Low-diffusion agents

Fig. 1. Schematic compartmental pharmacokinetic representation of different classes of contrast agents a. nonspecific agent (NSA e.g. iobitridol) b. low-diffusion agent (LDA) c. rapid-clearance blood-pool agent (RCBPA e.g. P743) d. slow-clearance blood-pool agent (SCBPA, e.g. P840). From Id e et al. (2001) Invest Radiol 26 41,with permission ( Lippincott Williams Wilkins)...

The simplest and most thoroughly studied solutions are those based on phosphoric acid at low temperatures (<35°C) which alone can fulfil all three requirements of acid solvent, film former (as metal phosphate) and diffusion agent by virtue of its viscosity. Thus copper and its main alloys of brasses and bronzes can be very effectively electropolished in 60-70% orthophos-phoric acid with the temperature maintained below 35°C under other conditions copper passivates or dissolves freely under mass transfer controlled conditions, but by varying the conditions appropriately polishing can be continued under mild agitation. An annotated polarisation curve is given in Fig. 11.7 readers are referred to recent studies for more detailed 2ispects " . 

Our data show that the clearance of the three MIMs tested was lower than that of the nonspecific and highly diffusible agent ioversol (Table 4). The model was validated by the use of FITC-BSA, which had a very low clearance from the upper part of the Transwell filters. 

Nitrogen, air, carbon dioxide, a mixture of air and helium, are examples of gaseous foaming agents used in the production of polymer foams. Nitrogen and air are preferred since they are inert, nontoxic, non-flammable and have a low diffusivity with respect to the majority of polymers. An air/helium mixture permits an easy control of the foam density. 

To choose the suitable whitening agent, one mnst bear in mind that its chemical composition must allow whitening of the tooth but have low diffusion capacity in the dentine and that the pH it affords should be almost neutral. 

Uses Dispersant, suspending agent, diffusion agent for eiectropiale bath additive Features Low foaming... 

Antlblaze 19. Antiblaze 19 (Mobil), a flame retardant for polyester fibers (134), is a nontoxic mixture of cycHc phosphonate esters. Antiblaze 19 is 100% active, whereas Antiblaze 19T is a 93% active, low viscosity formulation for textile use. Both are miscible with water and are compatible with wetting agents, thickeners, buffers, and most disperse dye formulations. Antiblaze 19 or 19T can be diffused into 100% polyester fabrics by the Thermosol process for disperse dyeing and printing. This requires heating at 170—220°C for 30—60 s. 

R = / -C H ), in low doses, exhibits the former behavior and is used primarily as an extradural agent in obstetrics. The lowest effective extradural concentration of etidocaine (21, X = CH, R = R = 2H, R = / -C H ), however, shows both adequate sensory and profound motor blockade so that it is useful in surgical situations where maximum neuromuscular blockade is necessary. In an isolated nerve preparation, bupivacaine blocks unmyelinated C fibers which are mainly responsible for pain perception at a much greater extent than the myelinated A fibers which carry motor impulses. It is postulated that absorption of bupivacaine by the vasculature at the site of injection, combined with the slow diffusion of this agent, results in an insufficient amount of the drug penetrating the large A fibers to cause motor conduction blockade. Clinically, motor block can be observed in some procedures. 

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