Transcript Final Poster - Research

In-Vivo Device for Measuring and Adjusting Lap-Band Pressure
John
1
Huidekoper ,
1
Koivuniemi ,
1
Mayhew ,
Andrew
David
1
2
Robert J. Roselli , Thomas P. Rauth
1Department
Chris
of Biomedical Engineering, 2Center for Surgical Weight Loss
Vanderbilt University, Nashville, TN, USA
INTRODUCTION
DESIGN OPTIMIZATION
Problem:
x y z b  4  10
6
z  y  zb  z g
2
g
Gastric Bypass:
2
3) Torque must be minimized





101325 x y z g
9
 31  10 x y V  x y101325 

x y zg  V


Torque(V)  0.163 
V

zg 

xy


V 
2

2


zg  y   zg 

xy
















 T
 x @V 0.5 mL

 T
 y @V 0.5 mL
J   T
m 
 zb @V 0.5 mL
 T

 z g @V 0.5 mL

T
x @V 1mL
T
y @V 1mL
T
zb @V 1mL
T
z g
@V 1mL
T

x @V  4 mL 

T

...
y @V  4 mL 

T

...
zb @V  4 mL 

T

...
z g

@V  4 mL 
...
1150
Pressure
Manually
Increased
1100
Automatic Compensation
1050
1000
Pressure
Manually
Decreased
950
900
Band Pressure
850
Automatic Compensation
Pressure Set Point
Upper Bound (1.5%)
Lower Bound (1.5%)
800
0
1
2
3
4
5
6
7
8
Time (min)
Laparoscopic Adjustable Gastric Banding (Lap-Band):
PROTOTYPE DESIGN
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
Dimension Optimization (cm): x = 2.0
y = 2.2
Figure 6: Automatic stepped response to applied pressure shift in Lap-Band
zb= 1.2
zg= 2.0
4.5
A)
B)
Torque Required by Motor (N-m)
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
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:
1) Must be able to hold 4 mL of saline
2) Levers must be able to push out saline
Problems with Current Surgical Options:
PROTOTYPE PERFORMANCE
Torque (N-m) as a function of expelled volume
(V, in m3) within the device is defined as follows:
Constraints
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.
C)
Proposed Solution:
Internalized automatic pressure control system
B
A
1
Schroeder
Pressure (mmHg)
Mark
1
Fritz ,
4
3.5
3
2.5
2
1.5
1
0.5
0
Pressure Adjustment
0
200
400
600
800
1000
Pressure in Lap-Band (mmHg)
Desired Curve
Loss of Pressure
Figure 7: Torque requirements to pump 4mL saline into Lap-Band
Rauth, Thomas. “Why use Pressure Directed Lap-Band Adjustment?” Vanderbilt Center for Surgical
Weight Loss, Nashville, TN. 17 Oct. 2006.
Figure 1: A) Location of Lap-Band in abdomen, B) Required pressure adjustments in the Lap-Band
Figure 3: A) AutoCAD pump schematic, B) Pump built to specifications, and C) Assembled pump attached to pressure tubing
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
-
Pressure Drop in
Lap-Band
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.
Pressure Transducer
Detects Changes
Pump Changes Volume
Of Saline in Lap-Band
+18 V
+18 V
GND
1.5 MΩ
Data Processing of
Multiple Readings
L297 Stepper
Controller
+5 V
RCT
Lap-Band
DIR
-18 V
5.6 MΩ
-
Motor Control Board
M1 M2 A
+
A’ B
ENA
GND
B’
Pressure
Transducer
+5 V
Chip Determines
Necessary Volume
Figure 2: Negative Feedback Loop of Circuit
DESIGN CONSTRAINTS
Must be able to pump 4 mL of saline at 2 atm gauge pressure
Stepper Motor
V+
+5V
V-
G
Pump
MPX2202A
Pressure Sensor
We intend to use the current Lap-Band technology
GND
V+
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
Stepper Motor
V-
DAQ
Digital
Input
Digital
I/O
Logic
LabVIEW
Gear Head
ENA
Figure 4: Prototype Electronics Schematic
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.
DIR
RCT
Bevel Box
We used a pacemaker as our precedent and guide for acceptable size
Maximized device lifetime
DISCUSSION
Figure 5: Pump in closed form with pressure sensor
ACKNOWLEDGEMENTS
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.