Aural canal, esophageal, and rectal temperatures during exertional heat stress and the subsequent recovery period

Agreement between the ventilated capsule and the KuduSmart® device for measuring sweating responses to passive heat stress and exercise

The present study assessed agreement between a wireless sweat rate monitor (KuduSmart® device) and the ventilated capsule (VC) technique for measuring: (i) minute-averaged local sweat rate (LSR), (ii) sweating onset, (iii) sudomotor thermosensitivity, and (iv) steady-state LSR, during passive heat stress and exercise. It was hypothesized that acceptable agreement with no bias would be observed between techniques for all assessed sweating characteristics. On two separate occasions for each intervention, participants were either passively heated by recirculating hot water (49 °C) through a tube-lined garment until rectal temperature increased 1 °C over baseline (n = 8), or a 60 min treadmill march at a fixed rate of heat production (∼500 W, n = 9). LSR of the forearm was concurrently measured with a VC and the KuduSmart® device secured within ∼2 cm. Using a ratio scale Bland-Altman analysis with the VC as the reference, the KuduSmart® device demonstrated systematic bias and not acceptable agreement for minute-averaged LSR (1.17 [1.09, 1.27], CV = 44.5%), systematic bias and acceptable agreement for steady-state LSR (1.16 [1.09,1.23], CV = 19.5%), no bias and acceptable agreement for thermosensitivity (1.07 [0.99, 1.16], CV = 23.2%), and no bias and good agreement for sweating onset (1.00 [1.00, 1.00], CV = 11.1%). In total, ≥73% of all minute-averaged LSR observations with the KuduSmart® device (n = 2743) were within an absolute error of <0.2 mg/cm2/min to the VC, the reference minimum detectable change in measurement error of a VC on the forearm. Collectively, the KuduSmart® device may be a satisfactory solution for assessing the sweating response to heat stress where a VC is impractical.

A Systematic Review of Post-Work Core Temperature Cooling Rates Conferred by Passive Rest

Physical work increases energy expenditure, requiring a considerable elevation of metabolic rate, which causes body heat production that can cause heat stress, heat strain, and hyperthermia in the absence of adequate cooling. Given that passive rest is often used for cooling, a systematic search of literature databases was conducted to identify studies that reported post-work core temperature cooling rates conferred by passive rest, across a range of environmental conditions. Data regarding cooling rates and environmental conditions were extracted, and the validity of key measures was assessed for each study. Forty-four eligible studies were included, providing 50 datasets. Eight datasets indicated a stable or rising core temperature in participants (range 0.000 to +0.028 °C min^-1), and forty-two datasets reported reducing core temperature (-0.002 to -0.070 °C min^-1) during passive rest, across a range of Wet-Bulb Globe Temperatures (WBGT). For 13 datasets where occupational or similarly insulative clothing was worn, passive rest resulted in a mean core temperature decrease of -0.004 °C min^-1 (-0.032 to +0.013 °C min^-1). These findings indicate passive rest does not reverse the elevated core temperatures of heat-exposed workers in a timely manner. Climate projections of higher WBGT are anticipated to further marginalise the passive rest cooling rates of heat-exposed workers, particularly when undertaken in occupational attire.

An assessment of the validity and reliability of the P022-P version of e-Celsius core temperature capsules

Core temperature monitoring is a research tool used in many studies, though most popularly, heat strain. Ingestible core temperature capsules are a non-invasive and increasingly popular choice for measuring core body temperature, particularly considering the well-established validation of capsule systems. A newer version of the e-Celsius ingestible core temperature capsule has been released since the preceding validation study resulting in a paucity of validated research for the current version of capsules, P022-P, used by researchers. Using a 1:1 ratio of propylene glycol to water in a circulating water bath, and a reference thermometer with resolution and uncertainty of 0.01 °C, we assessed the validity and reliability of 24 P022-P e-Celsius capsules in three groups of eight, at seven temperature plateaus between 35 °C, and 42 °C in a test-retest format. The systematic bias of these capsules across all 3360 measurements was found to be -0.038 °C ± 0.086 °C (p < .001), The TEST-RETEST evaluation revealed excellent reliability by way of a minute overall mean difference of 0.0095 °C ± 0.048 °C (p < .001), and an intraclass correlation coefficient of 1.00 for each of TEST and RETEST conditions. Although quite small, differences in systematic bias across temperature plateaus were observed for both the OVERALL bias-between 0.00066 °C and 0.041°C-and TEST/RETEST bias-between 0.00010 °C and 0.016 °C. We found that the new capsule version outperforms manufacturer guarantees, with half of the systematic bias observed in a validation study of the previous capsule version. Though these capsules tend to slightly underestimate temperature, we find they possess excellent validity and reliability between 35 °C and 42 °C.

Human temperature regulation under heat stress in health, disease, and injury

The human body constantly exchanges heat with the environment. Temperature regulation is a homeostatic feedback control system that ensures deep body temperature is maintained within narrow limits despite wide variations in environmental conditions and activity-related elevations in metabolic heat production. Extensive research has been performed to study the physiological regulation of deep body temperature. This review focuses on healthy and disordered human temperature regulation during heat stress. Central to this discussion is the notion that various morphological features, intrinsic factors, diseases, and injuries independently and interactively influence deep body temperature during exercise and/or exposure to hot ambient temperatures. The first sections review fundamental aspects of the human heat stress response, including the biophysical principles governing heat balance and the autonomic control of heat loss thermoeffectors. Next, we discuss the effects of different intrinsic factors (morphology, heat adaptation, biological sex, and age), diseases (neurological, cardiovascular, metabolic, and genetic), and injuries (spinal cord injury, deep burns, and heat stroke), with emphasis on the mechanisms by which these factors enhance or disturb the regulation of deep body temperature during heat stress. We conclude with key unanswered questions in this field of research.

Scoping review on the state of the integration of human physiological responses to evaluating heat-stress

OBJECTIVES

To determine the state of the literature on assessing heat-stress using physiological parameters. To provide recommendations to the nuclear industry regarding worker heat-stress management practices.

METHODS

A scoping review identified relevant articles. A search strategy was developed based on a research question concepts. Identified records were screened with inclusion-exclusion criteria. Included articles underwent data extraction using a qualitative data charting method. A thematic analysis and frequency counts were performed.

RESULTS

1687 articles were identified through four databases. The final inclusion consisted of 34 studies. Articles were classified by determinants of heat exposure risks: core body temperature (direct and indirect), scoring scale including core body temperature, scoring scale including human perception, and others. Heart rate and rectal temperature were the two most utilized physiological measurements.

CONCLUSION

A significant amount of literature examined estimation of core temperature using non-invasive methods, sometimes integrated into wearables. Heat-stress management practices could include perceptual measures to better evaluate heat-strain.

