Investigation of photoplethysmography and Near Infrared Spectroscopy for the assessment of tissue blood perfusion

Pulse Oximetry (PO) and Near Infrared Spectroscopy (NIRS) are among the most widely adopted optical techniques for the assessment of tissue perfusion. PO estimates arterial oxygen saturation (SpO₂) by exploiting light attenuations due to pulsatile arterial blood (AC) and constant absorbers (DC) at two different wavelengths. NIRS processes the attenuations of at least two wavelengths to calculate concentrations of Deoxygenated ([HHb]), Oxygenated ([HbO₂]), Total Haemoglobin ([tHb]) and Tissue Oxygenation Index (TOI). In this work we present the development and evaluation of a reflectance PPG probe and processing system for the assessment of tissue perfusion. The system adopts both Pulse Oximetry and NIRS principles to calculate SpO₂, [HHb], and [HbO₂] and [tHb]. The system has been evaluated on the forearm of 10 healthy volunteers during cuff-induced vascular occlusions. The presented system was able to estimate SpO₂, [HHb], [HbO₂] and [tHb], showing good agreement with state-of-the-art NIRS and conventional PO.