Temporal Thermometry Fails to Track Body Core Temperature during Heat Stress

A century of exercise physiology: concepts that ignited the study of human thermoregulation. Part 2: physiological measurements

In this, the second of four historical reviews on human thermoregulation during exercise, we examine the research techniques developed by our forebears. We emphasise calorimetry and thermometry, and measurements of vasomotor and sudomotor function. Since its first human use (1899), direct calorimetry has provided the foundation for modern respirometric methods for quantifying metabolic rate, and remains the most precise index of whole-body heat exchange and storage. Its alternative, biophysical modelling, relies upon many, often dubious assumptions. Thermometry, used for >300 y to assess deep-body temperatures, provides only an instantaneous snapshot of the thermal status of tissues in contact with any thermometer. Seemingly unbeknownst to some, thermal time delays at some surrogate sites preclude valid measurements during non-steady state conditions. To assess cutaneous blood flow, immersion plethysmography was introduced (1875), followed by strain-gauge plethysmography (1949) and then laser-Doppler velocimetry (1964). Those techniques allow only local flow measurements, which may not reflect whole-body blood flows. Sudomotor function has been estimated from body-mass losses since the 1600s, but using mass losses to assess evaporation rates requires precise measures of non-evaporated sweat, which are rarely obtained. Hygrometric methods provide data for local sweat rates, but not local evaporation rates, and most local sweat rates cannot be extrapolated to reflect whole-body sweating. The objective of these methodological overviews and critiques is to provide a deeper understanding of how modern measurement techniques were developed, their underlying assumptions, and the strengths and weaknesses of the measurements used for humans exercising and working in thermally challenging conditions.

Temperature thresholds and screening of febrile people by non-contact measurement of the face using infrared thermography - A methodology proposal

Recent outbreaks of infectious diseases such as Covid-19 that have fever as one of the symptoms drive the search for systems to track people with fever quickly and non-contact, also known as sanitary barriers. The use of non-contact infrared-based instruments, especially the infrared thermal imager, has widely spread. However, the screening process has presented low performance. This article addresses the choice of regions of interest on the human face for the analysis of the individual's fever, deals with the temperature thresholds used for this analysis, as well as the way to issue the recommendation to screen the person or not. The data collection and statistical analysis of temperatures of 198 volunteers allowed us to study and define the most appropriate face regions as targets for these barriers, as well as the temperature thresholds to be used for screening for each of these regions. Besides, the paper presents a probabilistic method based on the metrological quality of the sanitary barrier to the emission of recommendation for screening potentially febrile people. The developed method was tested in feverish and non-febrile volunteers, showing complete assertiveness in the tested cases.

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.

Non-contact infrared assessment of human body temperature: The journal Temperature toolbox

The assessment of human internal/core temperature (T core) is relevant in many scientific disciplines, but also for public health authorities when attempting to identify individuals with fever. Direct assessment of T core is often invasive, impractical on a large scale, and typically requires close contact between the observer and the target subject. Non-contact infrared thermometry (NCIT) represents a practical solution in which T core can potentially be assessed from a safe distance and in mass screening scenarios, by measuring skin temperature at specific anatomical locations. However, the COVID-19 pandemic has clearly demonstrated that these devices are not being used correctly, despite expert guided specifications available in International Standard Organization (ISO) documents. In this review, we provide an overview of the most pertinent factors that should be considered by users of NCIT. This includes the most pertinent methodological and physiological factors, as well as an overview on the ability of NCIT to track human T core. For practical use, we provide a checklist based on relevant ISO standards which are simple to follow and should be consulted prior to using NCIT for assessment of human T core. Our intention is for users of NCIT to adopt this checklist, which may improve the performance of NCIT for its ability to track T core.

Cooling intervention studies among outdoor occupational groups: A review of the literature

BACKGROUND

The purpose of this systematic review is to examine cooling intervention research in outdoor occupations, evaluate the effectiveness of such interventions, and offer recommendations for future studies. This review focuses on outdoor occupational studies conducted at worksites or simulated occupational tasks in climatic chambers.

