Neuroanatomic and behavioral correlates of urinary dysfunction induced by vaginal distension in rats.

The aim of the present study was to use a model of simulated human childbirth in rats to determine the damage to genitourinary structures and behavioral signs of urinary dysfunction induced by vaginal distension (VD) in female rats. In experiment 1, the length of the genitourinary tract and the nerves associated with it were measured immediately after simulated human delivery induced by VD or sham (SH) procedures. Electroneurograms of the dorsal nerve of the clitoris (DNC) were also recorded. In experiment 2, histological characteristics of the bladder and major pelvic ganglion of VD and SH rats were evaluated. In experiment 3, urinary parameters were determined in conscious animals during 6 h of dark and 6 h of light before and 3 days after VD or SH procedures. VD significantly increased distal vagina width (P < 0.001) and the length of the motor branch of the sacral plexus (P < 0.05), DNC (P < 0.05), and vesical nerves (P < 0.01) and decreased DNC frequency and amplitude of firing. VD occluded the pelvic urethra, inducing urinary retention, hematomas in the bladder, and thinness of the epithelial (P < 0.05) and detrusor (P < 0.01) layers of the bladder. Major pelvic ganglion parameters were not modified after VD. Rats dripped urine in unusual places to void, without the stereotyped behavior of micturition after VD. The neuroanatomic injuries after VD occur alongside behavioral signs of urinary incontinence as determined by a new behavioral tool for assessing micturition in conscious animals.

Comparison of air-charged and water-filled urodynamic pressure measurement catheters.

AIMS: Catheter systems are utilized to measure pressure for diagnosis of voiding dysfunction. In a clinical setting, patient movement and urodynamic pumps introduce hydrostatic and motion artifacts into measurements. Therefore, complete characterization of a catheter system includes its response to artifacts as well its frequency response. The objective of this study was to compare the response of two disposable clinical catheter systems: water-filled and air-charged, to controlled pressure signals to assess their similarities and differences in pressure transduction. METHODS: We characterized frequency response using a transient step test, which exposed the catheters to a sudden change in pressure; and a sinusoidal frequency sweep test, which exposed the catheters to a sinusoidal pressure wave from 1 to 30 Hz. The response of the catheters to motion artifacts was tested using a vortex and the response to hydrostatic pressure changes was tested by moving the catheter tips to calibrated heights. RESULTS: Water-filled catheters acted as an underdamped system, resonating at 10.13 ± 1.03 Hz and attenuating signals at frequencies higher than 19 Hz. They demonstrated significant motion and hydrostatic artifacts. Air-charged catheters acted as an overdamped system and attenuated signals at frequencies higher than 3.02 ± 0.13 Hz. They demonstrated significantly less motion and hydrostatic artifacts than water-filled catheters. The transient step and frequency sweep tests gave comparable results. CONCLUSIONS: Air-charged and water-filled catheters respond to pressure changes in dramatically different ways. Knowledge of the characteristics of the pressure-measuring system is essential to finding the best match for a specific application.

Stenosis Characterization and Identification for Dialysis Vascular Access.

Vascular access dysfunction is the leading cause of hospitalization for hemodialysis patients and accounts for the most medical costs in this patient population. Vascular access flow is commonly hindered by blood vessel narrowing (stenosis). Current screening methods involving imaging to detect stenosis are too costly for routine use at the point of care. Noninvasive, real-time screening of patients at risk of vascular access dysfunction could potentially identify high-risk patients and reduce the likelihood of emergency surgical interventions. Bruits (sounds produced by turbulent blood flow near stenoses) can be interpreted by skilled clinical staff using conventional stethoscopes. To improve the sensitivity of detection, digital analysis of blood flow sounds (phonoangiograms or PAGs) is a promising approach for classifying vascular access stenosis using non-invasive auditory recordings. Here, we demonstrate auditory and spectral features of PAGs which estimate both the location and degree of stenosis (DOS). Auditory recordings from nine stenosis phantoms with variable DOS and hemodynamic flow rate were obtained using a digital recording stethoscope and analyzed to extract classification features. Autoregressive modeling and discrete wavelet transforms were used for multiresolution signal decomposition to produce 14 distinct features, most of which were linearly correlated with DOS. Our initial results suggest that the widely-used auditory spectral centroid is a simple way to calculate features which can estimate both the location and severity of vascular access stenosis.

