Effects of a sudden flow reduction on red blood cell rouleau formation and orientation using RF backscattered power.

This study investigates the effects of sudden flow reductions versus a complete flow stoppage on the formation and orientation of RBC aggregates, or rouleau formation, using ultrasound backscattering. This was conducted through various experimentations on horse blood models.

Study Approach

In trying to assess the impact of flow reductions on red blood cell (RBC) aggregation, human blood was typically utilized. It was circulated at a high shear rate to disrupt the aggregates with measurements taken once the flow is completely stopped during the process of rouleau formation. This study, however, recognizes that a very low shear rate could also facilitate the formation of aggregates, hence the adoption of the approach to investigate both scenarios.

• The research aim was to understand the impact of abrupt flow reductions against a total flow stoppage on the kinetics or the rate of rouleau formation.
• The researchers used ultrasound backscattering as a tool to investigate this phenomenon.
• To represent different aggregation levels, horse blood models were used instead of human blood. This was achieved through the dilution of plasma with saline in different proportions.
• The blood was circulated at a rate of 1250 mL min-1 before reduction to fracture the aggregates.

Experiments and Observations

Using a 10-MHz transducer, the ultrasound radiofrequency (RF) signal was recorded from the tube’s center after instituting different levels of sudden flow reduction or total flow stoppage.

• It was observed that there was no increase in power following a complete stoppage of flow.
• However, when post reduction flow rates varied between 20 and 160 mL min-1, there was a proportional increase in the backscattered power mirroring the kinetics of RBC aggregation.
• There was a quicker and stronger echo build-up when the post-reduction flow rate was increased.
• For horse RBCs exhibiting high rouleau formation kinetics, an unusual pattern of backscattered power variation was noticed. This pattern involved a rapid power elevation to a plateau, then another quick increase and another plateau.
• To explain the power increases observed, rouleau formation, random disorientation and reorientation were postulated.

This study sheds new light on the relationship between blood flow rate reductions and the kinetics of rouleau formation, demonstrating the importance of flow velocity in the aggregation of red blood cells. It could have significant implications for understanding various pathological conditions in human beings where the aggregation or clumping of red blood cells is involved.