Over 40% of deaths within 24 hours of a traumatic injury are due to haemorrhage . The early application of life saving interventions, before the development of circulatory shock, is a priority in dealing with hemorrhage. Mortality can be significantly reduced when patients needing immediate care can be identified early. Traditionally patients are diagnosed based on their mental status, pulse and systolic blood pressure (dropping below 90 mmHg). However, it may be impossible to rescue patients when significant hypotension has developed.
The goal of this research is to verify the usability of a wearable device, including two sensors: an accelerometer attached to the chest and an infrared sensor attached to the finger/earlobe, to detect haemorrhage unobtrusively and in early stage. Ideally, the patients can wear such a system and signal processing can be performed on smartphones/tablets.
Our promising preliminary results has shown the usability of this technology, only using the sensor on the chest in forty subjects going through a graded lower body negative pressure (LBNP). LBNP was used to simulate hemorrhage in a laboratory environment. The addition of a sensor on the finger, as proposed in this proposal, will provide the possibility of measuring pulse transition time. The accelerometer sensor will be used as the proximal measurement site and, the infrared sensor, as the dorsal measurement site signal, in the pulse transit time estimation algorithm. In a separate preliminary study it is shown that, using the LBNP to induce circulatory shock, that the pulse transition time estimated using this method is related to blood pressure. It is hypothesize that addition of the new sensor on the finger will increase the sensitivity of hemorrhage detection.
 National Trauma Institute. http://www.nationaltraumainstitute.org/home/hemorrhage.html