Exposure to pulsed magnetic fields enhances motor recovery in cats after spinal cord injury.

Study Design: Animal model study of eight healthy commercial cats was conducted.

Objective: To determine whether pulsed electromagnetic field (PMF) stimulation results in improvement of function after contusive spinal cord injury in cats.

Summary Of Background Data: PMF stimulation has been shown to enhance nerve growth, regeneration, and functional recovery of peripheral nerves.

Directed and enhanced neurite growth with pulsed magnetic field stimulation.

Pulsed magnetic field (PMF) stimulation was applied to mammalian neurons in vitro to influence axonal growth and to determine whether induced current would direct and enhance neurite growth in the direction of the current. Two coils were constructed from individual sheets of copper folded into a square coil. Each coil was placed in a separate water-jacketed incubator.

Correlation of esophageal conductance measurements with aortic and left ventricular diameters and stroke volume.

Esophageal conductance measurements were correlated with hemodynamic events in 9 dogs chronically instrumented for measurement of left ventricular (LV) and aortic pressures, LV short axis and descending aortic diameters, and aortic blood flow. A four-electrode conductance catheter was positioned in the esophagus. Both an internal and an internal/external configuration were examined during anesthesia with hemodilution, pulmonary lavage and dobutamine infusion.

A box coil for the stimulation of biological tissue and cells in vitro and in vivo by pulsed magnetic fields.

An alternative coil system to the Helmoholtz coil-pair is described for the stimulation of biological tissue and cells: a relatively large box coil made of copper or aluminum sheet stock. The design is based on the principal determinant of the induced electric field, namely, the magnetic vector potential (A), in the equation, [formula: see text]. The second term in the equation is needed when boundaries of the conducting medium are in close proximity to the region of interest, such as in a culture dish.

Finite element model determination of correction factors used for measurement of aortic diameter via conductance.

Traditional methods for estimating the slope alpha and offset volume Vp for determining real-time chamber volume by the conductance catheter technique are not suited to measurements made in the aorta due to the relatively low resistivity of the aortic wall. We developed three distinct three-dimensional finite element models of the conductance catheter and surrounding tissues in order to predict alpha and Vp and to examine the nature of the electric field near the aortic wall. A heterogeneous isotropic model of the catheter, aorta and surrounding tissues accurately predicted the values of alpha and Vp.

In vivo measurement of real-time aortic segmental volume using the conductance catheter.

The goal of this investigation was to determine if the conductance catheter technique for chamber volume measurement could be applied in vivo to determine real-time phasic aortic segmental volume. A four-electrode conductance catheter was used to measure time-varying resistance of the descending thoracic aorta in open-chest, anesthetized dogs. Resistance was converted to segmental volume and the slope correction factor (alpha) and parallel conductance volume (Vp) were determined.

Effects of physical parameters on the cylindrical model for volume measurement by conductance.

Despite its undisputed utility for determining changes in ventricular pressure-volume relationships, the conductance catheter technique has not been proven reliable for measuring absolute volume. This limitation is due to violations of the assumptions inherent in the cylindrical model on which the method is based (i.e.

In vitro and finite-element model investigation of the conductance technique for measurement of aortic segmental volume.

This investigation examined the feasibility of applying the conductance catheter technique for measurement of absolute aortic segmental volume. Aortic segment volume was estimated simultaneously in vitro by using the conductance catheter technique and sonomicrometer crystals. Experiments were performed in five isolated canine aortas.

Effects of pulsed magnetic fields on neurite outgrowth from chick embryo dorsal root ganglia.

We have previously shown that neurite outgrowth from 6-day chick embryo dorsal root ganglia (DRG) in vitro was stimulated when nerve growth factor (NGF) and pulsed magnetic fields (PMF) are used in combination. 392 DRGs were studied in a field excited by a commercial PMF generator. We have now analyzed an additional 416 DRGs exposed to very similar PMF's produced by an arbitrary wavefrom generator and power amplifier.

Comparison of nuclear magnetic resonance spectroscopy with dual-photon absorptiometry and dual-energy X-ray absorptiometry in the measurement of thoracic vertebral bone mineral density: compressive force versus bone mineral.

31P nuclear magnetic resonance spectroscopy (NMRS) measurements were made on human T2 and T3 vertebral bodies. The bone mineral content (BMC) of isolated vertebral bodies minus the posterior elements and disks was measured using (1) NMRS on a 3.5 T, 85 mm bore GE Medical Systems NT-150 superconducting spectrometer, (2) a Lunar Corporation DPX-L dual-energy X-ray absorptiometry (DXA) scanner in an anterior-posterior (AP) orientation, (3) a Norland Corporation XR26 DXA scanner, also in an AP direction, and (4) a Norland Corporation model 2600 dual-photon absorptiometry (DPA) densitometer in both the AP and superior-inferior (SI) directions.

