Temporal Thermometry Fails to Track Body Core Temperature during Heat Stres
Temporal Thermometry Fails to Track Body Core Temperature during Heat Stres
Purpose: The aim of this study was to assess the accuracy of temporal scanning thermometry in monitoring internal temperature increases during passive heating.
Methods: Sixteen subjects (5 males and 11 females) underwent a whole-body passive heat stress (water-perfused suit) to increase internal temperature. Temperatures were obtained with a temporal scanner and with an ingestible-pill telemetry system that tracks intestinal temperature. Temperatures were recorded while subjects were normothermic (34°C water-perfusing suit) and every 10 min during passive heating (48°C water-perfusing suit).
Results: Heart rate (ECG), mean skin temperature (weighted six-site average), skin blood flow (laser Doppler flowmetry), and sweat rate (capacitance hygrometry) were all significantly elevated at the end of heating (all P < 0.001). Pre-heat stress temporal-derived temperature was not different from intestinal temperature (36.98 ± 0.09 vs 37.01 ± 0.09°C, respectively, P = 0.76). However, after 30 min of heating (the greatest duration of heating completed by all subjects), temporal-derived temperature decreased to below the pre-heat stress baseline (-0.22 ± 0.11), whereas intestinal temperature increased by 0.39 ± 0.07°C (P < 0.001 between the two methods). After 50 min of heating (N = 11), intestinal-derived internal temperature increased by 0.70 ± 0.09°C, whereas temporal-derived temperature decreased by 0.29 ± 0.10°C (P < 0.001). The group average (± SEM) R and slope between the two methods were 0.29 ± 0.08 and -0.34 ± 0.14, respectively.
Conclusion: These results demonstrate that temporal scanning does not track internal temperature, as measured via intestinal temperature, during passive heating. Given these findings, it is recommended that this technique not be used to assess temperature in hyperthermic diaphoretic subjects.
Regulation of internal (core) body temperature within a narrow range is vital for the well-being of humans. Consequently, the accurate assessment of body temperature is critical for medical practitioners, athletic trainers, etc. Pathological conditions that result in fever, as well as elevated environmental temperatures and/or exercise, can raise core temperature to dangerously high levels, resulting in reduced physical work capacity, heat illness, and death. Therefore, the precise measurement of core temperature in these situations is vital for the early detection and diagnosis of such pathological conditions.
A newly proposed, noninvasive method of internal temperature assessment, temporal scanning thermometry, has been developed for both clinical and home use; the primary advantages cited for this method are its simplicity and quick results. This method involves the use of an infrared scanner that detects the highest temperature of forehead skin, presumably from the temporal artery. From this value, the device estimates core temperature using a proprietary algorithm that incorporates compensation for the ambient temperature and "standard" temperature gradients from the skin to the body's core.
Since its introduction, a number of hospitals and clinics have switched to temporal scanning thermometry as their primary method of temperature measurement. For instance, a systematic survey of 101 hospitals in Texas, listed on the Web site http://dmoz.org/Health/Medicine/Facilities/Hospitals/North_America/United_States/Texas/, identified that approximately 30% use a temporal scanning device in at least one of their clinical departments. Similarly, these devices are used in the medical tent of the Boston Marathon to evaluate internal temperatures of runners receiving medical care (reported on the Web page http://www.exergen.com/medical/pressrel/april2005.htm). However, there have been conflicting findings regarding the accuracy of temporal scanners as a tool for measuring core temperature. For example, studies conducted on adult patients have concluded that the temporal artery thermometer does and does not concur with rectal/pulmonary artery temperature measurements. These latter studies were conducted in febrile patients, whereas the former study recorded temperatures of subjects in the normothermic range. These observations suggest that when core temperature is elevated, temporal scanning may not provide a good index of core temperature. A key limitation of prior assessments of temporal scanning devices is the absence of a change in temperature being imposed on the subject/patient, as would occur during the onset of a fever, during exposure to warm environments, and during sustained exercise. Thus, it is unknown whether this device accurately tracks changes in internal temperature. Therefore, the aim of this study was to compare responses from a clinical model of a temporal scanner thermometer with intestinal temperature during progressive increases in core temperature in healthy volunteers.
