Annals of Biomedical Engineering, Vol. 37, No. 7, July 2009 (Ó 2009) pp. 1425–1433 DOI: 10.1007/s10439-009-9705-2
Feasibility of Using a Computer Modeling Approach to Study SUI Induced by Landing a Jump YINGCHUN ZHANG,1 SEOGGWAN KIM,2 ARTHUR G. ERDMAN,2 KENNETH P. ROBERTS,1 and GERALD W. TIMM1 1 Department of Urologic Surgery, University of Minnesota, 725 Mayo Memorial Building, 420 Delaware Street S.E., Minneapolis, MN 55455, USA; and 2Department of Mechanical Engineering, University of Minnesota, Minneapolis, USA
(Received 20 October 2008; accepted 17 April 2009; published online 5 May 2009)
Abstract—Stress urinary incontinence (SUI) occurs due to anatomic and/or neurologic factors involving connective tissues, muscles and nerves. Although SUI is more common in post-menopausal and multiparous women, studies have also shown a high prevalence of SUI in young, physically fit female athletes. With a goal toward dynamic subject-specific mechanical characterization of the interaction between anatomical structures during physical activities that elicit SUI in females during physical or daily activities, a computer aided design (CAD)-based computer model of the female pelvis has been developed to test the feasibility of the computer modeling approach in understanding the measurable differences between stress-continent and stress-incontinent women. In the present study, a fluid–structure interaction analysis was conducted by using the finite element (FE) analysis technique based on the CAD-based computer model of the female pelvis to investigate the urine leakage in females during jumping. To the best of our knowledge, this is the first application of a fluid–structure interaction FE analysis approach in understanding the mechanisms of SUI in females. Through a series of computer simulations, the effects of varying impact forces determined by jumping height and bladder volume were investigated. The dynamic computer simulation results revealed that jumping heights have a significant influence on the volume of urine leakage caused by the landing impact of jumping. Bladder volume did not have a significant influence on leakage when the jumping heights were smaller than 1 ft, which indicates that normal walking (corresponds to a jumping height smaller than 0.1 ft) is not the primary cause of urine leakage for healthy females. The computer simulation results also showed that the deformation difference between the anterior and posterior portion of the female pelvis causes opening of the urethra and resultant urine leakage. The present study demonstrates the feasibility of using a computer modeling approach to study female SUI during physical and daily activities.
INTRODUCTION Stress urinary incontinence (SUI) occurs because of problems with connective tissues, muscles, and nerves that help to hold or release urine. It currently affects over 13 million Americans with the majority being females. Although SUI is more common in post-menopausal and multiparous women,13 studies have also shown a high prevalence of SUI in young, physically fit female athletes.4,6,9,14,16,19,20,22 Regarding the association of exercise type with female athletic SUI rate, it is noted that exercises that involve chronic, repetitive motion and involve high impact landing from jumping and running cause high SUI rates.6,16,20,22 New data also suggests a correlation between severity of SUI symptoms and physical inactivity.4,18 The symptoms of SUI that cause women to avoid sports participation may be one etiologic factor for physical inactivity in women.4,10,14,15 However, the mechanism of SUI in young female athletes remains unclear. Urodynamic studies provide a method for objectively assessing how the bladder and urethral coordinated functions of storing and releasing urine are operating in order to gain a better understanding of the occurrence of SUI and to assist with choosing an effective treatment. The complete urodynamic study consists of cystometry with electromyography, urethral profilometry and free uroflowmetry using a direct measuring approach.1 These techniques, however, cannot provide the detailed dynamic information of force, stress, strain, and resulting organ displacements of the bladder and urethra which are critical in understanding, diagnosing, and treating SUI problems. A computer modeling approach, which can provide us the dynamic biomechanical responses of the bladder, urethra, rhabdosphincter, and all the other organs and tissues inside the pelvis as well as their neural control, has the capability of fixing this gap. A few studies have been attempted in this field,3,7,8,10,24,25 in which the finite element (FE) method
Keywords—Finite element analysis, Fluid–structure interaction analysis, Female athletes, Stress urinary incontinence, Urologic pelvic floor disorder, Physical activity. Address correspondence to Yingchun Zhang, Department of Urologic Surgery, University of Minnesota, 725 Mayo Memorial Building, 420 Delaware Street S.E., Minneapolis, MN 55455, USA. Electronic mail:
[email protected]
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Ó 2009 Biomedical Engineering Society
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was employed to build a pelvis model. These previous pelvis models either did not include sufficient anatomical parts of the pelvis which are closely related to the lower urinary tract function, or used mechanical properties of the tissues from either dated literature or animal experimental data. With a goal toward the development of a dynamic subject-specific mechanical characterization the interaction between anatomical structures during physical activities that elicit SUI, a computer aided design (CAD)-based FE model of female pelvis has been developed to understand female SUI induced by the landing impact of jumping. CAD-based modeling of a complex structure, such as the female pelvis, requires some simplifying assumptions regarding its geometry. This modeling approach, however, has an advantage of much easier modification of the geometry and consequently makes a feasibility and parameter study for an advanced subject-specific computer model. This study describes a computer modeling approach that has the capability of characterizing the interaction between anatomical structures during physical activities that elicit SUI.
