Obstruction natural history

As in the management for CRVO, the purpose of such a procedure is to reestablish venous outflow by creating a chorioretinal anastomosis distal to the site of obstruction, to attempt to improve visual acuity by decreasing macular edema, and to decrease the conversion from nonischemic to ischemic vein occlusion. Fekrat and de Juan (77) reported on six eyes with branch vein occlusion of whom, three had successful anastomoses. Of the six eyes, the visual acuity improved one to three lines in two, remained unchanged in one, and decreased in three. This result does not appear to be significantly better than the natural history of visual acuity loss due to BRVO. 

It is useful to define the disease category in order to predict the natural history and specific intervention. It is well known that patients with primarily restrictive disorders can have both inspiratory and expiratory muscle weakness, and apart from noninvasive ventilation (NIV), they also need cough assistance (4,5). On the other hand, patients with obstructive disorders rarely need mechanical expiratory aids except when they have a severe infectious exacerbation at which time difficulties in clearing copious secretions can occur (4,6,7). 

Applegate KE, Ghei M, Perez-Atayde AR (1998) Prenatal detection of a Wilms tumor. Pediatr Radiol 29 65-67 Arnold AJ, Rickwood AMK (1990) Natural history of pelvi-ureteric obstruction detected by prenatal sonography. Br JUrol 65 91-96... 

Fletcher CM (1976) The natural history of chronic bronchitis and emphysema an eight-year study of early chronic obstructive lung disease in working men in London. Oxford University Press, Oxford, New York. XIX, p 272 Fletcher C and Peto R (1977) The natural history of chronic airflow obstruction. BMJ 1(6077) 1645-1648 Flynn MG (1994) Respiratory symptoms, bronchial responsiveness, and atopy in Fijian and Indian children. Am J Respir Crit Care Med 150(2) 415-420... 

The upper limit of gas velocity for particulate expansion is termed the minimum bubbling velocity, umb. Determining this can present difficulties as its value may depend on the nature of the distributor, on the presence of even tiny obstructions in the bed, and even on the immediate pre-history of the bed. The ratio umb/umf, which gives a measure of the degree of expansion which may be effected, usually has a high value for fine light particles and a low value for large dense particles. 

Acree (1993, 1997) summarized the history of GC-O, giving examples of its application in natural product chemistry. He speculated about its future, using it as a method to bridge the gap between sensory science and analytical chemistry. Acree emphasized the fact that none of the detectors used in gas chromatography is as sensitive as the human nose for many of the odorants found in foods. He noted that splitting devices can be altered by casual obstructions and, in all cases, reduce the dose of the odorant delivered to the sniffer . Deibler et al. (1999) reviewed the characteristics of the GC-O technique. 

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