Non-invasive measurement of hemoglobin content in blood

A non-invasive method of ascertaining the hemoglobin content in blood is presented here. The method proposed here uses a couple of photo-plethysmo-graphic (PPG) signals obtained by illuminating an extremity such as a finger or earlobe with monochromatic light at two different wavelengths. An empirical equation for calculation of hemoglobin content in blood is derived using a model for attenuation of light through skin-bone-tissue-blood in that extremity, well known extinction coefficients of hemoglobin (with and without oxygen) and data collected from a clinical study. The availability of PPGs at two different wavelengths facilitates the computation of, apart from hemoglobin content, heart rate, heart rate variability and oxygen saturation in arterial blood (SpO
2
) as well.