In-ear pulse oximetry in high altitude mountaineering

According to the world health organization, 40 billion people travel to regions of high altitudes every year. One the most dangerous diseases according to high altitudes is the acute mountain sickness, caused, inter alia, by reduced partial oxygen pressure. This work reflects the possibilities of a cardio-respiratory acute mountain sickness monitoring with wearable photoplethysmography sensors. Since common photoplethysmographic systems are often applied to peripherals, these systems are affected to hypothermia that may inhibit accurate measurement in critical situations. Therefore, we discuss the usability of the in-ear pulse oximetry for vital monitoring during high altitude activities. For this, we present an in-ear pulse oximeter system for continuous measurement of vital signs. The system is evaluated during a cold-pressure-test to simulate low temperature exposition or to stimulate the endogenous centralization, respectively. Furthermore, high altitude is simulated by reduces partial oxygen pressure in 10 healthy subject (up to 8500m equivalent, ideal conditions). It could be proved, that the sub-dermal perfusion in the inner ear channel is not affected by centralization and thus, enables stable measurement during hypothermia. Blood oxygen saturation (hypoxia) could be measured with high accuracy. Furthermore, the system was tested under a realistic scenario at approximately 3000m in Switzerland with promising results.