The influence of red blood cell (RBC) aggregation on transparency of blood in the red-near infrared spectral range is investigated. We argue that for relatively thin blood layers the light diffraction on aggregates becomes the dominant phenomenon. The nature of pulsatile changes of blood transparency is explained by pulsations of RBC aggregate size. For another case of over-systolic vessel occlusion the following time evolution of blood transparency strongly depends on light wavelength. This dependence may serve as a basis for an alternative approach to noninvasive blood tests: occlusion spectroscopy. Theoretical results well correspond to both in vivo and in vitro measurements reproducing pulsatile blood flow and long occlusion as well.

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Physiological blood coagulation/clotting is an essential biological process that is initiated by vessel injury and includes a cascade of enzymatic reactions finalized by fibrin polymerization and clot formation. We utilize dynamic light scattering (DLS) imaging to monitor in vivo red cell mobility as an indicator of blood coagulation. In the course of the experiments, blood flow is arrested using mechanical occlusion, and then laser injury is applied. We demonstrate that the combination of laser injury with DLS imaging on occluded blood vessels (i.e., under static conditions) is suitable to detect even subtle changes of plasma viscosity in the circulatory system, which reflects the process of clot development. This approach is noninvasive and has a relatively simple and easy-to-use technical design. Thus, the proposed methodology provides a promising tool for investigating blood clotting within the vasculature.

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We present a new non invasive method for assessing hemostasis in vivo. This method is based on the analysis of the movement characteristics of red blood cells (RBCs) during blood stasis condition. Stasis is intermittently induced by occlusion of arterial blood flow at the finger root. We assumed that under zero flow conditions, RBC movement is driven mostly by Brownian motion, and we characterized the RBC movement by utilizing the dynamic light scattering (DLS) technique in vivo. We found that during the stasis the RBCs diffusion coefficient in plasma decreases. We speculate that the RBC diffusion coefficient is most strongly related to endothelial and hemostatic activity. This assumption is supported by our findings that RBC move ment, being expressed through the characteristics of the measured DLS signal, is correlative to the biological age and also is related to the coagulation factors. This new method can serve as a new diagnostic and research tool for the assessment of hemostasis and vascular function.