Theoretical and experimental aspects of erythrocyte filterability testing; flow acceleration and systemic resistance

Blood cell filterability is an established method in blood rheology. The dynamics at flow onset and its relevance to the data interpretation is, however, not fully known. This paper aims to investigate what controls the length and slope of flow acceleration as the medium accelerates to reach the steady state, and how this phenomenon may interfere with the data output. The acceleration time was not constant. With buffer the steady-state flow showed a logarithmic correlation (p<0.05) versus acceleration time and a linear correlation (p<0.001) versus acceleration slope. With 5% erythrocyte resuspension the steady-state flow instead demonstrated a linear relationship versus acceleration time (p<0.001) and no correlation versus acceleration slope. A cut-off timing of 0.6 s is suggested to avoid artifacts associated with flow acceleration. The possible influence on data interpretation from the flow channel systemic resistance was also addressed, and found to significantly underestimate measurable changes in erythrocyte properties from unprocessed flow curves. This was despite the traditional correction for blank filtration flow. Both acceleration and effects from systemic resistance do probably have minor influence on the historic data interpretation but could perhaps be considered in the methodology to sharpen the data output.