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Biomedical subjects

S A Koff

Publications and source records attributed to S A Koff.

At least 55 records · Page 3Linked to original sources
PubMed1988

The shape of intestinal segments used for reconstruction.

The geometry of intact and detubularized intestinal segments is examined to establish guidelines for estimating the length of bowel required for urinary reconstruction. Because a sphere has the highest ratio of volume to surface area of any geometric form, whenever bowel is detubularized the resulting spherical reservoir will always hold a larger volume than the original cylinder, but unfortunately there is no simplistic formula to estimate this gain. Therefore, tables are presented which calculate the resulting volumes and the gain in volume of detubularized spherically shaped reservoirs used for bladder augmentation and substitution. These tables demonstrate the striking gain in volume that results from detubularizing bowel and provide guidelines for determining the length of bowel segments required for different types of urinary tract reconstruction.

Intestines↗
PubMed1986

Pathophysiology of ureteropelvic junction obstruction: experimental and clinical observations.

We compared experimental ligature-induced ureteropelvic junction obstruction in the dog with naturally occurring ureteropelvic junction obstruction in children to determine if clinical behavior and difficulties in diagnosis could be related to different types or components of obstruction at the ureteropelvic junction. Measurements of flow rate out of the ligature-obstructed canine renal pelvis demonstrated a pressure-dependent pattern in which flow increased linearly in response to increasing pressures. In 5 human kidneys with intrinsic ureteropelvic junction obstruction a similar pressure-dependent pattern was demonstrated. This was in contrast to 6 human kidneys with extrinsic mechanical ureteropelvic junction obstruction in which a volume-dependent pressure flow pattern occurred, such that urinary flow rate did not keep pace with increases in pelvic pressure. In some cases flow actually decreased at high pressures because the ureteropelvic junction became self-obstructing as the pelvis enlarged. These findings indicate that the precise pathological anatomy of the ureteropelvic junction defines the pattern of flow across the obstruction. The 2 different types of obstruction, pressure-dependent and volume-dependent flow restrictions, which exist are important determinants of the clinical behavior of the obstructed kidney insofar as its potential for progressive hydronephrosis. They also help to explain why diagnostic tests for assessing obstruction in hydronephrosis are inaccurate at times.

Animals↗
PubMed1986

Glomerular filtration rate in children: validation and longitudinal use of determination from the 99mTc DTPA renogram.

The glomerular filtration rate (GFR) was estimated from the technetium diethylenetriaminepentacetic (99mTc DTPA) renogram by empirically correlating the renogram and clearance of the tracer as measured by plasma disappearance kinetics. To expand the potential application of this technique from its original description, minor changes in methodology were made; a new regression was generated with 30 subjects, and that formula was then validated prospectively. For the 50 children and adolescents in the prospective series whose GFR normalized for surface area (NGFR = GFR X 1.73 m2/SA; SA, surface area) was less than 120 mL/min/1.73 m2; renal function was estimated with a mean residual error of 8.0 mL/min/1.73 m2, and a mean relative error of 11%. These results are at least as good as those in the initial report, thus validating this method in a prospective series. To examine the use of this method longitudinally, 129 examinations were reviewed in 55 subjects who had NGFR estimated from the renogram (estimated) on at least two occasions. For 28 sets of serial examinations, NGFR was also measured by the plasma disappearance of 99mTc DTPA (measured). The true change in function for each set of serial examinations was defined as the increment for whichever method (estimation or measurement) was more stable. The mean longitudinal errors were 2.1 and 4.8 mL/min/1.73 m2 for measured and estimated NGFR, respectively. The increments in NGFR for these methods were correlated with a regression line near identity and r = .852. This indicates that a change in estimated NGFR reflects a change in measured NGFR of similar magnitude. This method can accurately estimate GFR from the 99mTc DTPA renogram, and it can be used longitudinally to follow children with renal disorders.

Adolescent↗
PubMed1985

Pressure volume relationships in human hydronephrosis.

Pressure volume curves were obtained in 8 children with ureteropelvic junction obstruction prior to pyeloplasty after totally obstructing the ureteropelvic junction. All human renal pelves displayed a similar shape pressure volume curve. The human renal pelvis is able to accommodate to increasing volumes by maintaining a relatively low intrapelvic pressure Once its capacity is reached, pressures rise to pathologically high levels at a much faster rate. These findings suggest that hydronephrosis can be viewed as a compensatory mechanism which protects some kidneys from further overdistention, high intrapelvic pressures, and progressive renal deterioration by virtue of acquired changes in compliance, pelvic size, and renal function which limit the rate of pressure rise within the hydronephrotic kidney.

Child↗
PubMed1985

The abdominal neourethra in children: technique and long-term results.

The abdominal neourethra is a continent bladder tube that is applicable to selected children with anatomical urinary incontinence or urinary retention and a nonnavigable urethra. A 5 to 8-year followup is presented in 6 children in whom the abdominal neourethra afforded normal micturition through it or permitted intermittent catheterization. All children were dry between bladder emptyings as a result of a continence mechanism that combined a long elastic tube and a cephalad neourethral abdominal opening with a rectus striated muscle sphincter.

Abdomen↗
PubMed1985

Evaluation and management of the acute scrotum.

