Elfi-Tech (Israel)

This article examines the potential for non-invasive measurement of elevated levels of erythrocyte aggregation in vivo, which are linked to a higher risk of inflammatory processes. The study proposes the use of a dynamic light scattering approach to measure aggregability. The mDLS sensor modules consist of VICEL and two photodiodes, and two of these modules are placed on an inflatable transparent cuff. The cuff is then fitted to the subject's finger root, with one sensor module placed on each side of the root. Blood flow is temporarily halted for one minute using over-systolic inflation of the cuff, and signals from both sensors are recorded. Three groups of subjects were studied: a control group of 65 individuals, a group of 29 hospitalized COVID-19 patients, and a group of 34 hospitalized patients with inflammatory diseases. The experimental results demonstrated significant differences in signal kinetic behavior between the control group and the other two groups. These differences were attributed to the rate of RBC aggregation, which is associated with inflammation. The study underscores the potential for non-invasive diagnostic tools to assess inflammatory processes by analyzing RBC aggregation.

This article discusses the origin of PPG signals. Two plausible hypotheses are analyzed: the volumetric hypothesis and a model wherein the PPG is driven by the RBC aggregation process. To verify the model predictions, the PPG signals at the fingertip were measured. External pressure was applied to the fingertip, presumably reducing the blood flow. The results expressed in terms of gamma, used in pulse-oximetry, agree with the aggregation model. In addition, the oscillometric signal and the PPG signal amplitude were simultaneously measured in the fingertip. All of the experimental results favor the proposed aggregation mechanism as responsible the PPG signal.

PPG volumetric model is frequently adopted to explain the pulsatile nature of optical response for arterial pulsation. In this article we show that the pulsatile fluctuation of optical response can be explained in terms of the light scattering related changes. According to this assumption, these fluctuations are driven by the modulation the scattering coefficient associated with the blood flow hemodynamic effects. There was shown that the proposed model yields a good correspondence with the pulse-oximetry related parameters. Moreover, it was found that the experimental relationship between the red blood concentration in the blood (hematocrit) and the parameters being derived from the in vivo measured optical signals can be described in terms of this scattering driven model. There was demonstrated that the commonly used volumetric assumption fails to provide a reasonable description of the experimental results. The last fact can be used as a decisive argument in favor of the scattering driven model. This model can be used for better understanding of the pulse oximetry as well as for the guidance for the algorithmic development of the blood hemoglobin/ hematocrit in vivo.

Physiological blood coagulation is an essential biological process. Current tests for plasma coagulation (clotting) need to be performed <i>ex vivo</i> and require fresh blood sampling for every test. A recently published work describes a new, noninvasive, <i>in vivo</i> approach to assess blood coagulation status during mechanical occlusion¹. For this purpose, we have tested this approach and applied a controlled laser beam to blood micro-vessels of the mouse ear during mechanical occlusion. Standard setup for intravital transillumination videomicroscopy and laser based imaging techniques were used for monitoring the blood clotting process. Temporal mechanical occlusion of blood vessels in the observed area was applied to ensure blood flow cessation. Subsequently, laser irradiation was used to induce vascular micro-injury. Changes in the vessel wall, as well as in the pattern of blood flow, predispose the area to vascular thrombosis, according to the paradigm of Virchow's triad. In our experiments, two elements of Virchow's triad were used to induce the process of clotting <i>in vivo</i>, and to assess it optically. We identified several parameters that can serve as markers of the blood clotting process <i>in vivo</i>. These include changes in light absorption in the area of illumination, as well as changes in the pattern of the red blood cells' micro-movement in the vessels where blood flow is completely arrested. Thus, our results indicate that blood coagulation status can be characterized by non-invasive, <i>in vivo</i> methodologies.