AUTHOR=Falcone Tiziana , Del Ferraro Simona , Molinaro Vincenzo , Zollo Loredana , Lenzuni Paolo TITLE=A real-time biphasic Kalman filter-based model for estimating human core temperature from heart rate measurements for application in the occupational field JOURNAL=Frontiers in Public Health VOLUME=Volume 12 - 2024 YEAR=2024 URL=https://www.frontiersin.org/journals/public-health/articles/10.3389/fpubh.2024.1219595 DOI=10.3389/fpubh.2024.1219595 ISSN=2296-2565 ABSTRACT=Early identification of hypo-or hyperthermia is of vital importance and real-time monitoring of core temperature (𝐢𝑇) of the workers exposed to thermal environments is an extremely valuable tool. Among the existing literature studies, the model developed by Buller et al. in 2013 that generates real-time estimates of 𝐢𝑇 from heart rate (𝐻𝑅) measurements using the Kalman filter (KF), shows a good potential for occupational application. Some aspects could be improved though, to reliably handle the existing very wide range of workers and of work activities. This study presents a real-time 𝐢𝑇 estimation model, called Biphasic Kalman-filter-based (BKFB) model, based on 𝐻𝑅 measurement, with characteristics geared to application in the occupational field. Methods: Thirteen healthy subjects (six females and seven males) were included in the study to perform three consecutive tasks simulating work activities. During each test, an ingestible 𝐢𝑇 sensor was used to measure 𝐢𝑇, and a 𝐻𝑅 sensor to measure 𝐻𝑅. The methodology applied to develop the BKFB model was the KF. Results: An algorithm with a biphasic structure was developed, using two different models for the 𝐢𝑇 increasing and decreasing phases, with the capability of switching between the two based on a 𝐻𝑅 threshold. 𝐢𝑇 estimates were compared with 𝐢𝑇 measurements and the BKFB model achieved a sizeable reduction of the overall Root mean square error (RMSE) (0.28 Β± 0.12 Β°C) with respect to RMSE obtained using the Buller et al. model (0.34 Β± 0.16 Β°C). Discussion: BKFB model introduce some modifications over Buller et al. model for a more effective application in the occupational field. It was developed using data collected from a real sample of workers (heavily weighted towards middle- aged, not very fit and with a considerable fraction of female) and it also includes two different modelling of 𝐢𝑇 (for the up-and down-phase), which allows for better behavioral modeling in the two different stages. BKFB model provides 𝐢𝑇 estimates reasonably comparable to the measured intraabdominal temperature values in both the activity and recovery phases but is more practical and easier to use for a real-time monitoring system of the workers' thermal state.