MATERIALS AND METHODS Anatomy of the Female Pelvis The female pelvis is created by two innominate bones and the sacrum2,12,17 as shown in Fig. 1a. The inferior aperture, or pelvic outlet, is covered by the pelvic diaphragm; a set of thin broad muscles is attached to pelvic sidewall by vascular and connective tissue mesentery.5 The muscles of the pelvic diaphragm include the levator ani, a combined muscle sheet including the iliococcygeus, pubococcygeus, and puborectalis muscles, and the coccygeus muscle. Just inferior to the pelvic diaphragm the anterior half of the pelvic outlet is covered by the urogenital (UG) diaphragm. The UG diaphragm is composed of a deep transverse perineal muscle, spanning from one ischial tuberosity to the other, and the external urethral sphincter covered by the perineal membrane. The superficial transverse perineal muscle lies superior to the perineal membrane which is directly above the deep transverse perineal muscle, and separates the superficial and deep perineal compartments. Visceral structures supported by the UG and pelvic diaphragms include the uterus, the vagina, the bladder, and the urethra. The rectum lies behind the UG diaphragm and is supported primarily by the levator ani portion of the pelvic diaphragm. There are several sets of fascial ligaments that stabilize the pelvic viscera. The deepest and strongest of these are formed from the
FIGURE 1. Anatomical structure of the female pelvis and the corresponding CAD-based FE model with half of the model about sagittal plane except urine. (a) Anatomical structure of the female pelvis; (b) 3D FE model of the female pelvis which consists of the pelvic bone, uterus, vagina, rectum, pelvic diaphragm, uro-genital diaphragm, abdomen muscle, intestine, bladder, urethra, urine etc.
endopelvic fascia.23 These include the pubovesicle ligaments that support the bladder neck and urethra, and the pubocervical, transverse cervical (Cardinal), and ureterosacral ligaments that support the uterus. In addition, the peritoneal broad ligament supports the body of the uterus and the adnexa. The female pelvic viscera include the bladder, vagina, uterus, fallopian tubes, ovaries, and rectum. Each of these structures, with the exception of the ovaries, is composed primarily of smooth muscle. The pelvic and UG diaphragms support these structures and participate in their function by providing striated sphincter musculature. CAD-Based FE Model Building Procedure CAD-Based Geometry Model and Hexahedral Element Mesh Based on the understanding of the anatomical structure of the female pelvis, a three-dimensional (3D) FE model was built using the CAD technique as shown in Fig. 1b. The 3D FE model of female pelvis was built to include the pelvic bone, uterus, vagina, rectum, pelvic diaphragm, UG diaphragm, abdominal muscles, intestine, bladder, urethra, urine, etc., to model the actual anatomical structure of the female pelvis. For the ordinary static structural analyses, 3D FE modeling of structures with complex shapes can be done
Feasibility of Using a Computer Modeling Approach to Study SUI
without much simplification of the geometry using either a solid modeler or image based solid construction technique and tetrahedron mesh.3,7,10 Simulating the biomechanical responses of the human body during the landing impact of jumping requires dynamic, large deformation analysis with large mesh distortions. Tetrahedron elements without strong distortion resistance are known to be much less accurate than hexahedral elements in this case. In order to achieve the same accuracy of analysis results, the number of tetrahedron elements that will be required is 4 to 5 times more than the number of hexahedral elements. This will increase the model size and require more computing resource. In the present study, the female pelvis model was meshed with 8-noded hexahedral elements, as shown in Fig. 1b, to achieve the satisfied accuracy while keep the relative small model size (with the element number of 325,531 and node number of 82,918). The urethra was modeled with shell elements instead of solid elements to avoid low-quality elements. The urine inside the bladder was modeled using fluid elements in order to investigate urine leakage during jumping. Tissue Mechanical Properties Mechanical properties of the tissues involved in this study are listed in Table 1.7,26 Human tissues show visco-hyperelastic material characteristics,26 however, a quasi-linear material property was found in human urological soft tissues from our soft tissue tensile testing experiments when the stress level is below 70% of the maximal stress value. An example of this observation is shown in Fig. 2, which is the stress– strain curve obtained by performing the soft tissue testing procedure on a bladder wall tissue specimen from a fresh 18-year-old female cadaver. It was found in our preliminary FE analysis results that the peak stress values developed in the tissues during jumping were in this quasi-linear range of the stress strain profiles. Consequently linear material models were implemented in the present study to approximate the essential visco-hyperelastic material models. TABLE 1. Mechanical properties of the tissues involved in this study. Tissue Bladder Urethra Uterus Vagina Rectum Intestine Muscle Fascia Ligament
