In the general population, obesity (high BMI) is often considered as an important risk factor for many diseases and premature death. However, in patients with a certain disease, the risk of death in people with obesity was lower than that in people with normal weight. This abnormal correlation has caused widespread discussion, and different explanations have been given by physiology and epidemiology. Based on causal inference theory, this study used directed acyclic graphs to introduce the collision bias (also called collision-stratification bias). Through example demonstrations, this study explored whether and why the abnormal correlation between obesity and higher survival rates in patients with hyperglycemia exists. Finally, it was concluded that this abnormal correlation among patients with a certain disease (e.g., hyperglycemia in the current analysis) was partly or even totally caused by collider bias.

In the general population, obesity (high BMI) is often considered as an important risk factor for many diseases and premature death. However, in patients with a certain disease, the risk of death in people with obesity was lower than that in people with normal weight. This abnormal correlation has caused widespread discussion, and different explanations have been given by physiology and epidemiology. Based on causal inference theory, this study used directed acyclic graphs to introduce the collision bias (also called collision-stratification bias). Through example demonstrations, this study explored whether and why the abnormal correlation between obesity and higher survival rates in patients with hyperglycemia exists. Finally, it was concluded that this abnormal correlation among patients with a certain disease (e.g., hyperglycemia in the current analysis) was partly or even totally caused by collider bias.

OBJECTIVE:To investigate the effects of different drying methods on contents of active ingredients in leaves of Eu-commia ulmoides,and provide reference for establishing its drying methods after habitat harvesting. METHODS:Different drying methods [natural drying in the shade for 72 h,natural drying in the sunlight for 36 h,drying beside or over a fire(60℃6 h,80℃2 h,100℃1 h,120 ℃ 0.5 h),microwave vacuum freeze drying for 12 h,vacuum freeze drying for 12 h] were used for process-ing. HPLC was conducted to determine the contents of aucubin,geniposidic acid,chlorogenic acid and geniposide in samples and compare with the untreated fresh products. RESULTS:Contents of 4 ingredients in samples after the 2 freeze drying were close to these in fresh samples,which were higher than samples after other drying. CONCLUSIONS:Drying methods show significant ef-fects on the effective ingredients in leaves of E. ulmoides. Compared with natural drying in the shade and natural drying sunlight and drying beside or over a fire,microwave vacuum freeze drying and vacuum freeze drying can make better retention of the active ingredients in fresh leaves of E. ulmoides.

Objective: To investigate the situation of quality control of 3.0T magnetic resonance imaging (MRI) system. Methods: A series of indicators, including signal noise ratio(SNR), image uniformity, resolution of long-scale contrast, resolution of space, linearity and quality control of slice thickness, of 3.0T MRI system were measured by using Magphan SMR170 phantom (made by the phantom laboratory in American) on the Discovery MR 750 w system which made by GE company of American. And a series of formula, including SNR=(Sinside-Soutside)÷SDinside, U∑=(1-Smax-Smin/Smax+Smin ×100%, linearity=LR-LM/LR×100%、thickness=half of height and width ×0.25, were used to calculate SNR, image uniformity, linearity and quality control of slice thickness, and all of these results were used to evaluate the situation of quality control of 3.0T MRI system. Results:The results revealed that SNR of 3.0T MRI was 105, the imaging uniformity achieved to 99.13%, the resolution of long-scale contrast was 5mm/0.5mm, the resolution of space was 6 LP/cm, linearity achieved to 0.89% and the deviation of slice thickness was 0.6mm. All of these indicators has achieved the standards of detection. Conclusion: Through detecting the SNR, imaging uniformity, resolution, linearity and the deviation of slice thickness of 3.0T MRI system, the performance of the MRI can be accurately obtained, and these contribute to ensure the equipment operating in ideal situation.

Objective To investigate the expression of chemokine receptors CCR4,CCR6,CXCR3 on Th17 cell,and analyze the correlation between chemokine receptors and serum biochemical parameters of liver function test and hepatitis B virus (HBV) DNA load in peripheral blood of chronic hepatitis B (CHB) patients.Methods Thirty patients with CHB (CHB group) and 15 healthy persons (control group) were enrolled in the study.CCR4,CCR6,CXCR3 expression levels on Th17 cell were assayed by flow cytometry.The correlation between chemokine receptors and alanine aminotransferase (ALT),total bilirubin (TBil),and HBV DNA load were analyzed using Pearson' s correlation analysis,respectively.Results CCR4,CCR6,CXCR3 expression levels on CD4 + Th17 cell in CHB group were higher than that of control group.Moreover,the difference between them was statistically significant (P ＜ 0.05).CCR4,CCR6 expression levels on CD8 + Th17 cell in CHB group were higher than that of control group (P ＜ 0.05).Although CXCR3 expression level on CD8 + Th17 cell in CHB group was higher than that of control group,there was no significant difference between them (P ＞ 0.05).CCR4,CCR6 expression levels were positively correlated with serum ALT,HBV DNA load,respectively (P ＜ 0.05),but were not correlated with TBil (P ＞ 0.05).Conclusion Expression levels of chemokine receptor on Th17 cell were increased in patients with CHB and were positively associated with degree of liver inflammation.Therefore,CCR4,CCR6 expression on Th17 cell might be involved in liver injury resulted from Th17 cell.