Biomedical subjects

K J Dormer

Publications and source records attributed to K J Dormer.

39 records · Page 3Linked to original sources

PubMedDate not supplied

Long-term intracoronary ethanol administration electrophysiologic and morphologic effects.

The long-term intracoronary infusion of ethanol was used to evaluate the potential of ethanol to produce myocardial injury and cardiac rhythm disturbances. In 22 dogs, electrophysiologic testing was performed 48 hr after cessation of alcohol administration. Multiple premature ventricular beats occurred spontaneously in 3 dogs with spontaneous sustained monomorphic ventricular tachycardia observed in 1 dog. Provocative ventricular pacing produced ventricular tachycardia lasting 20 or more beats in 13 animals with sustained tachycardia observed in 3 animals. Provocative ventricular pacing in the presence of lidocaine or epinephrine produced sustained ventricular tachycardia in an additional 4 dogs. The electrophysiologic properties of Purkinje fibers from the zone receiving ethanol were altered when compared to the control zone. The resting membrane potential was decreased (-76 +/- 2 mV vs. -85 +/- mV, p less than 0.001) with a decrease in action potential amplitude (91 +/- 4 vs. 109 +/- 2 mV, p less than 0.001) and phase 0 upstroke (231 +/- 27 vs. 456 +/- 25 V/sec, p less than 0.02). Prolonged refractoriness was observed in the ethanol zone without a prolongation of action potential duration. Intramural lesions observed within the left circumflex distribution varied from focal acute myofibrillar degeneration and necrosis to severe local scarring. The data suggest that intracoronary ethanol administration at human abuse levels of blood alcohol concentrations produces histologic and electrophysiologic injury in the canine heart. The electrophysiologic ch changes provide a substrate sufficient for the induction and maintenance of ventricular arrhythmia.

Action Potentials↗

PubMedDate not supplied

Middle ear implantable hearing device: ongoing animal and human evaluation.

The first five patients have been permanently implanted with an electromagnetic middle ear implantable hearing device. Hearing tests were performed at the time of operation and at 8 weeks postoperatively with a coil held at the isthmus of the ear canal. All patients reported clear, high fidelity sound, as proven by speech discrimination scores. Improvements were seen in all frequencies, including 4,000 Hz. Improvement in pure tones as tested with an audiometer monitoring sounds amplified by a 3-V sound processor was as high as 50 dB sound pressure level. That which remains to be done is the final design of a compact, wearable sound processor with filtering and signal-processing capabilities to meet the needs of the sensorineural hearing-impaired population.

Animals↗

PubMedDate not supplied

A two-dimensional Doppler ultrasonic probe for flow measurement.

The use of a single-transducer pulsed-Doppler ultrasound system in clinical practice has been severely limited, not only by the effects of acoustics and physiologic parameters, but also by inaccuracy because the Doppler angle between the transducer axis and the flow velocity is unknown. In this study, a dual-transducer pulsed-Doppler ultrasound system was used because the Doppler angle could be directly calculated for more accurate determination of the fluid flow velocity vector. From the velocity estimate and velocity profiles, other flow characteristics such as volume flow rates and shear stress can also be estimated. Experimental results indicated that the new transducer model could increase the accuracy of fluid flow velocity measurement and thereby improve the ability to estimate the characteristics of turbulent fluid flow for research and diagnostic purposes.

Blood Flow Velocity↗