METHODS

This systematic review was performed in accordance with Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines. PubMed, Embase, and Web of Science were searched to identify original research on intervention studies published in peer-reviewed journals that aimed at reducing heat stress or heat-related illness from January 2000 to August 2020.

RESULTS

A systematic search yielded a total of 1042 articles, of which 21 met the inclusion criteria. Occupations with cooling intervention studies included agriculture (n = 5), construction (n = 5), industrial workers (n = 4), and firefighters (n = 7). The studies focused on multiple types of cooling interventions cooling gear (vest, bandanas, cooling shirts, or head-cooling gel pack), enhanced heat dissipation clothing, forearm or lower body immersion in cold water, water dousing, ingestion of a crushed ice slush drink, electrolyte liquid hydration, and modified Occupational Safety and Health Administration recommendations of drinking water and resting in the shade.

CONCLUSION

Current evidence indicates that using multiple cooling gears along with rest cycles may be the most effective method to reduce heat-related illness. Occupational heat-related illnesses and death may be mitigated by targeted cooling intervention and workplace controls among workers of vulnerable occupational groups and industries.

Effects of Casein Hydrolysate Ingestion on Thermoregulatory Responses in Healthy Adults during Exercise in Heated Conditions: A Randomized Crossover Trial

Food ingestion has been shown to affect thermoregulation during exercise, while the impact of protein degradant consumption remains unclear. We investigated the effects of casein hydrolysate ingestion on thermoregulatory responses during exercise in the heat. In a randomized, placebo-controlled, double-blind, crossover trial, five men and five women consumed either 5 g of casein hydrolysate or placebo. Thirty minutes after ingestion, participants cycled at 60% VO₂max until voluntary exhaustion wearing a hot-water (43 °C) circulation suit. Exercise time to exhaustion, body core temperature, forearm sweat rate, and forearm cutaneous vascular conductance did not differ different between the conditions. However, chest sweat rate and mean skin temperature increased upon casein hydrolysate ingestion compared with placebo during exercise. Increased chest sweat rate upon casein hydrolysate ingestion was associated with elevated sudomotor sensitivity to increasing body core temperature, but not the temperature threshold for initiating sweating. A positive correlation was found between chest sweat rate and plasma total amino acid concentration during exercise. These results suggest that casein hydrolysate ingestion enhances sweating heterogeneously by increasing peripheral sensitivity of the chest's sweating mechanism and elevating skin temperature during exercise in the heat. However, the physiological link between plasma amino acid concentration and sweat rate remains unclear.

Top 10 Research Questions Related to Preventing Sudden Death in Sport and Physical Activity

Participation in organized sport and recreational activities presents an innate risk for serious morbidity and mortality. Although death during sport or physical activity has many causes, advancements in sports medicine and evidence-based standards of care have allowed clinicians to prevent, recognize, and treat potentially fatal injuries more effectively. With the continual progress of research and technology, current standards of care are evolving to enhance patient outcomes. In this article, we provided 10 key questions related to the leading causes and treatment of sudden death in sport and physical activity, where future research will support safer participation for athletes and recreational enthusiasts. The current evidence indicates that most deaths can be avoided when proper strategies are in place to prevent occurrence or provide optimal care.

