Urinary tract anomalies and dysfunctional voiding: a spectrum dictated by the influence of amniotic pressure upon fetal urodynamics

Intra-abdominal pressure, intra-abdominal hypertension, and pregnancy: a review

The last several decades have seen many advances in the recognition and prevention of the abdominal compartment syndrome (ACS) and its precursor, intra-abdominal hypertension (IAH). There has also been a relative explosion of knowledge in the critical care, trauma, and surgical populations, and the inception of a society dedicated to its understanding, the World Society of the Abdominal Compartment Syndrome (WSACS). However, there has been almost no recognition or appreciation of the potential presence, influence, and management of intra-abdominal pressure (IAP), IAH, and ACS in pregnancy. This review highlights the importance and relevance of IAP in the critically ill parturient, the current lack of normative IAP values in pregnancy today, along with a review of the potential relationship between IAH and maternal diseases such as preeclampsia-eclampsia and its potential impact on fetal development. Finally, current IAP measurement guidelines are questioned, as they do not take into account the gravid uterus and its mechanical impact on intra-vesicular pressure.

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.

Increased intra-abdominal pressure results in both obstructive and nonobstructive types of impairments of renal pelvic excretion

An experimental study has been conducted to evaluate the effects of increased intra-abdominal pressure (IAP) on the excretion function from renal pelvis into the ureter.

METHODS

Sixteen adult male New Zealand rabbits were randomly allocated in two groups after obtaining basal scintigraphies. Group I consisted of 8 rabbits which were subjected to an increased IAP for ten day period. In Group II an other 8 rabbits were subjected to an increased IAP for 60 day period. At the end of the periods of increased IAP the post-pressure scintigraphic evaluations of both groups were carried out. Time to maximum activity (Tmax), T1/2 and T2/3 values of the radiopharmaceutical in the kidneys and down slope parameters (DS1/2, DS2/3) were calculated from the renogram curves of both right and left kidneys. Comparison of basal and post-pressure scintigrapies and the mean difference of the renogram parameters between groups were performed.

RESULTS

All basal scintigraphies were normal. Post-pressure scintigraphies revealed an obvious delay in the excretion phase in both groups. Both kidneys of a rabbit in group I revealed a non-obstructive pattern through responding well to administration of diuretic. Furthermore both kidneys of a rabbit from group II have revealed an obstructive pattern. T1/2 and T2/3 values were significantly elevated and mean DS1/2, DS2/3 were significantly decreased in post-pressure scintigraphies of the both groups without revealing a statistically significant difference between groups I and II. The mean difference of Tmax was significantly increased in group II.

CONCLUSION

The increases in IAP, through the compressive effect upon ureters together with a concomitant increase in intravesical pressure, may impair the passage of urine from renal pelvis into ureter. The impaired passage may play a role in the development of hydronephrosis which may either reveal a nonobstructive and/or obstructive pattern.

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

OBJECTIVE

To determine in vitro the effects of increments of external pressure on the pressure required to conduct fluid through ureters of various lengths at different flow rates, as the flow of a fluid through a collapsible tube is influenced by various factors (e.g. external pressure, the pressure gradient between the ends, the length and diameter of the tube, and the viscosity of fluid).

MATERIALS AND METHODS

Two in vitro systems were designed, composed of three parts, i.e. a perfusion line, an exit line and a container of two different widths in which short or long ureteric segments, obtained from cattle, could be placed; the ureter was connected to the perfusion and exit lines. Physiological saline was added to the container until the desired external pressure was applied to the ureter. The flow pressure (height of the perfusion line) was recorded when producing flows through ureters of varying length at 1.5 and 6 mL/min, and determined under various external pressures. The intra-ureteric pressure during flow was also monitored by a pressure transducer. The four combinations of long and short ureters with high and low flow rates were compared using analysis of variance, with the Pearson correlation coefficient used to evaluate the relationships between the various pressures.

RESULTS

There were close relationships between flow pressure and external pressure (r = 0.727), intra-ureteric and external pressure (r = 0.766), and the flow pressure and intra-ureteric pressure (r = 0.940, all P < 0.001). Increments in external pressure resulted in greater flow and intra-ureteric pressure (P < 0.05). Increases in flow pressure were more pronounced than increases in intra-ureteric pressure at the same external pressure (P < 0.05) at high flow rates. A longer ureter and higher flow rates caused greater intra-ureteric pressure (P < 0.05).

CONCLUSION

External pressure increases the pressure required to conduct fluid through a ureter and the effect is more pronounced at high flow rates. The length of the ureter also affects the flow pressure at high flow rates. Therefore, flow through the ureter follows the Poiseuille equation only at high flow rates. Thus, increases in intra-abdominal pressure may cause greater intrapelvic pressure and induce ureteric obstruction, contributing to the pathogenesis of hydronephrosis.

Renal pelvic pressure responds with augmented increases to increments in intraabdominal pressure

BACKGROUND/PURPOSE

Flow of a fluid through a collapsible tube is under the influence of various factors including the external compressing pressure. Because the intraabdominal pressure may compress the ureter, an experimental study has been planned to determine and compare the normal intraabdominal and renal pelvic pressures and the alterations in renal pelvic pressure in response to the increments in intraabdominal pressure in the rabbits.

METHODS

Eight adult rabbits were used for the experiment. Under general anesthesia, an urethral catheter, a nasogastric tube, and an intraperitoneal catheter were placed to measure intravesical (IVP), intragastric (IGP), and intraabdominal pressures (IAP), respectively. Intracranial pressure monitorization catheter was placed into the renal pelvis to monitor intrapelvic pressure (IPP). Basal pressure measurements have been recorded. The pressures have been recorded in every 5 minutes, and IAP has been increased gradually about 3 to 4 cm of water pressure in every step for 30-minute periods.

RESULTS

Increases in the intrapelvic pressure values have been significantly higher than the increases in the IAP (P < .001). A significant correlation has been found between IPP and IAP (P = .000, r = 0.866). By using linear regression analysis the relationship has been found to be IPP = 7.303 + 1.985 (IAP). Intragastric pressure values have been higher compared with IAP values (P < .001), whereas intravesical pressures have not differed from IAP (P > .05).

CONCLUSIONS

Elevations in IAP results in augmented increases in the IPP. Poiseuille and Laplace Laws suggest this augmented increase to resemble proximal ureteric obstruction. Increases in IAP may simulate proximal ureteric obstruction and may take part in the pathogenesis of hydronephrosis. J Pediatr Surg 36:901-904.