Effect of vaginal distension on blood flow and hypoxia of urogenital organs of the female rat.

Vaginal delivery of children causes traumatic injury to tissues of the pelvic floor and is correlated with stress urinary incontinence; however, the exact mechanism of organ and tissue injury leading to incontinence development is unknown. The purpose of this project was to test the hypothesis that vaginal distension results in decreased blood flow to, and hypoxia of, the urogenital organs responsible for continence, which would suggest an ischemic and/or reperfusion mechanism of injury. Thirteen female rats underwent vaginal distension for 1 h. Thirteen age-matched rats were sham-distended controls. Blood flow to the bladder, urethra, and vagina were determined using a microsphere technique. Hypoxia of these organs was determined by immunohistochemistry. Blood flow to all three organs was significantly decreased just before release of vaginal distension. Bladder blood flow decreased further immediately after release of vaginal distension and continued to be significantly decreased 15 min after the release. Blood flow to both the urethra and vagina tripled immediately after release, inducing a rapid return to normal values. Vaginal distension resulted in extensive smooth muscle hypoxia of the bladder, as well as extensive hypoxia of the vaginal epithelium and urethral hypoxia. Bladders from sham-distended rats demonstrated urothelial hypoxia as well as focal hypoxic areas of the detrusor muscle. We have clearly demonstrated that vaginal distension results in decreased blood flow to, and hypoxia of, the bladder, urethra, and vagina, supportive of hypoxic injury as a possible mechanism of injury leading to stress urinary incontinence.

LONG-TERM EVALUATION OF A NON-HERMETIC MICROPACKAGE TECHNOLOGY FOR MEMS-BASED, IMPLANTABLE PRESSURE SENSORS.

This paper reports long-term evaluation of a micropackage technology for an implantable MEMS pressure sensor. The all-polymer micropackage survived 160 days when subjected to accelerated lifetime testing at 85 °C in a 1% wt. saline solution. The package shows minimum effect on sensors' sensitivity and nonlinearity, which deviated by less than 5% and 0.3%, respectively. A 6-month in vivo evaluation of 16 MEMS-based pressure sensors demonstrated that the proposed micropackage has good biocompatibility and can protect the MEMS pressure sensor. To the best of our knowledge, these results establish new lifetime records for devices packaged using an all-polymer micropackaging approach.

Development of a mathematical model for the prediction of the area of venous leak.

Erectile dysfunction (ED) is an increasingly prevalent medical problem, affecting up to 50% of men aged between 40 and 70-y-old. Many cases are vasculogenic and some of these stem from the inability of the penis to store blood during erection due to leak into the venous system, termed corporo-venocclusive dysfunction (CVOD). The area of leakage during erection could be the most direct measure of erectile function but has not been investigated before. We have developed a simple mathematical model to determine the area of leak during erection and have tested it on data from both normal men (n=3) and men with venogenic impotence (n=16) undergoing dynamic infusion cavernosometry (DIC). The area of leak in the impotent group is significantly greater than in normal men at intracorporal pressures above 30 mmHg and reaches a plateau between 60 and 90 mmHg. Based on this study, we suggest that it may be necessary only to perform DIC at intracorporal pressures between 60 and 90 mmHg.

Effects of anesthesia on cystometry and leak point pressure of the female rat.

