Real-time prediction of heparin concentration in blood extracorporeal circulation by relaxation time distribution (RTD).

Heparin concentration c in a blood extracorporeal circulation has been real-timely predicted based on the relaxation strength Δεm at relaxation frequency fm extracted by relaxation time distribution (RTD). The simulated extracorporeal circulation was conducted to optimize the number of Δεm for the prediction of c using the porcine whole blood (WB) and low-leukocyte and -platelet blood (LLPB) under the condition of the gradual increment of c from 0 to 8 U/mL with constant flow rate and blood temperature. The experimental results show that among the three relaxation strengths Δε1, Δε2 and Δε3 (in ascending order of frequency), Δε2 at f2 = 5.2 ∼ 6.2 MHz and Δε3 at f3 = 42 ∼ 50 MHz were correlated to c. The Δε3 was decreasing with increasing c in both cases, which was influenced by the plasma macromolecular concentrations, while the Δε2 was increased with increasing c in WB case but was hardly changed in LLPB case because the Δε2 is influenced by the blood cell concentrations and the shape changes of blood cell membranes. Heparin concentration c is estimated by the linear regression formula cPRE=a1(Δε2-Δε2c=0)+a2(Δε3-Δε3c=0) (a1 = -0.991, a2 = -0.123) within the mean absolute percentage error (MAPE) of 0.291.