Photoplethysmographic logger with contact force and hydrostatic pressure monitoring

Oxygen saturation is a key parameter for assessing a patient condition. The present work aims to develop a stand-alone pulse oximeter and photoplethysmographic system. In addition, it incorporates a force sensor and a set of accelerometers to measure the contact force and the finger height offset relatively to the heart. Both the design of hardware and the development of firmware are presented. Currently, the system is able to retrieve a stable photoplethysmographic waveform and compute the oxygen saturation in real time. Signals acquired in a healthy subject led to a value of 91.5±1.1%. Both the height offset of the finger and the contact force between the finger and the probe proved to have influence in the photoplethysmographic waveform as well as in the oxygen saturation results.