Anesthetics operate by different mechanisms and are often used to perform urodynamics in animals. The objective of this study was to compare the effects of ketamine/xylazine and urethane anesthetics on filling, voiding, and leak point pressure (LPP) in female rats. Nineteen rats underwent awake cystometry 2 days after suprapubic bladder catheter implantation. Bladders were filled with saline (5 ml/hr), while bladder pressure was measured. Half the rats were then anesthetized with urethane i.p. and half were anesthetized with ketamine and xylazine i.p. (K/X). All rats then underwent cystometry and LPP testing under anesthesia. Spontaneous nonvoiding contractions were analyzed and capacity was determined by voiding or leakage. Capacity was significantly higher in awake rats (0.55 +/- 0.06 ml) than with either K/X (0.21 +/- 0.06 ml) or urethane (0.30 +/- 0.05 ml). The pressure just prior to voiding in awake cystometry (15.6 +/- 1.7 cm H2O) was not significantly different from that with either anesthetic (K/X: 10.1 +/- 1.0 cm H2O; urethane: 13.3 +/- 2.0 cm H2O). Spontaneous nonvoiding contractions occurred in 4 rats with urethane and 3 rats with K/X. The volume at which the first contraction occurred was significantly lower with K/X (0.05 +/- 0.02 ml) than urethane (0.19 +/- 0.04 ml). There was no significant difference in the frequency of spontaneous nonvoiding contractions between K/X (4.58 +/- 0.30/min) and urethane (5.16 +/- 2.66/min), nor was there a difference in LPP between anesthetics (K/X: 40.4 +/- 2.4 cm H2O; urethane: 36.2 +/- 3.9 cm H2O). The results suggest that urethane is preferable to K/X for anesthetized cystometry studies since it more closely simulates normal physiological responses.

Two mathematical models explain the variation in cystometrograms of obstructed urinary bladders.

Overdistension of the urinary bladder, secondary to outlet obstruction, causes cellular changes in the bladder wall, including hypertrophy of the smooth muscle cells, which increase bladder mass. To investigate the effects of increased mass on the cystometrogram (CMG), we have developed two mathematical models. In the first model, we assume that mass is added such that the largest bladder volume at zero transmural pressure, the zero pressure volume (ZPV), is constant, It predicts increased pressures and decreased compliance in the CMG. In the second model, we assume that both mass and ZPV increase proportionally. It predicts unchanged pressures, increased compliance, and increased capacity in the CMG. These results allow use to divide animal experiments in the literature into two groups. Cystometrograms performed on animals that have had outlet obstruction induced by a cuff method, inducing a small increase in mass, belong to the first group: hypertrophy with no change in ZPV. Cystometrograms performed on animals that have had outlet obstruction induced by a ligature method, inducing a large increase in mass, belong to the second group: hypertrophy with increased ZPV. We conclude that increased ZPV results from a more severe obstruction which is indicated by the increased capacity and compliance.

The effect of urinary bladder shape on its mechanics during filling.

Despite the normal variation in the shape of the urinary bladder, it has always been modeled as a sphere. We have investigated whether its steady-state pressure-volume relation would be significantly different if it were a spheroid. From pressure-volume curves of anesthetized dogs, we deduced stress-strain constitutive relationships for the bladder wall material. We then solved the equilibrium equations for prolate and oblate spheroids with these constitutive relationships and predicted stress, strain, and volume at 120 different transmural pressures and eight different eccentricities of both types of spheroids. The pressure-volume relation of the prolate spheroid never differed very much from that of a sphere. However, an oblate spheroid made of urinary bladder material is significantly more compliant than either a prolate spheroid or a sphere made of the same material. Applications include identification of the position of highest stress in the bladder wall, estimation of material properties of urinary bladders, and determination of the physiological signal indicating bladder fullness.

Erector spinae activation and movement dynamics about the lumbar spine in lordotic and kyphotic squat-lifting.

Activation of the erector spinae during squat lifts depends on the initial posture of the lumbar spine. The authors assessed erector spinae activation by electromyography during squat lifts from lordotic and kyphotic postures, measured kinematics of the lifts from digitized video images, and inferred torques from the kinematics, using a two-dimensional model of a human lifting in the sagittal plane, with a joint at L3. Lifts from the lordotic initial posture had peak electromyographic signals early in the lift, whereas lifts from kyphotic initial posture had an initial "flexor relaxation," and peak activity in the middle of the lift. Lumbar flexion was much greater in lifts from kyphotic initial position. Torques required about L3 were similar between the two postures, though somewhat larger initially in lifts from kyphosis. The largest torques were therefore sustained by flexed lumbar spines, during periods of little or no erector spinae activity, in lifts made from kyphotic initial position. A sizable portion of the early torque is inertial, and therefore strongly dependent on movement time. Movements with a 30-lb load in the hands were similar, in kinematics and electromyography, to unloaded lifts, though longer in duration. The clinical implications of the differences in activation with posture, the practical implications of the inertial component of torque, and the need for consideration of lumbar posture in future modeling of squat lifting are discussed.

