Date Published: June 30, 2017
Publisher: Public Library of Science
Author(s): Enrico Longato, Maria Garrido, Desy Saccardo, Camila Montesinos Guevara, Ali R. Mani, Massimo Bolognesi, Piero Amodio, Andrea Facchinetti, Giovanni Sparacino, Sara Montagnese, Urs Albrecht.
A popular method to estimate proximal/distal temperature (TPROX and TDIST) consists in calculating a weighted average of nine wireless sensors placed on pre-defined skin locations. Specifically, TPROX is derived from five sensors placed on the infra-clavicular and mid-thigh area (left and right) and abdomen, and TDIST from four sensors located on the hands and feet. In clinical practice, the loss/removal of one or more sensors is a common occurrence, but limited information is available on how this affects the accuracy of temperature estimates. The aim of this study was to determine the accuracy of temperature estimates in relation to number/position of sensors removed. Thirteen healthy subjects wore all nine sensors for 24 hours and reference TPROX and TDIST time-courses were calculated using all sensors. Then, all possible combinations of reduced subsets of sensors were simulated and suitable weights for each sensor calculated. The accuracy of TPROX and TDIST estimates resulting from the reduced subsets of sensors, compared to reference values, was assessed by the mean squared error, the mean absolute error (MAE), the cross-validation error and the 25th and 75th percentiles of the reconstruction error. Tables of the accuracy and sensor weights for all possible combinations of sensors are provided. For instance, in relation to TPROX, a subset of three sensors placed in any combination of three non-homologous areas (abdominal, right or left infra-clavicular, right or left mid-thigh) produced an error of 0.13°C MAE, while the loss/removal of the abdominal sensor resulted in an error of 0.25°C MAE, with the greater impact on the quality of the reconstruction. This information may help researchers/clinicians: i) evaluate the expected goodness of their TPROX and TDIST estimates based on the number of available sensors; ii) select the most appropriate subset of sensors, depending on goals and operational constraints.
Skin temperature has been comprehensively studied from a chronobiological stand point, with particular attention to its rhythm in relation to the onset of sleep [1–5].
Wireless sensors are a relatively unobtrusive, simple and reliable tool to measure skin temperature. However, the use of a full set of 9 sensors  for prolonged periods of time may represent a problem, both in active individuals (for example because the sensors may interfere with certain routine activities) and in elderly people or in patients, who may be unable to re-position a sensor that has been removed. Thus variations in the number of sensors and skin locations have been put forward, with as few as one sensor (on the foot or on the wrist) being proposed to estimate distal temperature [4,29,30]. However, limited literature data are available on how skin temperature recordings are affected when one or more sensors are missing.