Light source driver, photodiode and impedance sensing in plethysmographic measurements

This work combines photoplethysmographic and electrical impedance plethysmographic measurements. A lack of blood delivery and oxygenation during pregnancy may have fatal consequences for the fetus. Photoplethysmographic measurements illuminate the tissue and measure the change of light absorption. In this contribution a photoplethysmographic measurement system is presented. The hardware concept includes an analog signal processing circuit for the photodiode and a special driver circuit to power two light sources (red and infrared LED). For photoplethysmographic measurements only one LED is required, but in view of future purposes, such as pulse oximetry, a second LED is already implemented. Furthermore this paper shows results of electrical impedance plethysmography. This designed photoplethysmographic measuring in combination with impedance cardiography might be promising in examine of fetus.