Home monitoring of bladder pressure and volume in individuals with spinal cord injury and multiple sclerosis.

Individuals with spinal cord injury and multiple sclerosis are at high risk for developing kidney dysfunction due to high bladder pressures. We have developed a device for frequent monitoring of bladder pressures at home in those patients who use intermittent catheterization to empty their bladders. Of eight subjects enrolled in the study, only five conducted home recording of pressure. Vesical and abdominal pressures measured at home were significantly lower than clinical cystometric pressures. However, subtracted detrusor pressures obtained from home records and cystometric records were not significantly different. The home detrusor pressures were consistent over a large time and volume range. Therefore, the home monitoring method could be used to establish a normal range of bladder pressures at home and to rapidly identify high bladder pressures in advance of upper urinary tract deterioration.

Whole bladder mechanics during filling.

In addition to molecular and cellular properties, elemental and whole bladder properties are important to the function of the bladder during filling. The bladder pressure volume filling relation is dependent on all aspects of bladder tissue. Elemental mechanics properties include elasticity, viscoelasticity, and plastic deformation of bladder tissue. Whole bladder properties include bladder shape, mass, and distension. This paper reviews work on mathematical model aimed at determining the effect of whole bladder properties on bladder filling mechanics and outlines directions for the future.

Etiology of bladder dysfunction secondary to partial outlet obstruction. Calcium disregulation in bladder power generation and the ability to perform work.

Similar to all smooth muscle, contraction of urinary bladder smooth muscle depends upon a rise in intracellular free calcium, which results from both calcium influx from extracellular spaces and calcium release from intracellular stores (calcium-induced calcium release [CICR]). Recent studies from our laboratory demonstrate that one of the major dysfunctions induced by partial outlet obstruction is a marked reduction in the participation of CICR (from IP3-sensitive and IP3-insensitive sites on the sarcoplasmic reticulum [SR]) during stimulation by both field stimulation (neurotransmitter release) and by direct muscarinic stimulation (bethanechol). Experimentally, rabbit urinary bladder function can be evaluated using an isolated whole bladder model. The current study utilizes the isolated whole bladder model to compare the effects of partial outlet obstruction on the responses to field stimulation and bethanechol with the responses of normal bladders following inhibition of CICR with the combination of thapsigargin+ryanodine. The parameters measured include the magnitude of pressure generation, rate of pressure generation, time to maximal pressure generation, percent volume emptied, rate of emptying, power generation, and work performed (both total work and work per ml emptied). Partial outlet obstruction resulted in virtually identical alterations in the responses of the bladder to stimulation (field stimulation and bethanechol) to that of inhibition of CICR by thapsigargin+ryanodine. Thus, these studies provide strong support for our hypothesis that the contractile dysfunctions secondary to partial outlet obstruction are directly related to a marked inhibition of the CICR component of the response to both field stimulation and bethanechol.

Neural pathways of somatic and visceral reflexes of the external urethral sphincter in female rats.

The external urethral sphincter (EUS) plays a crucial role in maintaining urinary continence. The activity of the EUS is modulated by bladder and urethra sensory neurons. However, a complete understanding of the somatic or visceral sources that modulate the EUS is lacking. The aims of the present study were to characterize the response of the EUS to perineal skin, genital, rectal, and urethral mechanical stimulation, as well as to determine the peripheral neural pathways of the reflex. EUS reflex electromyographic activity (EMG), innervation of pelvic and perineal structures, and the anatomy of afferent and efferent nerves were determined in anesthetized female rats. The EUS responds to cutaneous as well as genital and rectal stimuli. However, the EUS EMG response is significantly larger when induced by genital stimulation. The dorsal nerve of the clitoris and the cavernous nerve both innervate the distal urethra and the distal vagina, as well as the clitoris and perigenital skin and are the main afferent pathways for the genito-sphincteric reflex. Efferent axons travel through the pudendal nerve and the lumbosacral trunk and converge in the motor branch of the lumbosacral plexus, which innervates the EUS. Because the nerves are located on the vaginal walls, they are susceptible to damage during childbirth. Physiology and anatomy of the different neural pathways that regulate EUS activity are important to consider when inducing nerve damage to create models of urinary incontinence.