Modulus of elasticity (MPa)
Density (kg/m3)
0.05 0.3 0.05 0.005 0.1 0.1 2.4 1.2 1.2
1030 1030 1030 1030 1030 1030 1040 1010 1010
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FIGURE 2. A Stress–Green Strain curve obtained by performing soft tissue testing procedure on a bladder wall tissue specimen from a fresh 18-year-old female cadaver.
In order to refine the pelvis model, a method to characterize the visco-hyperelastic material properties of human soft tissues by performing soft tissue testing procedures on urological tissue specimens harvested from fresh cadavers within 24 h of the time of death has been undertaken in our lab. Three soft tissue testing procedures (tensile tests, creep tests, and stress relaxation tests) were performed on urological soft tissue specimens to develop this urological tissue properties database. The completion of the database is still in process and the computer model of the female pelvis will be continuously refined by using updated visco-hyperelastic material properties of urological tissues involved in the model. Contacts and Interaction Conditions Both contact pairs and tie constraints were set up in the present pelvis model to describe the interaction conditions along the boundaries between different organs. The tie constraints were set to boundaries on which two neighboring organ surfaces would not have any relative sliding and/or disconnection during jumping. For example, the boundaries between pelvic bones and pelvic muscles as well as pelvic bones and pelvic ligaments were under this tie constraint. The contact pairs were set to boundaries on which two neighboring organ surfaces would slide and/or move apart during jumping. For example, the boundaries between pelvic muscles and fat tissues, pelvic muscles and pelvic ligaments, pelvic ligaments and fat tissues, bladder and uterus, uterus and colon, etc., all were able to slide under such contact conditions. Load Modulus This model assumed that the pelvic bones supported the superincumbent body during jumping and the entire pelvis model had an initial velocity Vinitial. Then
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the velocity of the bones was assumed to drop to zero in a very short time period Timpact after the subject’s feet touch the ground. Choices for Vinitial and Timpact, which describe the landing impact effects on the female pelvis and the organs inside caused by jumping, are critical in forming the load modulus which is a necessary part of the computer model. An ambulatory device was specifically developed for determining the real initial velocity Vinitial and impact period Timpact for each subject. The device consists of three sensors; the first sensor is an accelerometer (CXL25LP3 accelerometer, Crossbow Technology, Inc., San Jose, CA) for measuring the time-history acceleration of pelvis in three directions in an orthogonal coordinate system, the second sensor is an inclinometer (SQ-SI2X-360DA inclinometer, SignalQuest, Inc., Lebanon, NH) for measuring the pitch and roll angles of pelvis, and the third sensor is a urinary leakage detector for quantitatively measuring subjects’ urine leakage during jumping. The measurements from the accelerometer and inclinometer directly contributed to calculating the initial velocity Vinitial and impact period Timpact, while the measurements from the urinary leakage detector were used to evaluate UI during jumping. In human subject experiments, the accelerometer and inclinometer were fixed over the lower back at the level of the posterior iliac crest or lumbar spine of subject as shown in Fig. 3. All the measurements were collected wirelessly by a PC during subject’s physical or daily activities. The initial velocity Vinitial was estimated from the temporal acceleration recordings through the integration algorithm and the impact period Timpact was estimated from the temporal acceleration recordings in the impact parameters database. Those subject-specific landing impact parameters were
used to form the load modulus of the subject-specific pelvis model. Dynamic Finite Element Analysis A commercial finite element (FE) analysis software package LS-DYNA11 which has the capability of fluid–structure interaction analysis was chosen for this dynamic study. The Eulerian type of elements were chosen as fluid elements to model the urine in which the mesh was fixed in space and only material would move around over the mesh to avoid large element distortions. Consequently, there was no mesh distortion and the motion of fluids, such as urine, were adequately modeled. The interaction between the structure and fluid, i.e. the bladder wall and the urine inside, were detected by overlapping the solid and fluid elements. Note that the fluid elements must cover the entire volume of space where the solid elements reach while they are under deformation. A fluid like media, such as urine, was modeled as the viscosity material with no yield strength, no shear stiffness, and an equation of state relates the fluid pressure to the neighboring structures. LS-DYNA provides a viscosity material model in which the equations of state were defined and erosion in tension and compression was allowed. Viscosity of 0.87 9 10 3 N s, wave speed of 4.58 m/s and density of 1020 kg/m3 were used for the physical properties of urine.
