Intrahepatic blood flow assessment by Doppler ultrasonography: relationship among hepatic vein, portal vein, hepatic artery and portal pressure intraoperatively measured in patients with portal hypertension

Background: Abnormality of hepatic vein (HV) waveform evaluated by Doppler ultrasonography has been widely studied in patients with chronic liver disease. The paper investigates the relationship between HV waveform changes, portal vein velocity (PVVel), hepatic artery pulsatility index (HAPI) and portal pressure (PP) measured directly from patients with portal hypertension (PHT), aiming to discuss the cause of abnormal HV waveform. Methods: Sixty patients who had been clinically diagnosed with PHT and accepted surgical therapy, were investigated. PP was measured intraoperatively. HV waveform was categorized as triphasic, biphasic and monophasic. Two Doppler features PVVel and HAPI were measured and compared with both HV waveform changes and PP. Results: In patients group, the Doppler flow waveform in middle HV was triphasic in 31.6%, biphasic in 46.7%, monophasic in 21.6%. These figures were 88%, 8%, 2% respectively in healthy subjects. With the flattening of HV waveform, PP and HAPI increased significantly (r = 0.579, r = 00.438, respectively, p < 0.0001), while PVVel decreased significantly (r = -0.44, p < 0.0001). PP in patients with monophasic HV waveform was significantly higher than those with biphasic and triphasic waveform (p = 0.004, p = 0.003 respectively). The significant difference was similar for PVVel (p = 0.007, p < 0.0001). HAPI in patients with abnormal HV waveforms (monophasic or biphasic) was much higher than those with normal HV waveform (p = 0.001, p = 0.022, respectively). Conclusion: In patients of PHT, monophasic HV waveform indicates higher portal pressure, even measured directly from the portal venous system. The change trends that flattening of HV waveform accompanied by the increase of HAPI and decrease of PVVel support the inference that parenchymal fibrosis and fat infiltration reduce HV compliance being the cause of the abnormality of Doppler HV waveform from one perspective. Background Hepatic vein (HV) is the only draining vessels in liver, which has two supplying vessels, from liver sinus to the inferior vena cava (IVC). The thin-walled veins are anechoic under ultrasonographic scanning, have no valves, and can be distinguished from the portal veins. The spectrum of HVs can reflect changes of blood flow through tricuspid valve during the cardiac cycle leading to pulsatile changes of spectrum. The normal waveform of HVs is triphasic pattern with two hepatofugal phases related to atrial and ventricular diastole, and a short phase of retrograde (hepatopetal) flow caused by the pressure increase in the right atrium at atrial systole. With the increased stiffness of the liver parenchyma, especially around the HVs, hepatic waveform became decreased pulsatile with no retrograde flow, or even to a flat wave form eventually [1-3]. However, the exact cause of abnormality in HVs is still a controversial issue. A study suggested that terlipressin-induced improvement in the waveforms can be counted as a evidence that a hemodynamic effect of high portal pressure rather than a fixed structural abnormality was the pathogenic mechanism responsible [4]. Thus, the purpose of this study was to discuss the cause of HV waveform changes by evaluating the relationship among changes of intrahepatic blood flow and portal pressure (PP) measured intraopretively in patients with portal hypertension (PHT). Methods Patients Sixty patients with PHT without hepatocellular carcinomas and portal thrombosis referred to the Division of the Fourth Military Medical University Tangdu Hospital for surgical portosystemic shunts therapy from Aug 2008 to Jan 2010. The control group consisted of 30 healthy volunteers (22 men and 8 women) with no history of chronic liver disease and normal liver function tests. The severity of cirrhosis was graded according to Child-Pugh classification [5]. All subjects were included in the study provide informed consent to participate. The study was approved by the ethics committee of our institution. Doppler ultrasound Doppler ultrasonographic examinations were conducted with Acuson Sequire 512 (Siemens Acuson Co., Mountain View, California) and a 3.5 MHz phased array transducer. All patients and control subjects fasted overnight. Considering that the respiration manoeuvres can alter the HV flow patterns [6, 7], measurements of the parameter were made during suspended respiration. We selected the middle HV as the measuring object as results of the most consistent triphasic flow in healthy people and the most favorable Doppler angle. The Doppler gate was placed in the vessel at a point 2–3 cm away from the IVC to measure HV waveform. HV waveforms were classified as triphasic (reversed flow in at least one phase), biphasic (no reversed flow and with or without decreased phasic oscillation), or monophasic (flat and with or without fluttering). Velocity measurements were conducted at an angle between 30 and 60 degrees. The mean velocity of portal vein (PVVel) and hepatic artery pulsatility indexes (HAPI) were calculated automatically by the machine after the waveform trace for three cardiac cycles. In order to minimize variation and errors, all parameters were measured by the same observer on the same machine and were calculated as the mean of three consistent measurements. Measurement of PP During the operation, the right gastroepiploic vein was isolated and catheterized by a pressure gauge to measure the PP by an experienced surgeon, who had no knowledge of the Doppler results. A liver biopsy was sampled during the surgical operation. Morphologic changes of the liver were determined during the operation. Statistical analysis Results were given as mean±standard deviation. The results in patients with PHT and healthy controls were compared using an analysis of variance (ANOVA). Linear regression analysis was used to assess the correlations among all parameters. Results were considered significant at p < 0.05.