accessible incontinence control device -...
TRANSCRIPT
Accessible Incontinence Control Device
Biomedical Engineering Senior Design Group 17Zach HawkinsKristen HeckAmy Klemm
Amanda Streff
AdvisorsProfessor Paul King
Dr. Doug MilamDr. John Enderle
Abstract
Urinary incontinence, which is the inability to control urine flow, directly affects
twenty-five million adults in the United States. Incontinence is caused by a number of
conditions including loss of muscle tone, neurological disorders, or obstruction of the
urinary pathway. Inspired by the current gold standard, the AMS 800TM, the design
presented here is an artificial urinary sphincter. However, unlike the AMS 800TM, the
sphincter is controlled remotely using a radio signal, which rotates a servo. The rotation
of the servo causes a syringe to increase the pressure in tubing leading to a cuff, which
is secured around the patient’s urethra. The increased pressure results in the pinching-
off of the urethra, therefore, preventing urine flow. The device is a proof-of-concept that
requires a few modifications to ensure biocompatibility before being implanted. A plan
is laid out to further develop the device to include a bladder status indicator. The
highlight of the design is that it is easily operated by either the patient or a caregiver
allowing for better control and management of urine flow.
2
Introduction
Urinary incontinence, which is the inability to control urine flow, negatively affects
both men and women and occurs more frequently with age. Incontinence is typically
due to weakened pelvic floor or bladder muscles, neurological disease, or an
obstruction in the urinary tract.1 Regardless of the cause, the patient's quality of life is
greatly reduced. Sufferers will experience an increased chance for infection, skin
irritation, and embarrassment.
Urination, also known as micturition or voiding, is the process of excreting urine
from the urinary bladder through the urethra to the outside of the body. The process is
primarily under voluntary control and involves the
urinary bladder, urethra and two sphincters. The
bladder walls contain smooth muscle tissue called
the detrusor muscles, which are innervated by the
sympathetic and parasympathetic nerves.2 Located
at the base of the bladder, the internal sphincter
(Figure 1) consists of smooth muscle and is under
involuntary control. The external urethral sphincter
is located at the distal inferior end of the bladder, is composed of skeletal muscle, and is
under voluntary control. To urinate, the detrusor muscles contract, the sphincters relax,
and the abdominal muscles are voluntary contracted.
There are four main types of incontinence; urge incontinence, stress
incontinence, overflow incontinence and functional incontinence. Urge incontinence is
the involuntary loss of urine associated with an abrupt or strong desire to void. The
3
Figure 1: The bladder has two sphincters to prevent urine flow: an internal involuntary sphincter and an external voluntary sphincter.Gerard J. Tortora (1999) Principles of Human Anatomy (eight edition) John Willy & Sons Inc. , New York (Click image for larger version)
involuntary loss of urine during coughing, sneezing, and laughing is known as stress
incontinence. The other two types are overflow incontinence, the involuntary loss of
urine associated with over distension of the bladder, and functional incontinence, where
the individual has no recognition of need to void or the inability to make it to the toilet in
time. The main focus for this project is to address patients with urge and stress
incontinence.
There are a variety of conditions that lead to urinary incontinence. Neurological
disorders such as Parkinson’s disease, Multiple Sclerosis, and Alzheimer’s along with
strokes, brain tumors and spinal injuries can all result in incontinence problems.3
Hormone imbalances during menopause can also cause urinary issues in females. In
males, prostate cancer can result in incontinence symptoms. Finally, the loss of muscle
tone, either from old age or child birth, is another cause of urinary incontinence.
Urinary incontinence affects one in ten people over the age of sixty-five, but is
not limited to the elderly. The National Association For Continence (NAFC) estimates
that about twenty-five million adults in the United States experience urinary
incontinence. Both men and women are subject to incontinence, but women are twice
as likely to have issues.4 Incontinence can lead to medical problems such as infection or
skin irritation from the increased dampness. In addition, the embarrassment that
patients may experience can negatively affect their quality of life and prevent them from
leading a normal life. For example, some patients suffer from loss of self-esteem,
restriction of social and sexual activities, depression, and, in more severe cases,
dependence on caregivers. A device to manage urinary incontinence will allow patients
to function independently without the worry of embarrassment.
