Sergei G. Proskurin

Laser Doppler velocimetry: in-vitro and in-vivo measurements of biological fluid flows in restricted volumes

Laser Doppler velocimetry is an interferometric technique which allows to provide rapid. objective and non-invasive measurements of the flow velocities. The accuracy of these measurements depends on the apparatus function of the velocimeter which is the apparatus broadening of the Doppler spectrum. This is defined by the parameters of the optical and signal processing units of the velocimeter alone. In the majority of technical applications the probe volume of the conventional velocimeters is much smaller in extent than the dimensions characterizing the flow system under study. On the contrary the flows of biological fluids (protoplasm, blood, etc. ) are usually spacially restricted, so that the probe volume can be comparable to the characteristic dimension, e. g. the diameter, of the vessel . In these conditions the velocity gradients introduce the additional gradient broadening to the Doppler spectra which can exceed the apparatus broadening. This reduces the possibilities of the velocimeter to measure the velocity profiles in the investigated flows which are sometimes the main objectives of the study. But at the same time the gradient broadening carries the information on the velocity gradients which in certain cases can be extracted.

Potentialities of laser Doppler microscopy in biomedical research

Laser Doppler (LD) microscopy is a technique providing local measurements of directed flow velocities and diffusion coefficients of cells, intracellular protoplasmic constituents, macromolecular aggregates, etc. In our group a computer- and video-aided sign-sensitive scanning laser Doppler microscope (LDM) has been designed, constructed and applied to the study of different biological objects. In this paper some new results are presented in connection with the development of LD microscopy.

Laser Doppler microscopy of biological objects with different optical properties

Quite a number of experimental techniques are used in biomedical research involving the registration of flow velocities of biological fluids. These arc: particle image velocimetry, ultrasonic Doppler velocimetry, speckle microscopy, transmission grating microscopy, etc. Each of these methods has its advantages but none of them provides means to study all the variety of biological objects and dynamic phenomena, via performing noninvasive measurements. An essential alternative method is laser Doppler (LD) spectroscopy and microscopy, based on the registration of Doppler frequency shifts of laser radiation scattered from moving particles. The method yields high spatial and temporal resolution and hence can be used in different fields of biophysics and biomedicine [1,2,3]. The amount of the integral information, averaged over all the particles traversing the probe volume, the real-time mode of measurements, the possibility of registration of the flow velocity profiles -all this makes LD microscopy an efficient method enabling to study biological objects of different levels of complexity with broad range of optical properties. The possibility of fluid flow measurements in live objects with the LD technique was first shown in 1972 [4] and since then the potentialities of this technique have been studied extensively [5, 6, 7J. Nonetheless, though there arc no apparent technical reasons which would prevent from designing an LD microscope (LDM) as a commercial device, LD microscopy has not become yet a conventional technique. There still exist problems of Doppler spectra interpretation and evaluation of data experimentally obtained from biological objects with different opticai properties. These will be discussed below. We describe here an LDM designed in Moscow State University specifically for biophysical and biomedical applications on the basis of our earlier experience in application of LD spectroscopy to the study of intracellular hydrodynamics [8] and of haemodynamics [9). The potentialities of the LDM are illustrated by the results of real time measurements of oscillating flow velocities in relation to two different phenomena: 1 -protoplasmicstreaming in plasmodium of myxomycete Physarum, and 2 -bloodflow in aquarium Danio rerio fish embryo. To carry out measurements in biological objects with different optical properties and a broad range of values of measured parameters the following innovations have been introduced: - inl.roduction of controlled high stability frequency shift in the probing beams; - two-steps formation of optimal probe volume; - generation of the output signal with high signal-to-noise ratio both in analog and in photon ounting regimes; - arrangement of computer controlled fast scanning;- elaboration of the software for signal processing and calculation of parameters under study

Decrease of hydrodynamic resistance in rat mesenteric arterioles in response to injection of polyethylene oxide polyox WSR-301

Adequate blood supply of tissues and organs is essential to the normal functioning of the organism. From the hemodynamic point of view, this is achieved, in particular, through variation of the ratio between local microcirculatory resistances. Since the classical studies of Poiseuille [6], the role of the diameter of resistive vessels arterioles in the total blood flow resistance and in the redistribution of the blood flow in the microcirculatory bed has been well documented. However, the particular contribution of the flow pattern to these processes, for example, microdisturbances caused by the pulsatile flow, the movement of formed elements in a shear flow, at bifurcations of the yessets has been less studied, primarily due to methodological complications of both a physiological and a mathematical nature. High-molecular linear polymers are widely used in hydrodynamics, as they reduce the hydrodynamic resistance of the liquid by acting on the time structure of the flow [3,9]. When injected into the circulation, these substances reduce to a greater or lesser extent the total vascular resistance due to a drop of the systemic arterial pressure and/or increase of the cardiac out-

Nonstationary blood-flow measurement in growing fish embryos with laser Doppler microscopy

A theoretical aspect of frequency domain measurements of tissue optical parameters is considered. In the framework of radiative transfer theory the expressions have been obtained, which describe dependence of modulation M and phase shift (Delta) (Theta) of scattered radiation on frequency. As an example, the results of processing of experimental data are presented.

Pulsating blood-flow monitoring in developing fish embryos and rat mesentery by laser Doppler microscopy

Laser Doppler (LD) microscopy is a technique, providing high-resolution noninvasive measurements of microstructures dynamics. It can be used in different fields of biophysics and biomedicine. This technique yields quantitative information on diffusion coefficients, velocities, and velocity profiles of dynamic microstructures in vivo and in vitro. LD microscopy is an alternative method of velocity measurement to such methods as computer- aided microphotography and imaging, diffraction grating microscopy, FRAP, etc. In this paper we describe the results of our LDM measurements of one of the main hemodynamic parameters -- the blood-flow velocities in the microvessels of Salmo salar and Danio rerio fish embryos, as well as of the rat mesentery.