Dilatant system

Pharmacology Iloprost is a synthetic analog of prostacyclin PGl2- Iloprost dilates systemic and pulmonary arterial vascular beds. 

Mecfianism of Action A prostaglandin that dilates systemic and pulmonary arterial vascular beds, alters pulmonary vascular resistance, and suppresses vascular smooth muscle proliferation. Therapeutic Effect Improves symptoms and exercise tolerance in patients with pulmonary hypertension delays deterioration of condition. Pharmacokinetics Protein binding 60%. Metabolized in liver. Primarily excreted in urine minimal elimination in feces. Half-life 20-30 min. 

Rensing H, Jaeschke H, Bauer 1, Patau C, Datene V, Pannen BH and Bauer M, Differential activation pattern of redox-sensitive transcription factors and stress-inducible dilator systems heme oxygenase-1 and inducible nitric oxide synthase in hemorrhagic and endotoxic shock. Cril Care Med 29(10) 1962-71,2001. 

Fig. 5.10a-c. MMMIHS highly distended stomach on contrast study with slow passage of contrast. Very little peristaltic activity. a,b Note the unusual microcolon and distended bladder (catheter). Secondary hydronephrosis because of dilated bladder, c Dilated system can be seen on EU, with the atonic, large bladder with dilatation of the pyelocaliceal system... 

Obviously in the case of dilatancy the electric double layer creates a strong repulsion between the particles upon their close approach, so that the particles are prevented from being pressed against one another, and easily slip past each other owing to the presence of the thin layer of liquid between them. Hence the system flows easily, provided the stresses are sufficiently weak to allow the liquid to flow through the capillary spaces between the particles. But when it is triad to deform the dilatant system too quickly, the liquid, flowing in the narrow capillary canals between the particles, cannot follow these movements, so that further displacements are inhibited, and the system behaves more or less like a solid. 

Acute myocardial infarction can be limited by streptokinase which dissolves fresh clots and opens the artery, but muscle death and necrosis causes a mechanical defect. Subsequent infarcts cause further muscle death and ultimately lead to defective ventricular function and cardiac failure. There is the need for simple alarm systems to detect acute myocardial infarction and less traumatic invasive procedures to dissolve the clot and dilate the artery immediately. Coronary arteries ramify and branch in 3-dimensional space and the present generation of balloon catheters for percutaneous transluminal coronary angioplasty carries a small but definite risk. New, non-traumatic guidewires, low profile dilatation systems and more powerful dilatation balloons which will not rupture the artery are needed. 

When that stress is exceeded, the shear rate grows. Further stress leads finally to linear (Newtonian) behaviour. Examples of plastic systems are chocolate, butter, cheese, various spreads and ice cream. In pseudoplastic systems the observed viscosity decreases with an increase in shear stress. An example of a pseudoplastic system is pudding. Dilatant systems resist deformation more than in proportion to the apphed force. The shear rate is growing much faster than that of Newtonian fluids and viscosity increases with an increase in shear stress. At low apphed forces, the system behaves as a Newtonian fluid. Examples of dilatants systems are honey with added dextran and a slurry of wet beach sand. Thixotropic systems become more fluid (they have lower viscosity) with increasing time of an apphed force. If the apphed force ceases to operate, the original viscosity of the system is restored due to a reversible transformation of the sol gel type. Examples of thixotropic systems are mayonnaise, ketchup, whipped and hardened fats, butter and processed cheeses. Rheopectic systems exhibit behaviour opposite to that of thixotropic systems. Their viscosity increases with increasing time of apphed force. An example is whipped egg white. 

There are no contraindications. However, there are limitations In the presence of poor renal function, accurate estimation of DRF and/or drainage may not be possible. In the presence of marked hydronephrosis, the interpretation of poor drainage is difficult since this could be due to either partial hold-up or simply because of the reservoir effect of the dilated system. In the presence of calculus obstruction, a renogram may be undertaken, but no furosemide should be administered. 

Fig. 5.14. UPJ obstruction. Gd enhancement, a Delayed opacification of the right dilated system, b Curves of enhancement showing abnormal pat-rJ tern to the right and normal pattern to the left...

Fig. 15.19a,b. Infected uretero-hydronephrosis. a Transverse scan of the left kidney. The urine within the dilated system is echogenic. b Sagittal scan of the left flank. It displays the highly dilated left ureter filled with echogenic urine... 

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