Purpose: The aim of this study was to assess the accuracy of temporal scanning thermometry in monitoring internal temperature increases during passive heating.
Methods: Sixteen subjects (5 males and 11 females) underwent a whole-body passive heat stress (water-perfused suit) to increase internal temperature. Temperatures were obtained with a temporal scanner and with an ingestible-pill telemetry system that tracks intestinal temperature. Temperatures were recorded while subjects were normothermic (34°C water-perfusing suit) and every 10 min during passive heating (48°C water-perfusing suit).
Results: Heart rate (ECG), mean skin temperature (weighted six-site average), skin blood flow (laser Doppler flowmetry), and sweat rate (capacitance hygrometry) were all significantly elevated at the end of heating (all P < 0.001). Pre-heat stress temporal-derived temperature was not different from intestinal temperature (36.98 ± 0.09 vs 37.01 ± 0.09°C, respectively, P = 0.76). However, after 30 min of heating (the greatest duration of heating completed by all subjects), temporal-derived temperature decreased to below the pre-heat stress baseline (-0.22 ± 0.11), whereas intestinal temperature increased by 0.39 ± 0.07°C (P < 0.001 between the two methods). After 50 min of heating (N = 11), intestinal-derived internal temperature increased by 0.70 ± 0.09°C, whereas temporal-derived temperature decreased by 0.29 ± 0.10°C (P < 0.001). The group average (± SEM) R and slope between the two methods were 0.29 ± 0.08 and -0.34 ± 0.14, respectively.
Conclusion: These results demonstrate that temporal scanning does not track internal temperature, as measured via intestinal temperature, during passive heating. Given these findings, it is recommended that this technique not be used to assess temperature in hyperthermic diaphoretic subjects.
Regulation of internal (core) body temperature within a narrow range is vital for the well-being of humans. Consequently, the accurate assessment of body temperature is critical for medical practitioners, athletic trainers, etc. Pathological conditions that result in fever, as well as elevated environmental temperatures and/or exercise, can raise core temperature to dangerously high levels, resulting in reduced physical work capacity, heat illness, and death. Therefore, the precise measurement of core temperature in these situations is vital for the early detection and diagnosis of such pathological conditions.
A newly proposed, noninvasive method of internal temperature assessment, temporal scanning thermometry, has been developed for both clinical and home use; the primary advantages cited for this method are its simplicity and quick results. This method involves the use of an infrared scanner that detects the highest temperature of forehead skin, presumably from the temporal artery. From this value, the device estimates core temperature using a proprietary algorithm that incorporates compensation for the ambient temperature and "standard" temperature gradients from the skin to the body's core.
Since its introduction, a number of hospitals and clinics have switched to temporal scanning thermometry as their primary method of temperature measurement. For instance, a systematic survey of 101 hospitals in Texas, listed on the Web site http://dmoz.org/Health/Medicine/Facilities/Hospitals/North_America/United_States/Texas/, identified that approximately 30% use a temporal scanning device in at least one of their clinical departments. Similarly, these devices are used in the medical tent of the Boston Marathon to evaluate internal temperatures of runners receiving medical care (reported on the Web page http://www.exergen.com/medical/pressrel/april2005.htm). However, there have been conflicting findings regarding the accuracy of temporal scanners as a tool for measuring core temperature. For example, studies conducted on adult patients have concluded that the temporal artery thermometer does and does not concur with rectal/pulmonary artery temperature measurements. These latter studies were conducted in febrile patients, whereas the former study recorded temperatures of subjects in the normothermic range. These observations suggest that when core temperature is elevated, temporal scanning may not provide a good index of core temperature. A key limitation of prior assessments of temporal scanning devices is the absence of a change in temperature being imposed on the subject/patient, as would occur during the onset of a fever, during exposure to warm environments, and during sustained exercise. Thus, it is unknown whether this device accurately tracks changes in internal temperature. Therefore, the aim of this study was to compare responses from a clinical model of a temporal scanner thermometer with intestinal temperature during progressive increases in core temperature in healthy volunteers.
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