Low Ambient Temperature Exposition Impairs the Accuracy of a Non-invasive Heat-Flux Thermometer

Background

Indirect core body temperature (CBT) monitoring from skin sensors is gaining attention for in-field applications thanks to non-invasivity, portability, and easy probe positioning. Among skin sensors, heat-flux devices, such as the so-called Double Sensor (DS), have demonstrated reliability under various experimental and clinical conditions. Still, their accuracy at low ambient temperatures is unknown. In this randomized cross-over trial, we tested the effects of cold temperature exposition on DS performance in tracking CBT.

Methods

Twenty-one participants were exposed to a warm (23.2 ± 0.4°C) and cold (−18.7 ± 1.0°C) room condition for 10 min, following a randomized cross-over design. The accuracy of the DS to estimate CBT in both settings was assessed by quantitative comparison with esophageal (reference) and tympanic (comparator) thermometers, using Bland–Altman and correlation analyses (Pearson’s correlation coefficient, r, and Lin’s concordance correlation coefficient, CCC).

Results

In the warm room setting, the DS showed a moderate agreement with the esophageal sensor [bias = 0.09 (−1.51; 1.69) °C, r = 0.40 (p = 0.069), CCC = 0.22 (−0.006; 0.43)] and tympanic sensor [bias = 2.74 (1.13; 4.35) °C, r = 0.54 (p < 0.05), CCC = 0.09 (0.008; 0.16)]. DS accuracy significantly deteriorated in the cold room setting, where DS temperature overestimated esophageal temperature [bias = 2.16 (−0.89; 5.22) °C, r = 0.02 (0.94), CCC = 0.002 (−0.05; 0.06)]. Previous exposition to the cold influenced temperature values measured by the DS in the warm room setting, where significant differences (p < 0.00001) in DS temperature were observed between randomization groups.

Conclusion

DS accuracy is influenced by environmental conditions and previous exposure to cold settings. These results suggest the present inadequacy of the DS device for in-field applications in low-temperature environments and advocate further technological advancements and proper sensor insulation to improve performance in these conditions.

Evaluation of the physiological changes in prehospital health-care providers influenced by environmental factors in the summer of 2020 during the COVID-19 pandemic

Aim

Wearing personal protective equipment (PPE) is essential to prevent infection transmission, but the risk of heatstroke increases with wearing PPE in a humid and hot environment. Therefore, we aimed to examine how environmental parameters change the body physiology in a hot environment during the coronavirus disease (COVID-19) pandemic.

Methods

This was a retrospective cohort study extracted from the MEDIC Japan heatstroke prevention database, which was recorded between 1 August and 7 September, 2020. Its database is a registry collection from seven healthy health-care providers. Subjects recorded their own vital signs (forehead and tympanic temperature, blood pressure, pulse rate, and oxygen saturation) and environmental factors (type of weather, wet-bulb globe temperature [WBGT], air temperature, humidity, and location) every hour during their working shift.

Results

From 323 records, a weak positive but statistically significant correlation was observed between WBGT and pulse rate (correlation coefficient [95% confidence interval], r = 0.34 [0.23, 0.45]) and between WBGT and core body temperature. Forehead temperature had a stronger correlation than tympanic temperature (forehead, r = 0.33 [0.21, 0.43]; tympanic, r = 0.17 [0.05, 0.28]), which also showed a larger effect (forehead, η² = 0.08; tympanic, η² = 0.05). The effect size of oxygen saturation measured outdoors was large (η² = 0.30). Forehead temperature increased abruptly at 28°C WBGT and at 33°C air temperature.

Conclusion

A hot environment significantly affected forehead temperature, and the daytime imposed a high risk of heatstroke. To avoid heatstroke, environmental parameters are important to note as outdoor environments had a large effect on vital sign changes depending on the time of day.

Insight into the use of tympanic temperature during target temperature management in emergency and critical care: a scoping review

BACKGROUND

Target temperature management (TTM) is suggested to reduce brain damage in the presence of global or local ischemia. Prompt TTM application may help to improve outcomes, but it is often hindered by technical problems, mainly related to the portability of cooling devices and temperature monitoring systems. Tympanic temperature (T_Ty) measurement may represent a practical, non-invasive approach for core temperature monitoring in emergency settings, but its accuracy under different TTM protocols is poorly characterized. The present scoping review aimed to collect the available evidence about T_Ty monitoring in TTM to describe the technique diffusion in various TTM contexts and its accuracy in comparison with other body sites under different cooling protocols and clinical conditions.

METHODS

The scoping review was conducted following the guidelines of the Preferred Reporting Items for Systematic Review and Meta-Analysis extension for scoping reviews (PRISMA-ScR). PubMed, Scopus, and Web of Science electronic databases were systematically searched to identify studies conducted in the last 20 years, where T_Ty was measured in TTM context with specific focus on pre-hospital or in-hospital emergency settings.

RESULTS

The systematic search identified 35 studies, 12 performing T_Ty measurements during TTM in healthy subjects, 17 in patients with acute cardiovascular events, and 6 in patients with acute neurological diseases. The studies showed that T_Ty was able to track temperature changes induced by either local or whole-body cooling approaches in both pre-hospital and in-hospital settings. Direct comparisons to other core temperature measurements from other body sites were available in 22 studies, which showed a faster and larger change of T_Ty upon TTM compared to other core temperature measurements. Direct brain temperature measurements were available only in 3 studies and showed a good correlation between T_Ty and brain temperature, although T_Ty displayed a tendency to overestimate cooling effects compared to brain temperature.

CONCLUSIONS

T_Ty was capable to track temperature changes under a variety of TTM protocols and clinical conditions in both pre-hospital and in-hospital settings. Due to the heterogeneity and paucity of comparative temperature data, future studies are needed to fully elucidate the advantages of T_Ty in emergency settings and its capability to track brain temperature.

Roundtable on Preseason Heat Safety in Secondary School Athletics: Prehospital Care of Patients With Exertional Heat Stroke

OBJECTIVE

First, we will update recommendations for the prehospital management and care of patients with exertional heat stroke (EHS) in the secondary school setting. Second, we provide action items to aid clinicians in developing best-practice documents and policies for EHS. Third, we supply practical strategies clinicians can use to implement best practice for EHS in the secondary school setting.

DATA SOURCES

An interdisciplinary working group of scientists, physicians, and athletic trainers evaluated the current literature regarding the prehospital care of EHS patients in secondary schools and developed this narrative review. When published research was nonexistent, expert opinion and experience guided the development of recommendations for implementing life-saving strategies. The group evaluated and further refined the action-oriented recommendations using the Delphi method.

CONCLUSIONS

Exertional heat stroke continues to be a leading cause of sudden death in young athletes and the physically active. This may be partly due to the numerous barriers and misconceptions about the best practice for diagnosing and treating patients with EHS. Exertional heat stroke is survivable if it is recognized early and appropriate measures are taken before patients are transported to hospitals for advanced medical care. Specifically, best practice for EHS evaluation and treatment includes early recognition of athletes with potential EHS, a rectal temperature measurement to confirm EHS, and cold-water immersion before transport to a hospital. With planning, communication, and persistence, clinicians can adopt these best-practice recommendations to aid in the recognition and treatment of patients with EHS in the secondary school setting.

