To the editor, We read with great interest the recent article in Hepatology by Ahmed et al.1 Impressively, Ahmed and colleagues not only adjusted for cardiovascular disease (CVD) risk factors in baseline but also adjusted for changes in CVD risk factors over time. The associations between hepatic steatosis and incident CVD and all-cause mortality were attenuated when accounting for a change in CVD risk factors over time. However, we have different views on the appropriateness of the adjustment for changes in CVD risk factors over time. On the one hand, CVD risk factors, especially type 2 diabetes,2 are associated with the development of NAFLD, so the time-varying covariates of CVD risk factors may reflect changes in the severity of NAFLD. On the other hand, time-varying covariates of CVD risk factors may be associated with the corresponding treatments received by the patients, and these treatments may have additional effects on hepatic steatosis. For example, statins have been shown to reduce the risk of NAFLD occurrence and fibrosis in a large population study.3 Similarly, a meta-analysis has suggested that thiazolidinedione and glucagon-like peptide-1 receptor agonists were effective in attenuating hepatic fat content.4 As a result, adjusting for changes in CVD risk factors over time may underestimate the association between NAFLD and outcomes defined by the study. In addition, we noted that Ahmed et al1 adjusted for the risk factors of CVD together. However, it seemed that not all included risk factors were associated with NAFLD-related CVD events. A recent meta-analysis5 has shown significant effects of type 2 diabetes and plasma LDL-cholesterol concentrations, rather than body mass index, smoking, or hypertension, on the association between NAFLD and the risk of CVD events. Therefore, an overall discussion of all included CVD risk factors may result in an exaggeration of certain factors. In conclusion, it is important to adjust for CVD risk factors, but whether adjusting for changes in CVD risk factors over time is appropriate and which CVD risk factors should be taken into account may need further discussion.
On the basis of the one-dimensional theory design method and by imitating the design method of ordinary centrifugal pumps the hydraulic design of screw centrifugal pump impeller was performed.By means of an actual example,the design process was introduced in detail and the drawing of axial plane projection,axial section,and streamline clipping were given.Some problems occurred in the process of split point division of the axial streamline with traditional method were analyzed and the improvement method of hydraulic design of centrifugal pump impellers was presented.This method could be used to solve the problems such as the difficulty with the determination of the inlet side during streamline clipping and the difficulty with the presentation of trend of streamline propagation at the centrifugal part of the flange of the screw centrifugal pump impeller.
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