Objective To investigate the effect of left ventricular assist device (LVAD) and aortic graft angle on hemodynamics of aortic valve. Methods Three models of aorta and aortic valve with 45°, 60° and 90° anastomosis angles between LVAD and aorta were constructed, and an in vitro pulsating table was built for in vitro experiments. Using particle image velocimetry (PIV) system, three moments in the cardiac cycle ( T1 systolic peak, T rapid closure, T3 diastolic peak), were selected to study the hemodynamic state of aortic valve. Results Velocity vector, vorticity and viscous shear stress were used to evaluate the effect of LVAD anastomosis angle on hemodynamics of aortic valve. During the period of rapid valve closure, with the increase of graft angle, the blood flow velocity near the valve wall, the average vorticity and the maximum viscous shear stress all increased. Conclusions When the graft angle is lower, the impact velocity of blood on the valve is smaller, and the shear force on the valve decreases, so that the valve is in a better hemodynamic environment. This study provides references for the selection of anastomotic angles in clinical operations.

Objective:To explore the distribution characteristics and antibiotic resistance of pathogen in children with hematological disorders and cancers complicated with sepsis in pediatric intensive care unit (PICU).Methods:The clinical data of children with hematological disorders and cancers complicated with sepsis hospitalized at Shenzhen Children′s Hospital affiliated to China Medical University from January 2016 to August 2023 were retrospectively analyzed. Patients were divided into survival group and death group based on the outcome of sepsis on 28 days after diagnosis.Results:A total of 202 sepsis episodes occurred in 176 children were enrolled in this study. Among all, 144 (71.3%) cases of bloodstream infection, 59 (29.2%) cases of pulmonary infection, 21 (10.4%) cases of abdominal infection, 9 (4.5%) cases of soft tissue infection, 9 (4.5%) cases of nervous system infection, and 3 (1.5%) cases of urinary tract infection. A total of 244 pathogenic strains were identified, in which 74 (30.3%) cases were gram-positive bacteria. The top 3 pathogens isolated were Coagulase negative Staphylococcus (21 strains), Staphylococcus aureus (19 strains) and Streptococcus pneumoniae (13 strains). Gram-negative bacteria accounted for 122 (50.0%) strains, in which top 3 were Klebsiella pneumonia (33 strains), Escherichia coli (25 strains), and Pseudomonas aeruginosa (23 strains). Fungi comprised 48 (19.7%) strains:the top 3 were Candida tropicalis (14 strains), Candida albicans (10 strains), Aspergillus and Pneumocystis jirovecii (7 strains each). The incidence of Acinetobacter baumannii, Stenotrophomonas maltophilia, and Pseudomonas aeruginosa were significantly higher in death group compared to survival group[9.0%（6/67）vs. 2.3%（4/177）, χ2＝3.971 ，P＝0.046; 9.0%（6/67）vs. 1.1%（2/177）, χ2＝7.080 ，P＝0.008;16.4%（11/67）vs. 6.8%（12/177）, χ2＝5.288 ，P＝0.021]. The samples of 57 cases were simultaneously detected by both culture and metagenomic next-generation sequencing (mNGS). Pathogens were detected in 25 cases by both culture and mNGS. In 30 cases, pathogen detection were mNGS positive but culture negative. Two cases showed positive results only with culture. A total of 79 (46.8%) strains were multi-drug resistant bacteria, including 27 (34.2%) strains of gram-positive bacteria and 52 (65.8%) strains of gram-negative bacteria. A total of 174 (86.1%) children with sepsis received empirical anti-infective drugs within 24 hours of fever onset. A total of 124 (61.4%) cases were appropriately covered by the initial empirical antibiotics, while 40 (19.8%) cases were not adequately covered and 10 (5.0%) cases had incomplete coverage. Despite the inclusion of pathogenic in the coverage, resistance to initial antibiotics was observed in 22 (10.9%) cases. Fifty-one patients died. Conclusion:The predominant pathogens responsible for sepsis in PICU with hematological disorders and cancers is gram-negative bacteria, followed by gram-positive bacteria and fungi. In comparison to healthy children with sepsis, there is a higher incidence of fungal infections among hematological disorders and cancers. The proportion of multi-drug resistant bacteria infection is high. Early identification and combination of local etiological distribution and drug resistance, along with the empirical selection of appropriate anti-infection treatment strategies, can greatly enhance survival rate.