RESULTS The dynamic biomechanical responses of the entire female pelvis and the urinary leakage information caused by the landing impact of jumping were achieved
FIGURE 3. Placement of the ambulatory device including a tri-axial accelerometer, a bi-axial inclinometer and a urinary leakage detector. (a) Frontal view; (b) back view.
Feasibility of Using a Computer Modeling Approach to Study SUI
by performing dynamic FE analysis by means of LS-DYNA based on the computer models. Considering this is a feasibility study rather than a subject-specific study to simulate the real biomechanical response of the female pelvis during jumping, it was assumed in the computer simulations that the pelvic bones supported the superincumbent body and the pelvic bones stopped immediately and completely as soon as the feet touched the ground. The bladder was assumed to be fully filled with urine, and the effects of jumping heights and bladder volumes on the amount of urinary leakage were investigated. The results of three jumping heights (1, 2, and 3 ft) were compared to that of a normal daily walking height (0.1 ft) and the bladder volumes were chosen to be 50, 100 and 200 mL. The 1st computer simulation of a female subject jumping from a 3-feet high table with 100 mL urine inside her bladder was conducted and it took around 900 s of CPU time for a single run on an IBM supercomputer with 312 Power4 processors in the Minnesota Supercomputing Institute (MSI) at the University of Minnesota. Dynamic computer simulation results showed that it took approximately 7 ms for the lower portion of the pelvis to reach its lowest vertical position and come back to its normal position after the pelvic bones completely stopped. Figure 4 shows the results from this computer simulation. Figure 4a shows the initial pelvis geometry model without any deformation at 0.0 ms. Figure 4b shows the model deformation caused by the jumping impact at 2.7 ms after the pelvic bones completely stopped. Here we can clearly see the model geometry deformation caused the opening of the urethra and the urine was traveling into the urethra through the urethro-vesical junction. Figure 4c shows the model deformation 7 ms after the pelvic bones completely stopped. We found that the lower portion of the pelvis almost reached its lowest point at this time instant and the model geometry deformation caused by the jumping impact is much larger than that at 2.7 ms. The interesting phenomenon here was that the urethra already closed at this time instant although the bladder deformation is very large. Figure 5 shows the dynamic status of urine flow inside of the bladder and urethra observed from the computer simulation results. Figure 5a shows urine flow at 0.0 ms when the pelvic bones just completely stopped. The bladder deformation has not yet started and there was no urethra opening and urine leakage. Figure 5b shows the urine flow at 4.3 ms after the pelvic bones completely stopped, where the urethra opened widely in the region near the bladder neck, and a remarkable amount of urine flowed into the urethra from the bladder. Figure 5c shows that the urethra began to close in the region near the bladder neck
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FIGURE 4. Deformation of the bladder and opening of the urethra for a case of simulating a female subject jumping from a 3-feet high table with 100 mL urine inside the bladder without urine in the bladder. The model deformation caused urethra opening at (a) 0.0 ms, (b) 2.7 ms, and (c) 7 ms, after the pelvic bones completely stopped.