Induced Regenerative Elastic Matrix Repair in LOXL1 Knockout Mouse Cell Cultures: Towards Potential therapy for Pelvic Organ Prolapse.

Impaired elastic matrix remodeling occurs in reproductive tissues after vaginal delivery. This has been linked to development of pelvic organ prolapse (POP) for which there currently is no pharmacologic therapy. Hyaluronan oligomers and transforming growth factor beta 1 (termed elastogenic factors, EFs) have been shown to significantly enhance tropoelastin synthesis, elastic fiber assembly, and crosslinking by adult vascular smooth muscle cells (SMCs). The goal of this study was to ascertain if these factors similarly improve the quantity and quality of elastic matrix deposition by vaginal SMCs (VSMCs) isolated from lysyl oxidase like-1 knock out (LOXL1 KO) mouse model of POP. Cells isolated from whole vagina of a LOXL1 KO mouse (multiparous, stage 3 prolapse) were cultured and identified as SMCs by their expression of various SMC markers. Passage 2 vaginal SMCs (VSMCs; 3×104/10 cm2) were cultured for 21 days with EFs. Cell layers and spent medium aliquots were assessed for elastin content and quality. EF-treated VSMCs proliferated at a similar rate to untreated controls but synthesized more total elastin primarily in the form of soluble matrix elastin. Elastin mRNA was also increased compared to controls. The elastic matrix was significantly denser in EF-treated cultures, which was composed of more mature, non-interrupted elastic fibers that were absent in controls. The results are promising towards development of a therapy to enhance regenerative elastic matrix repair in post-partum female pelvic floor tissues.

Increased duration of simulated childbirth injuries results in increased time to recovery.

Stress urinary incontinence (SUI) development is strongly correlated with vaginal childbirth, particularly increased duration of the second stage of labor. However, the mechanisms of pelvic floor injury leading to SUI are largely unknown. The aim of this study was to determine the effects of increased duration of vaginal distension (VD) on voiding cystometry, leak point pressure testing, and histology. Sixty-nine virgin female rats underwent VD with an inflated balloon for either 1 or 4 h, while 33 age-matched rats were sham-VD controls. Conscious cystometry, leak point pressure testing, and histopathology were determined 4 days, 10 days, and 6 wk after VD. The increase in abdominal pressure to leakage (LPP) during leak point pressure testing was significantly decreased in both distension groups 4 days after distension, indicative of short-term decreased urethral resistance. Ten days after VD, LPP was significantly decreased in the 4-h but not the 1-h distension group, indicating that a longer recovery time is needed after longer distension duration. Six weeks after VD, LPP was not significantly different from sham-VD values, indicating a return toward normal urethral resistance. In contrast, 6 wk after VD of either duration, the distended rats had not undergone the same increase in voided volume as the sham-VD group, suggesting that some effects of VD do not resolve within 6 wk. Both VD groups demonstrated histopathological evidence of acute injuries and tissue remodeling. In conclusion, this experiment suggests pressure-induced hypoxia as a possible mechanism of injury in vaginal delivery.

Does it matter, the shape of the bladder?

To determine if the pressure-volume curve of the urinary bladder is dependent on its shape, we compared the pressure-volume curves of spherical, prolate spheroidal, and oblate spheroidal bladders, all made of the same material. We found that oblate spheroidal bladders are significantly more compliant than either spherical or prolate spheroidal bladders. Since the capacity of normal oblate spheroidal bladders is not larger in vivo than those of any other shape bladder, we have concluded that bladder fullness can not be determined by transmural bladder pressure alone.