Experimental and theoretical studies of the influence of pulse pressure oscillations on the processes of microhemocirculation

Abstract

UDC 532.546 The influence of pulse pressure oscillations on the processes of transcapillary exchange in the hemodynamics has been investigated by experimental and numerical methods. The active role of microvessel walls in the mass transfer has been confirmed. On the basis of the generalized nonstationary Starling scheme patterns of transcapillary exchange with alternation of the filtration and reabsorption processes have been determined. Flows in the interstitial space have been modeled numerically. It has been established that the presence of pulsations promotes enhancement of the transcapillary exchange. process in the vital activity of the organism creating for it the indispensable tissue homeostasis. Homeostasis is the physiological process of maintaining internal stability in the organism balancing its various parameters, for example, blood pressure, temperature, and acid-base balance when the ambient conditions are changed. In this connection, in the last few decades microhemocirculation has still been the most important problem of experimental and clinical medi- cine. The urgency of this problem is that the solution of many questions of practical medicine depends on its success- ful experimental and clinical handling. It should be recognized thereby that the functioning of the microhemo- circulation link of the cardiovascular system is still a little-studied branch of biomechanics. To advance in this field of knowledge, it is necessary that representatives of biology, medicine, physics, and applied mathematics conduct interdis- ciplinary integrated basic research. According to the modern traditional concepts of transcapillary exchange, all capillaries of the regional capil- lary network are functionally equivalent (1). It is assumed that in the regional capillary network along the full length of any single capillary penetration of carbon dioxide into the interstitial space and further into the erythrocyte occurs. As the gas combines with water in erythrocytes, carbonic acid is formed and its dissociation is a source of hydrogen ions. According to the known Bohr effect, hydrogen ions promote release of oxygen from erythrocytes. Moreover, it is assumed that within the limits of any single capillary the counterflow of oxygen and carbonic acid dissolved in the blood plasma is due to molecular physical diffusion without account for the slowness of the process. However, blood stays in the capillary for a short time insufficient for the necessary chemical transformations to take place in the cap- illary lumen and for oxygen to go outside the limits of its walls. As our experimental studies have shown, the tradi- tional concepts on transcapillary exchange are contradictory. New Concepts on Transcapillary Exchange. In the transport function of the heart and large arteries, the for- mation of a helical blood flow in the cardiovascular system (2, 3), and in the biomechanics of the microhemocircula- tion link the appearance of local transverse shifts of microvessel walls in the acoustic range (4-6), are of fundamental importance. The energy of the rotational component in the helical blood flow ensures the existence of a distributed