Abstract
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.
Highlights
Skin temperature has been comprehensively studied from a chronobiological stand point, with particular attention to its rhythm in relation to the onset of sleep [1,2,3,4,5].Contactless infrared and conductive devices are the most common tools used for measuring skin temperature [6,7,8]
A total of 13 healthy volunteers [five males; mean age: 47.3 ± 14.5 (22–65) years] were enrolled. They were excluded if they were under 18 years of age; could not/were unwilling to comply with the study procedures, had misused alcohol in the preceding 6 months, had undertaken shift work or intercontinental travel in the preceding four months, or were on chronic medical treatment
The use of a full set of 9 sensors [7] for prolonged periods of time may represent a problem, both in active individuals and in elderly people or in patients, who may be unable to re-position a sensor that has been removed
Summary
Skin temperature has been comprehensively studied from a chronobiological stand point, with particular attention to its rhythm in relation to the onset of sleep [1,2,3,4,5].Contactless infrared and conductive devices are the most common tools used for measuring skin temperature [6,7,8]. Contactless infrared thermometers and infrared thermography have proven effective in diverse settings [6,8,9] They are difficult to use in free-living conditions, for long periods of continuous acquisition [6,8,9]. Conductive wireless sensors are unobtrusive to wear [7,16], in free-living conditions and for long periods of time [7,13,17]. Their limitations are the finite lifetime of their battery and the fact that recordings can only be viewed once complete, not allowing for adjustments during acquisition
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