PubMed Health⌕ Search
Home/Archive/PubMed

PubMed · 1773761

Optimizing magnetic stimulator design.

J Cadwell
View original source ↗Export metadata ↓

Abstract

Optimal magnetic stimulation depends on application and design. The best design generates the desired depolarization current in the desired area with acceptable current speed. Power and cooling requirements, electrical and mechanical safety, stimulus rate, reliability, and ease of use are additional considerations. By understanding the interactions among these requirements, suitable choices are made. Magnetic stimulation requires moving enough charge through an electrically sensitive tissue to depolarize it reliably. Usually there is a need to depolarize a delimited volume of tissue and to repeat the depolarization at convenient intervals. A good design achieves the focality and speed needed for the application. Since the applications for magnetic stimulation are varied, however, the designs for the stimulators also will be different, and defining the application (or applications) is, therefore, a requirement for optimization.

Explore related subjects

Electric ConductivityElectromagnetic FieldsElectromagnetic PhenomenaEquipment DesignMagneticsJournal Article

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

J Cadwell. 1991. Optimizing magnetic stimulator design.. https://pubmed.ncbi.nlm.nih.gov/1773761/

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related citations

PubMed1992

Black lipid membranes of tetraether lipids from Thermoplasma acidophilum.

Black lipid membranes were formed of tetraether lipids from Thermoplasma acidophilum and compared to the bilayer forming lipids diphytanoylphosphatidylcholine and diphythanylglucosylglycerol. Bilayer-forming lipids varied in thickness of black lipid membranes due to the organic solvent used. Measurements of the specific membrane capacitance (Cm = 0.744 microF/cm2) showed that the membrane-spanning tetraether lipids from Thermoplasma acidophilum form a monolayer of a constant thickness of 2.5-3.0 nm no matter from which solvent. This finding corresponds to the results of Gliozzi et al. for the lipids of another archaebacterium, Sulfolobus solfataricus. Black lipid membranes were formed at room temperature with a torus from bilayer-forming lipids, however, the torus could also be formed by the tetraether-lipid itself at room temperature and at defined concentration. In these stable black lipid membranes, conductance was measured in the presence of valinomycin, nonactin, and gramicidin. At 10(-7) M concentration, valinomycin mediated higher conductance in membranes from tetraether lipids (200-1200 microS/cm2) than from bilayer-forming lipids (125-480 microS/cm2). Nonactin, at 10(-6) M concentration, mediated a 6-fold higher conductance in a tetraether lipid membrane than in a bilayer, whereas conductance, in the presence of 5 x 10(-11) M gramicidin could reach higher values in bilayers than in tetraether lipid monolayers of comparable thickness. Monensin did not increase the conductance of black lipid membranes from tetraether lipids under all conditions applied in our experiments. Poly(L-lysine) destroyed black lipid membranes. Lipopolysaccharides from Thermoplasma acidophilum were not able to form stable black lipid membranes by themselves. The lipopolysaccharide complexes from Thermoplasma acidophilum and from Escherichia coli decreased the valinomycin-mediated conductance of monolayer and bilayer membranes. This influence was stronger than that of the polysaccharide dextran.

Electric Conductivity↗
PubMed1992

Repulsive interactions and mechanical stability of polymer-grafted lipid membranes.

Liposome membranes containing lipids with covalently attached poly(ethylene glycol) (PEG-lipid) are currently being developed as drug delivery systems. These, so called, 'Stealth' liposomes have a relatively long half life (approximately 1 day) in blood circulation and show an altered biodistribution in vivo. The extended lifetime appears to result from a steric stabilization of the liposome by the grafted polymer. In order to characterize the surface structures that promote steric stability in such polymer-grafted lipid bilayer systems, we have used X-ray diffraction to measure the structural organization and interbilayer repulsion for lipid/cholesterol (2:1) bilayers incorporating 4 mol% of a PEG-lipid in which the molecular weight of the PEG moiety was 1900 g/mol. At this concentration, applied pressure versus interbilayer distance relations showed that the grafted polymer moiety extended approximately 50 A from the lipid surface and gave rise to a strong, slowly decaying repulsive pressure between membranes that opposed their close approach. Also, the pressure vs. distance relations were only modestly altered by changing the ionic strength of the medium (1 mM NaCl and 100 mM NaCl). Therefore, even though the PEG-lipid headgroup bears a negative charge, the long range pressure cannot be due primarily to an electrostatic double layer pressure. Measurements of lipid bilayer elasticity using micropipet manipulation showed that PEG-lipid did not change the cohesive properties of lipid/cholesterol liposomes which was consistent with the X-ray structural data showing that the PEG-lipid did not change the normal structure of the bilayer interior. From these data we conclude that the repulsive barrier properties of lipid-grafted PEG polymer chains originate mainly from a steric pressure and that this simple polymer steric stabilization is the basis for the extended in vivo circulation times observed for polymer-grafted liposomes.

Electric Conductivity↗