Development of a method for estimating oesophageal temperature by multi-locational temperature measurement inside the external auditory canal

We aimed to develop a practical method to estimate oesophageal temperature by measuring multi-locational auditory canal temperatures. This method can be applied to prevent heatstroke by simultaneously and continuously monitoring the core temperatures of people working under hot environments. We asked 11 healthy male volunteers to exercise, generating 80 W for 45 min in a climatic chamber set at 24, 32 and 40 °C, at 50% relative humidity. We also exposed the participants to radiation at 32 °C. We continuously measured temperatures at the oesophagus, rectum and three different locations along the external auditory canal. We developed equations for estimating oesophageal temperatures from auditory canal temperatures and compared their fitness and errors. The rectal temperature increased or decreased faster than oesophageal temperature at the start or end of exercise in all conditions. Estimated temperature showed good similarity with oesophageal temperature, and the square of the correlation coefficient of the best fitting model reached 0.904. We observed intermediate values between rectal and oesophageal temperatures during the rest phase. Even under the condition with radiation, estimated oesophageal temperature demonstrated concordant movement with oesophageal temperature at around 0.1 °C overestimation. Our method measured temperatures at three different locations along the external auditory canal. We confirmed that the approach can credibly estimate the oesophageal temperature from 24 to 40 °C for people performing exercise in the same place in a windless environment.

Equivalence Study of Two Temperature-Measurement Methods in Febrile Adult Patients With Cancer

PURPOSE/OBJECTIVES

To assess equivalence of temperatures taken via temporal artery and oral methods in febrile inpatients with cancer.
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DESIGN

Repeated measures equivalence design.
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SETTING

24-bed hematology-oncology unit and 36-bed blood and marrow transplantation unit at H. Lee Moffitt Cancer Center and Research Institute, a National Cancer Institute-designated comprehensive cancer center in Tampa, Florida.
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SAMPLE

Convenience sample of 58 febrile inpatients using 60 temperature measurements.
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METHODS

Two instruments were used.

MAIN RESEARCH VARIABLES

Temperature readings from oral and temporal artery measurements.
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FINDINGS

A two one-sided test (TOST) technique with a delta of 0.2ºF was performed to assess equivalence of the oral and temporal artery measures. Within each team member, the oral and temporal artery measures were assessed using the TOST technique. The hypothesis of equivalence was rejected for all three team members. 
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CONCLUSIONS

The use of the Exergen TAT-5000 for temperature measurement as a noninvasive alternate to the oral method for febrile adult patients in the hematology-oncology population was not supported. 
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IMPLICATIONS FOR NURSING

The Exergen TAT-5000 is not a reliable instrument for detecting fevers in the hematology-oncology patient population because the temporal artery measures were not equivalent to oral measures, and considerable variation occurred for the three nurses. Alternative methods for accurate temperature collection need to be investigated, particularly for febrile, neutropenic patients who cannot tolerate the oral probe.

Validation of an ingestible temperature data logging and telemetry system during exercise in the heat

Aim: Intestinal temperature telemetry systems are promising monitoring and research tools in athletes. However, the additional equipment that must be carried to continuously record temperature data limits their use to training. The purpose of this study was to assess the validity and reliability of a new gastrointestinal temperature data logging and telemetry system (e-Celsius™) during water bath experimentation and exercise trials. Materials and Methods: Temperature readings of 23 pairs of e-Celsius (T_eC) and VitalSense (T_VS) ingestible capsules were compared to rectal thermistor responses (T_rec) at 35, 38.5 and 42°C in a water bath. Devices were also assessed in vivo during steady-state cycling (n = 11) and intermittent running (n = 11) in hot conditions. Results: The water bath experiment showed T_VS and T_eC under-reported T_rec (P<0.001). This underestimation of T_rec also occurred during both cycling (mean bias vs T_VS: 0.21°C, ICC: 0.84, 95% CI: 0.66–0.91; mean bias vs. T_eC: 0.44°C, ICC: 0.68, 95% CI: 0.07–0.86, P<0.05) and running trials (mean bias vs. T_VS: 0.15°C, ICC: 0.92, 95% CI: 0.83–0.96; mean bias vs. T_eC: 0.25, ICC: 0.86, 95% CI: 0.61–0.94, P<0.05). However, calibrating the devices attenuated this difference during cycling and eliminated it during running. During recovery following cycling exercise, T_eC and T_VS were significantly lower than T_rec despite calibration (P<0.01). Conclusion: These results indicate that both T_eC and T_VS under-report T_rec during steady-state and intermittent exercise in the heat, with T_eC predicting T_rec with the least accuracy of the telemetry devices. It is therefore recommended to calibrate these devices at multiple temperatures prior to use.