Exertional Heat-Stroke Management Practices and Intentions Among Secondary School Football Athletic Trainers

CONTEXT

Athletic trainers (ATs) are educated and trained in appropriate exertional heat-stroke (EHS) management strategies, yet disparities may exist between intended and actual uses in clinical practice.

OBJECTIVE

To examine the intended and actual uses of EHS management strategies among those who did and those who did not treat patients with suspected cases of EHS during the 2017 high school (HS) American football preseason.

DESIGN

Cross-sectional study.

SETTING

Online questionnaire.

PATIENTS OR OTHER PARTICIPANTS

A total of 1016 ATs who oversaw patient care during the 2017 HS American football preseason.

MAIN OUTCOME MEASURE(S)

Responding HS ATs recorded whether they had or had not managed patients with suspected EHS events during the 2017 HS American football preseason. Those who had managed patients with suspected cases of EHS reported the management strategies used; those who had not managed such patients described their intended management strategies. For each management strategy, z tests compared the proportions of actual use among ATs who managed patients with suspected EHS with the proportions of intended use among ATs who did not manage such patients.

RESULTS

Overall, 124 (12.2%) ATs treated patients with suspected EHS cases during the 2017 HS American football preseason. Generally, the proportions of intended use of management strategies among ATs who did not treat patients with suspected EHS were higher than the actual use of those strategies among ATs who did. For example, ATs who did treat patients with suspected EHS were more likely than those who did not treat such patients to intend to take rectal temperature (19.6% versus 3.2%, P < .001) and immerse the athlete in ice water (90.1% versus 51.6%, P < .001).

CONCLUSIONS

Inconsistencies occurred between intended and actual use of EHS management strategies. The standard of care for managing patients with suspected cases of EHS was not consistently used in clinical practice, although ATs who did not treat EHS stated they intended to use these management strategies more frequently. Future researchers should identify factors that preclude ATs from using the standard of care when treating patients with suspected cases of EHS.

2020 International Consensus on First Aid Science With Treatment Recommendations

This is the summary publication of the International Liaison Committee on Resuscitation's 2020 International Consensus on First Aid Science With Treatment Recommendations. It addresses the most recent published evidence reviewed by the First Aid Task Force science experts. This summary addresses the topics of first aid methods of glucose administration for hypoglycemia; techniques for cooling of exertional hyperthermia and heatstroke; recognition of acute stroke; the use of supplementary oxygen in acute stroke; early or first aid use of aspirin for chest pain; control of life- threatening bleeding through the use of tourniquets, haemostatic dressings, direct pressure, or pressure devices; the use of a compression wrap for closed extremity joint injuries; and temporary storage of an avulsed tooth. Additional summaries of scoping reviews are presented for the use of a recovery position, recognition of a concussion, and 6 other first aid topics. The First Aid Task Force has assessed, discussed, and debated the certainty of evidence on the basis of Grading of Recommendations, Assessment, Development, and Evaluation criteria and present their consensus treatment recommendations with evidence-to-decision highlights and identified priority knowledge gaps for future research. The 2020 International Consensus on Cardiopulmonary Resuscitation (CPR) and Emergency Cardiovascular Care (ECC) Science With Treatment Recommendations (CoSTR) is the fourth in a series of annual summary publications from the International Liaison Committee on Resuscitation (ILCOR). This 2020 CoSTR for first aid includes new topics addressed by systematic reviews performed within the past 12 months. It also includes updates of the first aid treatment recommendations published from 2010 through 2019 that are based on additional evidence evaluations and updates. As a result, this 2020 CoSTR for first aid represents the most comprehensive update since 2010.

2020 International Consensus on First Aid Science With Treatment Recommendations

This is the summary publication of the International Liaison Committee on Resuscitation's 2020 International Consensus on First Aid Science With Treatment Recommendations. It addresses the most recent published evidence reviewed by the First Aid Task Force science experts. This summary addresses the topics of first aid methods of glucose administration for hypoglycemia; techniques for cooling of exertional hyperthermia and heatstroke; recognition of acute stroke; the use of supplementary oxygen in acute stroke; early or first aid use of aspirin for chest pain; control of life-threatening bleeding through the use of tourniquets, hemostatic dressings, direct pressure, or pressure devices; the use of a compression wrap for closed extremity joint injuries; and temporary storage of an avulsed tooth. Additional summaries of scoping reviews are presented for the use of a recovery position, recognition of a concussion, and 6 other first aid topics. The First Aid Task Force has assessed, discussed, and debated the certainty of evidence on the basis of Grading of Recommendations, Assessment, Development, and Evaluation criteria and present their consensus treatment recommendations with evidence-to-decision highlights and identified priority knowledge gaps for future research.

Hearables: New Perspectives and Pitfalls of In-Ear Devices for Physiological Monitoring. A Scoping Review

Technological advancements are opening the possibility of prolonged monitoring of physiological parameters under daily-life conditions, with potential applications in sport science and medicine, and in extreme environments. Among emerging wearable technologies, in-ear devices or hearables possess technical advantages for long-term monitoring, such as non-invasivity, unobtrusivity, good fixing, and reduced motion artifacts, as well as physiological advantages related to the proximity of the ear to the body trunk and the shared vasculature between the ear and the brain. The present scoping review was aimed at identifying and synthesizing the available evidence on the use and performance of in-ear monitoring of physiological parameters, with focus on applications in sport science, sport medicine, occupational medicine, and extreme environment settings. Pubmed, Scopus, and Web of Science electronic databases were systematically searched to identify studies conducted in the last 10 years and addressing the measurement of three main physiological parameters (temperature, heart rate, and oxygen saturation) in healthy subjects. Thirty-nine studies were identified, 24 performing temperature measurement, 12 studies on heart/pulse rate, and three studies on oxygen saturation. The collected evidence supports the premise of in-ear sensors as an innovative and unobtrusive way for physiological monitoring during daily-life and physical activity, but further research and technological advancement are necessary to ameliorate measurement accuracy especially in more challenging scenarios.

Post-exercise cold-water immersion improves the performance in a subsequent 5-km running trial

Various post-exercise strategies have been proposed to accelerate recovery during periods of training. However, the effects of water immersion (WI) temperature on recovery amid multiple daily exercise bouts are not well investigated.

PURPOSE

To evaluate the effects of cold and warm water immersion temperatures between acute exercise bouts vs. no WI recovery on running performance.

