| Microvascular red blood cell (RBC) flow is an enormously complex and dynamically variable process. Variations appear as temporal fluctuations within vessels, and spatially, along or between vessels in a network. These variations occur on many different time scales and highlight microcirculatory regulation at many levels. These regulatory effects have a finite, measurable history that varies from one capillary to another. Does this variability result from random or deterministic processes?;It was hypothesized that the dynamics observed result from non-linear dynamic processes. A variety of factors influence the passage of RBCs in capillaries and flow fluctuations may result from complicated feedback and regulatory systems. Viewing the microcirculation as highly time varying and dynamic, we focused on using new approaches to acquiring and analyzing time series data.;Videotape records of capillary blood flow in-vivo in the rat extensor digitorum longus muscle, were made for up to 60 minutes using in-vivo video microscopy. Time series records of RBC velocity were generated, and chaotic time series analysis was used to analyse the in-vivo data, and data from a mathematical model of a microcirculatory network.;Results indicate that the time series distributions of RBC velocity demonstrate behaviour typical of a nonlinear transformation of another process. Pressure and Resistance, are postulated to impact the time series distributions, thus influencing the dynamics of RBC flow. The combined action of these factors and other mechanisms, may contribute to the quasi-random nature of the time series distributions of RBC velocity. This was consistent with the model data analysed. It is postulated that rheology contributes at least 2 to 3 degrees of freedom to the dynamics of the microcirculation, whereas myogenic, flow dependent and other dynamic mechanisms contribute at least 7 and 10 degrees of freedom.;This study provides new insights into understanding the microcirculation by demonstrating that variations in RBC velocity contain important information about the functioning of the microvasculature in regulating blood flow, and are not just random fluctuations. Further work is needed to determine whether, the dynamics of the underlying mechanisms that affect these time series records, themselves exhibit deterministic chaos. |