Effect of wearing an N95 filtering facepiece respirator on superomedial orbital infrared indirect brain temperature measurements

To determine any effect of wearing a filtering facepiece respirator on brain temperature. Subjects (n = 18) wore a filtering facepiece respirator (FFR) for 1 h at rest while undergoing infrared thermography measurements of the superomedial periobital region of the eye, a non-invasive indirect method of brain temperature measurements we termed the superomedial orbital infrared indirect brain temperature (SOIIBT) measurement. Temperature of the facial skin covered by the FFR, infrared temperature measurements of the tympanic membrane and superficial temporal artery region were concurrently measured, and subjective impressions of thermal comfort obtained simultaneously. The temperature of the skin under the FFR and subjective impressions of thermal discomfort both increased significantly. The mean tympanic membrane temperature did not increase, and the superficial temporal artery region temperature decreased significantly. The SOIIBT values did not change significantly, but subjects who switched from nasal to oronasal breathing during the study (n = 5) experienced a slight increase in the SOIIBT measurements. Wearing a FFR for 1 h at rest does not have a significant effect on brain temperatures, as evaluated by the SOIIBT measurements, but a change in the route of breathing may impact these measurements. These findings suggest that subjective impressions of thermal discomfort from wearing a FFR under the study conditions are more likely the result of local dermal sensations rather than brain warming.

Heat stroke

Heat stroke is a life-threatening condition clinically diagnosed as a severe elevation in body temperature with central nervous system dysfunction that often includes combativeness, delirium, seizures, and coma. Classic heat stroke primarily occurs in immunocompromised individuals during annual heat waves. Exertional heat stroke is observed in young fit individuals performing strenuous physical activity in hot or temperature environments. Long-term consequences of heat stroke are thought to be due to a systemic inflammatory response syndrome. This article provides a comprehensive review of recent advances in the identification of risk factors that predispose to heat stroke, the role of endotoxin and cytokines in mediation of multi-organ damage, the incidence of hypothermia and fever during heat stroke recovery, clinical biomarkers of organ damage severity, and protective cooling strategies. Risk factors include environmental factors, medications, drug use, compromised health status, and genetic conditions. The role of endotoxin and cytokines is discussed in the framework of research conducted over 30 years ago that requires reassessment to more clearly identify the role of these factors in the systemic inflammatory response syndrome. We challenge the notion that hypothalamic damage is responsible for thermoregulatory disturbances during heat stroke recovery and highlight recent advances in our understanding of the regulated nature of these responses. The need for more sensitive clinical biomarkers of organ damage is examined. Conventional and emerging cooling methods are discussed with reference to protection against peripheral organ damage and selective brain cooling.

Clinical Performance of Infrared Consumer-Grade Thermometers

Background and Purpose: Technology of ear infrared (IR) thermometers has improved. This study compared a modern ear thermometer to forehead or temporal artery thermometers. Methods: Temperatures were measured with a heated-tip ear thermometer, a temporal artery thermometer, 3 forehead thermometers, and a thermistor-based reference thermometer in monitor mode. Results: In 171 subjects, mean bias with the forehead thermometers was significantly higher (p< .001) than with the ear thermometer (0.01 °C ± 0.41 °C). In 64 febrile subjects, bias with the ear thermometer was significantly lower than with 3 of the other thermometers. A false-negative reading was less likely with the ear thermometer (8%) versus the others (55%, 56%, 28%, and 47%). Conclusions: Modern ear thermometry provides more precise measurements closer to those of a reference thermometer and is less likely to give false-negative readings than forehead or temporal artery measurements.

