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The efficiency of a hemodialyzer is largely dependent on its ability to facilitate diffusion between blood and dialysis solution. The diffusion process can be impaired if there is a mismatch between blood and dialysate flow distribution in the dialyzer. This article describes the distribution of the blood and dialysate flows in hollow-fiber hemodialyzers analyzed with a computerized scanning technique. Blood flow distribution was studied in vitro by dye injection in the blood compartment during experimental extracorporeal circulation using human blood with hematocrit (Hct) adjusted at 25 and 40%. Sequential images were obtained with a helical scanner in a 1-cm-thick fixed longitudinal section of the dialyzer. Average and regional blood flow velocity and wall shear rates were measured by using the reconstructed imaging sequence. The method allowed the calculation of single-fiber blood flow and single-fiber wall shear rate (SF wSh) in different regions of the hemodialyzer. In 38 patients on chronic hemodialysis, creatinine and phosphate clearance displayed a significantly negative correlation with Hct (P < 0.05), but this correlation was not found for urea, although a trend toward reduction could be observed. The suggested explanation of this phenomenon is the significant reduction in effective plasma water flow across the hemodialyzer in presence of a progressive rise in Hct. The second explanation for this phenomenon may be found in the nonhomogeneous distribution of blood flow within the fibers observed at the sequential imaging. This, in fact, could also explain the negative trend observed for urea. At higher Hct levels, single-fiber blood flow velocity and SF wSh were significantly lower in the fibers situated at the periphery of the bundle. At the same time, SF wSh tended to decrease in peripheral fibers, showing a value near half of that observed in the central fibers of the bundle (165 versus 301 s(-1)). A similar technique was used to study the flow distribution in the dialysate compartment in three different types of hemodialyzers with characteristic dialysate compartment design: (A) standard configuration; (B) space yarns (spacing filaments preventing contact between fibers); and (C) Moiré structure (wave-shaped fibers to prevent contact between adjacent fibers). Clinical sessions of hemodialysis were also carried out to measure blood- and dialysate-side urea clearances in the different hemodialyzers. Macroscopic and densitometric analysis revealed that flow distribution was most homogeneous in the dialyzer with Moiré structure (type C) and least homogeneous in the standard dialyzer (type A). Space yarns (type B) gave an intermediate dialysate flow distribution. Urea clearance (P < 0.001) increased significantly with types B and C, compared with the standard dialyzer. Type C had the highest clearances, although they were not significantly greater than type B. In conclusion, a significant blood-to-dialysate flow mismatch may occur in hollow-fiber hemodialyzers due to either uneven blood flow distribution or a dialysate channeling phenomenon external to the fiber bundle. Improvement in dialyzer design may overcome these problems, at least in part.

Computed tomography (CT) of parotid gland was performed on 40 patients, immediately following sialography. The results of the combined CT-sialography were compared with those of sialography alone and are presented here. We have come to the conclusion that the main indication for this method, in the study of the parotid gland, is the mass-pathology, particularly situated in deep-lobe and in the pharyngo-maxillary space.

Hydronephrosis in infancy and childhood is a frequent urinary malformation and is almost always congenital. In over 80% of the cases it is due to ureteropelvic junction obstruction; much less frequently it is due to anomalous renal vessels, sometimes associated to ureteropelvic junction obstruction. In this paper the Authors analyze their experience in the surgical treatment of this urinary malformation. 234 hydronephrosis out of 222 patients were operated on from January 1972 to June 1985. 61 hydronephrosis were operated on in 55 infants under 1 year. Primary nephrectomy was carried out only in 9 of the 234 hydronephrosis operated on (3.9%) and in 3 of the 61 hydronephrosis operated on in infants less than 1 year old (4.9%). All the 55 infants but one showed a significant radiological improvement after pyeloplasty. 28 infants but one showed a significant radiological improvement after pyeloplasty. 28 infants for a total of 30 hydronephrosis had a glomerular filtration rate determination during sequential scan for individual kidney function assessment. 90% of the kidneys operated on showed a normal or slightly reduced glomerular filtration rate. Recent advances in prenatal echographic diagnosis and relationship between obstructive uropathy, renal development and pulmonary hypoplasia are discussed. The Authors stress out the importance of early diagnosis to improve surgical results.

The experience about 73 defecographic exams performed in pediatric age is reported. The casuistry is critically analyzed, taking into consideration the most recent non radiological diagnostic improvements. In the authors' opinion, defecography in pediatric age is advisable in the diagnosis and post-operative control of fecal incontinence. In the other cases radiology may be substituted by other less invasive and sometimes more precise methods.