The application of an orderly diagnostic protocol to the conditions causing the acute scrotum will allow all cases to be classified rapidly, with either a presumptive diagnosis of torsion or other surgical conditions that require surgery or exclusion of torsion with confidence. It is imperative, however, in those cases in which the acute scrotum is not operated on that sufficiently long follow-up be done to prove that in each and every case the testis and scrotal contents return to normal, so that an occult neoplasm will not be innocently neglected.

Acute Disease↗
PubMed1984

One-stage membranous urethroplasty in childhood.

Seven boys with short membranous urethral strictures were treated with a single stage perineal urethroplasty. Anterior urethral mobilization lengthened the urethra sufficiently for a bulboprostatic anastomosis free of tension and in no case was transpubic surgery required. The result was ultimately satisfactory for all children. Although the perineum is proportionately narrower in children than in adults, the depth of the membranous urethra from the skin level is reduced to an even greater degree. As a result exposure of the membranous urethra in children, particularly young children, often is easier than might be anticipated on the basis of imagined miniaturization of adult dimensions. We recommend an initial perineal approach for all short membranous urethral strictures in children with conversion to the transpubic approach if complications or a longer stricture is encountered.

Adolescent↗
PubMed1984

Diuretic radionuclide localization of upper urinary tract obstruction.

In 59 children with proved upper urinary tract obstruction diuretic radionuclide ureteral scans provided an accurate assessment of ureteral dilatation sufficient to distinguish ureteropelvic from ureterovesical obstruction. As a result, this test may be used instead of more invasive studies, such as retrograde or antegrade pyelography, to determine the site of obstruction in many cases of hydronephrosis.

Adolescent↗
PubMed1984

Vesicoureteral reflux in triplets.

During an investigation for urinary tract infections in 3-month-old triplets similar patterns of vesicoureteral reflux were noted. To our knowledge, this is the first report of vesicoureteral reflux in triplets. The patterns of inheritance in vesicoureteral reflux and the need for sibling evaluation are discussed.

Female↗
PubMed1984

Glomerular filtration rate in children: determination from the Tc-99m-DTPA renogram.

Analysis of the Tc-99m-DTPA renogram is usually limited to calculating the relative function of each kidney. To develop a method to determine the absolute glomerular filtration rate (GFR), various methods of analyzing the renogram were examined to determine which gave the best correlation with GFR. That regression could then be used to predict GFR without the need for blood samples. Fifty children were studied using Tc-99m-DTPA renograms and GFR measured simultaneously by plasma disappearance. The renogram variables were adjusted for detector sensitivity and for dose divided by weight, which was used as an index of plasma concentration. GFR correlated better with the slope of the second phase than with the area under the renogram curve. For the best correlation with GFR (using background subtraction and depth correction) r = .971 and the mean residual = 4.8 ml/min. For GFR normalized for body surface area (using background subtraction and no depth correction) r = .954 and the mean residual = 9.1 ml/min/1.73 m2. This method can accurately estimate GFR from the renogram in children.

Adolescent↗
PubMed1983

Diuretic radionuclide urography.

Diuretic radionuclide urography is a modification of conventional renography which utilizes the administration of intravenous furosemide to distinguish dilated, non-obstructed, hydronephrotic systems from those with significant mechanical obstruction. Diagnostic patterns are derived from computer generated time-activity histograms that depict the accumulation and washout of radiotracer before and after diuretic injection. In dilated but non-obstructed systems, diuresis produces a decline in activity. In obstructed systems, there is a failure of radiotracer washout in response to diuresis and no decline in activity is observed. The procedure is applicable to patients of all ages with suspected upper urinary tract obstruction. Clinical and experimental data support the accuracy and utility of this methodology and define its limitations and pitfalls.

Animals↗
PubMed1983

Determinants of progression and equilibrium in hydronephrosis.

Upper urinary tract urodynamic parameters were measured serially in 12 dogs subjected to partial ureteropelvic junction obstruction. Measurements of pressure-volume relationships (pelvimetrics) and the physiologic capacity of the renal pelvis were important predictors of hydronephrotic equilibrium which occurred only in kidneys whose pelvic urine volume remained lower than the renal pelvic capacity. Because of acquired changes in compliance and renal function, the same degree of obstruction caused progressive hydronephrosis at low pelvic volumes but not at high volumes in some kidneys. Hydronephrosis can thus be viewed as a compensatory mechanism which protects the kidney against further dilation and elevated intrapelvic pressure.

Animals↗
PubMed1983

The uninhibited bladder in children: effect of treatment on recurrence of urinary infection and on vesicoureteral reflux resolution.

We studied and treated prospectively 62 neurologically normal children with vesicoureteral reflux using urodynamic techniques to identify uninhibited bladder contractions with voluntary sphincteric obstruction (dyssynergia). All children received antibiotic prophylaxis. Anticholinergic drugs were used additionally to treat uninhibited bladder contractions. During 6 years of followup treatment of uninhibited contractions produced a 4-fold reduction in the incidence of recurrent urinary infection and tripled the rate of reflux resolution compared to controls. These data suggest that uninhibited contractions with voluntary sphincter obstruction are an important prognostic finding in children with reflux, which when treated successfully can alter the disease course and may make surgical therapy of reflux unnecessary for some.

Adolescent↗