1. In-Vivo Device for Measuring and Adjusting Lap-Band Pressure Mark Fritz 1, John Huidekoper 1, Andrew Koivuniemi 1, David Mayhew 1, Chris Schroeder 1 Robert J. Roselli 1, Thomas P. Rauth 2 1 Department of Biomedical Engineering, 2 Center for Surgical Weight Loss Vanderbilt University, Nashville, TN, USA INTRODUCTION ACKNOWLEDGEMENTS PROTOTYPE DESIGN DEVICE FUNCTIONALITY  Eliminates need for infusion- port  Provides personalized pressure regimen  Eliminates pressure fluctuations  Allows wireless communication with care provider  Records pressure reading for signal processing and evidence based medical treatment DESIGN CONSTRAINTS Figure 6: Automatic stepped response to applied pressure shift in Lap-Band 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. Desired Curve Pressure Adjustment Loss of Pressure Pressure Drop in Lap-Band Pressure Transducer Detects Changes Data Processing of Multiple Readings Chip Determines Necessary Volume Pump Changes Volume Of Saline in Lap-Band - A B Figure 1: A) Location of Lap-Band in abdomen, B) Required pressure adjustments in the Lap-Band Rauth, Thomas. “Why use Pressure Directed Lap-Band Adjustment?” Vanderbilt Center for Surgical Weight Loss, Nashville, TN. 17 Oct. 2006. Figure 2: Negative Feedback Loop of Circuit Figure 5: Pump in closed form with pressure sensor PROTOTYPE PERFORMANCE Problem: Currently, 1 in 50 Americans are extremely obese as measured by their Body Mass Index (BMI), and the number is growing. Though nearly all are unable to effectively reduce their weight using traditional methods, only 1.5% elect to get surgical treatment. Problems with Current Surgical Options: Gastric Bypass:  Mortality rate of 1 in 200  Non-reversible, non-adjustable  Extended recovery: 1-2 weeks incapacitation, 6 weeks to full recovery  Possible malabsorption issues lead to lack of vitamins and essential amino acids Laparoscopic Adjustable Gastric Banding (Lap-Band):  Band pressure decreases over time  Frequent clinical visits for pressure adjustment  Significant weight loss only occurs shortly after the clinical adjustment  Difficulty finding infusion-port can lead to damaged tubing, which requires device replacement Proposed Solution: Internalized automatic pressure control system  Must be able to pump 4 mL of saline at 2 atm gauge pressure  We intend to use the current Lap-Band technology  In addition our pump will be sutured along the abdominal wall, so all dimensions should be kept to a minimum and the material must be biocompatible  We used a pacemaker as our precedent and guide for acceptable size  Maximized device lifetime DESIGN OPTIMIZATION DISCUSSION We have succeeded in creating a system that can monitor pressure and adjust it to around a set point value. Our pump prototype, which has been designed to minimize both overall volume and required motor torque, effectively produces and holds the required pressures. When our programmed LabVIEW interface is coupled to the pump, an appropriate pressure sensor, and stepper motor, the device is able to compensate for pressure changes in the Lap-Band and maintain the band pressure within a 3% overall tolerance. Our pump is capable of holding pressures as high as 3.25 atm, which exceeds the maximum pressure requirement of the device. Future work for this device needs to focus on redesigning the pump to make it more easily implantable as our prototype was designed for ease of manufacture and testing, and does not have an appropriate exterior design for implantation. An implanted device would also require a feedback mechanism designed to continually monitor the integrity of the device and alert doctors when something is wrong. Once this has been done, further testing and animal trials can begin. 1) Must be able to hold 4 mL of saline 2) Levers must be able to push out saline We performed a constrained multivariable optimization to find the dimensions to minimize the necessary motor torque using MATLAB’s Optimization Toolbox and the Jacobian matrix below: Our prototype consists of a pump (Figure 3), powered by a stepper motor that is controlled by a motor control board under the direction of a LabVIEW script. LabVIEW processes pressure data from a pressure transducer and uses the data to direct motor movement based on a pressure set point. Figure 4: Prototype Electronics Schematic LabVIEW Digital I/O Logic Stepper Motor V++5VV-G MPX2202A Pressure Sensor DAQ Digital Input GND ENA DIR RCT V+ V- M1M2AA’BB’ +18 V - + 5.6 MΩ -18 V 1.5 MΩ L297 Stepper Controller Motor Control Board RCT DIR ENA GND +18 V +5 V GND +5 V M1M2AA’BB’ Constraints 3) Torque must be minimized Torque (N-m) as a function of expelled volume (V, in m 3 ) within the device is defined as follows: Lap-Band Pressure Transducer Pump Stepper Motor Gear Head Bevel Box Pressure Manually Increased Pressure Manually Decreased Band Pressure Automatic Compensation Dimension Optimization (cm): x = 2.0 y = 2.2 z b = 1.2 z g = 2.0 A)B)C) Figure 3: A) AutoCAD pump schematic, B) Pump built to specifications, and C) Assembled pump attached to pressure tubing Figure 7: Torque requirements to pump 4mL saline into Lap-Band