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

Abstract

BackgroundIndirect 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.MethodsTwenty-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).ResultsIn 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.ConclusionDS 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.

Comparing body temperature measurements using the double sensor method within a wearable device with oral and core body temperature measurements using medical grade thermometers—a short report

“…On top of the PPG sensor, the chest patch provides body temperature using the double sensor method ( Figure 1 ), in which body temperature is calculated from two temperature thermistors separated by an insulating disk with a known heat transfer coefficient. Various studies have suggested the reliability and validity of heat-flux approaches and double sensor technology under different environmental conditions, as well as in clinical conditions ( Sakuragi et al, 1993 ; Gunga et al, 2009 ; Kimberger et al, 2009 ; 2013 ; Teunissen et al, 2011 ; Xu et al, 2013 ; Mazgaoker et al, 2017 ; Mendt et al, 2017 ; Gómez-Romero et al, 2019 ; Janke et al, 2021 ; Masè et al, 2022 ). Integrating this sensor allows for the first time the collection of all five basic vital signs needed in clinical practice using a single wearable device.…”

Noninvasive Temperature Measurements in Tissue-Simulating Phantoms Using a Solid-State Near-Infrared Sensor

“…Current technologies for monitoring body temperature for wellness and fitness applications rely on the measurement of skin surface temperatures. While skin surface temperatures are easy to measure, the relationship between the skin’s surface and core body temperatures is not straightforward [ 7 , 8 ]. Converting a skin surface measurement to a core body temperature demands knowledge of the heat transfer processes between (1) the core body volume and the skin surface, and (2) the skin surface and the ambient surroundings.…”

“…Converting a skin surface measurement to a core body temperature demands knowledge of the heat transfer processes between (1) the core body volume and the skin surface, and (2) the skin surface and the ambient surroundings. A variety of heat transfer models are available to account for surface-to-environment heat flux when coupled with the so-called double sensor experimental configuration, originally proposed by Gunga and co-workers [ 7 , 8 , 9 ]. A more sophisticated heat transfer model, recently proposed by Shan et al [ 10 ], accounts for the effects of blood perfusion within the tissue matrix.…”