4
The goal of our project is to design a device that is easily operated by either the
patient or a caregiver that allows for better control and management of urine flow. The
design is intended to be capable of being controlled by patients with disabilities and it
will allow for the desired and controlled emptying of the bladder while indicating to the
patient or caregiver the status of the bladder.
Considering the size of the population with incontinence and that our design can
be used for most cases of incontinence, the market potential of a male and female
accessible incontinence control device is high. Our implantable device design will assist
incontinence patients in urge retraining and discretionary urination, which are the two
most common concerns. Doctors may recommend using this device for all their
patients, for this product has a large competitive advantage over most other clinical
options, which often involve an indwelling catheter. The fact that this device does not
require a catheter is an advantage because it minimizes infections and does not require
frequent check-ups to insert a clean catheter. Therefore, we believe patients will prefer
this type of implant. In addition, because the device is patient controlled, discrete and
does not require a catheter, it will allow them to control their symptoms with more
comfort and privacy.
Methodology
The Design Process
The current gold standard for urinary incontinence control is the AMS 800TM
Urinary Control System. Completely implantable and made of silicone elastomer, the
AMS 800TM is an artificial urinary sphincter controlled by a fluid filled pressure reservoir.
5
Figure 2: The AMS 800TM is made of silicone elastomer and is implanted with the cuff around the urethra.http://www.st-josef-moers.de/fachabteilungen/ uro/53252197a91257606.html
The device is manually controlled
by the patient. In men, the pump
is located in the scrotum, and, in
females, the pump is located in the
labia. To void, the patient must
squeeze the pump three to four
times to release the pressure in the cuff that is around the urethra. After urination, the
cuff automatically refills with the saline stored in the reservoir.
An alternative option for incontinence control is the male sling
InVance/AdVance. However, this option is only good for moderate incontinence. If a
patient needs more than two to three pads a day they then require a device such as the
AMS 800TM. 5
Despite the success of the AMS 800TM, there are still areas where it could be
improved. For example, the device is problematic for people with disabilities and
dexterity issues. Also, since many surgeries require catheterization, patients with the
device that go into surgery can have complications. The urethra may erode due to
excessive constriction if the device is not disabled when the patient is catheterized.
In order to make the device easier to use for all patients and to avoid urethral
erosion, our goal is to make a device that is electronically controlled and easily turned
on and off. Our initial design was to complement the AMS 800TM by placing an
1 http://www.mayoclinic.com/health/urinary-incontinence/DS00404/DSECTION=3
3 http://www.mayoclinic.org/urinary-incontinence/types.html
4 http://www.fda.gov/fdac/features/2005/505_incontinence.html
6
Figure 3: Design Idea II - The orange circle represents the urethra and the gray areas are all electromagnets.
electronically controlled cuff around the pump. Instead of having the patient manually
pump the device when they needed to void, they would externally activate the pumping
of the device. The wireless signal from pressing a button outside the body would
communicate with an RC receiver connected to a mechanism strapped around the
pump. The RC receiver would send an electrical pulse to electromagnets that would
compress the pump. Therefore, instead of the patient manually pumping the device,
they would simply press the button four times to electronically release the fluid from the
pressure cuff. The distance the cuff needed to be depressed was measured and the
force necessary to accomplish this depression was calculated. The force was found to
be too great to control the pump with electromagnets considering the restricted space.
Based on this realization, we decided to use electromagnets in a different way.
We changed our project direction from building upon
the AMS 800TM to designing our own unique device, shown
in Figure 3. Our initial cuff design used the same concept
of electromagnets, but for the purpose of collapsing the
urethra. A similar silicone elastomer cuff would be used to
encase the electromagnets. A latching system with springs
would be used to keep the urethra compressed, so a
constant power source would not be needed. All the
supporting electronics would be housed in a silicone elastomer bubble with the wires
going to the device also encased in silicone. Again, an external button would trigger a
current pulse in the electronics bubble. The pulse would travel through the wires and to
the electromagnet. The pulse would cause the electromagnet to attract the opposing
7
magnet. After the attraction, the notches would latch the magnets in place and the
power would no longer be required. Once the patient needs to void, they again would
press a button to administer a current pulse. This current pulse would attract the
magnets that release the spring loaded latches.