METHODS

Nine recreationally trained men (age: 24.0 ± 6.0 years old) participated in four experimental sessions using a crossover design. Each experimental session consisted of unilateral eccentric knee flexion exercise and 90 min of treadmill running at 70% of peak oxygen consumption followed by 15 min of WI at 15°C, 28°C or 38°C or passive recovery seated at room temperature (CON). Four hours following WI or CON, subjects completed a 5 km running time trial. Rectal temperature (Trec), heart rate, and excess post-exercise oxygen consumption (EPOC) were measured.

RESULTS

Statistical analyses indicated that time trial performance was not affected by post-exercise recovery by WI (P > .05). The magnitude-based inferences indicated that 15°C (+ 3.6 ± 7.8%) likely and 28°C (+ 3.2 ± 7.5%) possibly improved recovery compared with CON, while the effect of 38°C (- 0.1 ± 12.3%) on recovery was unclear. During WI, heart rate and rectal temperature were not different from CON, but EPOC was higher in 15°C and 28°C compared to CON. Trec in 15°C was lower than CON from the 15th min post WI. EPOC was also greater in 15°C post WI compared to CON.

CONCLUSION

WI at 15°C and 28°C following acute exercise likely and possibly, respectively, improved subsequent 5 km running time trial performance. We speculate that the faster recovery in core temperature post-exercise may underlie these improvements in recovery.

Motor performance is preserved in healthy aged adults following severe whole-body hyperthermia

Healthy aging is associated with a progressive decline in motor performance and thermoregulatory efficiency. Functional consequences of severe whole-body hyperthermia on neurophysiological functions in healthy aged men have not been investigated. To determine whether severe whole-body hyperthermia (increase in rectal temperature of about 2.5 °C) induced by lower-body heating in older men (64-80 years, n = 9) would suppress excitability of reflexes, voluntarily and electrically induced ankle plantar flexor contractile properties were compared with those in young men (19-21 years, n = 11). Though no aging effect on hyperthermia-induced reflex amplitudes was observed, a decrease in maximal H-reflex and V-wave latencies was found to be greater in older than in young men. In older men, lower-body heating was accompanied by a significant increase in twitch and tetani test torque in parallel with a greater decrease in muscle contraction time. There was no temperature-depended aging effect on the voluntary activation and maximal voluntary torque production. Despite delayed and weakened thermoregulation and age-related decline in neuromuscular function, motor performance in whole-body severe hyperthermia is apparently preserved in healthy aging.

Cold-Water Immersion Cooling Rates in Football Linemen and Cross-Country Runners With Exercise-Induced Hyperthermia

CONTEXT

  Ideal and acceptable cooling rates in hyperthermic athletes have been established in average-sized participants. Football linemen (FBs) have a small body surface area (BSA)-to-mass ratio compared with smaller athletes, which hinders heat dissipation.

OBJECTIVE

  To determine cooling rates using cold-water immersion in hyperthermic FBs and cross-country runners (CCs).

DESIGN

  Cohort study.

SETTING

  Controlled university laboratory.

PATIENTS OR OTHER PARTICIPANTS

  Nine FBs (age = 21.7 ± 1.7 years, height = 188.7 ± 4 cm, mass = 128.1 ± 18 kg, body fat = 28.9% ± 7.1%, lean body mass [LBM] = 86.9 ± 19 kg, BSA = 2.54 ± 0.13 m2, BSA/mass = 201 ± 21.3 cm2/kg, and BSA/LBM = 276.4 ± 19.7 cm2/kg) and 7 CCs (age = 20 ± 1.8 years, height = 176 ± 4.1 cm, mass = 68.7 ± 6.5 kg, body fat = 10.2% ± 1.6%, LBM = 61.7 ± 5.3 kg, BSA = 1.84 ± 0.1 m2, BSA/mass = 268.3 ± 11.7 cm2/kg, and BSA/LBM = 298.4 ± 11.7 cm2/kg).

INTERVENTION(S)

  Participants ingested an intestinal sensor, exercised in a climatic chamber (39°C, 40% relative humidity) until either target core temperature (Tgi) was 39.5°C or volitional exhaustion was reached, and were immediately immersed in a 10°C circulated bath until Tgi declined to 37.5°C. A general linear model repeated-measures analysis of variance and independent t tests were calculated, with P < .05.

MAIN OUTCOME MEASURE(S)

  Physical characteristics, maximal Tgi, time to reach 37.5°C, and cooling rate.

RESULTS

  Physical characteristics were different between groups. No differences existed in environmental measures or maximal Tgi (FBs = 39.12°C ± 0.39°C, CCs = 39.38°C ± 0.19°C; P = .12). Cooling times required to reach 37.5°C (FBs = 11.4 ± 4 minutes, CCs = 7.7 ± 0.06 minutes; P < .002) and therefore cooling rates (FBs = 0.156°C·min-1 ± 0.06°C·min-1, CCs = .255°C·min-1 ± 0.05°C·min-1; P < .002) were different. Strong correlations were found between cooling rate and body mass (r = -0.76, P < .001), total BSA (r = -0.74, P < .001), BSA/mass (r = 0.73, P < .001), LBM/mass (r = 0.72, P < .002), and LBM (r = -0.72, P < .002).

CONCLUSIONS

  With cold-water immersion, the cooling rate in CCs (0.255°C·min-1) was greater than in FBs (0.156°C·min-1); however, both were considered ideal (≥0.155°C·min-1). Athletic trainers should realize that it likely takes considerably longer to cool large hyperthermic American-football players (>11 minutes) than smaller, leaner athletes (7.7 minutes). Cooling rates varied widely from 0.332°C·min-1 in a small runner to only 0.101°C·min-1 in a lineman, supporting the use of rectal temperature for monitoring during cooling.

Influence of body composition on physiological responses to post-exercise hydrotherapy

This study examined the influence of body composition on temperature and blood flow responses to post-exercise cold water immersion (CWI), hot water immersion (HWI) and control (CON). Twenty-seven male participants were stratified into three groups: 1) low mass and low fat (LM-LF); 2) high mass and low fat (HM-LF); or 3) high mass and high fat (HM-HF). Experimental trials involved a standardised bout of cycling, maintained until core temperature reached 38.5°C. Participants subsequently completed one of three 15-min recovery interventions (CWI, HWI, or CON). Core, skin and muscle temperatures, and limb blood flow were recorded at baseline, post-exercise, and every 30 min following recovery for 240 min. During CON and HWI there were no differences in core or muscle temperature between body composition groups. The rate of fall in core temperature following CWI was greater in the LM-LF (0.03 ± 0.01°C/min) group compared to the HM-HF (0.01 ± 0.001°C/min) group (P = 0.002). Muscle temperature decreased to a greater extent during CWI in the LM-LF and HM-LF groups (8.6 ± 3.0°C) compared with HM-HF (5.1 ± 2.0°C, P < 0.05). Blood flow responses did not differ between groups. Differences in body composition alter the thermal response to post-exercise CWI, which may explain some of the variance in the responses to CWI recovery.

