theresults demonstrate superior performance of the Welch's method over the Yule-Walker'smethod in separating before and after the three simulated heat-stress inductions. © 2015 Elsevier Ireland Ltd.


PubMed | University of New South Wales, Massachusetts Institute of Technology, National Critical Care and Trauma Response Center, University of British Columbia and 2 more.
Type: Letter | Journal: Computer methods and programs in biomedicine | Year: 2015

There are a limited number of studies on heat stress dynamics during exercise using the photoplethysmogram (PPG). We investigate the PPG signal and its derivatives for heat stress assessment using Welch (non-parametric) and autoregressive (parametric) spectral estimation methods. The preliminary results of this study indicate that applying the first and second derivatives to PPG waveforms is useful for determining heat stress level using 20-s recordings. Interestingly, Welchs and Yule-Walkers methods in agreement that the second derivative is an improved detector for heat stress. In fact, both spectral estimation methods showed a clear separation in the frequency domain between measurements before and after simulated heat-stress induction when the second derivative is applied. Moreover, the results demonstrate superior performance of the Welchs method over the Yule-Walkers method in separating before and after the three simulated heat-stress inductions.


Walker A.,University of Canberra | Driller M.,University of Waikato | Brearley M.,National Critical Care and Trauma Response Center | Rattray B.,University of Canberra | Rattray B.,University of Canberra
Applied Physiology, Nutrition and Metabolism | Year: 2014

Firefighters are exposed to hot environments, which results in elevated core temperatures. Rapidly reducing core temperatures will likely increase safety as firefighters are redeployed to subsequent operational tasks. This study investigated the effectiveness of cold-water immersion (CWI) and iced-slush ingestion (SLUSH) to cool firefighters post-incident. Seventy-four Australian firefighters (mean } SD age: 38.9 } 9.0 years) undertook a simulated search and rescue task in a heat chamber (105 } 5 °C). Testing involved two 20-min work cycles separated by a 10-min rest period. Ambient temperature during recovery periods was 19.3 } 2.7 °C. Participants were randomly assigned one of three 15-min cooling protocols: (i) CWI, 15 °C to umbilicus; (ii) SLUSH, 7 g・kg-1 body weight; or (iii) seated rest (CONT). Core temperature and strength were measured pre-and postsimulation and directly after cooling. Mean temperatures for all groups reached 38.9 } 0.9 °C at the conclusion of the second work task. Both CWI and SLUSH delivered cooling rates in excess of CONT (0.093 and 0.092 compared with 0.058 °C・min-1) and reduced temperatures to baseline measurements within the 15-min cooling period. Grip strength was not negatively impacted by either SLUSH or CONT. CWI and SLUSH provide evidence-based alternatives to passive recovery and forearm immersion protocols currently adopted by many fire services. To maximise the likelihood of adoption, we recommend SLUSH ingestion as a practical and effective cooling strategy for post-incident cooling of firefighters in temperate regions. © 2014, Published by NRC Research Press.


Brearley M.,National Critical Care and Trauma Response Center | Norton I.,National Critical Care and Trauma Response Center | Kingsbury D.,Sir Charles Gairdner Hospital | Maas S.,Suzuki Racesafe
International Journal of Sports Physiology and Performance | Year: 2014

Introduction: Anecdotal reports suggest that elite road motorcyclists suffer from high core body temperatures and physiological and perceptual strain when competing in hot conditions. Methods: Four male non-heat-acclimatized elite motorcyclists (3 Superbike, 1 Supersport) had their gastrointestinal temperature, heart rate, and respiratory rate measured and recorded throughout practice, qualifying, and race sessions of an Australian Superbike and Supersport Championship round contested in tropical conditions. Physiological strain was calculated during the sessions, and fluid-balance measures were taken during practice and qualifying. Rider thermal sensation was assessed immediately postsession. Results: Mean ambient temperature and relative humidity were 29.5-30.2°C and 64.5-68.7%, respectively, across the sessions. Gastrointestinal temperature rose from 37.6°C to 37.7°C presession at a median rate of 0.035°C, 0.037°C ,and 0.067°C/min during practice, qualifying, and race sessions to reach medians of 38.9°C, 38.8°C, and 39.1°C postsession, respectively. The peak postsession gastrointestinal temperature was 39.8°C. Median heart rates were ~164, 160, and 177 beats/min during the respective practice, qualifying, and race sessions, contributing to median physiological strain of 5.5, 5.6, and 6.2 across the sessions. Sweat rates were 1.01 and 0.90 L/h during practice and qualifying sessions, while rider thermal sensation was very hot after each session. Conclusions: This investigation confirms that elite road motorcyclists endure moderate to high physiological strain during practice, qualifying, and race sessions, exhibiting more-rapid rates of body-heat storage, higher core body temperatures, and higher physiological and perceptual strain than their stock-car-racing counterparts when competing in tropical conditions. © 2014 Human Kinetics, Inc.


Brearley M.,National Critical Care and Trauma Response Center
Journal of Military and Veterans' Health | Year: 2012

Exercise together with environmentally induced heat stroke continue to pose a problem for military operations in hot climates. A variety of cooling strategies are required by the military to mitigate the risk of heat stroke due to the variety of climates and physical workloads encountered by defence personnel, combined with their individual physical characteristics and uniforms/protective attire. This paper highlights that cooling is traditionally applied as a treatment for heat stroke rather than used to prevent its onset. Recent evidence from the field of sport science demonstrated that cold fluid consumption can act as a heat sink to blunt the rise of core body temperature. Furthermore, the addition of crushed ice to beverages substantially improves its heat storage potential, resulting in decreased core body temperature and enhanced endurance performance. While crushed ice will not be universally available in defence settings, it is a strategy that requires minimal equipment, is relatively quick to prepare, is not labour intensive and does not require the removal of a soldier's uniform. The military should therefore consider the use of crushed ice ingestion as a preventative measure against heat stroke.


PubMed | National Critical Care and Trauma Response Center
Type: Journal Article | Journal: Workplace health & safety | Year: 2016

The common practice of workers resting in the shade to dissipate body heat can be complemented by ingestion of crushed ice or immersion in temperate water to rapidly lower core body temperature.

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