A practical optodynamic study was performed to determine the usability of different lengths of laser pulses for the generation of ultrasonic transients in a solid material. The aim of the study was ...to evaluate the possibility of a dual use for a laser pulse—for laser material processing, on the one hand, and for the ultrasonic wave generation on the other—with both processes being combined on the same production line. The propagation of the laser-generated ultrasonic waves is evaluated by detecting and measuring with a PID-controlled stabilized interferometer. Thus, both systems provided the basic tools, the generation and detection of ultrasonic waves, for an ultrasonic, laser-based, non-destructive material evaluation. The ultrasonic transients generated by ‘classical’ nanosecond laser pulses were compared with the transients generated by industrial laser pulses with a duration of a few tenths of a microsecond. The experimental results are compared with the results of a time-of-flight analysis that also involved part of a mode-conversion analysis for both regimes in a layered material structure. The differences between the two waveforms were assessed in terms of their visibility, wavelength and resolution. The limit values were calculated and estimated for the laser-pulse parameters, when such pulses are intended for use in an ultrasonic, laser-based, non-destructive evaluation. The possibility of using an industrial marking laser for laser ultrasound generation is thus demonstrated.
A study of a pulsed laser ablation process is presented from a novel, optodynamic aspect. By quantitative analysis of laser-induced bulk ultrasonic and blast waves in the air the ablation dynamics is ...characterized. In this way the influence of the laser pulse parameters and of the interacting material on the ablation process was assessed. By the analysis of the laser drilling process of thin layered samples the material influence was demonstrated. Besides the ultrasonic evaluation of the laser pulse power density the plasma shielding for 10 ns laser pulses was analyzed by the same method. All measurements were noncontact. Bulk waves in the solid and blast waves in the air were measured simultaneously, an interferometric and a probe beam deflection method were used, respectively.
Ultrasonic pulses were generated by low-intensity laser pulses and detected by optical techniques and by conventional transducers. The one-dimensional model describing the resulting displacement at ...the sample back surface was experimentally confirmed. Ultrasonic displacements were detected by a stabilized Michelson interferometer and by a piezoelectric transducer, simultaneously. The calibration was extrapolated to an extremely low intensity range where displacements of the order of magnitude of 10
−14 m were generated and detected by piezoelectric transducers.
Atrial fibrillation is the most common cardiac arrhythmia, and no current therapy is ideal for control of this condition. Experimental studies suggest that angiotensin II-receptor blockers (ARBs) can ...influence atrial remodeling, and some clinical studies suggest that they may prevent atrial fibrillation.
We conducted a large, randomized, prospective, placebo-controlled, multicenter trial to test whether the ARB valsartan could reduce the recurrence of atrial fibrillation. We enrolled patients who were in sinus rhythm but had had either two or more documented episodes of atrial fibrillation in the previous 6 months or successful cardioversion for atrial fibrillation in the previous 2 weeks. To be eligible, patients also had to have underlying cardiovascular disease, diabetes, or left atrial enlargement. Patients were randomly assigned to receive valsartan or placebo. The two primary end points were the time to a first recurrence of atrial fibrillation and the proportion of patients who had more than one recurrence of atrial fibrillation over the course of 1 year.
A total of 1442 patients were enrolled in the study. Atrial fibrillation recurred in 371 of the 722 patients (51.4%) in the valsartan group, as compared with 375 of 720 (52.1%) in the placebo group (adjusted hazard ratio, 0.97; 96% confidence interval CI, 0.83 to 1.14; P=0.73). More than one episode of atrial fibrillation occurred in 194 of 722 patients (26.9%) in the valsartan group and in 201 of 720 (27.9%) in the placebo group (adjusted odds ratio, 0.89; 99% CI, 0.64 to 1.23; P=0.34). The results were similar in all predefined subgroups of patients, including those who were not receiving angiotensin-converting-enzyme inhibitors.
Treatment with valsartan was not associated with a reduction in the incidence of recurrent atrial fibrillation. (ClinicalTrials.gov number, NCT00376272.)
Dynamic left ventricular outflow tract (LVOT) obstruction was thought to be a hallmark of hypertrophic obstructive cardiomyopathy, especially in those cases with isolated asymmetric septal ...hypertrophy and systolic anterior motion (SAM) of the mitral valve. Recently, several authors described the occurrence of a dynamic LVOT obstruction during acute coronary insufficiency in ventricles without significant myocardial hypertrophy. The LVOT gradient was reported to disappear following resolution of the ischemic syndrome. Furthermore, it was reported that LVOT obstruction in the setting of acute myocardial infarction could predispose to cardiac rupture. We describe four cases with acute anterior myocardial infarction complicated with a dynamic LVOT obstruction documented by transthoracic Doppler echocardiogram. The detection of the dynamic LVOT obstruction allowed us to optimize the pharmacological treatment in each case. In spite of therapy, two of our patients worsened progressively to fatal cardiogenic shock and cardiac rupture. In conclusion, the development of a LVOT obstruction during acute anterior myocardial infarction has to be considered a serious and potentially fatal complication.
PDF
