A new approach towards defibrillation electrodes: highly conductive isotropic carbon fibers.

A new carbon fiber material was studied for its potential benefit in defibrillation electrodes. Miniaturization of the fiber production can result in small strands with extremely large surface areas. Two carbon fiber patches and a single carbon fiber bundle were used for the purposes of this study, and the results were compared to those obtained with conventional titanium/mesh patch electrodes. Tests performed in a saline filled tank revealed considerably lower resistances through the carbon material when compared to standard mesh electrodes. There was also a higher peak current flow with lower voltage. The carbon fibers exhibited lower impedance for defibrillation and this may be related to low polarization known to occur with carbon materials. This new carbon material may prove to be useful and further research is required.

Relation between epicardial electrograms and signal-averaged electrocardiograms after acute myocardial infarction in dogs.

Signal-averaged electrocardiograms allow the non-invasive detection of late potentials which represent locally delayed conduction in the myocardium. To validate this method, it is necessary to compare the signal-averaged data with electrograms recorded directly from the heart. However, the studies performed to date involve only a consecutive collection of the invasively and non-invasively obtained data. To obtain a more direct comparison, we examined this relation at operation by simultaneous epicardial and signal-averaged measurements. Acute infarction in animals was chosen, because the ischemic area is a zone of delayed conduction whose presence can be verified in a signal-averaged electrocardiogram. For this purpose, the left anterior descending artery, proximal of large septal and diagonal branches, was tied off in nine mongrel dogs after thoracotomy. Before infarction, a signal-averaged electrocardiogram was recorded from the body surface. At the same time, epicardial electrograms were performed using bipolar electrodes both from the supply area of the left anterior descending artery and from that of the circumflex artery. Five minutes after coronary ligation, both the epicardial measurements and the signal-averaged electrocardiogram were repeated on the open thorax. Before occlusion of the left anterior descending artery, narrow activation complexes occurred in general in the epicardial electrograms and no late potentials were recorded in any dog by the signal-averaged electrocardiogram. Five minutes after coronary ligation, fractionated and prolonged electrograms occurred in the epicardial recordings from the ischemic zone, while the activation complexes in the uninfarcted supply area of the circumflex artery remained unchanged.(ABSTRACT TRUNCATED AT 250 WORDS)

Radionuclide assessment of a normal left ventricular response to exercise in patients without evidence of heart disease.

The aim of this study was to define normal left ventricular performance at rest and during supine bicycle exercise with equilibrium radionuclide ventriculography in a normal population other than young healthy volunteers. Thirty-one patients (mean age 45 years +/- 9 SD) with chest pain of varying origin and no evidence of heart disease proven by means of noninvasive and invasive techniques were studied. Left ventricular ejection fraction (LVEF) at rest averaged 0.64 +/- 0.07 SD and increased with peak exercise to 0.73 +/- 0.08 SD (P less than 0.005). Change in LVEF from rest to maximum exercise ranged within 0-0.19. Six patients (19%) failed to augment LVEF with exercise to more than 0.05; none of the patients dropped LVEF during exercise. Multivariate analysis revealed no significant predictors of LVEF response to exercise. However, there was a tendency that resting LVEF and enddiastolic volume index with exercise might influence LVEF response to exercise. Peak left ventricular ejection rate (LVER) at rest averaged 3.3 s-1 +/- 0.6 SD and increased to 5.1 s-1 +/- 1.1 SD (P less than 0.005) with exercise. Peak left ventricular early filling rate (LVFR) was 2.8 s-1 +/- 0.6 SD at rest and was measured 5.5 s-1 +/- 1.3 SD at maximum exercise (P less than 0.005). Left ventricular enddiastolic volume (EDV) did not change significantly from rest to maximum exercise, whereas left ventricular endsystolic volume (ESV) decreased to 79% +/- 19 SD (P less than 0.01) of the value at rest.(ABSTRACT TRUNCATED AT 250 WORDS)

Using social indicators to locate mental health facilities.

The following article reports the results of a process designed to improve the accessibility of psychiatric inpatient services by identifying sites which are closest to the greater number of people in need. Facility locations and catchment areas for a test region are noted along with facility sites arrived at by a more conventional approach. The estimated travel time was 11 percent lower in the test methodology. This finding indicates that major improvements in the reduction of travel time are possible when quantitative techniques are applied by mental health planners.