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Biomedical subjects

B J Roth

Publications and source records attributed to B J Roth.

151 records · Page 9Linked to original sources
PubMedDate not supplied

Magnetic stimulation of axons in a nerve bundle: effects of current redistribution in the bundle.

Recently, we developed a model of magnetic stimulation of a concentric axon in an anisotropic nerve bundle. In that earlier paper, we considered a single axon surrounded by a nerve bundle represented as a homogeneous anisotropic monodomain medium. In this paper we extend our previous calculations to examine excitation of axons within a nerve bundle without neglecting the presence of other axons in the nerve bundle. A three-dimensional axial symmetry volume conductor model is used to determine the transmembrane potential response along an axon due to induced electric fields produced by a toroidal coil. Our principal objective is to examine the effect of current redistribution to other axons in the bundle on excitation characteristics. We derive the transmembrane potential along an axon for two currently available models of current redistribution: the biodomain model and the spatial--frequency monodomain model. Results indicate that a reduction in the transmembrane potential along an axon due to the presence of other nerve fibers in the bundle is observed. Axons located at the periphery of a nerve bundle have lower thresholds and different excitation sites compared with axons located near the center of a nerve bundle.

Axons↗
PubMedDate not supplied

Effect of a perfusing bath on the rate of rise of an action potential propagating through a slab of cardiac tissue.

Experiments show that the rate of rise of the action potential depends on the direction of propagation in cardiac tissue. Two interpretations of these experiments have been presented: (i) the data are evidence of discrete propagation in cardiac tissue, and (ii) the data are an effect of the perfusing bath. In this paper we present a mathematical model that supports the second interpretation. We use the bidomain model to simulate action potential propagation through a slab of cardiac tissue perfused by a bath. We assume an intracellular potential distribution and solve the bidomain equations analytically for the transmembrane and extracellular potentials. The key assumption in our model is that the intracellular potential is independent of depth within the tissue. This assumption ensures that all three boundary conditions at the surface of a bidomain are satisfied simultaneously. One advantage of this model over previous numerical calculations is that we obtain an analytical solution for the transmembrane potential. The model predicts that the bath reduces the rate of rise of the transmembrane action potential at the tissue surface, and that this reduction depends on the direction of propagation. The model is consistent with the hypothesis that the perfusing bath causes the observed dependence of the action-potential rate of rise on the direction of propagation, and that this dependence has nothing to do with discrete properties of cardiac tissue.

Action Potentials↗
PubMedDate not supplied

Coronary artery calcification at CT as a predictor for cardiac complications of thoracic surgery.

PURPOSE: Our goal was to determine the predictive value of coronary artery calcification (CAC) on preoperative CT of the thorax for cardiac complications of noncardiac thoracic surgery. METHOD: Of 117 patients undergoing noncardiac thoracic surgical procedures between January 1, 1993, and June 1, 1995, at our institution, 75 had inpatient records and chest CTs available for retrospective review. Inpatient records were reviewed for postoperative cardiac complications (arrhythmia, hypotension with ECG changes, myocardial infarction, congestive heart failure, stroke, and death). The CT scans were scored for the presence and extent of CAC by an independent observer. RESULTS: Six of the 75 patients had cardiac complications including 1 death. Thirty-nine of the 75 patients had a CAC score of > or = 7. The sensitivity, specificity, positive predictive value, and negative predictive value of a CAC score of > or = 7 for cardiac complications were 100, 71, 23, and 100%, respectively. CONCLUSION: The presence of CAC on preoperative CT scanning is associated with cardiac complications of noncardiac thoracic surgery; however, the positive predictive value is low. The absence of CAC was a reliable predictor of a favorable postoperative cardiac course.

Adult↗
PubMedDate not supplied

Physicians' estimates of the probability of myocardial infarction in emergency room patients with chest pain.

To evaluate the ability of emergency room physicians to estimate the probability of myocardial infarction in patients with acute chest pain, the authors gathered historical, physical, and electrocardiographic information from 492 patients at the time of their presentation. The physicians admitted 30% of them to intensive care: 53 of the 61 patients with infarctions (sensitivity = 87%) and 96 of the 431 without infarctions (specificity = 78%). Overall, 36% of those admitted had infarctions. The physicians' numeric estimate of the probability of infarction was a good univariate discriminator of infarction, as demonstrated by Receiver Operator Characteristics analysis, and, as indicated by their actual operating point, they seemed to maximize the accuracy of patient classification rather than sensitivity or specificity. Logistic regression analysis identified the physicians' probability estimate as the strongest multivariate predictor of infarction, considering all other clinical information available.

Adult↗