Background In order to acquire a high quality image with a low radiation dose, prospective electrocardiogram （ECG）-triggered computed tomography coronary angiography （CTCA） requires a stable heart rate （HR） 〈 6...Background In order to acquire a high quality image with a low radiation dose, prospective electrocardiogram （ECG）-triggered computed tomography coronary angiography （CTCA） requires a stable heart rate （HR） 〈 65 beats/min. Esmolol has the advantage of reduc-ing HR. The objective of this article is to assess the value of intravenous esmolol treatment before prospective ECG-tr/ggered high-pitch spiral acquisition for CTCA. Methods From March 2013 to June 2013, 313 patients underwent prospective ECG-triggered CTCA. Two hundred and thirty two of them received esmolol before angiography. We retrospectively analyzed clinical characteristics, esmolol dose, radiation exposure dose, and the change in HR and blood pressure in these 232 patients. Results A total of 232 patients with a HR 〉 65 beats/rain before CTCA examination received intravenous esmolol treatment （mean dose of 57.26±15.39 rag）, The mean initial HR （HR1）, slowest HR （HR2）, and the HR 30 min after HR2 （HR3） were 75.06± 5.59, 60.75 ±4.00, and 75.54 ± 5.96 beats/min, respectively （HR1 vs. HR2, P 〈 0.0001; HRI vs. HR3, P = 0.377）. The mean time from esmolol administration to HR2 was 24.25 ± 4.97 s and the mean effective radiation dose was 2.28 ± 0.02 mSv. Conclusions HR could be rapidly controlled at an optimum level with intravenous esmolol before prospective ECG-triggered high-pitch spiral acquisition for CTCA. Consequently, the patients received a very low radiation dose.展开更多
When interrupting short circuit fault by 40.5-kV vacuum circuit breakers, it is significant to eliminate multiple restrike phenomena, which occur frequently and result in high overvoltage and even interruption failure...When interrupting short circuit fault by 40.5-kV vacuum circuit breakers, it is significant to eliminate multiple restrike phenomena, which occur frequently and result in high overvoltage and even interruption failure. A synthetic circuit that can supply a DC recovery voltage after current zero was used to study multiple restrike phenomena in switching. Some key factors including breaking current, clearance between open contacts, electrode structure and contact material, which may affect restrike characteristics, were studied. Under various clearances, the statistical probability of restrike was obtained. As a result, the best scope of clearance between open contacts was found. The performance of CuCr50/50 and CuCr75/25 material were compared. Two kinds of electrode structures, namely 1/2 coil structure and cup-shaped axial magnetic structure, were tested. After a high-current interruption, conditioning effoct was realized and the probability of restrike decreased.展开更多
文摘Background In order to acquire a high quality image with a low radiation dose, prospective electrocardiogram （ECG）-triggered computed tomography coronary angiography （CTCA） requires a stable heart rate （HR） 〈 65 beats/min. Esmolol has the advantage of reduc-ing HR. The objective of this article is to assess the value of intravenous esmolol treatment before prospective ECG-tr/ggered high-pitch spiral acquisition for CTCA. Methods From March 2013 to June 2013, 313 patients underwent prospective ECG-triggered CTCA. Two hundred and thirty two of them received esmolol before angiography. We retrospectively analyzed clinical characteristics, esmolol dose, radiation exposure dose, and the change in HR and blood pressure in these 232 patients. Results A total of 232 patients with a HR 〉 65 beats/rain before CTCA examination received intravenous esmolol treatment （mean dose of 57.26±15.39 rag）, The mean initial HR （HR1）, slowest HR （HR2）, and the HR 30 min after HR2 （HR3） were 75.06± 5.59, 60.75 ±4.00, and 75.54 ± 5.96 beats/min, respectively （HR1 vs. HR2, P 〈 0.0001; HRI vs. HR3, P = 0.377）. The mean time from esmolol administration to HR2 was 24.25 ± 4.97 s and the mean effective radiation dose was 2.28 ± 0.02 mSv. Conclusions HR could be rapidly controlled at an optimum level with intravenous esmolol before prospective ECG-triggered high-pitch spiral acquisition for CTCA. Consequently, the patients received a very low radiation dose.
文摘When interrupting short circuit fault by 40.5-kV vacuum circuit breakers, it is significant to eliminate multiple restrike phenomena, which occur frequently and result in high overvoltage and even interruption failure. A synthetic circuit that can supply a DC recovery voltage after current zero was used to study multiple restrike phenomena in switching. Some key factors including breaking current, clearance between open contacts, electrode structure and contact material, which may affect restrike characteristics, were studied. Under various clearances, the statistical probability of restrike was obtained. As a result, the best scope of clearance between open contacts was found. The performance of CuCr50/50 and CuCr75/25 material were compared. Two kinds of electrode structures, namely 1/2 coil structure and cup-shaped axial magnetic structure, were tested. After a high-current interruption, conditioning effoct was realized and the probability of restrike decreased.