Unplanned perioperative hypothermia and agreement between oral, temporal artery, and bladder temperatures in adult major surgery patients

Accurate body core temperature measurement is essential in perioperative areas to quickly recognize and address abnormal temperatures. The purposes of this prospective, descriptive study were to accurately identify unplanned perioperative hypothermia (UPH) in 64 elective major surgery patients; to describe factors that increased the risk of UPH; to describe active/passive warming measures; to describe thermal comfort in patients with and without UPH; and to compare oral, temporal artery, and bladder temperatures. Based on bladder temperatures, 52% of the patients had UPH in the operating room (OR) and 42% on postanesthesia care unit (PACU) admission. The temporal artery thermometer did not detect any hypothermia. Descriptive data and Bland-Altman plots showed lack of agreement between the temporal artery thermometer readings and those of the oral and bladder thermometers. The patient's thermal comfort report did not accurately reflect hypothermia. Factors found to increase the risk of UPH included older age, BMI lower than 30, and OR ambient temperature lower than 68°F. All but one patient had active warming in the OR; active warming was infrequently used in the PACU. Based on our findings and findings in previous studies, we do not recommend using the temporal artery thermometer in perioperative areas. To prevent UPH, we recommend aggressive use of convective and conductive warming measures in perioperative areas and increasing OR ambient temperatures.

Clinical nurse specialist-led evaluation of temporal artery thermometers in acute care

PURPOSE

A systematic review of literature and intensive evaluation were conducted using a quality process to assess temporal artery thermometer (TAT) accuracy in an acute-care setting.

BACKGROUND

Inaccurate temperature measurements were reported following adoption of the TAT. Concern for patient safety and outcomes generated a need to reevaluate use of the TAT.

DESCRIPTION OF THE PROJECT

Using components of evidence-based practice and intensive evaluation processes, a clinical nurse specialist (CNS)-led team evaluated existing research, assessed current practice, and obtained additional clinical data.

OUTCOMES

Existing research provides inadequate evidence to support use of the TAT for acutely ill hospitalized patients. Findings from an intensive evaluation indicated low interrater reliability in controlled testing, inaccurate technique by staff despite retraining, lack of nurse confidence in the accuracy of the device, and a need for continuous costly retraining. These findings are consistent with findings in a University HealthSystem Consortium report.

SUMMARY AND CONCLUSIONS

A multifaceted evaluation process was needed for the team to compile data, identify issues, and make decisions. A recommendation was made to discontinue use of the TAT.

IMPLICATIONS

: Clinical nurse specialists have the knowledge and ability to provide clinical leadership at a system level. When usual processes result in safety concerns, the CNS provides leadership to identify patterns, provide direction, creatively integrate evaluation processes, synthesize findings, and uses his/her influence within the system to change practice.

Core-temperature sensor ingestion timing and measurement variability

CONTEXT

Telemetric core-temperature monitoring is becoming more widely used as a noninvasive means of monitoring core temperature during athletic events.

OBJECTIVE

To determine the effects of sensor ingestion timing on serial measures of core temperature during continuous exercise.

DESIGN

Crossover study.

SETTING

Outdoor dirt track at an average ambient temperature of 4.4°C ± 4.1°C and relative humidity of 74.1% ± 11.0%.

PATIENTS OR OTHER PARTICIPANTS

Seven healthy, active participants (3 men, 4 women; age  =  27.0 ± 7.5 years, height  =  172.9 ± 6.8 cm, body mass  =  67.5 ± 6.1 kg, percentage body fat  =  12.7% ± 6.9%, peak oxygen uptake [Vo(2peak)]  =  54.4 ± 6.9 mL•kg⁻¹•min⁻¹) completed the study.

INTERVENTION(S)

Participants completed a 45-minute exercise trial at approximately 70% Vo(2peak). They consumed core-temperature sensors at 24 hours (P1) and 40 minutes (P2) before exercise.

