Splanchnic arterial doppler parameters in portal hypertension

Abstract

We read with great interest the article by Taourel et al. 1 on the relationships among Doppler measurements of splanchnic vessels, hepatic venous pressure gradient (HVPG), variceal size, and Child-Pugh class in patients affected by alcoholic cirrhosis. The authors found a significant inverse correlation of portal velocity and portal vein flow with HVPG. On the other hand, no correlation was evident between Doppler resistance index (RI) in the hepatic or superior mesenteric arteries and HVPG.In our opinion, the two latter findings present some methodological limitations, which make the possible correlation between these arterial Doppler parameters and HPVG unlikely to be definitively excluded. The hepatic artery RI was measured at the porta hepatis and not inside the liver. The former sampling site, however, adds more information than the latter. In fact, we have previously demonstrated that differences in hepatic artery Doppler impedance indexes between normal and diseased livers become less evident the nearer to the aorta. 2 Consequently, a difference in hepatic artery RI between normal and diseased livers was only found when measured inside the liver, either when increased 2-4 or decreased, as also recently shown in this journal. 4 Furthermore, in the work by Taourel et al., the hepatic artery RI was not corrected according to the heart rate, as proposed by Mostbeck et al. for parenchymal arteries, 5 so that it is not possible to exclude that differences in heart rates among patients could have hindered a final positive resultThe superior mesenteric artery RI was used by Taourel et al. to correlate the degree of splanchnic vasodilatation, a landmark of cirrhotic hyperkinetic circulation, with portal pressure, but no statistically significant relationship was found. 1 Some recent data show that the pulsatility index is more sensitive than the RI in detecting early impedance changes in the superior mesenteric artery. 6 This seems to be caused by the disappearance of the postsystolic reversal of flow in cirrhosis, differently from the usual pattern of normal fasting subjects. 6 Thus, early circulatory alterations, affecting only this short reversal of flow, can only influence the superior mesenteric artery pulsatility index, but have no effect on the RI. In addition, the measurement of the pulsatility index, being insensitive to heart rate, avoids the related biases. This is particularly important in this district, because an adequate correction for heart rate is prevented by the peculiar flow trace.We believe, therefore, that the use of the pulsatility index, rather than the RI, could offer more precise information about the superior mesenteric arterial district and that this index should be used to search for correlation with HVGP.In conclusion, we believe that further methodological refinements might improve the interesting splanchnic hemodynamic findings of Taourel et al.