High speed synchrotron X-ray imaging studies of the ultrasound shockwave and enhanced flow during metal solidification processes

The highly dynamic behaviour of ultrasonic bubble implosion in liquid metal, the multiphase liquid metal flow containing bubbles and particles, and the interaction between ultrasonic waves and semisolid phases during solidification of metal were studied in situ using the complementary ultrafast and high speed synchrotron X-ray imaging facilities housed respectively at the Advanced Photon Source, Argonne National Laboratory, US, and Diamond Light Source, UK. Real-time ultrafast X-ray imaging of 135,780 frames per second (fps) revealed that ultrasonic bubble implosion in a liquid Bi-8 wt. %Zn alloy can occur in a single wave period (30 kHz), and the effective region affected by the shockwave at implosion was 3.5 times the original bubble diameter. Furthermore, ultrasound bubbles in liquid metal move faster than the primary particles, and the velocity of bubbles is 70 ~ 100% higher than that of the primary particles present in the same locations close to the sonotrode. Ultrasound waves can very effectively create a strong swirling flow in a semisolid melt in less than one second. The energetic flow can detach solid particles from the liquid-solid interface and redistribute them back into the bulk liquid very effectively

Relationship of Heart Rate Variability to Parasympathetic Effect

Background —Baroreflex-mediated parasympathetic stimulation has variable effects on heart rate variability (HRV). We postulated that a quadratic function would describe the relationship between HRV and parasympathetic effect better than a linear function. Methods and Results —Twenty-nine normal volunteers (15 women; mean age 39±12 years) were studied after β-adrenergic blockade with intravenous propranolol. Five-minute ECG recordings were made during graded infusions of phenylephrine and nitroprusside to achieve baroreflex-mediated increases and decreases in parasympathetic effect, respectively. Time- and frequency-domain measures of HRV were calculated from the R-R interval tachograms. The R-R interval and the vagal-sympathetic effect (VSE=R-R interval/intrinsic R-R interval) were used as indices of parasympathetic effect. The data were fit to both quadratic and linear models. In each case, the quadratic model (with a negative coefficient for the squared term) was superior to the linear model. There was some evidence that age influenced the responsiveness of the HRV parameters with changing parasympathetic effect, although the regression analysis was significant only in the models for MSSD ( P <0.03) and pNN50 ( P <0.001). Conclusions —The relationship between HRV and parasympathetic effect is best described by a function in which there is an ascending limb where HRV increases as parasympathetic effect increases until it reaches a plateau level; HRV then decreases as parasympathetic effect increases. Because there is marked interindividual variation in this relationship, differences in HRV between individuals may reflect differences in this relationship and/or differences in autonomic effects

Abstract 20082: Feasibility of His Bundle Pacing in Patients Meeting Criteria for Cardiac Resynchronization Therapy and Implantable Cardioverter-defibrillator

Objective: The role of His bundle pacing to physiologically narrow QRS duration in patients meeting criteria for CRT/CRT-D is not well understood. Methods: Patients with CRT/CRT-D indication with failed CS lead placement, suboptimal coronary venous targets, or those who opted for His bundle pacing underwent implantation of a His bundle lead, along with an RV defibrillator lead if indicated. In all patients, the His bundle pacing lead was placed into the LV lead port with CRT pulse generator. The LV-RV offset was programmed at maximum, with RV lead subthreshold to minimize fusion. An atrial lead was implanted if the patient was not in permanent atrial fibrillation. Results: Thirteen patients (65±18 years, 7 males, mean LVEF 27.3±8.9%, QRS duration 180±30ms, and 11 with LBBB) underwent His bundle pacing. The mean PR interval in this cohort was 220±111ms, 3 patients had complete heart block, 3 had permanent atrial fibrillation, and 9 required ICD placement. The His pacing lead (Medtronic 3830 Select Secure) was successfully placed in 12 of 13 patients, with narrowing of the QRS duration to 120±23ms (p&lt;0.0001). No complications or lead dislodgements were seen. At 6-month follow up, LVEF increased by an average of 18.7%, and left ventricular internal dimension in diastole(LVIDd) decreased by 0.9cm. Echocardiographic global longitudinal strain improved from -9.1 to -10.5%. Conclusions: In patients meeting criteria for CRT/CRT-D implantation, QRS narrowing achieved by His bundle pacing is feasible, and is associated with favorable mechanical and clinical outcomes. </jats:p