Special phenomena occurring in small blood vessels: Models, interpretation and importance for life

This article deals with special phenomena that characterize the blood circulation in arterioles and venules (size range 50–500 μm: the Fåhræus-effect, the Fåhræus–Lindqvist effect and vasomotion. These phenomena were discovered a long time ago and have been the subject of various conjectures, both about the physical causes and the physiological effects. Some of these conjectures have turned out to be wrong, but in any case, it is confirmed that these phenomena have a fundamental importance for life. A series of studies by the present authors between 2016 and 2023 have provided a physical interpretation of such phenomena based on rigorous mathematical models. Furthermore, our analysis includes the study of the combination of vasomotion and the Fåhræus–Lindqvist effect. We emphasize how these effects influence each other and why they prove to be very important for life by enhancing venous circulation and making the process of peripheral O₂/CO₂ exchange more efficient. Particular attention will be paid to the latter aspect and the comparison of the model results with the experimental results collected over the years. The material is structured to emphasize the effectiveness of the mathematical approach and its consistency with the underlying physiology and experimental measurements.