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Biomedical subjects

A R Leblanc

Publications and source records attributed to A R Leblanc.

4 recordsLinked to original sources
PubMed1982

Electrophysiology of the chemically sympathectomised dog.

The contribution of the sympathetic nervous system in the definition of various electrophysiological variables was studied in chemically sympathectomised dogs. Chemical sympathectomy was obtained following intravenous injection of 50 mg X kg-1 of 6-hydroxydopamine. Sympathectomised dogs presented significant increases in: basic sinus period, sino-atrial conduction time (SACT), AH and HV intervals of the His bundle electrogram, atrial functional (AFRP) and effective (AERP) refractory periods, atrio-ventricular node functional (AVNFRP) and effective (AVNERP) refractory periods, ventricular functional (VFRP) and effective (EVRP) refractory periods and atrial (AMAP) and ventricular (VMAP) monophasic action potential durations. Corrected sinus recovery time (CSRT) was not affected by chemical sympathectomy. Neither was the atrial ERP/MAP duration ratio. This new form of sympathectomy affects all the levels of the cardiac conduction system. Such results are in accordance with those obtained with surgical sympathectomy or the use of beta-blocking agents.

Animals↗
PubMed1979

Computer processing of intracardiac electrograms for conduction studies.

Computer techniques developed to process intracardiac signals recorded in dogs are presented. The signals under measurement are the auricular and ventricular monophasic action potentials and the His bundle electrogram. Computerized measurement of significant timing parameters on simultaneous recordings of these signals can assess quite precisely changes in the normal conduction scheme of the heart provoked by different experimental protocols. Increased accuracy is mainly due to the objective way of defining wave onsets and the processing power of the system used. Signal recording, signal acquisition, automatic waveform measurements, interactive process and production of end result graphs by computer are all described.

Action Potentials↗
PubMedDate not supplied

The effect of compression on clinical diagnosis of glaucoma based on non-analyzed confocal scanning laser ophthalmoscopy images.

BACKGROUND AND OBJECTIVE: To evaluate the effect of different image compression formats of non-analyzed Heidelberg Retina Tomography (HRT; Heidelberg Engineering, Heidelberg, Germany) images on the diagnosis of glaucoma by ophthalmologists. MATERIALS AND METHODS: Thirty-three topographic and reflectance images taken with the HRT representing different levels of disease were transformed using nine different compression formats. Three independent ophthalmologists, masked as to contour line and stereometric parameters, classified the original and compressed HRT images as normal, suspected glaucoma, or glaucoma, and Kappa agreement coefficients were calculated. RESULTS: The Tagged Image File Format had the largest file size and the Joint Photographic Experts Group (JPEG) 2000 format had the smallest size. The highest Kappa coefficient value was 1.00 for all ophthalmologists using the Tagged Image File Format. Kappa values for JPEG formats were all in the range of good to excellent agreement. Kappa values were lower for Portable Network Graphic and Graphics Interchange Format compression formats. CONCLUSION: Image compression with JPEG 2000 at a ratio of 20:1 provided sufficient quality for glaucoma analysis in conjunction with a relatively small image size format, and may prove to be attractive for HRT telemedicine applications. Further clinical studies validating the usefulness of interpreting non-analyzed HRT images are required.

Data Compression↗