5.6 ms after the pelvic bones completely stopped, but the volume of urine was already pushed into the middle part of the urethra. Figure 5d shows that at 7 ms after the pelvic bones completely stopped, the urethra has closed, but urine has already been pushed out of the body and generated the urine leakage although there was still a very small amount of residual urine in the middle portion of the urethra. The influence of jumping heights on the amount of urine leakage at different levels of bladder volumes of 50, 100, and 200 mL was investigated through a series of computer simulations based on the present CADbased female pelvis computer model. The computer simulation results in Fig. 6 show that the amount of
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FIGURE 5. Urine flow in the case simulating a female subject jumping from a 3-feet high table with 100 mL urine inside the bladder. The urethra opening and resulting urine flow at (a) 0.0 ms, (b) 4.3 ms, (c) 5.6 ms, and (d) 7 ms, after the pelvic bones completely stopped.
Bladder Volume : 50ml Bladder Volume : 200ml
Bladder Volume : 100ml
Urine Leakage (ml)
0.1 0.08 0.06 0.04 0.02 0 0
0.5
1
1.5
2
2.5
3
3.5
Jumping Height (ft)
FIGURE 6. The influence of jumping heights on urine leakage at various bladder volumes.
urine leakage increases significantly as the jumping height increases when the bladder volume is greater than 100 mL. In the case with the bladder volume of
100 mL, the amount of urine leakage was increased over 30 times, from 0.002 to 0.061 mL as the jumping height increased from 1 to 3 ft. In the case with the bladder volume of 200 mL, the amount of urine leakage was increased by 50 times, from 0.002 mL to as high as 0.1 mL as the jumping height increased from 1 to 3 ft. Even for the case with only 50 mL urine in the bladder, an increase of urinary leakage was also observed when the jumping height increased, the amount of urine leakage, which increased from 0.001 to 0.006 mL as the jumping height increased from 1 to 3 ft, is increased by six times. Similarly, the influence of the bladder volume on the amount of urine leakage at jumping heights of 0.1, 1.0, 2.0, and 3.0 ft was investigated through a series of computer simulations based on the CAD-based female pelvis computer model (see Fig. 7). Notice that the bladder volume did not have noticeable influence on the amount of urine leakage when the jumping height was smaller than 1 ft. In the lowest jumping height
Feasibility of Using a Computer Modeling Approach to Study SUI Jump Height : 0.1feet Jump Height : 2 feet
Jump Height : 1 foot Jump Height : 3 feet
Urine Leakage (ml)
0.1 0.08 0.06 0.04 0.02 0 0
50
100
150
200
250
Urine Amount inside the Bladder (ml)
FIGURE 7. The influence of bladder volume on urine leakage at different levels of jumping heights.
level of 0.1 ft which corresponds to the jumping height in normal walking, there was no urine leakage at all for all three levels of bladder volumes. Even in the case with 1 ft jumping height, the urine leakage only increased from 0.001 to 0.002 mL as the bladder volume increased from 50 mL to as large as 200 mL. Those results indicate that the jumping height did not have a significant influence on the amount of urine leakage for the jumping height cases lower than 1 ft. However, for the cases with the jumping heights over 2 ft, the bladder volume shows significant influence on the amount of urine leakage. In the case with a jumping height of 2 ft, the amount of urine leakage increased from 0.0042 to 0.0342 mL which is more than eight times larger as the bladder volume increased from 50 to 200 mL. In the case with a jumping height of 3 ft, the amount of urine leakage increased from 0.006 to as large as 0.1 mL or 16 times larger, as the bladder volume increased from 50 to 200 mL.
