Non-invasive sensor for an in vivo hemoglobin measurement

NIR-spectroscopy and Photoplethysmography (PPG) is used for a measurement of blood components. The absorption-coefficient of blood differs at different wavelengths. This fact is used to calculate the optical absorbability characteristics of blood which is yielding information about blood components like hemoglobin (Hb) and arterial oxygen saturation (SpO₂). The measured PPG time signals and the ratio between the peak to peak pulse amplitudes are used for a calculation of these parameters. The newly developed optical sensor systems use up to five wavelengths in the range of 600nm to 1400nm for a measurement of the hemoglobin concentration, oxygen saturation and pulse. This noninvasive multi-spectral measurement method was tested with prototype-devices based on radiation of monochromatic light emitted by laser diodes and by using light emitting diodes (LED) through an area of skin on the finger. The sensors assembled in this investigation are fully integrated into wearable finger clips.