Photoplethysmography for the Assessment of Haemorheology

Abstract

Haemorheology has been long identified as an early biomarker of a wide range of diseases, especially cardiovascular diseases. This study investigates for the first time the suitability of Photoplethysmography (PPG) as a non-invasive diagnostic method for haemorheological changes. The sensitivity of both PPG components (AC and DC) to changes in haemorheology were rigorously investigated in an in vitro experimental setup that mimics the human circulation. A custom-made reflectance PPG sensor, a pressure transducer and an ultrasonic Doppler flowmeter were used to map changes in flow dynamics and optical responses in an arterial model. The study investigated the effect of shear rates by varying fluid pumping frequencies using 4 set-points and the effect of clot formation using a chemical trigger. Both PPGAC amplitudes and PPGDC levels showed significant (p < 0.001) changes during the increase in shear rates and an immediate change after thromboplastin activation. The findings highlight that PPG has the potential to be used as a simple non-invasive method for the detection of blood characteristics, including disaggregation, radial migration and cross-linking fibrin formations. Such capability will enable the assessment of the effects of clotting-activators and anticoagulants (including non-pharmacological methods) and might aid in the early non-invasive assessment of cardiovascular pathologies.

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

“…The changes in concentration in oxy-, deoxy-, and total hemoglobin were calculated by applying the modified Beer-Lambert law to the red and infrared PPG signals acquired from the forearm, following Eqs. (6)- (8). The extinction coefficients for the estimation of HbO 2 and HHb were obtained from published data on human blood spectra.…”

“…5 PPG has found its utility in a vast number of applications, such as neonatal care, hemorheology assessment, pulse transit time investigation, and measurements from body cavities and organs. [6][7][8][9][10][11][12] Near-infrared spectroscopy (NIRS) is another noninvasive optical technique, which measures variations in local blood perfusion by estimating changes in oxy-hemoglobin, deoxyhemoglobin, and total hemoglobin. 13 These physiological variables are determined using the Beer-Lambert law, correlating the attenuation of light A, through a medium with the concentration C of the absorber (chromophore) present in the solution.…”

In silico and in vivo investigations using an endocavitary photoplethysmography sensor for tissue viability monitoring

“…9 Recently, there has been a plethora of interest in extending the application of PPG beyond pulse oximetry, for example, in the assessment of vascular mechanics, heart rate, blood pressure, tissue perfusion, respiration, and mental stress. [10][11][12][13][14][15][16] To continuously monitor the intestinal perfusion and oxygenation, an endocavitary PPG sensor has been proposed. 17 The proposed sensor can be inserted through the anal orifice of a patient to capture the PPG signal by illuminating the colon utilizing light emitters of dual wavelength, corresponding to red and infrared.…”

Design and Development of a Modular, Multichannel Photoplethysmography System

“…In particular since its potential use as a diagnostic tool for measuring physiological variables beyond arterial oxygen saturation and heart rate (HR), such as venous oxygen saturation [4], pulse rate variability [5], pulse wave velocity (PWV) [6], blood pressure [7], and pulse transit time (PTT) [8] has been demonstrated. These newly derived variables are now being used as diagnostic markers for conditions such as arterial stiffness [9], hypertension, peripheral vascular disease [10], stress, endothelial dysfunction [11], and haemorheology [12]. Furthermore, PPG has generated immense interest in the development of unique sensor technology utilizing either miniaturized optoelectronic components or optical fibers, to measure the volumetric changes directly from organs such as the esophagus [13], liver, bowel [14], brain [15], ear canal [10], and other vascular tissues such as free flaps [16].…”