Increased intra-abdominal pressure alters the contractile properties of rabbit bladder

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.

Results from the International Conference of Experts on Intra-abdominal Hypertension and Abdominal Compartment Syndrome. I. Definitions

OBJECTIVE

Intra-abdominal hypertension (IAH) and abdominal compartment syndrome (ACS) have been increasingly recognized in the critically ill over the past decade. The variety of definitions proposed has led to confusion and difficulty in comparing one study to another.

DESIGN

An international consensus group of critical care specialists convened at the second World Congress on Abdominal Compartment Syndrome to standardize definitions for IAH and ACS based upon the current understanding of the pathophysiology surrounding these two syndromes.

METHODS

Prior to the conference the authors developed a blueprint for the various definitions, which was further refined both during and after the conference. The present article serves as the final report of the 2004 International ACS Consensus Definitions Conference and is endorsed by the World Society of Abdominal Compartment Syndrome (WSACS).

RESULTS

IAH is redefined as an intra-abdominal pressure (IAP) at or above 12 mmHg. ACS is redefined as an IAP above 20 mmHg with evidence of organ dysfunction/failure. ACS is further classified as either primary, secondary, or recurrent based upon the duration and cause of the IAH-induced organ failure. Standards for IAP monitoring are set forth to facilitate accuracy of IAP measurements from patient to patient.

CONCLUSIONS

State-of-the-art definitions for IAH and ACS are proposed based upon current medical evidence as well as expert opinion. The WSACS recommends that these definitions be used for future clinical and basic science research. Specific guidelines and recommendations for clinical management of patients with IAH/ACS are published in a separate review.

Acute alterations in biochemistry, morphology and contractility of rat isolated urinary bladder via increased intra-abdominal pressure

OBJECTIVE

To determine the acute effects of increased intra-abdominal pressure (IAP) on the biochemistry, morphology and contractility of the rat isolated urinary bladder using an experimental laparoscopy model.

METHODS

We divided 24 adult female Sprague-Dawley rats into three groups. The control group (group I) was not subjected to increased IAP. In groups II and III, IAPs of 10 and 20 mm Hg, respectively, were established by carbon dioxide pneumoperitoneum for 60 min. Thirty minutes after desufflation, the rat urinary bladder dome was removed for in vitro pharmacological investigation, measurement of malondialdehyde (MDA) levels and histopathological examination. Statistical comparisons between groups were performed.

RESULTS

Tissue MDA levels in groups II and III were significantly higher than in the control group. In group II, only the lamina propria was significantly damaged. However, the epithelium, lamina propria, and serosa were significantly damaged in group III. Acetylcholine potentiated contractions in both IAP groups. Increased responses to electrical field stimulation in the IAP groups were significant only in group II.

CONCLUSIONS

In this experimental model, 10 and 20 mm Hg of IAP induced by pneumoperitoneum increased MDA levels and caused important changes in the morphology and contractile response of the urinary bladder.

Changes in bladder of rabbits subjected to elevation of intraabdominal pressures

BACKGROUND/PURPOSE

An experimental study has been conducted to evaluate the effects of increased intraabdominal pressure (IAP) on the morphology of the bladder of rabbits.

METHODS

Experiments were performed on 20 adult male New Zealand rabbits. Six rabbits served as the control group (group I). Seven rabbits were subjected to increased IAP of 7 cm H2O for 10 days through installing air into the abdominal cavity (group II). Increased IAP was maintained for 60 days in another group of 7 rabbits (group III). Bladders were removed and fixed in 10% formalin for routine process. Paraffin sections of 5 to 7 microm were stained with H & E for light microscopic evaluation. Histopathologic parameters were scored, and the mean scores according to groups were compared by 1-way analysis of variance (ANOVA). The mean values of groups were compared separately by Tukey-Kramer multiple comparison test. In these tests, P value less than.05 was considered statistically significant.

RESULTS

All of the bladder strips obtained from animals subjected to 10 days of pressure increase (group II) showed mild to severe degree of vacuolation and desquamation of urothelium. Both vacuolation and desquamation of urothelium were present in all of the strips obtained from rabbits with 60 days pressure increase (group III). Additionally, there were infiltration and congestion of the urothelium together with vacuolation, suburothelial edema, and desquamation in 4 group III rabbits. Moderate or severe congestion in the lamina propria was present in bladder strips of group II rabbits. The congestion of the lamina propria was advanced, and additional moderate to severe inflammation was present in 4 rabbits of group III. Mean histopathologic scores of urothelium (P <.00001) and lamina propria (P =.002) differed significantly among groups. When the groups were compared one by one, the differences between the group I and group II and group II and III were significant (P <.05). Although serosa appeared normal in both group I and II, moderate congestion and infiltration of the serosa was present in the bladder strips of group III (P <.05).

CONCLUSION

Increases in IAP for even 10 days show damaging effects on the bladder. Extended period resulted in augmentation of the damage.

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.