Validity of Core Temperature Measurements at 3 Rectal Depths During Rest, Exercise, Cold-Water Immersion, and Recovery

CONTEXT

  No evidence-based recommendation exists regarding how far clinicians should insert a rectal thermistor to obtain the most valid estimate of core temperature. Knowing the validity of temperatures at different rectal depths has implications for exertional heat-stroke (EHS) management.

OBJECTIVE

  To determine whether rectal temperature (Trec) taken at 4 cm, 10 cm, or 15 cm from the anal sphincter provides the most valid estimate of core temperature (as determined by esophageal temperature [Teso]) during similar stressors an athlete with EHS may experience.

DESIGN

  Cross-sectional study.

SETTING

  Laboratory.

PATIENTS OR OTHER PARTICIPANTS

  Seventeen individuals (14 men, 3 women: age = 23 ± 2 years, mass = 79.7 ± 12.4 kg, height = 177.8 ± 9.8 cm, body fat = 9.4% ± 4.1%, body surface area = 1.97 ± 0.19 m2).

INTERVENTION(S)

  Rectal temperatures taken at 4 cm, 10 cm, and 15 cm from the anal sphincter were compared with Teso during a 10-minute rest period; exercise until the participant's Teso reached 39.5°C; cold-water immersion (∼10°C) until all temperatures were ≤38°C; and a 30-minute postimmersion recovery period. The Teso and Trec were compared every minute during rest and recovery. Because exercise and cooling times varied, we compared temperatures at 10% intervals of total exercise and cooling durations for these periods.

MAIN OUTCOME MEASURE(S)

  The Teso and Trec were used to calculate bias (ie, the difference in temperatures between sites).

RESULTS

  Rectal depth affected bias (F2,24 = 6.8, P = .008). Bias at 4 cm (0.85°C ± 0.78°C) was higher than at 15 cm (0.65°C ± 0.68°C, P < .05) but not higher than at 10 cm (0.75°C ± 0.76°C, P > .05). Bias varied over time (F2,34 = 79.5, P < .001). Bias during rest (0.42°C ± 0.27°C), exercise (0.23°C ± 0.53°C), and recovery (0.65°C ± 0.35°C) was less than during cooling (1.72°C ± 0.65°C, P < .05). Bias during exercise was less than during postimmersion recovery (0.65°C ± 0.35°C, P < .05).

CONCLUSIONS

  When EHS is suspected, clinicians should insert the flexible rectal thermistor to 15 cm (6 in) because it is the most valid depth. The low level of bias during exercise suggests Trec is valid for diagnosing hyperthermia. Rectal temperature is a better indicator of pelvic organ temperature during cold-water immersion than is Teso.

Non-invasive Measures of Core Temperature versus Ingestible Thermistor during Exercise in the Heat

The accuracy of core temperature (T_c) thermometry from temporal, tympanic, and oral thermometry devices has been variable during exercise in a hot, humid environment. The purpose of the present study was to cross-validate temporal, two tympanic devices, and oral devices compared to an ingestible thermistor during exercise in a hot, humid environment. Fourteen young, active adults (6 women) completed a graded exercise test until voluntary exhaustion in an environmental chamber (35.5 ± 0.6 °C, 53.9 ± 5.8 % RH). There was no statistical difference in mean temperature between tympanic device 1 and pill-based core temperature (PBT_c) measurements across all time points and were positively correlated (0.357; P<0.001). Temperatures of tympanic device 2 were statistically higher than PBT_c (37.8 ± 0.7 ºC vs. 37.6 ± 1.0 ºC; respectfully) (P=0.008). At all time points, temperatures for the second tympanic device and PBT_c were positively correlated (0.192; P=0.043). Temporal and PBT_c values did not differ across time points and were positively correlated (0.262; P=0.005) across all time points. Mean oral temperature was significantly less than mean PBT_c across all time points. (37.0 ± 0.4 ºC vs. 37.6 ± 1.0 ºC, respectively) (P<0.001). Across all time points, oral and PBT_c were positively correlated (0.262; P=0.010). Tympanic and temporal devices can reflect T_c while exercising in a hot, humid environment. However, care should be taken when selecting the tympanic or temporal measurement device and validation is advised prior to heat illness mitigation in the field.

Accuracy of Tympanic Temperature Measurement in Firefighters Completing a Simulated Structural Firefighting Task

INTRODUCTION

In the course of their duties, firefighters risk heat stroke and other medical conditions due to exertion in high-temperature environments. Infrared tympanic temperature measurement (TTym) is often used by Emergency Medical Services (EMS) to assess the core body temperature of firefighters. The accuracy of TTym in this setting has been called into question. Hypothesis/Problem This study aimed to examine the accuracy of TTym for core body temperature assessment at emergency firefighting events compared with gastrointestinal temperature measurement (TGI) as measured by ingestible thermometers.

METHODS

Forty-five (42 male, three female) professional urban firefighters from an Australian fire service completed two 20-minute work periods in a 100°C (± 5°C) heat chamber while wearing personal protective clothing (PPC) and breathing apparatus (weighing approximately 22 kg). Measurements were taken immediately before entering, and on exiting, the heat chamber. Tympanic temperature was assessed by an infrared tympanic thermometer and TGI was measured by ingestible sensor and radio receiver.

RESULTS

Complete data were available for 37 participants. Participant temperatures were higher on exiting the heat chamber than at baseline (TTym: 35.9°C (SD=0.7) vs 37.5°C (SD=0.8); TGI: 37.2°C (SD=0.4) vs 38.6°C (SD=0.5)). Tympanic temperature underestimated TGI on average by 1.3°C (SD=0.5) before entering the chamber and by 1.0°C (SD=0.8) following the exercise. Using pooled data, the average underestimation was 1.2°C (SD=0.7).

CONCLUSION

Tympanic thermometers cause an unreliable measure of core body temperature for firefighters engaged in fire suppression activities. Accurate and practical measures of core body temperature are required urgently.

Ice ingestion with a long rest interval increases the endurance exercise capacity and reduces the core temperature in the heat

Background

The timing in which ice before exercise should be ingested plays an important role in optimizing its success. However, the effects of differences in the timing of ice ingestion before exercise on cycling capacity, and thermoregulation has not been studied. The aim of the present study was to assess the effect of length of time after ice ingestion on endurance exercise capacity in the heat.

Methods

Seven males ingested 1.25 g kg body mass⁻¹ of ice (0.5 °C) or cold water (4 °C) every 5 min, six times. Under three separate conditions after ice or water ingestion ([1] taking 20 min rest after ice ingestion, [2] taking 5 min rest after ice ingestion, and [3] taking 5 min rest after cold water ingestion), seven physically active male cyclists exercised at 65% of their maximal oxygen uptake to exhaustion in the heat (35 °C, 30% relative humidity).

