RESUMO
A special bipolar pacing catheter for use in magnetocardiographic investigations has been developed. Several investigations have shown that it is fully compatible to both biomagnetic and MR imaging and thus serves as an ideal reference point for intracardial stimulation in magnetocardiography.
Assuntos
Cateterismo Cardíaco/instrumentação , Eletrocardiografia/instrumentação , Campos Eletromagnéticos , Imageamento por Ressonância Magnética/instrumentação , Marca-Passo Artificial , Processamento de Sinais Assistido por Computador/instrumentação , Arritmias Cardíacas/diagnóstico , Arritmias Cardíacas/fisiopatologia , Eletrodos , Sistema de Condução Cardíaco/fisiopatologia , HumanosRESUMO
Five different two-parameter models were fitted to published data from 30 studies to identify an approximate mathematical form of the relationship between fertility in cattle and the number of inseminated spermatozoa. In all cases, the first parameter defines the maximum attainable fertility, and the second scales the dose according to the percentage of the maximum attained. The best model was the hyperbolic dose-response curve used in pharmacology to analyse the effect of drugs. There is evidence that the semen of individual bulls differs in both parameters of the models and that therefore the viability of semen may be multidimensional. This might explain why measures of semen quality have hitherto been found to correlate poorly with fertility. The hypothesis that spermatozoa are subject to the law of mass action at the ovum predicts these and some other aspects of fertility, and indicates that heterospermic inseminations may provide an efficient way of estimating the parameters of semen.
Assuntos
Bovinos , Fertilidade/fisiologia , Inseminação Artificial/veterinária , Espermatozoides/fisiologia , Animais , Biologia Computacional , Feminino , Inseminação Artificial/métodos , Masculino , Modelos Biológicos , Contagem de EspermatozoidesRESUMO
The magnetic fields caused by electrical activity of the human heart can be coherently measured with a highly sensitive, multichannel, superconducting quantum interference-device system and can enable noninvasive localization of the underlying electrical activity. The magnetocardiograms (MCGs) of 10 patients with spontaneous premature ventricular complexes (PVCs), three patients with ventricular tachycardia (VT), and four healthy subjects with induced paced beats were recorded for 2-15 minutes. After correction for superimposed repolarization activity, the site of origin of the arrhythmias was localized from the magnetic field distribution at the onset of the ectopic beats. The localization results of paced beats showed an error of a few millimeters in relation to the position of the catheter tip. The results of spontaneous PVC and VT were confirmed with endocardial mapping or associated with ischemic lesions. The authors conclude that multichannel magnetocardiographic studies enable the completely noninvasive localization of ventricular arrhythmias.