RESUMO
A 45-year-old male with anteroseptal myocardial infarction was referred to our hospital. The patient was previously admitted to another hospital with coronavirus disease-2019 pneumonia for 2â¯weeks; he was discharged 2â¯weeks before presentation to our institution. He received conventional treatment for coronavirus disease-2019, including administration of heparin. A moderate decrease in platelet count was observed on admission, and emergent angiography was performed under a definitive diagnosis of acute coronary syndrome. The angiography revealed occlusion of the left anterior descending artery. Percutaneous coronary intervention was performed; however, the occlusion did not improve owing to persistent thrombosis in the distal left anterior descending artery. Therefore, we induced intra-aortic balloon pumping to improve coronary blood flow and obtained Thrombolysis in Myocardial Infarction grade 2 flow. Following percutaneous coronary intervention, we detected a further decrease in platelets and positivity for heparin-induced thrombocytopenia antibody, leading to the diagnosis of heparin-induced thrombocytopenia. Subsequently, oral anticoagulation was introduced, and the symptoms did not recur. Learning objective: Treatment with heparin is indicated for patients with coronavirus disease-2019 (COVID-19) because of derangement of the coagulation system. However, this approach contributes to the development of heparin-induced thrombocytopenia (HIT). We report a case of acute coronary syndrome due to HIT with COVID-19. HIT is commonly reported in patients with COVID-19. Thus, attentive monitoring of the platelet count and considering the possibility of HIT are indispensable when treating acute coronary syndrome in patients with previous history of COVID-19.
RESUMO
Several studies have been conducted on the fatigue behavior of copper and 7-3, and 6-4 brasses. However, there have been fewer studies on the fatigue behavior and fatigue crack growth (FCG) properties of free-cutting brass, primarily because emphasis has been placed on the development of lead-free free-cutting brass. In this study, fatigue experiments were performed in the atmosphere at room temperature using three types of free-cutting, two types of bismuth (Bi)-based (with different grain sizes), and lead (Pb)-based brasses. It was found that lead-free Bi-based free-cutting brass had approximately the same fatigue performance as that of Pb-based free-cutting brass. It was also clarified that the addition of Bi or Pb initiated fatigue cracks, and that the crack growth period occupied most of the fatigue life. Differences in the FCG behavior of the three free-cutting brasses were observed in the low ΔK range. The modified linear fracture mechanics parameter M was used to quantitatively analyze the fatigue life and FCG behavior (short surface cracks). A comparison between the calculated and experimental results showed that M was useful.
RESUMO
Fatigue crack growth (FCG) experiments were performed using a low-temperature extruded magnesium alloy AZ31 with texture. Under a constant maximum stress intensity factor (Kmax), the stress ratio R was changed from 0.1 to -1 during the fatigue crack growth process, and the FCG behavior before and after the R change was investigated. As a result, tensile twins were generated owing to the fatigue load on the compression side of R = -1, and the FCG velocity was accelerated. In addition, when the maximum compressive stress at R = -1 (|(σmin)R = -1|) exceeded the compressive yield strength of the material (σcy), the FCG velocity after R fluctuation greatly accelerated. On the other hand, under the condition |(σmin)R = -1| < σcy, the degree of acceleration of the FCG velocity due to R fluctuation was small. In either case, the degree of acceleration in the FCG increased as the Kmax value increased. The above FCG acceleration mechanism due to the R fluctuation was considered based on the observation of the deformation and twinning states of the fatigue crack tip, the fatigue crack closure behavior, and the cyclic stress-strain curve of the fatigue process. The FCG acceleration mechanism was as follows: First, the driving force of the FCG increased owing to the increase in crack opening displacement due to the generation of tensile twins. Second, the coalescence of the main crack and a plurality of microcracks were generated at the twin interface. The elasto-plastic FCG behavior after the stress ratio fluctuations is defined by the effective J-integral range ΔJeff.
