Vitals
All three of the disorders are broken into three stages. In stage one, defining vitals (like temperature for hypothermia) is not much, and changes in other relative vitals (heart rate, SpO2, etc.) still lies within reasonable range of outdoor activity. The subject can remain conscious and level-headed during this stage, so it is likely that they can spot the developing symptoms themselves and take measures necessary. However, starting from stage two, all these three disorders will start to impair the hiker’s ability to think straight and perform action to prevent disorder from development. And the vitals will start to show significant deviation from normal range so that they can be detected.
Core body temperatureCore body temperature is the defining vital for two of the disorders we are detecting for. Therefore the device will have to sample all range of possible human core body temperature. It have been reported that a girl with 13 ºC body temperature in hypothermia eventually survived, and that is the lowest record, therefore we set a 10 ºC lower range limit. Our body can not handle heat as well though. At 42 ºC protein will start to denature and permanent brain damage is going to develope. It is near impossible for body temperature to reach 45 ºC, so we set it as the upper range limit. Stage II hypothermia starts below 35 ºC and stage II hyperthermia starts above 38.5ºC. Therefore a minimum of 0.5 ºC accuracy is reasonable for detecting stage II disorders.
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Heart rateHeart rate is an important vital to help identify all three symptoms. Hypothermia/ hyperthermia can lead to the extreme low or extreme high heart rate, so we will need to sample the entire range. Keeping that in mind, 0-240 BPM is the range of choice. Im measuring heart rate, it is more important to identify how much the heart rate is deviating from the baseline than get the exact value in BPM, so we are allowed 3 BPM of error margin, a relatively loose one.
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SP O2Pulse oximetry (SpO2) is the concentration of oxygen in blood with 100% being saturation. Normal human resting SpO2 is 95%-100%. In extreme cases pulse oximetry can go below 70%, but very rare it do occur. Therefore 60-100% range should capture all possible SpO2 level. Pulse oximeters usually perform well in high SpO2 and can have up to 5% margin of error at extreme low SpO2. We will have to work with this error range.
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Vital |
Core body temperature |
Heart rate |
SP O2 |
Range |
10 - 50 ºC |
0 - 240 BPM |
60% - 100% |
Accuracy |
0.5ºC |
3 BPM |
0.5%-5% |