New ear sensor for mobile, continuous and long term pulse oximetry

Pulse oximetry is a valuable monitoring technology used at present mainly for immobile patients. The reason for the limitation concerning the user\´s mobility is due principally to unsuitable sensors and sensor locations. This is particularly the case with finger sensors, which tend to work best in respect to signal quality i.e. modulation depth, but are quite susceptible to motion artifacts. In order to achieve mobility for pulse oximetry monitoring, an ear canal sensor was developed. This area was chosen based on the assumption that intensive movement and acceleration of this part of the body is generally avoided as it produces unpleasant feelings. An unusual and so far unknown light path had to be used in the ear canal sensors for which we suggest the expression "circummission pulse oximetry", since the optoelectronic components face outside the canal and away from each other, generating a minimal effective light path of a semicircle within the auditory canal\´s wall. Surprising findings included modulation depth and omega values, indicating shunt levels even lower than in transmission pulse oximetry finger sensors. We concluded that finger sensors, which have so far been considered free of shunt light by many researchers, actually do involve some shunt light. Circummission pulse oximetry proved impressively resistant to motion and revealed good signal quality even when heavily moving the entire trunk/body. Therefore we believe that the mobile pulse oximetry monitoring system presented here might open up possibilities for a variety of monitoring applications: extending from medical to leisure settings, from inpatients to outpatients, from rehab-training to mountain climbing, from fire fighting to sleep apnea screening.