Results

Participants cycled significantly longer following both ice ingestion with a long rest interval (46.0 ± 7.7 min) and that with a short rest interval (38.7 ± 5.7 min) than cold water ingestion (32.3 ± 3.2 min; both p < 0.05), and the time to exhaustion was 16% (p < 0.05) longer for ice ingestion with a long rest interval than that with a short rest interval. Ice ingestion with a long rest interval (−0.55 ± 0.07 °C; both p < 0.05) allowed for a greater drop in the core temperature than both ice ingestion with a short rest interval (−0.36 ± 0.16 °C) and cold water ingestion (−0.11 ± 0.14 °C). Heat storage under condition of ice ingestion with a long rest interval during the pre-exercise period was significantly lower than that observed with a short rest interval (−4.98 ± 2.50 W m⁻²; p < 0.05) and cold water ingestion (2.86 ± 4.44 W m⁻²).

Conclusions

Therefore, internal pre-cooling by ice ingestion with a long rest interval had the greatest benefit on exercise capacity in the heat, which is suggested to be driven by a reduced rectal temperature and heat storage before the start of exercise.

Cryotherapy-Induced Persistent Vasoconstriction After Cutaneous Cooling: Hysteresis Between Skin Temperature and Blood Perfusion

The goal of this study was to investigate the persistence of cold-induced vasoconstriction following cessation of active skin-surface cooling. This study demonstrates a hysteresis effect that develops between skin temperature and blood perfusion during the cooling and subsequent rewarming period. An Arctic Ice cryotherapy unit (CTU) was applied to the knee region of six healthy subjects for 60 min of active cooling followed by 120 min of passive rewarming. Multiple laser Doppler flowmetry perfusion probes were used to measure skin blood flow (expressed as cutaneous vascular conductance (CVC)). Skin surface cooling produced a significant reduction in CVC (P < 0.001) that persisted throughout the duration of the rewarming period. In addition, there was a hysteresis effect between CVC and skin temperature during the cooling and subsequent rewarming cycle (P < 0.01). Mixed model regression (MMR) showed a significant difference in the slopes of the CVC-skin temperature curves during cooling and rewarming (P < 0.001). Piecewise regression was used to investigate the temperature thresholds for acceleration of CVC during the cooling and rewarming periods. The two thresholds were shown to be significantly different (P = 0.003). The results show that localized cooling causes significant vasoconstriction that continues beyond the active cooling period despite skin temperatures returning toward baseline values. The significant and persistent reduction in skin perfusion may contribute to nonfreezing cold injury (NFCI) associated with cryotherapy.

Comparison of estimated core body temperature measured with the BioHarness and rectal temperature under several heat stress conditions

Monitoring and measuring core body temperature is important to prevent or minimize physiological strain and cognitive dysfunction for workers such as first responders (e.g., firefighters) and military personnel. The purpose of this study is to compare estimated core body temperature (Tco-est), determined by heart rate (HR) data from a wearable chest strap physiology monitor, to standard rectal thermometry (Tre) under different conditions.  Tco-est and Tre measurements were obtained in thermoneutral and heat stress conditions (high temperature and relative humidity) during four different experiments including treadmill exercise, cycling exercise, passive heat stress, and treadmill exercise while wearing personal protective equipment (PPE).  Overall, the mean Tco-est did not differ significantly from Tre across the four conditions. During exercise at low-moderate work rates under heat stress conditions, Tco-est was consistently higher than Tre at all-time points. Tco-est underestimated temperature compared to Tre at rest in heat stress conditions and at a low work rate under heat stress while wearing PPE. The mean differences between the two measurements ranged from -0.1 ± 0.4 to 0.3 ± 0.4°C and Tco-est correlated well with HR (r = 0.795 - 0.849) and mean body temperature (r = 0.637 - 0.861).  These results indicate that, the comparison of Tco-est to Tre may result in over- or underestimation which could possibly lead to heat-related illness during monitoring in certain conditions. Modifications to the current algorithm should be considered to address such issues.

Optimizing Cold Water Immersion for Exercise-Induced Hyperthermia: A Meta-analysis

PURPOSE

Cold water immersion (CWI) provides rapid cooling in events of exertional heat stroke. Optimal procedures for CWI in the field are not well established. This meta-analysis aimed to provide structured analysis of the effectiveness of CWI on the cooling rate in healthy adults subjected to exercise-induced hyperthermia.

METHODS

An electronic search (December 2014) was conducted using the PubMed and Web of Science. The mean difference of the cooling rate between CWI and passive recovery was calculated. Pooled analyses were based on a random-effects model. Sources of heterogeneity were identified through a mixed-effects model Q statistic. Inferential statistics aggregated the CWI cooling rate for extrapolation.

RESULTS

Nineteen studies qualified for inclusion. Results demonstrate CWI elicited a significant effect: mean difference, 0.03°C·min(-1); 95% confidence interval, 0.03-0.04°C·min(-1). A conservative, observed estimate of the CWI cooling rate was 0.08°C·min(-1) across various conditions. CWI cooled individuals twice as fast as passive recovery. Subgroup analyses revealed that cooling was more effective (Q test P < 0.10) when preimmersion core temperature ≥38.6°C, immersion water temperature ≤10°C, ambient temperature ≥20°C, immersion duration ≤10 min, and using torso plus limbs immersion. There is insufficient evidence of effect using forearms/hands CWI for rapid cooling: mean difference, 0.01°C·min(-1); 95% confidence interval, -0.01°C·min(-1) to 0.04°C·min(-1). A combined data summary, pertaining to 607 subjects from 29 relevant studies, was presented for referencing the weighted cooling rate and recovery time, aiming for practitioners to better plan emergency procedures.

CONCLUSIONS

An optimal procedure for yielding high cooling rates is proposed. Using prompt vigorous CWI should be encouraged for treating exercise-induced hyperthermia whenever possible, using cold water temperature (approximately 10°C) and maximizing body surface contact (whole-body immersion).

Comparison of Gastrointestinal and Rectal Temperatures During Recovery After a Warm-Weather Road Race

CONTEXT

It has been well established that gastrointestinal temperature (TGI) tracks closely with rectal temperature (TREC) during exercise. However, the field use of TGI pills is still being examined, and little is known about how measurements obtained using these devices compare during recovery after exercise in warm weather.

OBJECTIVE

To compare TGI and TREC in runners who completed an 11.3-km warm-weather road race and determine if runners with higher TGI and TREC present with greater passive cooling rates during recovery.

DESIGN

Cross-sectional study.

SETTING

Field.

PATIENTS OR OTHER PARTICIPANTS

Thirty recreationally active runners (15 men, 15 women; age = 39 ± 11 years, weight = 68.3 ± 11.7 kg, body fat = 19.2% ± 5.0%).

MAIN OUTCOME MEASURE(S)

The TGI and TREC were obtained immediately after the race and during a 20-minute passive rest at the 2014 Falmouth Road Race (heat index = 26.2°C ± 0.9°C). Temperatures were taken every 2 minutes during passive rest. The main dependent variables were mean bias and limits of agreement for TGI and TREC, using Bland-Altman analysis, and the 20-minute passive cooling rates for TGI and TREC.