DISCUSSION Dynamic computer simulation of female SUI induced by the landing impact of jumping was successfully conducted in the present study based on the CAD-based female pelvis model. By using fluid– structure interaction analysis technique, the dynamic deformation of the bladder, urethra and other organs inside the female pelvis as well as the induced urine leakage caused by the landing impact of jumping were clearly observed. To the best of our knowledge, this is the first time that a fluid–structure interaction FE analysis study in understanding the mechanisms of SUI in females has been reported. The results presented here could not possibly be achieved through the traditional urodynamic studies. One technical advantage of the present study was that the urine was
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modeled using the Eulerian type of elements in the pelvis model with a viscosity material with no yield strength, no shear stiffness, and an equation of state which relates the fluid pressure to the surrounding structures, so that the fluid–structure interaction analysis was successfully conducted to investigate urine leakage. Figure 4 showed the model deformation caused a wide opening of the urethra at 2.7 ms after the pelvic bones completely stopped, but the urethra closed at 7 ms when the much larger model deformation was generated. Although the time values are non-physiologic in amplitude, this geometrical simulation study suggests that the opening of urethra and the resulting urine leakage might be caused by the inconsistent deformation of regions near the bladder neck in the female pelvis, not caused by the absolute deformation amounts. Reviewing the dynamic information of the biomechanical response of the pelvis during jumping, we noticed that the posterior portion of the pelvis is pulled up by the sacrum and ilium and supported by the pelvic diaphragm, while the anterior portion is supported by the pubis and ischium with the additional support from the UG diaphragm thereby limiting the movement of the bladder. This causes a noticeable difference between the amount of deformation of the back and front portions of the pelvic floor. The maximum displacement of the posterior pelvis is much larger than that of the anterior pelvis, which causes opening and slight funneling of the urethra as shown in Fig. 5b. As the movement continues in time, the posterior portion of the pelvis starts to bounce up and closes the urethra, shown in Fig. 5c. The maximum opening diameter of the urethra at the urethro-vesical junction was 4.76 mm at 4.3 ms. We can conclude that the ilium, ischium and UG diaphragm, as well as the sacrum and pubis play a very important role in opening or closing the urethra, which is directly related to the occurrence of urine leakage. This information strongly influenced us to include these organs in our future subject-specific pelvis model as the necessary parts, although, some of them are very difficult to model because of the small size and irregularity of the geometry. The elastic material properties were applied in the present CAD-based pelvis model instead of viscohyperelastic material properties because the viscohyperelastic property data of human tissues were not available. We are performing soft tissue testing experiments on urological tissue specimens from fresh cadavers to develop our urological tissue property database. We plan to model the pelvic floor tissues with visco-hyperelastic material property data in future pelvis models after this database is completed.
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FIGURE 8. Subject-specific FE model of the female pelvis from a 20-year-old subject’s specific high resolution MR images. The model consists of 35 anatomical parts in total including 10 pelvic muscles, 10 pelvic ligaments, 6 pelvic bones, skin, fat tissues, bladder, urethra, uterus, vagina and colon, rectum, anus, etc.
As a feasibility study, some simplifying assumptions were made to use a CAD-based pelvis modeling approach to model a complex structure such as the female pelvis. For example, the urethra was modeled as thin layer with shell elements although the urethral wall actually consists of four layers from lumen to outer wall including the vascular plexus, the longitudinal and circular smooth muscle and circumferential striated muscle.21 This modeling approach, however, has an advantage of much easier modification of the geometry and is consequently suitable for a feasibility and parameter study for future advanced subject-specific pelvis modeling studies. In order to overcome this limitation to develop a subject-specific pelvis model, female athletes with and without SUI were recruited to participate in the study under the University of Minnesota Institutional Review Board (IRB) guidelines. The subject-specific geometry models of their pelvis and the corresponding FE meshes were reconstructed from subject-specific high resolution contrast MR images. A generated realistic geometry FE model of a 20-year-old female subject’s pelvis is shown as an example in Fig. 8. The model consists of 35 anatomical parts including 10 pelvic muscles, 10 pelvic ligaments, 6 pelvic bones, skin, fat tissues, bladder, urethra, uterus, vagina and colon, rectum, anus, etc. The ambulatory device was used on the participants to characterize their specific landing impact parameters including the acceleration and inclination of their pelvis during jumping. Thus the initial velocity Vinitial and impact period Timpact were calculated from the time-history measurements to form the subject-specific load modulus of their specific pelvis models. The visco-hyperelastic material properties of urological tissues involved in the pelvis model will be used to refine the model after the database is
completed. The future plan is to conduct dynamic FE analysis based on the subject-specific pelvis model, so that dynamic mechanical behavior of the integrated lower urinary tract system can be correlated with the dynamic biomechanical response of pelvis caused by physical or daily activities, further advancing our understanding of the mechanisms of SUI in females. CONCLUSIONS The present study demonstrated the feasibility of using a computer modeling approach to study female SUI by correlating dynamic mechanical behavior of the integrated lower urinary tract system with the dynamic biomechanical response of pelvis, and suggested the computer modeling approach has the capability to advance our understanding of the mechanisms of SUI.
ACKNOWLEDGMENTS This work was supported by the National Science Foundation Grant #0646818, MIMTeC (an NSF I/UCRC), the Minnesota Medical Foundation, the University of Minnesota Supercomputing Institute, and the Medical Devices Center of the Institute for Engineering in Medicine at the University of Minnesota.
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