On-Line Electrical Impedance Measurement for Monitoring Blood Viscosity during On-Pump Heart Surgery

Abstract

Background: The viscosity of blood (η) as well as its electrical impedance at 20 kHz at high shear rate depends on hematocrit, temperature, concentration of macromolecules and red cell deformability. The aim of our study was to investigate the relation between viscosity and electrical impedance in a heart-lung machine-like set-up, because during on-pump heart surgery considerable viscosity changes occur. Methods: Blood of 10 healthy volunteers was examined under temperature variation between 18.5 and 37°C at four different levels of hemodilution. Blood viscosity was examined with a golden-standard technique, i.e. a Contraves LS 30 Couette viscometer, and the results were compared with measurements of the electrical resistivity (R) at 20 kHz by a specially designed device in series with the tubing system of a heart-lung machine. All measurements were performed at a shear rate of 87 s^–1. Results: Using stepwise multiparameter regression analysis (SPSS) a highly significant correlation was found (r² = 0.882) between viscosity (η) and resistivity (R). Adding the variables sodium ([Na⁺]) and fibrinogen ([Fibr]) concentration the coefficient of correlation further improved to r² = 0.928 and the relation became: η = –0.6844 + 0.038 R + 0.038 [Na⁺] + 0.514 [Fibr]. All coefficients showed a statistical significance of p < 0. 001. Conclusions: Electrical impedance measurement is feasible in a heart-lung machine-like set-up and allows accurate continuous on-line estimation of blood viscosity; it may offer an adequate way to record and control viscosity changes during on-pump heart surgery.

Electrical Characteristics of Various Submucosal Injection Fluids for Endoscopic Mucosal Resection

“…The exact reason of the highest resistivity of fibrinogen solution is not clear and warrants further investigation. However, one study in order to utilize a continuous on-line estimation of blood viscosity during on-pump heart surgery showed a remarkably high correlation between viscosity and electrical resistivity [20]. This study also supported previous studies reporting the influence of fibrinogen on blood viscosity and (electrical) resistivity [21].…”

Prediction of RBC aggregability and deformability by whole body bioimpedance measurements analyzed according to Hanai's mixture conductivity theory

“…The influence of hematocrit on impedance has been directly assessed in vivo in flowing blood within the same range of frequencies as we used [17]. It appears that in this range of frequencies hematocrit increases in vivo resistivity of flowing blood by 2.5 .cm per % (read on the figure of [17]), while on the whole body it decreases average body's extracellular resistivity by 0.1 .cm per %.…”

“…This relation is close enough to make bioimpedance a tool for the monitoring of hematocrit and RBC aggregation. When impedance is directly measured in vivo with electrodes inserted into the blood stream, it still exhibits strong positive correlations with hematocrit and blood viscosity [16,17]. Conductivity of blood is proportional to spatial average velocity of RBC, so that blood resistivity is proportional to hematocrit, RBC aggregation, whole blood viscosity and RBC rigidity.…”

A re-evaluation of modelling of the current flow between electrodes: consideration of blood flow and wounds

“…But there may be a flaw. The resistance of the skin is proportional to its blood content, since blood has the lowest resistivity of any body tissue [20] (the resistance of bone is 170 O m 71 while that of blood is 1.6 O m 71 [21]). Therefore blood resistivity has a large impact on the limb: even if there is a small change in blood hydration, resistivity of the whole limb changes significantly [22].…”