Investigating optical path and differential pathlength factor in reflectance photoplethysmography for the assessment of perfusion

Abstract

Photoplethysmography (PPG) is an optical noninvasive technique with the potential for assessing tissue perfusion. The relative time-change in the concentration of oxyhemoglobin and deoxyhemoglobin in the blood can be derived from DC part of the PPG signal. However, the absolute concentration cannot be determined due to the inadequate data on PPG optical paths. The optical path and differential pathlength factor (DPF) for PPG at red (660 nm) and infrared (880 nm) wavelengths were investigated using a heterogeneous Monte Carlo model of the human forearm. Using the simulated DPFs, the absolute time-change in concentrations were determined from PPG signals recorded from the same tissue site. Results were compared with three conditions of approximated DPFs. Results showed the variation of the optical-path and DPF with different wavelengths and source-detector separations. Approximations resulted in significant errors, for example, using NIRS DPF in PPG led to "cross talk" of -0.4297 and 0.060 and an error of 15.16% to 25.18%. Results confirmed the feasibility of using the PPG (DC) for the assessment of tissue perfusion. The study also identified the inappropriateness of the assumption that DPF is independent of wavelength or source-detector separations and set the platform for further studies on investigating optical pathlengths and DPF in PPG.

Validation of an Inverse Fitting Method of Diffuse Reflectance Spectroscopy to Quantify Multi-Layered Skin Optical Properties

“…Although there are some fluctuations in the curves of f blood and StO 2 which are likely caused by motion artifacts, f blood and StO 2 during the occlusions apparently deviated from the baseline and the deviations were much larger than standard deviations during the baselines. The decreases in StO2 during both occlusions are similar to results reported in previous studies [33,[37][38][39][40], and are expected because tissue consumes oxygen and no oxygenated blood is supplied under the occlusions. We observed that f blood decreased slightly during both arterial and venous occlusions, which are not in agreement with trends often reported [33,[35][36][37]40].…”

“…The decreases in StO2 during both occlusions are similar to results reported in previous studies [33,[37][38][39][40], and are expected because tissue consumes oxygen and no oxygenated blood is supplied under the occlusions. We observed that f blood decreased slightly during both arterial and venous occlusions, which are not in agreement with trends often reported [33,[35][36][37]40]. This discrepancy might be partly, due to the short SDS used in the current SRDRS system that is more sensitive to the micro-circulation in the superficial dermis.…”

“…To demonstrate the applicability of the F-ANN forward model and inverse fitting procedure on in-vivo skin optical property estimation, we took in-vivo measurements using the SRDRS system and conducted cuff occlusion experiments according to previous studies [33][34][35][36][37]. The current study was approved by the Institutional Review Board at National Taiwan University, and the informed consent was obtained from each healthy volunteer.…”

Novel Polydimethylsiloxane (PDMS) Pulsatile Vascular Tissue Phantoms for the In-Vitro Investigation of Light Tissue Interaction in Photoplethysmography

“…Chatterjee et al [12] utilise Monte Carlo simulations to examine the distribution of photons within perfused skin. They concluded that the Differential Pathlength Factor (DPF) is dependent on wavelength and source-detector separations contrary to prior assumptions [13]. Although such studies are producing interesting results, a common limitation is the static nature of the simulation design where arterial pulsations are ignored.…”

Estimating the Dependence of Differential Pathlength Factor on Blood Volume and Oxygen Saturation using Monte Carlo method

“…A number of research works have been carried out previously to evaluate the dependence of DPF on tissue location, sensor geometry, optical wavelength and age [3], [4], [5], [6]. Recent studies have also identified a variation in DPF between larger and smaller source-detector separations, typically used in noninvasive applications such as Near-Infrared Spectroscopy (NIRS) and Photoplethysmography (PPG), respectively [7]. The importance of an accurate DPF assessment for a specific application has been demonstrated in previous works that have shown significant cross-talk errors in the measured concentration of oxyhaemoglobin and deoxyhaemoglobin for an inaccuracy in the DPF value [9], [10], [11].…”