Abstract
Optical sensors are increasingly becoming important and relevant in the field of non-invasive diagnostics because of simple construction, easy to use and relatively inexpensive in comparison with other tools. The Photoplethysmography (PPG) optical sensors are capable of measuring the blood volumetric changes in the subcutaneous vessels in conjunction with sensitive temperature sensors that measures breathing activity. Frequency spectrum of the PPG signal shows a peak around 0.12 Hz other than the two principal frequency components (cardiac peak –1 Hz ( fh ) and respiratory peak –0.25 Hz ( fb )). The prominence of the low-frequency relaxation rhythms appears around 0.12 Hz ( fl ) in conjunction with the respiratory peak during deep breathing.
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