While working with our electromagnets, we experimented with a servo and push
rod as the collapsing device. In the most primitive form, a dial connected to the servo
was turned to rotate the servo, which moved the push rod. A small, solid cylinder was
attached to the end of the push rod. A similar sized piece of plastic, in the shape of a
half cylinder was used in the cuff to surround the urethra. When the servo was
activated, the push rod was propelled toward the plastic half cylinder and the urethra
was collapsed.
The push rod design appeared to have more potential than the electromagnetic
cuff, so our work focused on improving this design. Two initial problems were identified:
first, the servo was not strong enough, and, second, a straight metal push rod was not
realistic for a biological application. A more powerful servo was ordered, and new push
rod ideas were brainstormed. It was decided that the new design needed to be
powerful enough to collapse the urethra, yet flexible enough to enable easier
implantation of the device. The thrusting mechanism needed to travel from the
electronics housing to the urethral cuff. Looking back towards the AMS 800TM, it was
decided that using fluid as the driving source would work best. In addition, the device,
including all the electronics, needed to be small and implantable. According to Dr. Doug
Milam, a urological surgeon at Vanderbilt University Medical Center, the current location
where AMS 800TM reservoir is placed has room for something about the size of a tennis
8
Figure 4: The RC receiver acquires the radio signal and sends an electrical signal to the servo, which rotates and pushes the fluid through the tubing to force the plunger in the cuff to pinch the urethra closed.
ball. Therefore, the entire device’s supporting electronics needed to fit inside a tennis
ball. Also, there was still the desire to control the device remotely, so a radio signal was
used for communication between the implanted device and the external control.
Results
Prototype Function
First, the device would be surgically implanted. The cuff would be secured
around the urethra at the neck of the bladder. The cuff is rigid and has a hinge on one
side. The cuff can be opened far enough to
allow the urethra to pass through. Similar to
how the current gold standard cuff operates, a
silicone tab on the outside of the cuff has a
small hole. The tab is pulled around the cuff
and secured in place by pushing a knob
through the button hole in the cuff. The
electronics housing is implanted in the
peritoneal cavity of the patient.
The prototype operates by simply moving the throttle stick of a radio controller up
causing the controller to send out a radio signal, as shown in Figure 4. Strong enough
to penetrate multiple layers of tissue, the signal is picked up by the RC receiver, which
generates an electrical signal to the servo. The servo rotates clockwise about 100
degrees. Attached to the servo is a push rod, which is also attached to a plunger inside
a stationary syringe tip. The moving servo and push rod compress the plunger forward
9
Figure 5: The prototype’s electronics were housed in a tennis ball to demonstrate the amount of space used.
to force fluid out of the syringe tip and into the
tubing. The pressure increases inside the tubing
and forces the fluid into the other syringe tip. As
the fluid fills the syringe tip, the plunger attached to
the cuff moves away from the tubing and deeper
into the cuff. The urethra collapses between the
pushing plunger and reinforced cuff, preventing
urine flow.
When voiding is desired, the servo must be
rotated counterclockwise. To move the servo in
the opposite direction, the throttle stick on the radio
controller is pulled down initiating the same sequence of events. A radio signal is
transmitted from the controller to the RC receiver. An electrical signal is sent to the
servo, which causes it to rotate counterclockwise. The rod attached to the servo pulls
the plunger back creating a drop in pressure inside the syringe tip. The pressure drop
causes fluid to fill the syringe tip. The pressure change pulls the fluid out of the syringe
tip attached to the cuff. Therefore, the plunger releases the urethra and urine is able to
flow freely.
Cost
The prototype was fairly inexpensive to make costing less than $100.00. The
primary costs were the servo, RC receiver, and batteries. The servo and RC receiver
each cost approximately $35.00. Because the batteries were Lithium ion rechargeable
10
batteries, both cost about $20.00 each. The tubing, wiring, and hardware that were
used for the construction of the prototype were donated samples, so there was no cost
incurred. The syringes all cost under a dollar each. The tennis ball used to show the
approximate size of the electronics was donated. Tools used during construction were
provided by the Vanderbilt University Biomedical Engineering department at no cost.