MAIN OUTCOME MEASURE(S)

Core temperature was recorded continuously (1-minute intervals) using a wireless data logger worn by the participants. All data were analyzed using a 2-way repeated-measures analysis of variance (trial × time), Pearson product moment correlation, and Bland-Altman plot.

RESULTS

Fifteen comparisons were made between P1 and P2. The main effect of time indicated an increase in core temperature compared with the initial temperature. However, we did not find a main effect for trial or a trial × time interaction, indicating no differences in core temperature between the sensors (P1  =  38.3°C ± 0.2°C, P2  =  38.3°C ± 0.4°C).

CONCLUSIONS

We found no differences in the temperature recordings between the 2 sensors. These results suggest that assumed sensor location (upper or lower gastrointestinal tract) does not appreciably alter the transmission of reliable and repeatable measures of core temperature during continuous running in the cold.

Validity and reliability of devices that assess body temperature during indoor exercise in the heat

CONTEXT

When assessing exercise hyperthermia outdoors, the validity of certain commonly used body temperature measuring devices has been questioned. A controlled laboratory environment is generally less influenced by environmental factors (eg, ambient temperature, solar radiation, wind) than an outdoor setting. The validity of these temperature measuring devices in a controlled environment may be more acceptable.

OBJECTIVE

To assess the validity and reliability of commonly used temperature devices compared with rectal temperature in individuals exercising in a controlled, high environmental temperature indoor setting and then resting in a cool environment.

DESIGN

Time series study.

SETTING

Laboratory environmental chamber (temperature = 36.4 +/- 1.2 degrees C [97.5 +/- 2.16 degrees F], relative humidity = 52%) and cool laboratory (temperature = approximately 23.3 degrees C [74.0 degrees F], relative humidity = 40%).

PATIENTS OR OTHER PARTICIPANTS

Fifteen males and 10 females.

INTERVENTION(S)

Rectal, gastrointestinal, forehead, oral, aural, temporal, and axillary temperatures were measured with commonly used temperature devices. Temperature was measured before and 20 minutes after entering the environmental chamber, every 30 minutes during a 90-minute treadmill walk in the heat, and every 20 minutes during a 60-minute rest in mild conditions. Device validity and reliability were assessed with various statistical measures to compare the measurements using each device with rectal temperature. A device was considered invalid if the mean bias (average difference between rectal and device temperatures) was more than +/-0.27 degrees C (+/-0.50 degrees F).

MAIN OUTCOME MEASURE(S)

Measured temperature from each device (mean and across time).

RESULTS

The following devices provided invalid estimates of rectal temperature: forehead sticker (0.29 degrees C [0.52 degrees F]), oral temperature using an inexpensive device (-1.13 degrees C [-2.03 degrees F]), temporal temperature measured according to the instruction manual (-0.87 degrees C [-1.56 degrees F]), temporal temperature using a modified technique (-0.63 degrees C [-1.13 degrees F]), oral temperature using an expensive device (-0.86 degrees C, [-1.55 degrees F]), aural temperature (-0.67 degrees C, [-1.20 degrees F]), axillary temperature using an inexpensive device (-1.25 degrees C, [-2.24 degrees F]), and axillary temperature using an expensive device (-0.94 degrees F [-1.70 degrees F]). Measurement of intestinal temperature (mean bias of -0.02 degrees C [-0.03 degrees F]) was the only device considered valid. Devices measured in succession (intestinal, forehead, temporal, and aural) showed acceptable reliability (all had a mean bias = 0.09 degrees C [0.16 degrees F] and r >or= 0.94]).

CONCLUSIONS

Even during laboratory exercise in a controlled environment, devices used to measure forehead, temporal, oral, aural, and axillary body sites did not provide valid estimates of rectal temperature. Only intestinal temperature measurement met the criterion. Therefore, we recommend that rectal or intestinal temperature be used to assess hyperthermia in individuals exercising indoors in the heat.