The effects of flow rate, length and external pressure upon the pressure required for fluid to flow through a ureter

Tandem ureteral stents drainage lowers renal pelvis pressure in malignant ureteral obstruction: Experimental and computational models

Malignant ureteral obstruction may lead to impaired renal function and requires drainage by a percutaneous nephrostomy tube or an internal ureteric stent. Usage of stiff tandem ureteral stents may decrease stent failure rates. In this paper we combined computational and in vitro models to examine the flow in a malignant ureteral obstruction (MUO) managed by 4 methods of drainage: single soft stent, single stiff stent, soft tandem ureteral stents, and stiff tandem ureteral stents. Pressure at the renal pelvis was the primary outcome of the computational and in vitro models. Different drainage modalities were compared using ANCOVA. Results of computational and in vitro models agreed completely. Drainage by stiff tandem ureteral stents provides lower renal pelvis pressure levels compared with single and soft stents (p < 0.001), especially for high levels of external pressure. Usage of stiff tandem ureteral stents may decrease stent-failure rates and postpone the need for percutaneous nephrostomy tube insertion.

Effect of increased intra-abdominal pressure on urinary system development in fetal rabbits

AIM

To investigate the effect of increased intra-abdominal pressure (IAP) on the fetal urinary system.

MATERIALS AND METHODS

Pregnant rabbits (15-day gestation) were used. Control (n = 5) and experimental (EG, n = 4) groups underwent intraperitoneal catheter placement. The IAP was increased by intraperitoneal air insufflations during the third trimester in the EG. At term, organ weight and organ weight/body weight (BW) ratios were noted, histological examination of the urinary system organs was performed, and the apoptotic indexes were calculated.

RESULTS

BW and total renal weight were significantly increased in the EG (38.65 ± 8.34 g vs 49.36 ± 8.81 g, p = 0.008; and 0.406 ± 0.132 g vs 0.531 ± 0.129 g, p = 0.02). Total renal weight/BW ratio did not differ between groups (0.0103 ± 0.001 vs 0.0107 ± 0.001; p = 0.33). Bladder weight and bladder weight/BW ratio was also significantly increased in the EG (0.067 ± 0.014 g vs 0.114 ± 0.026 g, p = 0.00; and 0.00175 ± 0.00026 vs 0.00229 ± 0.00036, p = 0.001). Immature glomeruli and collecting tubules, and a thin and underdeveloped muscular layer in the ureter and bladder were encountered in the EG, and the apoptotic cell index was significantly increased (p < 0.05).

CONCLUSION

Increased IAP has an adverse effect on fetal urinary system development, and may play a role in the pathogenesis of various congenital abnormalities of the urinary system.

Increased maternal intraabdominal pressure alters the contractile properties of fetal rabbit bladder

BACKGROUND/PURPOSE

Increased intraabdominal pressure (IAP) causes impairment of urine flow by compressing the urine-transporting structures and leads to development of various types of anatomical and functional abnormalities in the urinary system. An intrauterine experiment was conducted to determine the relationship between IAP and intraamniotic pressure (IAMNP) and the effects of increased IAMNP on the contractile properties of fetal bladder in the rabbit model.

MATERIALS AND METHODS

Fourteen time-mated pregnant rabbits were used. A preliminary study (n = 5, 20-day gestation) was performed to determine the relation between IAP and IAMNP. Intraabdominal pressure and IAMNP were recorded through an intraperitoneal catheter and 2 intraamniotic transducers, respectively. Basal IAP and IAMNP were recorded. Then, IAP was increased for 4 cm H(2)O in each subsequent 30-minute period until reaching 20 cm H(2)O. Control (n = 5) and experiment (n = 4) group animals underwent intraperitoneal catheter placement in the 15th day of gestation. Intraabdominal pressure was increased by intraperitoneal air insufflations from 20th day to term in the experiment group. At term, the fetal bladders were excised and the contractile activity was then recorded isometrically. Electrical field stimulation was applied, and contractile responses to carbachol and high potassium (20 mmol/L KCl) were also evaluated.

RESULTS

A strong relationship was found between IAMNP and IAP and defined as IAMNP = IAP x 0.8 + 2.0 (R(2) = 0.816, P = .000). Increased IAP did not change basal rhythmic activity but resulted in frequency-related electrical field stimulation responses being higher contractility responses for frequencies below 10 Hz (P < .05) and similar responses at and above 10 Hz. Bladders imposed to elevated IAP displayed greater sensitivity to carbachol with a shift to the left in the concentration-response curve. High potassium-induced contractions had a shorter rise time (P < .05) but similar contraction amplitudes and half decay times in bladders imposed to increased IAP.