Market Analysis
Last year, 8,200 AMS 800TM artificial urinary sphincters were sold in the United
States, each costing roughly $8500 for the device alone.5 The production cost for the
AMS 800TM was estimated at $4000. It is estimated that the costs associated with the
final design of the device presented in this paper will be approximately double those of
the AMS 800. The AMS 800 does not have a cost of maintenance because re-
implantation with revision is the only form of correction for failure. Likewise, the device
design described here will also have no maintenance costs. Of the devices implanted,
25% are revised in five years, which is fairly high compared to 7-9% revisions for
Implantable Penile Prosthesis (IPP). A portion of the entire cost, the device and
surgical implantation, is covered by insurance. Blue Cross Blue Shield, the largest
insurance provider, pays Vanderbilt University Medical Center the cost of the device,
10% of the cost of the device, plus typical charges. The total amount paid is about
$19,000-$20,000. Since complete replacement is the only option for correcting a
malfunction, this cost is the same for every revision.5
Since our device is more advanced, the cost would be much greater. Based on
the complex electronics, batteries and wireless control, we project our device to cost
11
$14,000. We expect the production cost to be around $8000. We expect insurance to
use the same plan for coverage for our device since we expect a long implantation and
battery life, and few possibilities for malfunction.
Safety Issues
As with any implantable device, there are many safety and biocompatibility
issues that need to be considered. First, a silicone coating on the implanted device
helps ensure biocompatibility. In addition, the tubing should be filled saline solution and
sealed properly to prevent fluid exchange between the device and the body.
Safety issues occur within other facets of the device as well. The cuff must be
tight enough to guarantee no unnecessary leaks, but not so tight as to cause urethral
erosion. Similarly, no excessive pressure should occur in the system.
The electronics also pose a few concerns. Safety issues such as electrical
hazards, for example shock, should be considered. The batteries can also malfunction
and circuit errors can occur. With the proper trouble shooting and clinical trials, the
main safety issues can be evaluated and corrected. In order to ensure that the receiver
hears the correct radio signal, both the receiver and radio are set to a specific
frequency. The crystal that is selected tunes the frequency. There are other receivers
that have a code that will sync with a radio. There are also specific channels that are
reserved along with radio bands specifically for medical devices.
FDA Approval
12
Once our device is up to standards for an implantable incontinence control
device it would be considered a Class III device. The most regulated devices are in
Class III. The amendments define a Class III device as one that supports or sustains
human life or is of substantial importance in preventing impairment of human health or
presents a potential, unreasonable risk of illness or injury.6 Therefore, a Pre-market
Approval (PMA) application would be necessary to gain FDA approval. If the PMA is
approved, it essentially gives the company desiring to market the device, a license to do
so. The AMS 800 received their original PMA approval on June 14, 2001. They applied
for another PMA to make improvements on their device on October 13, 2006. Since the
original PMA was approved, up until April 1, 2008, ten reports have been posted on the
MAUDE database. MAUDE data represents reports of adverse events involving
medical devices.7 Examples of some of the complaints include necessary device
removal due to urethra erosion, need for re-implantation because of a leaky implant,
device malfunction, improper fitting of cuff due to urethral atrophy and tubing erosion.
Four of the ten complaints came after the device revision. Our device aims to correct
for such malfunctions and safety concerns.
Discussion
Final Design Ideas
Clearly, the prototype cannot be implanted as is. However, it is well on its way.
First, the electronics housing, currently a tennis ball, would need to be replaced with a
6 http://www.fda.gov/cdrh/pmapage.html
7 http://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfMAUDE/search.CFM
13
biocompatible silicone casing that is approximately the same size and seals off the
electronics from the body. Furthermore, the cuff itself will need to be miniaturized a bit
further and coated with a biocompatible silicone. Of course, the patient is not expected
to carry around a remote control that is normally used for model airplanes, so the
technology in the remote control will need to be transferred to a more manageable
controller. Ideally, a wristwatch-like control will be utilized to send the radio signal to the
implanted device. The wristwatch would also have a screen alerting the patient of
bladder capacity, as well as whether or not the device is activated.
