Human Injury Severity Assessment for Outdoor Emergency Rescue Based on Wearable Photoplethysmogram Devices

To provide timely outdoor emergency rescue, it is necessary to assess the human injury severity (HIS) in real time and proactively send a distress signal when an injury is detected. In the past years, there have been many studies on HIS assessment. However, these studies commonly use bulky medical equipment for human physiological measurements, making them inappropriate to be applied outdoors. Given that Photoplethysmogram (PPG) sensors, which are small in size and low in power cost, can measure a series of human physiological indicators, many studies have embedded PPG sensors into wearable devices, e.g., smartwatches, to enable human health monitoring. Based on PPG technology, a series of human physiological indicators such as heart rate, respiratory rate, oxygen saturation and blood pressure can be measured over long periods of time. This article aims to investigate the way of using a wearable PPG device to assess HIS for outdoor activity scenarios. First, the feasibility of using PPG-derived data to assess HIS is discussed. Then, a database used for HIS assessment research is built. Next, the PPG-based human physiological features used for HIS assessment are extracted. Later, six HIS assessment models, including LR, LDA, Linear_SVM, RBF_SVM, RF and CatBoost, were investigated. Experimental results show that the CatBoost model demonstrates overall optimal performance for assessing mild injury cases, while the RBF_SVM model exhibits superior performance for assessing moderate and severe injury cases.