RESULTS

No differences were evident between TGI and TREC throughout passive rest (P = .542). The passive cooling rates for TGI and TREC were 0.046 ± 0.031°C·min(-1) and 0.060 ± 0.036°C·min(-1), respectively. Runners with higher TGI and TREC at the start of cooling had higher cooling rates (R = 0.682, P < .001 and R = 0.54, P = .001, respectively). The mean bias of TGI during the 20-minute passive rest was -0.06°C ± 0.56°C with 95% limits of agreement of ±1.09°C.

CONCLUSIONS

After participants completed a warm-weather road race, TGI provided a valid measure of body temperature compared with the criterion measure of TREC. Therefore, TGI may be a viable option for monitoring postexercise-induced hyperthermia, if the pill is administered prophylactically.

National Athletic Trainers' Association Position Statement: Exertional Heat Illnesses

OBJECTIVE

To present best-practice recommendations for the prevention, recognition, and treatment of exertional heat illnesses (EHIs) and to describe the relevant physiology of thermoregulation.

BACKGROUND

Certified athletic trainers recognize and treat athletes with EHIs, often in high-risk environments. Although the proper recognition and successful treatment strategies are well documented, EHIs continue to plague athletes, and exertional heat stroke remains one of the leading causes of sudden death during sport. The recommendations presented in this document provide athletic trainers and allied health providers with an integrated scientific and clinically applicable approach to the prevention, recognition, treatment of, and return-to-activity guidelines for EHIs. These recommendations are given so that proper recognition and treatment can be accomplished in order to maximize the safety and performance of athletes.

RECOMMENDATIONS

Athletic trainers and other allied health care professionals should use these recommendations to establish onsite emergency action plans for their venues and athletes. The primary goal of athlete safety is addressed through the appropriate prevention strategies, proper recognition tactics, and effective treatment plans for EHIs. Athletic trainers and other allied health care professionals must be properly educated and prepared to respond in an expedient manner to alleviate symptoms and minimize the morbidity and mortality associated with these illnesses.

Post-warm-up muscle temperature maintenance: blood flow contribution and external heating optimisation

Purpose

Passive muscle heating has been shown to reduce the drop in post-warm-up muscle temperature (T_m) by about 25 % over 30 min, with concomitant sprint/power performance improvements. We sought to determine the role of leg blood flow in this cooling and whether optimising the heating procedure would further benefit post-warm-up T_m maintenance.

Methods

Ten male cyclists completed 15-min sprint-based warm-up followed by 30 min recovery. Vastus lateralisT_m (T_mvl) was measured at deep-, mid- and superficial-depths before and after the warm-up, and after the recovery period (POST-REC). During the recovery period, participants wore water-perfused trousers heated to 43 °C (WPT43) with either whole leg heating (WHOLE) or upper leg heating (UPPER), which was compared to heating with electrically heated trousers at 40 °C (ELEC40) and a non-heated control (CON). The blood flow cooling effect on T_mvl was studied comparing one leg with (BF) and without (NBF) blood flow.

Results

Warm-up exercise significantly increased T_mvl by ~3 °C at all depths. After the recovery period, BF T_mvl was lower (~0.3 °C) than NBF T_mvl at all measured depths, with no difference between WHOLE versus UPPER. WPT43 reduced the post-warm-up drop in deep-T_mvl (−0.12 °C ± 0.3 °C) compared to ELEC40 (−1.08 ± 0.4 °C) and CON (−1.3 ± 0.3 °C), whereas mid- and superficial-T_mvl even increased by 0.15 ± 0.3 and 1.1 ± 1.1 °C, respectively.

Conclusion

Thigh blood flow contributes to the post-warm-up T_mvl decline. Optimising the external heating procedure and increasing heating temperature of only 3 °C successfully maintained and even increased T_mvl, demonstrating that heating temperature is the major determinant of post-warm-up T_mvl cooling in this application.

Water immersion in the treatment of exertional hyperthermia: physical determinants

PURPOSE

We examined the effect of differences in body surface area-to-lean body mass ratio (AD/LBM) on core temperature cooling rates during cold water immersion (CWI, 2°C) and temperate water immersion (TWI, 26°C) after exercise-induced hyperthermia.

METHODS

Twenty male participants were divided into two groups: high (315.6 ± 7.9 cm·kg, n = 10) and low (275.6 ± 8.6 cm·kg, n = 10) AD/LBM. On two separate occasions, participants ran on a treadmill in the heat (40.0°C, 20% relative humidity) wearing an impermeable rain suit until rectal temperature reached 40.0°C. After exercise, participants were immersed up to the nipples (arms remained out of the water) in either a CWI (2°C) or a TWI (26°C) circulated water bath until rectal temperature returned to 37.5°C.

RESULTS

Overall rectal cooling rates were significantly different between experimental groups (high vs low AD/LBM, P = 0.005) and between immersion conditions (CWI vs TWI, P < 0.001). Individuals with a high AD/LBM had an approximately 1.7-fold greater overall rectal cooling rate relative to those with low AD/LBM during both CWI (high: 0.27°C·min ± 0.10°C·min vs low: 0.16°C·min ± 0.10°C·min) and TWI (high: 0.10°C·min ± 0.05°C·min vs low: 0.06°C·min ± 0.02°C·min). Further, the overall rectal cooling rates during CWI were approximately 2.7-fold greater than during TWI for both the high (CWI: 0.27°C·min ± 0.10°C·min vs TWI: 0.10°C·min ± 0.05°C·min) and the low (CWI: 0.16°C·min ± 0.10°C·min vs TWI: 0.06°C·min ± 0.02°C·min) AD/LBM groups.

CONCLUSION

We show that individuals with a low AD/LBM have a reduced rectal cooling rate and take longer to cool than those with a high AD/LBM during both CWI and TWI. However, CWI provides the most effective cooling treatment irrespective of physical differences.

National Athletic Trainers' Association Position Statement: Exertional Heat Illnesses

OBJECTIVE

To present best-practice recommendations for the prevention, recognition, and treatment of exertional heat illnesses (EHIs) and to describe the relevant physiology of thermoregulation.

BACKGROUND

Certified athletic trainers recognize and treat athletes with EHIs, often in high-risk environments. Although the proper recognition and successful treatment strategies are well documented, EHIs continue to plague athletes, and exertional heat stroke remains one of the leading causes of sudden death during sport. The recommendations presented in this document provide athletic trainers and allied health providers with an integrated scientific and clinically applicable approach to the prevention, recognition, treatment of, and return-to-activity guidelines for EHIs. These recommendations are given so that proper recognition and treatment can be accomplished in order to maximize the safety and performance of athletes.

