Assessment of Electrical Impedance of the Liver and Spleen under Occlusion of Hepatic Blood Flow

Introduction. Liver resection remains the main trend in the treatment for primary and metastatic liver tumors and provides better overall and disease-free 5-year survival compared with conservative treatment options. Extensive liver resection is accompanied by the risk of post-resection liver failure. There is currently no absolute algorithm for determining the prognosis of post-resection liver failure. One of the ways to find new approaches to assessing the prognosis and diagnosing post-resection liver failure is bioimpedance analysis of the liver.
The aim of the study was to assess the effect of hepatic blood flow occlusion on changes in the electrical impedance of the liver and spleen.
Materials and methods. The study involved 20 male Wistar rats weighed 180-270 g. In the first series, experimental animals underwent occlusion of the hepatic blood flow for 15 minutes, and then underwent reperfusion (n=10). In the second series, occlusion of the hepatic blood flow was carried out for 90 minutes (n=10). Under general anesthesia, a median laparotomy was performed, followed by the application of a vascular clip to an analogue of the hepatoduodenal ligament, followed by clamping of the bile duct, hepatic artery and portal vein for 15 minutes in the first series and 90 minutes in the second series of the experiment. Invasive bioimpedansometry of the liver was performed using an original device for measuring the impedance of biological tissues BIM-II (RF patent No. 2366360). The data obtained were analysed at a frequency of 2 kHz, the hepatosplenic index (HSI) was calculated as the ratio of the average electrical impedance of the liver to the average electrical impedance of the spleen.
Results. The 1st series of experiments. After applying the clips to the hepatoduodenal ligament analogue, the value of the electrical impedance of the liver parenchyma at a frequency of 2 kHz did not change and amounted to 2.3 (2.11; 3.1) kΩ versus 2.34 (2.05; 2.81) kΩ registered before manipulation. The median spleen impedance decreased statistically significantly from 2.7 (2.07; 3.5) kΩ to 1.63 (1.47; 2.04) kΩ (p <0.05). After 15-minute occlusion of the hepatic blood flow, the electrical impedance of the liver parenchyma statistically significantly increased by 1.47 times and amounted to 3.98 (2.64; 4.59) kΩ. The median value of spleen impedance was 1.86 (1.52; 2.23) kΩ, and was statistically significantly lower (p<0.05) than before the clip application. After reperfusion, the liver impedance decreased to 3.11 (2.06; 5.11) kΩ, and the spleen impedance was 2.08 (1.53; 2.55) kΩ, while both parameters were statistically significantly different from the initial values. The dispersion coefficient D2kHz/20kHz of the liver statistically significantly increased to 2.10 (1.67; 2.58) 15 minutes after the clip application relative to the parameters before vascular exclusion – 1.71 (1.44; 2.08) and immediately after clamping analogue of the hepatoduodenal ligament – 1.60 (1.46; 2.11). After reperfusion, the dispersion coefficient D2kHz/20kHz of the liver parenchyma did not differ from the initial values and amounted to 1.79 (1.52; 2.29). The dispersion coefficient D2kHz/20kHz of the spleen decreased significantly immediately after occlusion of the hepatic blood flow from 1.54 (1.28; 1.71) to 1.36 (1.20; 1.62) and was at the corresponding level, including that after reperfusion. Fifteen minutes after the clip application, the dispersion coefficient D2kHz/20kHz of the spleen was statistically significantly lower than the values of D2kHz/20kHz of the liver (p<0.05) – 1.42 (1.19; 1.6) versus 2.1 (1.67; 2.58). Before vascular exclusion of the liver, the median HSI was 0.89 (0.72, 1.11). After the clip application, the HSI parameter statistically significantly increased to 1.43 (1.28; 1.95) due to a decreased electrical impedance in the spleen parenchyma. After 15-minute ischemia, HSI statistically significantly increased to 2.01 (1.26; 2.68), and after reperfusion it remained at a level higher than the initial level. 
The 2nd series of experiments. Before vascular exclusion, the electrical impedance of the liver parenchyma of experimental rats was 2.39 (1.8, 2.57) kΩ. After 15 minutes, the electrical impedance increased significantly to 3.2 (3.08; 3.32) kΩ, which was consistent with the results of the previous experiment. After 30, 45, 60 and 90 minutes, the impedance values of the liver parenchyma did not change and were increased if compared with the initial level. The coefficient of the electrical impedance dispersion of the liver increased statistically significantly after 15-minute ischemia and remained at a high level until the end of the experiment. After the clip application, the HSI parameter statistically significantly increased after 15 minutes and remained at a level higher than the initial level in 30 minutes, 45 minutes, 60 minutes, 90 minutes of ischemia.
Conclusions. After vascular exclusion of the liver, interrelated changes in the electrical impedance of the liver and spleen occurred within 15 minutes. These processes are mainly associated with changes in blood supply to the studied organs and ischemia effects.