Energy absorption characteristics of football helmets under low and high rates of loading.

The purpose of this study was to examine the force-deformation characteristics of football helmets subjected to compressive loading on the crown surface. Tests were conducted at quasi-static and dynamic rates of loading. Energies were computed from the force-deformation data.

A probe for measuring current density during magnetic stimulation.

Time-varying magnetic fields induce currents in conductive media, and when the induced current is large enough in excitable tissue, stimulation occurs. This phenomenon has been applied to the human brain and peripheral nerves for diagnostic evaluation of the neural system. One important aspect that is presently unknown is the current level necessary in tissue for stimulation induced by magnetic fields.

Comparison of the compression strength of human vertebral bodies with the mass and density of apatite: a study by 31P NMR spectroscopy.

The force needed to fracture individual human thoracic and lumbar vertebral bodies is compared with the mass and density of apatite. 31P NMR spectrometry was used to quantify the apatite, because it permits the mineral content of bone to be determined noninvasively with minimal nonspecific interference from the organic matrix or from variations in composition of the marrow. Experiments were performed with bones of similar structure and function from a single individual with no history of trabecular fractures, to compensate for the effects of the other variables that affect bone strength.

In vivo 31P nuclear magnetic resonance spectroscopy of bone mineral for evaluation of osteoporosis.

The mineral content of stationary bone samples can be quantified by 31P nuclear magnetic resonance (NMR) spectroscopy. The assay can be performed in regions of the anatomy that pose problems for absorptiometric techniques, because the mineral content is measured within a selected volume without concern for the geometry of the bone. In vivo 31P NMR spectra of the bones in human fingers and wrist are reported.

Noninvasive evaluation of mineral content of bone without use of ionizing radiation.

The mineral content of bone can be quantified by recording a 31P NMR spectrum while the bone is stationary. The quantity of mineral in the bone is determined from the spectrum with a reference standard by comparison of relative peak areas. The phosphate of bone mineral is readily distinguished from inorganic phosphate and phosphorylated metabolites dissolved in cytosol and from the head groups of phospholipids in membranes.

Blood flow measurement by NMR.

The current status of blood flow measurement using nuclear magnetic resonance (NMR) techniques is reviewed. This includes both the continuous-wave method developed at the Medical College of Wisconsin and the Veterans Administration Medical Center and various pulsed methods, particularly those used in NMR Imagers. This is preceded by a brief review of the background of NMR blood flow measurement beginning in 1956 at the Laboratory of Technical Development of the National Heart, Lung, and Blood Institute.

NMR proton imaging.

A broad-based review of NMR imaging is presented from the viewpoint of one who has followed this new modality since its conception, but who has been working in the allied area of NMR blood flow measurement. Organizations working in NMR imaging throughout the world are identified, and clinical applications of several commercial systems are illustrated. The different pulse sequences currently used, as well as focused selective excitation are discussed in detail.

Nuclear magnetic resonance and transcutaneous electromagnetic blood flow measurement.

Static and alternating magnetic fields are employed in blood flowmeters using nuclear magnetic resonance (NMR) principles and electromagnetic induction by a moving conductor (TEM). Both techniques require high steady magnetic fields, obtained either from permanent magnets or from electromagnets. A relatively homogeneous magnetic field is needed for NMR, but, though important for calibration, homogeneity is not critical for TEM.

In vivo evaluation of nuclear magnetic resonance flowmetry: blood flow through the normal forearm.

A cylindrical crossed-coil nuclear magnetic resonance flowmeter has been developed to measure arterial blood flow through the human forearm. This paper describes the in vivo studies to evaluate the performance of the instrument. Flow rates were comparable to values reported in the literature.

The NMR blood flowmeter--applications.

Nuclear Magnetic Resonance (NMR) permits the noninvasive measurement of blood flow signals unimpaired by clothes, bandages, casts, etc. The cylindrical crossed-coil NMR blood flowmeter was used to measure blood flow through a cross-section of the human forearm. Two calibration procedures are described: one for pulsatile flows and the other for flows with a high non-pulsatile component.

The NMR blood flowmeter--design.

Two types of crossed-coil nuclear magnetic resonance (NMR) blood flowmeter detectors have been developed for the noninvasive measurement of blood flow. The first is a cylindrical coil configuration suitable for limb blood measurement. A cylindrical flowmeter (12.