Thermometry and interpretation of body temperature

Abstract

This article reviews the historical development and up-to-date state of thermometric technologies for measuring human body temperature (BT) from two aspects: measurement methodology and significance interpretation. Since the first systematic and comprehensive study on BT and its relation to human diseases was conducted by Wunderlich in the late 19th century, BT has served as one of the most fundamental vital signs for clinical diagnosis and daily healthcare. The physiological implication of BT set point and thermoregulatory mechanisms are briefly outlined. Influential determinants of BT measurement are investigated thoroughly. Three types of BT measurement, i.e., core body temperature, surface body temperature and basal body temperature, are categorized according to its measurement position and activity level. With the comparison of temperature measurement in industrial fields, specialties in technological and biological aspects in BT measurement are mentioned. Methodologies used in BT measurement are grouped into instrumental methods and mathematical methods. Instrumental methods utilize results of BT measurements directly from temperature-sensitive transducers and electronic instrumentations by the combination of actual and predictive measurement, invasive and noninvasive measurement. Mathematical methods use several numerical models, such as multiple regression model, autoregressive model, thermoregulatory mechanism-based model and the Kalman filter-based method to estimate BT indirectly from some relevant vital signs and environmental factors. Thermometry modalities are summarized on the dichotomies into invasive and noninvasive, contact and noncontact, direct and indirect, free and restrained, 1-D and n-D. Comprehensive interpretation of BT has an equal importance as the measurement of BT. Two modes to apply BT are classified into real-time applications and long-term applications. With rapid advancement in IoT infrastructure, big data analytics and AI platforms, prospects for future development in thermometry and interpretation of BT are discussed.

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

“…In direct mode thermometers, the output T corresponds to the T of the sensor, which is thermally coupled to the measuring site (Ring et al, 2010 ). Thermistor-based thermometers work in direct mode and utilize the intrinsic property of materials, such as metallic oxides, to change their electrical resistance as a function of T. Thermistor-based thermometers include a metallic probe, usually encapsulated in an impermeable material, such as a soft rubber earplug, an electronic circuitry to measure the resistance change and a microprocessor for calibration and data display (Chen, 2019 ). Potential limitations of direct approaches may include a slow time response to reach thermal equilibrium with the measuring site, and difficulties in placing the sensor close to the desired body site.…”

“…Infrared (IR) thermometers, the most widespread methodology to measure tympanic T, are adjusted-mode thermometers, based on the detection of the IR radiation emitted by the TM and its conversion to an electrical signal. IR tympanic thermometers (IRTT) are usually composed of a probe tip with lenses to focus the IR light, a sensing electronic module (thermopile or pyroelectric sensor) for signal transduction, and a microprocessor circuitry for data calibration and display (Chen, 2019 ). Although standard requirements for IRTT recommend clinical accuracy of ±0.3°C for target T in the range 33–42°C at ambient temperatures of 16–33°C ( ISO 80601-2-56 , 2017 ), actual accuracy in the clinical setting may be affected by several factors, related—but not limited—to patient variability (gender, age, thermoregulation, handedness), local phenomena (excessive cerumen, ear major infection or surgery, tissue cooling due to repeated measurements), operator's experience, device maintenance, and environmental conditions (humidity, temperature).…”

Fundamental Concepts of Human Thermoregulation and Adaptation to Heat: A Review in the Context of Global Warming

“…Mean Tsk is estimated from the composite of body-surface temperatures measured at the chest (30%), arm (30%), thigh (20%) and leg (20%) [60]. However, these indicators of Tb are seldom used in thermoregulation research mainly because Tsk is subjected to the influenced of Tev and not Tb alone [7,[61][62][63][64]. Tc, on the other hand, is regulated centrally by the brain to respond in a controlled manner to changes in thermal balance (heat production, absorption and dissipation) within the body [1,8].…”

“…Tc, on the other hand, is regulated centrally by the brain to respond in a controlled manner to changes in thermal balance (heat production, absorption and dissipation) within the body [1,8]. For more than a century, Tc has been used as the main Tb indicator for diagnosing fever, defining hypothermia and hyperthermia, and for indicating the associated risk of heat and cold injuries [7,63].…”

An automated system for body temperature monitoring of children, people with disabilities and bedridden people using a continuous analysis

“…Usually people measure body temperature at different parts of the skin: in ear (tympanic), at forehead, under the armpit (axillary), in the mouth, etc. Mainly, mercury, electronic (often called digital), stripe and non-contact infrared thermometers are mainly used to measure human body temperature [9][10][11][12][13][14][15][16][17].…”