DOI: 10.6084/m9.figshare.14390765.v8
title: greenteg-core-axillary

description: Core body temperature measures from a single subject with a non-24 circadian rhythm disorder, aged 33 years old at the start of measurements, weight between 72 and 77.5 kg.<br>The core body temperature measurements were done non-invasively with the GreenTEG CORE Research device, attached to the side of a Polar Pro chest strap band, placed on the axillary per the manufacturer's recommendations. The device captures core body temperature and skin temperature every second (1Hz sampling rate). It can store up to 3.5 days of data and takes 3h30 to 7h for data download, hence the gaps, which are placed during circadian daytime whenever possible. This device is able to measure the core body temperature using dual heat flux method (DHFM) with an in-house AI algorithm that replaces the standard DHFM equation to obtain more reliable readings according to the manufacturer. At the time of this experiment, this was the first and only wearable thermometer using heat flux technology.<br>The measurements are much more reliable since January 2021 so prefer to analyze the data from this date onwards. The device was changed in January 2021 for a new one because the old one broke due to a mechanical pressure flaw in the design. Since January 2021, an experimental attachment design using velcro sticked vertically on the CORE and with a loop around the Polar Pro band was conceived by the author/subject to avoid this mechanical flaw, and this had the unexpected side effect of improving significantly the reliability and extent of the surface of the CORE being in contact with the skin, so that measures are much more reliable and systematically reflect the circadian rhythm. Usually, the circadian night can be detected simply as being periods with a temperature below 36.5°C with this new attachment system.<br>Along with the sleep diaries, this is the most reliable circadian rhythm monitoring marker so far from preliminary results.<br>Note on data columns: most columns are encrypted gibberish data. Only the core body temperature, skin temperature flux 1, and timestamp are accessible and should be processed, the other columns can and should be discarded. More precisely, only the following columns are available (from the manufacturer's documentation):<br>* time [UTC-OFS=+0100] Timestamp of the data point in the format ‘DD:MM:YYYY hh:mm:ss’* timestamp [us] Timestamp in UNIX time in us (microseconds elapsed since January 1th 1970).* Hf_a0 Raw heat flux sensor signal of heat path A in ADC counts (unitless).* Temp_a0 [mC] Uncorrected temperature signal of heat path A in millidegree Celsius.* Cbt [mC] Core body temperature estimation output in millidegrees.<br><br>Note: Cbt needs to be divided by 1000 to get the core body temperature value in celsius degrees.<br>The following columns are not available and can be dropped as they are filled with random values: hf_a1, Temp_a1, ax, ay, az, Battery_voltage [mV].<br>Heat flux sensor A value can be obtained as follows:<br>Heat flux sensor A voltage [in uV] = hf_a0 [in counts] * 1.953125 uV<br><br>Skin temperature for sensor A can be obtained as follows:<br>Skin Temperature A [in °C] = (temp_a0 [in mC] – T0off) /1000<br><br>T0off is an offset that is defined once in the header of each CSV file.<br>There is a gap during January 2021, as this is the period the 1st device broke, before getting replaced by the manufacturer. The new dataset with the new device starts on 21th January 2021, with a new vertically oriented velcro attachment system devised by the author, which prevents the device from breaking and improves skin contact and hence data quality. It is recommended to analyze data after 21th January 2021 as it is likely the least noisy.<br>Each file represents one acquisition session of up to 3.5 days, hence they can be concatenated to study a longer time period.<br>Note: On 2021-05-29T21_25_00, an attempt to optimize further the disposition of the velcro was done by changing the orientation from vertical to diagonal, so that the CORE device was oriented on skin as a losange instead of a square, which would theoretically further increase skin contact and data quality, since the chest strap now pushes on the two corners in the horizontal middle, with much less chances that it gets stuck in a local equilibrium at either of the vertical corners. Unfortunately, the data quality was worse (the high and low phases were not correlated with empirical sleep-wake data anymore, there were no high nor low phases anymore), suggesting that the two heat flux sensors are vertically positioned in the middle line of the device (one temperature sensor at the top and one at the bottom), and hence that a vertical orientation is likely the most optimal orientation despite reduced skin contact compared to diagonal. Hence, on 2021-06-06T01_00_00, the disposition of the velcro band was reverted back to vertical. Only one session was acquired with the diagonal orientation, the file is named accordingly.<br>To postprocess the data for analysis, ensure that the first 30 min of each file / new data collection session is removed, as the sensor takes some time to converge to the true current body temperature. It will always start too high at first (because the equation for dual heat flux will show a high value when the sensor is cold when it was not worn), and then gradually lowers until it converges to the equilibrium which represents the current core body temperature.<br>