Two possible concepts were generated to measure bladder capacity feedback
system. One idea was to suture tiny transmitters on the exterior of the bladder. The
transmitters would be placed in such a way that triangulation could be used to
determine how much the bladder has expanded and thus how full the bladder is. The
other idea incorporates an existing technology, but modified. Portable ultrasound
devices are available to measure bladder capacity. If this device is modified to be worn
continuously under the patients clothing the bladder status would always be available to
the patient. Modifications required include developing a strap to hold the device in
place and flattening the device to make it less noticeable while being worn.
Of all the people with incontinence problems, 85% have intact normal bladder
sensation, compliance and contractility. Less than 15% have functional incontinence.
Once the bladder status indicator is integrated into the current design, the device will be
suitable for all types of incontinence.5 For example, patients with functional
incontinence, who do not recognize the need to void, will be notified when the bladder
14
reaches capacity. Therefore, not only will the device be useful for patients suffering
from stress and urge incontinence, but also form functional incontinence.
Testing
Upon completion of our device, testing will ensue. The first step will be to use an
animal model. Male dogs are the most suitable model for incontinence device testing.
First a S/P sphincterotomy5 will be necessary to make an incision of the sphincter
muscles so they are no longer functional. Our device can then be implanted and tested
for proper functioning. If positive results are found after a six month study, human
testing can occur. A one year human study is then necessary to demonstrate safety
and efficacy of the device. As demonstrated by the AMS 800, most failures occur within
the first year of implantation. As
depicted in Figure 6, the failure curve
follows the trend of a bathtub curve.
Multiple failures are not common again
until ten years after the device has been
implanted. Therefore, a one year
human study should be sufficient to
determine if the device can properly and safely function in humans.
Hypothetical Clients
Figure 6 The failure curve for the AMS 800 was used to determine the time length necessary for a suitable human study with a new device.
15
The greatest feature of this design is its ease of use. Once the device is
implanted and calibrated, the patient only needs to push a button to activate and
deactivate the device. The button could be adapted to the patient, too. For example,
an individual with more severe dexterity issues, such as Jerry who suffers from
Parkinson’s disease, could simply use a larger button. On the other hand, patients like
Jamie, a serious wheelchair basketball athlete, may prefer a more discrete system. In
addition, the fact that the device is clearly activated or deactivated is beneficial to both
patients and doctors. Patients will not have to question the status of the device.
Doctors and nurses can be sure that the device is deactivated if catheterization is
required for any reason, such as a surgical procedure. Therefore, the urethral erosion
that occurs when the AMS 800TM is not properly deactivated during catheterization can
be eliminated.
Conclusions
We succeeded in accomplishing the design goals that were set for us by the
RECR competition. We improved on the current gold standard device, the AMS 800,
by creating a push button to operate our device. With the external, wireless control, the
device is easier for patients with disabilities to operate. The device successfully
empties and prevents urine flow from the bladder when the patient desires. After a few
modifications, based on the life of the batteries available, the device has the potential to
be implanted within a patient, and can remain there for at least thirty days.
Future Directions and Recommendations
16
In the future, our device needs to be further miniaturized. It must also be brought to
standards for implantable devices by making it biocompatible and reducing safety
concerns. The external control must also be integrated with an interface that will display
the status of the bladder volume. After success is seen with the urinary system,
treatment of fecal incontinence with this device may be possible.
Appendix
Design Purchases
Hobby lobby: servos, receiver, servo adjuster, crystal, batteryServos: HS-55 Sub Micro Servo and HS-85 "Mighty Micro" Plus Metal Gear, Ball BearingReceiver: Hitec Micro 05S 5 Channel Receiver with Auto-ShiftCrystal: Hitec Crystal for Micro 05
P.E.P. Specializing in Plastic Engineered Products: silicone medical tubing
References
2 de Groat, William C., “Anatomy of the Central Neural Pathways Controlling the Lower Urinary Tract” Functional Urology towards the Next Millennium. Proceedings of the 4th International Congress of the Dutch Urological Association (DUA-IV). November 5-7, 1997, Maastricht, The Netherlands
5 Dr. Doug Milam, Vanderbilt University Medical Center Urology Department
17