In-Vivo Device for Measuring and Adjusting Lap-Band Pressure Mark Fritz1, John Huidekoper1, Andrew Koivuniemi1, David Mayhew1, Chris Schroeder1

Robert J. Roselli1, Thomas P. Rauth2

1Department of Biomedical Engineering, 2Center for Surgical Weight LossVanderbilt University, Nashville, TN, USA

INTRODUCTION DEVICE FUNCTIONALITY

MARKET OVERVIEW

ACKNOWLEDGEMENTS

AUTOCAD PROTOTYPE

PROTOTYPE DESIGN

Eliminates need for transcutaneous-portProvides personalized pressure regimenEliminates pressure fluctuationsAllows wireless communication with care providerRecords pressure reading for signal processing and evidence based medical treatment

The potential market for this device is very high.  There are about 9 million extremely obese Americans in the country, which correlates to about 1 in 50 persons. 'Extremely obese' is defined as a person who has a Body Mass Index (BMI) of over 40. The index is calculated using a ratio between a person's height and weight. Trends suggest that the BMI will increase in the future since the number has quadrupled since 1980. Also of these 9 million Americans that can be considered for corrective weight loss surgery, only about 1.5% actually have the surgery. This population of extremely obese people is the target market for our product. Since the target population continues to grow, it stands to reason that the market will continue to be robust. By targeting a market of Americans who want to lose weight and live a healthy lifestyle, and by focusing our positioning strategy to offer greater returns, we should be able to have great success in the market.

We will have multiple competitive advantages over other technologies. First since we are using a Lap-Band, we will have all of the advantages that it has over gastric bypass, such as a decreased rate of fatalities due to surgery. Also, our internal control system will not require a wider incision than the current device, but will work more effectively. The internal pump will not only be less painful for the patient by eliminating external fillings by needle but also will be more effective than current available products. We can hold a constant pressure in the band—this allows quicker and steadier weight loss. Also by eliminating the port needed to fill the device, we are eliminating a main source of device failure which will help our competitive advantage. We will also be able to decrease the number of patient visits to the doctor, thus saving the patient time and money. This is the main consumer appeal of the device. The fact that the automated pump will allow weight loss to start immediately instead of six weeks post-op will also increase the consumer desire for our product. If the decline of doctor visits reduces the total insurance cost, the likelihood of Medicare coverage for the device is increased. If this were to happen, our device could greatly tap into the market because more people would be willing to undergo the procedure. Since our product will be much more effective than the current technology, we will use the fact that you will have all the advantages of gastric bypass without the health concerns. This will allow us to move into a new niche market of people that want to get healthy but are afraid of the dangers of surgery.

The people who are currently using the Lap-Band for weight loss have tried many other weight loss methods, all of which have been demonstrably ineffective for these patients. This device allows them to lose enough weight to have a healthier body mass index and live a longer, more fulfilling life. The laparoscopic band is also a much less risky surgical procedure, and is removable after performing its function, unlike gastric bypass surgery. This will permit more people to be helped by the device. The current surgical approach also requires periodic refilling of the lap-band through an external port and catheter. Our device will eliminate this refilling, allowing the doctors who perform the procedure to attend to other patients.

PROTOTYPE PERFORMANCE

With the rise in obesity and the morbidity and costs of obesity-related medical conditions, long-term weight reduction has become an important goal for the 25% of the U.S. population classified as obese. Since many of the traditional weight loss methods such as diet and exercise fail to deliver long-term weight loss, surgical management for the morbidly obese has been shown to be the most effective means of producing long-term weight loss. Current options for surgical management of morbid obesity include open gastric bypass, laparoscopic gastric bypass and laparoscopic adjustable gastric banding (Lap-Band System, Inamed, Santa Barbara, CA). Since the FDA approved the use of the device in 2001, the Lap-Band has ranked second in the US among all bariatric surgeries behind gastric bypass. It is the most commonly preferred method of surgery for morbid obesity in Europe, South America, and Australia. Up to date, surgeons have placed more than 300,000 Lap-Bands in patients world-wide [1]. Since the Lap-Band procedure is completely reversible and individually adjustable to patient needs, its popularity has increased in recent years. The Lap-Band works by being laparoscopically implanted and having a band snapped around the fundus of the stomach. The band contains an inflatable diaphragm which can be filled with up to 4 mL of saline. Inflating the band with saline applies pressure to the stomach and functionally decreases the volume of the stomach and obstructs the passage of food. The volume of saline in the band can be adjusted as the diaphragm of the band is connected by tubing to an implantable infusion-port which sits within the soft tissue of the abdominal wall. The subcutaneous port can be accessed via hypodermic needle and can thus alter the volume of saline to fit a physician-supervised caloric restriction regimen. The pressure and volume in the band are checked at clinical visits every four to eight weeks. Although the volume of saline remains constant between visits, the pressure in the band decreases with time, requiring the physician to inject more saline to maintain weight loss. This loss of pressure over time complicates the use of the Lap-Band as significant weight loss only occurs shortly after the clinical adjustment and then decreases with the decreasing pressure in the band until the next clinical visit. There are further complications with the infusion-port as it can be difficult to locate and puncturing can result in soft tissue infection, infusion-port leakage and damage to the connection tubing. Although not very common, these complications can carry significant risks of morbidity.

[1] – The International Laparoscopic Obesity Surgery Team. “LAP-BAND Statistics.” Laparoscopic Gastric Banding. 2005. April 4, 2007. < http://www.obesitylapbandsurgery.com/statmain.html >

FUTURE WORK

SAFETY CONSIDERATIONS

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•Software used = Autodesk Inventor 5

•Physics Machine Shop then fabricated our device from the specifications below

•All dimensions below are in millimeters

Figure 5: Screw Torque as a function of Lap-Band pressure Figure 6: Self-Adjusting Lap-Band Pressure over Time

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We would like to thank Dr. Roselli for his guidance, and Dr. Rauth for providing the project idea and initial research. We would also like to thank Dr. Paul King for his advice and financial support of our project.

Extensively test prototype

Pressure control studies

Prototype Characterization

Animal research

Design more efficient control mechanisms

Redesign device exterior to make implantable

Desired Curve

Pressure Adjustment

Loss of Pressure

Stepper Motor

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MPX2202A

Pressure Sensor

Microcontroller

DSP56F801 Digital Signal

Controller

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24 kΩ-12 V

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L297 Stepper Controller

Motor Control Board

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Design Safe SuggestionsDurable casingLong battery lifeSituate device far from vital organsProvide fail safe to alert Doctor in case of device failure.

Pressure Drop in Lap-Band

Pressure TransducerDetects Changes

Data Processing of Multiple Readings

Chip Determines Necessary Volume

Pump Changes VolumeOf Saline in Lap-Band

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Figure 4: Pump Schematics

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Figure 1: A) Location of Lap-Band in abdomen, B) Obesity Growth Rates in the United States, C) Required pressure adjustments in the Lap-Band, D) Isovolumetric pressure loss

Rauth, Thomas. “Why use Pressure Directed Lap-Band Adjustment?” Vanderbilt Center for Surgical Weight Loss, Nashville, TN. 17 Oct. 2006.

Our prototype consists of a pump (Figure 4) that is powered by a stepper motor, whose movement is controlled by a motor control board, under the direction of a microcontroller. The microcontroller receives input from a pressure transducer which reads the pressure in the Lap-Band and processes the data to direct motor movement.

Figure 3: Prototype Electronics Schematic

Figure 7: Pump in opened form along with circuit board

Figure 2: Negative Feedback Loop of Circuit

Figure 8: Pump in closed form with pressure sensor