Device for monitoring heat stress
A wearable heat stress monitor ( 100 ) comprising: a first sensor ( 110 ), the first sensor ( 110 ) comprising an electrode ( 115 ) for sensing a sweat parameter ( 110 A) and at least one further sensor ( 120 ) for sensing a body parameter or an environmental parameter ( 120 A). The heat stress monitor ( 100 ) further comprises a processor ( 130 ) to determine a heat stress level based on the sweat parameter ( 110 A) sensed by the first sensor ( 110 ) and the body parameter or environmental parameter ( 120 A) sensed by the at least one further sensor ( 120 ) and an output module ( 140 ) for outputting information based on the heat stress level determined by the processor ( 130 ).
1 . A wearable heat stress monitor comprising:
an analog front end module configured to generate an electrical excitation signal from a waveform generator therein,
a first sensor electrically coupled with the analog front end module, the first sensor comprising a plurality of co-planar electrodes for sensing an admittance of epidermal sweat by detecting said electrical excitation signal generated by the waveform generator and transmitted from a first of the plurality of co-planar electrodes and received by at least another electrode of the plurality of co-planar electrodes, wherein at least one of said electrodes is connected to ground of the analog front end module;
at least one further sensor for sensing a body parameter or an environmental parameter;
a processor to determine a heat stress level by multiplying a sweat analyte concentration determined from the admittance sensed by the first sensor and the body parameter or environmental parameter sensed by the at least one further sensor by a piecewise function,
wherein the piecewise function has a zero value when the admittance is fluctuating and a non-zero value when the admittance is stable, increasing in a non-fluctuating manner or decreasing in a non-fluctuating manner; and
an output module for controlling a user interface element to visually display information of the heat stress level determined by the processor.
2 . The heat stress monitor of claim 1 wherein the detected sweat analyte is sodium chloride, a sodium ion or chlorine ion.
3 . The heat stress monitor of claim 1 wherein the at least one further sensor comprises a heart rate sensor and a body temperature sensor or an environmental humidity sensor.
4 . The heat stress monitor of claim 1 wherein the processor is configured to determine the heat stress level based on normalized values of the sensed admittance, the body parameter and/or the environmental parameter.
5 . The heat stress monitor of claim 1 wherein the processor is configured to determine the heat stress level based on applying a respective weighting to each parameter, the weighting applied to the sensed admittance being greater than the weighting(s) applied to the other parameter(s).
6 . The heat stress monitor of claim 1 wherein the processor is configured to generate a projected future value of the heat stress level based on heat stress levels determined for previous time periods.
7 . The heat stress monitor of claim 6 wherein the processor is configured to generate the projected future value of the heat stress level based on a gradient of the heat stress level over previous time periods.
8 . The heat stress monitor of claim 6 wherein the processor is configured to cause the output module to generate an audio or visual alert on the user interface element indicating a risk of dangerous heat stress in response to the projected future value of the heat stress level exceeding a predetermined threshold.
9 . The heat stress monitor of claim 7 wherein the processor is configured to cause the output module to generate an audio or visual alert on the user interface element indicating a risk of dangerous heat stress in response to the projected future value of the heat stress level exceeding a predetermined threshold.
10 . The heat stress monitor of claim 1 wherein the processor is configured to determine the user is at a heat cramp stage in response to the the sensed admittance being above a first threshold and a heart rate parameter being equal to or above a second threshold.
11 . The heat stress monitor of claim 10 wherein the processor is configured to determine that the user is at the heat exhaustion stage in response to determining that the sensed admittance is above a third threshold, while the temperature parameter is equal to or above a fourth threshold, but below a fifth threshold.
12 . The heat stress monitor of claim 11 wherein the processor is configured to determine that the user is at the heat stroke stage when subsequent to detecting heat cramp or a heat exhaustion stage, the sensed admittance sensed by the first sensor enters an abnormal range and the body temperature exceeds a sixth threshold.
13 . The heat stress monitor of claim 1 wherein the processor is configured to use a machine learning model to determine the heat stress level, a projected future heat stress level and/or a heat stress stage.
14 . The heat stress monitor of claim 1 wherein the heat stress monitor comprises a clip for fixing the heat stress monitor to an item of clothing in a position in which the electrode is proximate the skin of the user.
15 . The heat stress monitor of claim 1 wherein the first sensor, at least one further sensor, processor and output module are provided on a flexible adhesive patch for attachment to the user's skin.
16 . The heat stress monitor of claim 1 wherein the first sensor, at least one further sensor, processor and output module are provided on a band suitable for wearing on a user's limb or forehead and optionally wherein the heat stress monitor is integrated into a smart-watch.
17 . The heat stress monitor of claim 1 wherein the processor is determined to detect periods of instability when the sweat parameter is unstable, and disregard sensed admittance values sensed in said periods of instability when determining the heat stress level.
18 . The heat stress monitor of claim 17 wherein the processor is configured to detect initial and end stages of sweating based on fluctuations in detected admittance and disregard sensed admittance values sensed in the initial and end stages of sweating when determining the heat stress level.