CONCLUSION

Intraamniotic pressure is affected by IAP in pregnant rabbits in accordance with an equation (IAMNP = IAP x 0.8 + 2.0). Increased IAMNP changes contractile properties of the fetal rabbit bladder without affecting spontaneous activity and shortens the rise time of high potassium-induced contractions. Increased IAMNP also results in cholinergic hypersensitivity in fetal bladders. These results may explain the mechanism of dysfunctional voiding and abnormal bladder function observed in conditions in which IAP and/or IAMNP are elevated.

Prenatally detected ureteropelvic junction obstruction: clinical features and associated urologic abnormalities

Urologic congenital anomalies associated with ureteropelvic obstruction (UPJO) have been previously characterized; however, less data are available regarding these associations in a prenatally diagnosed population. A retrospective study was conducted to evaluate significant clinical features and urological anomalies associated with prenatally diagnosed UPJO. The records of 143 children with prenatally diagnosed hydronephrosis secondary to UPJO were retrospectively reviewed. The gender, side of obstruction, degree of hydronephrosis, associated clinical features, and urological anomalies were noted. Hundred and forty-three children (M/F = 2.7) with a total of 198 affected renal units (RU) presenting with unilateral (61%) or bilateral (39%) UPJO were enrolled. In cases of unilateral obstruction, the left side was affected in 60 children (68%). The grade of hydronephrosis was Grade 1 in 56 RU (28%), Grade 2 in 51 RU (26%), Grade 3 in 50 RU (25%) and Grade 4 in 41 RU (21%). Associated clinical features included prematurity (n = 7, 4.9%), twinning (n = 5, 3.5%) and presentation with renal failure (RF) (n = 2). Excluding contralateral UPJO, other urologic anomalies were encountered in 29 patients (20.3%). Associated vesicoureteral reflux (VUR) was encountered in 11 patients (7.7%, M/F = 2.7). Pyeloplasty was required more often in children with associated VUR (54.5 vs. 18.2%) (P = 0.01). Contralateral multicystic dysplastic kidney (MCDK) was encountered in six patients (M/F = 2), one of whom presented with RF. One child carried the diagnosis of Schinzel-Giedion syndrome (SGS), demonstrating severe developmental and neurological disorders and bilateral hydronephrosis. The more frequent occurrence of UPJO in males with predominantly left-sided location, association with VUR and MCDK, and increased frequency of bilaterality in our prenatally diagnosed patients were similar to historical reports. In addition, prematurity and twinning were independently associated with UPJO. The higher rate of pyeloplasty in patients with associated reflux warrants further investigation.

The length and collapsibility of the ureter play roles in the augmented reflection of intraabdominal pressure into the renal pelvis

BACKGROUND/PURPOSE

Flow of a fluid through a collapsible tube is under the influence of various factors including the external compressing pressure. The intraabdominal pressure (IAP) should influence the flow through the ureter. Therefore, an experimental study was planned to investigate the effects of ureteral length and external compressing pressure onto the intrapelvic pressure (IPP) in rabbits.

METHODS

Nineteen adult rabbits were used for the experiment. Under general anesthesia, an intraperitoneal and an intrapelvic catheter were placed to measure IAP and IPP. A urethral catheter was placed for bladder decompression. After this standard preparation, a ureteric stent was placed in the ureter in group 1 (n = 7). Distal or proximal ureter transection was performed in group 2 (n = 6) and group 3 (n = 6), respectively. Basal pressure measurements have been recorded. Then the pressures were recorded every 5 minutes, and IAP was increased gradually for 4 cm of water pressure in each subsequent 30-minute period. All analyses were performed for a standard IAP interval (5 to 25 cm H2O).

RESULTS

IAP did not differ between groups (P = .08). IPP values were significantly higher than the corresponding IAP values in each group (P = .0001). IPP showed significant difference between IAP values of groups (P = .0001). IPP was significantly increased in group 2 when compared with group 1 and group 3 (P = .0001; P = .0001), but no difference was encountered between groups 1 and 3 (P = .1). There has been a strong relationship between IPP and IAP values in all groups. The Rsq values were 0.912, 0.783, and 0.943 for group 1, group 2, and group 3, respectively (P < .0001). Mathematic relations between IPP and IAP also were analyzed. The relations were IPP = 3.9 + 1.10 x IAP, IPP = 10.3 + 1.10 x IAP, and IPP = 3.3 + 1.12 x IAP for groups 1, 2, and 3, respectively.

CONCLUSIONS

Renal pelvis pressure responds with augmented increases to increments in IAP in urinary tracts with different ureteric lengths. Increase in IPP is more pronounced in longer ureters possibly owing to increased resistance to flow. Prevention of ureteric wall collapse reverses the augmented increase in IPP responses. Therefore, both the length and collapsibility of the ureter play a detrimental role in the generation of augmented IPP responses to increments in IAP. The magnitude of IPP as a response to increments in IAP can be estimated by using mathematical relations between IPP and IAP. Increases in IAP may simulate proximal ureteric obstruction and may take part in the pathogenesis of hydronephrosis.