RECOMMENDATIONS

Athletic trainers and other allied health care professionals should use these recommendations to establish onsite emergency action plans for their venues and athletes. The primary goal of athlete safety is addressed through the appropriate prevention strategies, proper recognition tactics, and effective treatment plans for EHIs. Athletic trainers and other allied health care professionals must be properly educated and prepared to respond in an expedient manner to alleviate symptoms and minimize the morbidity and mortality associated with these illnesses.

Effect of air temperature on the rectal temperature gradient at rest and during exercise

The purpose of the current study was to determine the effect of air temperature on the rectal temperature gradient at rest and during exercise. It was hypothesized that the rectal temperature gradient would be exacerbated in cold environments and attenuated in warm environments both at rest and during exercise. Each subject completed three exercise bouts on a motor driven treadmill at approximately 55% of their previously determined maximal oxygen uptake. Three different air temperatures (10, 22, 39°C) were used for the exercise bouts. Rectal temperature was measured at rest and every 5 min during each exercise bout using 4 temperature sensors affixed at 4, 7, 10 and 13 cm past the anal sphincter. Readings obtained from the 4-cm depth were significantly (p<0.05) lower than those obtained at deeper insertion depths both at rest and during exercise for all three air temperatures. Furthermore, the results showed that the rectal temperature gradient was exacerbated in cold environments and attenuated in warm environments both at rest and during exercise.

Evidence that transient changes in sudomotor output with cold and warm fluid ingestion are independently modulated by abdominal, but not oral thermoreceptors

Two studies were performed to 1) characterize changes in local sweat rate (LSR) following fluid ingestion of different temperatures during exercise, and 2) identify the potential location of thermoreceptors along the gastrointestinal tract that independently modify sudomotor activity. In study 1, 12 men cycled at 50% Vo2peak for 75 min while ingesting 3.2 ml/kg of 1.5°C, 37°C, or 50°C fluid 5 min before exercise; and after 15, 30, and 45-min of exercise. In study 2, 8 men cycled at 50% Vo2peak for 75 min while 3.2 ml/kg of 1.5°C or 50°C fluid was delivered directly into the stomach via a nasogastric tube (NG trials) or was mouth-swilled only (SW trials) after 15, 30, and 45 min of exercise. Rectal (Tre), aural canal (Tau), and mean skin temperature (Tsk); and LSR on the forehead, upper-back, and forearm were measured. In study 1, Tre, Tau, and Tsk were identical between trials, but after each ingestion, LSR was significantly suppressed at all sites with 1.5°C fluid and was elevated with 50°C fluid compared with 37°C fluid (P < 0.001). The peak difference in mean LSR between 1.5°C and 50°C fluid after ingestion was 0.29 ± 0.06 mg·min(-1)·cm(-2). In study 2, LSR was similar between 1.5°C and 50°C fluids with SW trials (P = 0.738), but lower at all sites with 1.5°C fluid in NG trials (P < 0.001) despite no concurrent differences in Tre, Tau, and Tsk. These data demonstrate that 1) LSR is transiently altered by cold and warm fluid ingestion despite similar core and skin temperatures; and 2) thermoreceptors that independently and acutely modulate sudomotor output during fluid ingestion probably reside within the abdominal area, but not the mouth.

Telemetry pill versus rectal and esophageal temperature during extreme rates of exercise-induced core temperature change

Core temperature measurement with an ingestible telemetry pill has been scarcely investigated during extreme rates of temperature change, induced by short high-intensity exercise in the heat. Therefore, nine participants performed a protocol of rest, (sub)maximal cycling and recovery at 30 °C. The pill temperature (T(pill)) was compared with the rectal temperature (T(re)) and esophageal temperature (T(es)). T(pill) corresponded well to T(re) during the entire trial, but deviated considerably from T(es) during the exercise and recovery periods. During maximal exercise, the average ΔT(pill)-T(re) and ΔT(pill)-T(es) were 0.13 ± 0.26 and -0.57 ± 0.53 °C, respectively. The response time from the start of exercise, the rate of change during exercise and the peak temperature were similar for T(pill) and T(re.) T(es) responded 5 min earlier, increased more than twice as fast and its peak value was 0.42 ± 0.46 °C higher than T(pill). In conclusion, also during considerable temperature changes at a very high rate, T(pill) is still a representative of T(re). The extent of the deviation in the pattern and peak values between T(pill) and T(es) (up to >1 °C) strengthens the assumption that T(pill) is unsuited to evaluate central blood temperature when body temperatures change rapidly.

Cold-water immersion and the treatment of hyperthermia: using 38.6°C as a safe rectal temperature cooling limit

CONTEXT

Cold-water immersion is recommended for the immediate field treatment of exertional heat stroke. However, concerns exist over potential overcooling of hyperthermic individuals during cold-water immersion.

OBJECTIVE

To evaluate the recommendation that removing previously hyperthermic individuals from a cold-water bath at a rectal temperature (T(re)) of 38.6°C would attenuate overcooling.

DESIGN

Controlled laboratory study.

SETTING

University research laboratory.

PATIENTS OR OTHER PARTICIPANTS

Participants included 6 men and 4 women (age  =  22 ± 3 years, height  =  172 ± 10 cm, mass  =  67.8 ± 10.7 kg, body fat percentage  =  17.1% ± 4.5%, maximum oxygen consumption  =  59.3 ± 8.7 mL·kg(-1)·min(-1)).

INTERVENTION(S)

After exercising at an ambient temperature of 40.0°C for 38.5 ± 9.4 minutes, until T(re) reached 39.5°C, participants were immersed in a 2.0°C circulated water bath until T(re) decreased to either 37.5°C or 38.6°C. Subsequently, participants were removed from the water bath and recovered for 20 minutes at an ambient temperature of 25°C.

MAIN OUTCOME MEASURE(S)

Rectal and esophageal temperatures were measured continuously during the immersion and recovery periods.

RESULTS

Because of the experimental design, the overall time of immersion was greater during the 37.5°C trial (16.6 ± 5.7 minutes) than the 38.6°C trial (8.8 ± 2.6 minutes) (t(9)  =  -4.740, P  =  .001). During the recovery period after cold-water immersion, both rectal (F(1,9)  =  50.540, P < .001) and esophageal (F(1,6)  =  20.365, P  =  .007) temperatures remained greater in the 38.6°C trial than in the 37.5°C trial. This was evidenced by low points of 36.47°C ± 0.70°C and 37.19°C ± 0.71°C for rectal temperature (t(9)  =  2.975, P  =  .016) and of 35.67°C ± 1.27°C and 36.72°C ± 0.95°C for esophageal temperature (t(6)  =  3.963, P  =  .007) during the recovery period of the 37.5°C and 38.6°C trials, respectively.

CONCLUSIONS

Immersion for approximately 9 minutes to a rectal temperature cooling limit of 38.6°C negated any risk associated with overcooling hyperthermic individuals when they were immersed in 2°C water.