Investigation of photoplethysmography and arterial blood oxygen saturation from the ear-canal and the finger under conditions of artificially induced hypothermia

Pulse oximeters relay on the technique of photoplethysmography (PPG) to estimate arterial oxygen saturation (SpO₂). In conditions of poor peripheral perfusion such as hypotension, hypothermia, and vasoconstriction, pulse oximeters become inaccurate or provide no reading. This is due to the poor quality of the PPG signals detected at that instance. In order to overcome this problem, the ear canal has been proposed as a alternative measurement site for measuring reliable SpO₂. Hence, an ear canal PPG sensor was developed along with a PPG processing system. The performance of the sensor was evaluated by measuring the red and infrared PPGs and SpO₂ from 10 healthy volunteers undergoing artificially induced hypothermia. The results from the ear canal sensor were compared with simultaneously acquired results from the finger. Hypothermia was induced by exposing the volunteers to cold temperatures of 10 ± 1°C. The results acquired suggest that the ear canal pulse oximeter endures more in estimating SpO₂ values accurately when compared with the more common finger pulse oximeter.