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In-Vivo Active Pressure Monitoring System
Presented by
Mahmoud Mohamed Abdallah Sayed
Ahmed
The Main Idea
•
Medical examinations often extract localized symptoms rather
than systemic observations and snap shots rather than continuous
monitoring.
•
Using these methodologies, one cannot discretely analyze how a
patient’s lifestyle affects his/her physiological conditions and if
additional symptoms occur under various stimuli.
•
So the solution is in a minimally invasive implantable pressure
sensing system that actively monitors long-term physiological
changes in real-time.
The Main Idea
•
Kidney stones, ureter strictures, tumors, and uretopelvic junction
obstruction block the upper urinary track. And a Symptom of
urinary blockage is elevated pressure.
•
So the system investigates pressure changes in the upper urinary
tract per degree of obstruction.
•
An implantable active pressure sensor has been developed for the
continuous measurement of elevated pelvic and ureteral renal
pressures.
The Main Idea
•
Benefits of the in-vivo pressure monitoring system:
1.
The continuous, active monitoring of pressure within the upper urinary
track
2.
The real-time automated distribution of data to a patient’s PDA
3.
The aggregation of data to a online database that stores information for
later analysis of the symptoms
4.
The remote in-vivo reconfiguration of the software
The Main Achievements
• System Architecture:
Sensor
Skin
Sensor Node
The Main Achievements
•
The system integrates three components:
–
Sensor Node: Mica2Dot(Atmega 128L microcontroller and
wireless transmitter) with a signal conditioning circuit and
battery.
–
Pressure Sensor: ultra-small, low-cost OEM pressure die.
–
Base Station: a pocket PC that gathers and processes data
from the sensor node.
•
The System Operation:
1.
The Mica2Dot sends pressure readings to a PDA/Pocket PC.
2.
The PDA visualizes the data and can perform more complex data
processing, such as decision support
The Main Achievements
•
Features:
– wire-free system measures pressure
– Working hours: forty-eight hours
– Range: twenty feet away
– Remotely reconfigurable software
– The multi-channel transmitter is has a center frequency of 868/916 Mhz
with adata rate of 38.5 kbps.
– The radio uses 27mA of power while transmitting and 10mA of power
while receiving
The Main Achievements
•
In-vivo active pressure monitoring system unique features:
1. Active Pressure Monitoring (own internal power supply)
• Higher transmission range
• Ubiquity in deployment
• communicate with such as PDAs.
2. Collection Mechanism
• Uploads the data to an online database.
• This allows for the later analysis of the data to determine
patterns in how one’s lifestyle affects the internal urinary
track pressure and the long-term progression of urinary
track blockage.
The Challenges
•
Pressure Transducers
– The desired range of pressure sensing in the application was 0 to 1 PSI
with accuracy of 0.02 PSI.
– So the voltage span will be approximately 6mv.
– The small degree of voltage can be considerably affected by
environmental noise.
– The voltage range must fully utilize the 0 to 3 voltage range
The Challenges
•
Pressure Transducers
The Challenges
• Pressure Transducers
– So precise signal conditioning circuit is developed for:
• Stabilizing excitation voltage: The sensor excitation voltage
needs to be steadied at 3V.
• Electrical noise reduction: Considerable noise is generated
within the circuit and must be accurately filtered out.
• Voltage amplification
• Offset voltage removal: The sensors bridge is not
symmetric when no pressure is applied. This lack of
symmetry results in an offset voltage that reduces the
voltage swing between 0 to 1 PSI.
The Challenges
•
Catheter Design
– The Catheter must be
• Biocompatible
• Maneuverable
– So The conductors are individually PTFE insulated and the catheter body
is sheathed in silicone rubber.
– The conductors are soldered to bonding pads on a PCB substrate and
encapsulated with biocompatible epoxy.
– The monitoring system includes stress relief measures to ensure
additional robustness and to relieve the anticipated forces exerted on
the system during packaging and implantation,.
The Challenges
•
Catheter Design
The Challenges
•
Biocompatible Packaging
– Unsatisfactory packaging can:
• Degrades the performance of the sensor
• Result in device failure
• Result a severe immunogenic response from the subject
– Most researchers package their implantable sensors with only silicone
dipping or parylene.
– However, most silicones are not designed to be used internally and
parylene has been shown to attract immunogenic cells.
The Challenges
•
Biocompatible Packaging
The Challenges
•
Biocompatible Packaging
– The system is packaged with two dual passivation layers:
• parylene
– conforms to any geometry on the micro-scale.
– high resistance to permeation and solvent absorption
– strengthens wire bonds at interfaces.
• medical grade encapsulant.
– excellent bulk property
– malleability to surface properties.
– The sensor was evaporated a thin layer of parylene to combat
the volatile environments in the body and the harsh chemicals
in post processing.