Drag Reducing Polymers Improves Microvascular Perfusion After Extracorporeal Circulation
Authors: Govender Krianthan , Cabrales Pedro 
Published: May 2022

Drag reducing polymers (DRPs) have been used in various engineering applications, such as the transfer of crude oil or seawater in pipelines. The use of DRPs has crossed into the bioengineering sphere, with previous ex‐vivo and in‐vivo studies suggesting that the addition of DRPs decreases the erythrocyte cell free layer (CFL) or cell depleted layer near the vessel wall and increases microvascular blood flow. The objective of this study was to investigate whether the addition of DRPs would improve microvascular perfusion in a rodent model of extracorporeal circulation (ECC).

Male Golden Syrian hamsters were instrumented with a dorsal skinfold window chamber, along with an arterial catheter into the right carotid artery to monitor blood pressure and heart rate. During ECC, animals were anesthetized with isoflurane, and a drainage cannula was inserted through the left jugular. The animal was connected to the circuit, primed with either lactate ringers (LR group) or 5 PPM 500 kDa polyethylene glycol in lactate ringers (DRP group). Blood was drained from the jugular cannula, run through a peristaltic pump and bubble trap, before entering the carotid catheter for reinfusion. The circuit was run for 90 minutes in total, with 60 minutes at a flowrate equivalent to 15% of the animal’s cardiac output. Measurements were taken before ECC (baseline, BL) and after 1, 2, and 24 hrs post‐ECC. At each timepoint, microvessel (arterioles and venules) diameter, red blood cell velocity and functional capillary density (FCD) were measured using intravital microscopy.

Arteriole and venule hemodynamics are displayed in Figure 1. The arteriole results showed an interesting contrast between effects at 1 hr and 24 hrs post‐ECC. At 1 hr post‐ECC, the DRP group displayed a statistically lower arteriole diameter compared to the LR group, but no statistical difference in blood flow between the two groups. At 24 hrs post‐ECC, no difference in arteriole diameter was observed between groups, while arteriole blood flow was statistically higher in the DRP group compared to the LR group. In venules, no changes were observed between groups at 1 hr post‐ECC. However, at 2 and 24 hrs post‐ECC, the DRP group had a statistically significant higher diameter compared to the LR group. Venular blood flow was statistically elevated in the DRP group at 24 hrs post‐ECC compared to the LR group. Figure 2 shows the changes in FCD. FCD was lower for both DRP and LR groups at 1 and 2 hrs post‐ECC when compared to BL levels. The DRP group displayed a higher FCD at 2 hrs post‐ECC compared to the LR group. At 24 hrs however, while the DRP group was able to recover back to BL levels, the LR group was statistically lower than BL.

From these results we conclude that the addition of DRPs to priming fluids for ECC procedures may be beneficial in preserving microvascular perfusion 24 hrs post‐ECC. This may help reduce the risk of ischemic injury, production of pro‐inflammatory markers, and development of multiorgan dysfunction. Further research is warranted to optimize the DRPs parameters, such as concentration and molecular weight.