Measurement of characteristic frequency of red blood cells and thrombogenic process for various hematocrit values using dielectric relaxation method

Abstract

Dielectric relaxation method has been proposed for the possibility of real-time detection of thrombosis by exploiting the electrical properties of the blood. In-vitro experiments were conducted with bovine blood to measure relative permittivity and dielectric loss in the case of various hematocrit values under static blood condition. As a result, the relaxation frequency of the electrode and red blood cells were observed at 20 kHz and 2 MHz respectively. The characteristics frequency showing the permittivity of the red blood cells membrane was in the range of 60 kHz to 1 MHz. The time variations of resistivity and relative permittivity were observed at this frequency range of characteristics frequency of red blood cell membrane. Resistivity and relative permittivity measured at this frequency range increased in the case of the increase in the hematocrit values. Additionally, a peak was observed in the temporal change in relative permittivity only in the case of that frequency range. Moreover, from the results of visual check of thrombosis, this peak indicated the start of the micro-thrombus formation. This phenomenon was specific to the thrombosis, and was observed only in the presence of red blood cells. The experiments showed the possibility of the real time detection of thrombosis for implantable ventricular assistance devices, heart-lung machines and artificial kidney.

Analysis of the influence of volume and red blood cell concentration of a thrombus on the permittivity of blood

“…Based on our understanding that relative permittivity began to rise when the RBCs began to aggregate and form the thrombus, we refer to this as the thrombus detection time, as shown in Figure 4b. According to our visual observation results, as presented in [14], and based on the analysis shown in Figure 4b, we conclude that increases in relative permittivity accurately indicate RBC aggregation in the frequency range of 100 kHz to 600 kHz. This observation is consistent with our observations in Figure 3.…”

“…In both cases, the authors clearly noted RBC aggregation at the frequency studied. We analyzed the frequency spectrum in detail, as shown in Figure 4, using raw data of a previous study [14]. Based on our understanding that relative permittivity began to rise when the RBCs began to aggregate and form the thrombus, we refer to this as the thrombus detection time, as shown in Figure 4b.…”

“…We then measured capacitance C at various frequencies f (201 points between 1 kHz and 5 MHz). We obtained the mean values of C based on an average of 3 plots for each f. As per the procedure explained by Park et al [14], we calculated the relative permittivity ε' using these measured C values. All experiments were conducted at room temperature.…”