RESUMO
Objective To study dynamic compression performance of adipose tissues, so as to further reveal the damage mechanism, and provide references for medical treatment.Methods Based on the improved split Hopkinson pressure bar (SHPB) experimental device, the adipose tissue dynamic compression experiment was conducted. The stress-strain curves of adipose tissues at different strain rates were obtained. Then the numerical model of SHPB was established, and the experimental process was simulated and analyzed. The numerical simulation for penetration process of 32 mm diameter rubber non-lethal projectile into the simulated target in human abdomen was carried out.Results Adipose tissues had a noticeable strain rate effect. The stress-strain curves at two high strain rates were approximately straight lines. The slope was similar, and the elastic modulus was 3.25 MPa, which was about 6 times of that under a quasi-static state. The simulation curves of fat SHPB were consistent with the experimental curves, which verified correctness of the constitutive model. In the process of non-lethal projectile penetrating human abdomen, an annular convex area similar to water wave appeared on skin surface, and the fat layer absorbed about 67% of the impact kinetic energy.Conclusions The experimental data of adipose tissues are very accurate. Numerical simulation can reproduce the penetration process well, and provide references for studying the damaging effect of non-lethal weapons on human body.
RESUMO
Objective To evaluate the effectiveness of lumbosacral plexus block combined with the use of dexmedetomidine in elderly patients undergoing proximal femoral nail antirotation (PFNA).Methods A total of 60 patients received elective PFNA were divided into tracheal intubation combined with inhalation anesthesia group (group G) and ultrasound and nerve stimulator-guided lumbosacral plexus block following with dexmedetomidine infusion group (group N).Then we observed HR,SBP,DBP for both groups at the time entering the theater (T0),immediately after tracheal intubation or after dexmedetomidine infusion (T1),skin incision moment (T2) and 30 minutes after skin incision (T3).Visual analogue scale (VAS) scores were assessed for both groups at the time point of 2,6,12,24 and 48 hours after surgery.The number of use of patient controlled intravenous analgesia (PCIA),assessment of consciousness status 1-3 days after surgery,adverse reactions were recorded for both groups as well.The following post-surgery data were recorded:the time of first feeding,first urination and first ambulation,the length of hospitalization,the expense of hospital stay.Results HR,SBP,DBP of the group G changed more significantly at T1,T2,T3 than those of T0 (P＜0.05).The VAS scores and the number of use of PCIA of group N were lower than those of group G at all time points after operation (P＜0.05).The group N had lower CAM-CR scores and less adverse reactions of nausea and vomiting and dizziness than those of group G on days 1 to 3 after surgery (P＜0.01).Compare to group G,the group N were early in terms of post-operation first feeding,first urination and first ambulation (P＜0.01).The length of hospitalization was shorter and the cost of the hospital stay was lower in the group N than the group G (P＜0.01).Conclusion Ultrasound and nerve stimulator-guided lumbosacral plexus block combined with low dose of dexmedetomidine could meet the needs of elderly patients undergoing PFNA.