Thermedical (United States)

Inability to eliminate intramural arrhythmogenic substrate may lead to recurrent ventricular tachycardia after catheter ablation. The aim of the present study was to evaluate intramural and full thickness lesion formation using a heated saline-enhanced radiofrequency (SERF) needle-tip catheter, compared with a conventional ablation catheter in normal and infarcted myocardium. Twenty-two adult mongrel dogs (30-40 kg, 15 normal and 7 myocardial infarct group) were studied. Lesions were created using the SERF catheter (40 W/50 °C) or a standard contact force (CF) catheter in both groups. Comparing SERF to CF ablation, the SERF catheter produced larger lesion volumes than the standard CF catheter-even with >20 g of CF-in both normal (983.1±905.8 versus 461.9±178.3 mm3; P=0.023) and infarcted left ventricular myocardium (1052.3±543.0 versus 340.3±160.5 mm3; P=0.001). SERF catheter lesions were more often transmural than standard CF lesions with >20 g of CF in both groups (59.1% versus 7.7%; P<0.001 and 60.0% versus 12.5%; P=0.017, respectively). Using the SERF catheter, mean depth of ablated lesions reached 90% of the left ventricular wall in both normal and infarcted myocardium. The SERF catheter created more transmural and larger ablative lesions in both normal and infarcted canine myocardium. SERF ablation is a promising new approach for endocardial intramural and full thickness ablation of ventricular tachycardia substrate that is not accessible with current techniques.

Abstract We have performed experiments that indicate TNT contamination is present on surfaces exposed to TNT vapor, and that TNT contamination is transferred rapidly between proximate surfaces. Contaminated surfaces continue to be nearly constant sources of TNT vapor for some time after removal of the primary source.

Electrical stimulation of the spinal cord has been practiced as a therapy by the medical community for nearly two decades. Despite optimistic expectations, interest and participation in spinal cord stimulation have been moderate. Considering the declining number, worldwide, of papers dealing with this therapeutic method in humans, it appears that, following a surge of interest in the late 1970s, the technique is losing adherents (or, at best, progressing slowly.) Over the same period there has been rapid growth of much new clinical technology, particularly cardiac pacing. The reasons for this slow progress lie in several areas, including technology and neuroanatomy. It remains for the neurological research scientist to identify more precise and effective approaches to central neural therapy, and for the engineer to find better methods of directing stimulating energies to specific target tissues. Until such breakthroughs are realized, implanting physicians can only continue to analyze patient data in an attempt to refine the techniques that are possible today.

Medical causes that led to the development of artificial hearts are reviewed. Ventricular assist systems are compared with other designs. A discussion of the functioning and surgical implantation of Thermedics Corporation's ventricular assist pump provides a context for an analysis of technical challenges still to be solved.

In the past five years, rapid progress has been achieved in thermionic conversion devices. The lifetime of experimental devices has been extended from a few hundred hours to over ten thousand hours. Overall efficiencies of over 14% have been measured on several devices at temperatures consistent with practical heat sources. Reproducibility of devices has been improved greatly as evidenced by the construction and testing of several large batches of similar converters. Hardware devices intended to fit the envelopes and restraints of specific systems have been designed and are now under development. Preliminary results achieved during these developmental efforts are quite promising. Although recent progress has been encouraging, much work remains to make thermionic conversion devices useful as real system components. Converter designs must be matched better to overall power system parameters and heat sources. The reproducibility of converters must be investigated in more detail to determine the present state of the art and to formulate requirements for improved processing techniques. More life-testing under well simulated environments must be done on hardware devices designed to fit system needs. This paper will review the progress achieved in experimental and hardware devices. The problems that were solved in achieving this progress will be discussed. A description will also be presented of the problems remaining to achieve practical thermionic hardware.

The present capabilities of thermionic converters are described, and their potential is evaluated in terms of the performance improvement based on the present understanding of the process. A discussion is included of several techniques expected to improve the power output and the efficiency of converters in the near future. A variable-parameter research converter is described. Typical types of data obtained from such a device are examined to evaluate its performance. The dependence of the volt-ampere characteristics on various converted parameters is analyzed. The discussion includes the maxima and minima that appear in the output charactecistics because of the interdependencies of converted parameters.