In-vivo Blood Pressure Sensor

1
In-vivo Blood Pressure Sensor

• Anup Pillai
• Dhanya Premkumar Nair

2
Outline

• Current blood pressure sensors in use
• Background
• Long-Term Implantable Blood Pressure Monitoring
  System and Advantages
• Wireless Battery less In VIVO Blood
  PressureSensing Micro system and Advantages
• System Architecture
• Our Objectives
• Timeline and Division of work
• Conclusions

3
Need to measure blood pressure

• To diagnose critical medical conditions like
  hypertension
• -causes strokes, heart attacks, heart failures
• Low blood pressure causes hypotension, which
  results in dizziness, fainting or shock

4
Conventional blood pressure monitoring systems
(non-invasive sensors)

• Auscultatory method

• Mercury Manometer

5
Current blood pressure sensors in use
With the new sensor, no cuff is required Device
takes advantage of the method called pulse wave
velocity which allows blood pressure to be
calculated by measuring the pulse at 2 points
along an artery This was developed at MIT's
d'Arbeloff Laboratory for Information Systems and
Technology
6
Outline

• Current blood pressure sensors in use
• Background
• Long-Term Implantable Blood Pressure Monitoring
  System and Advantages
• Wireless Battery less In VIVO Blood
  PressureSensing Micro system and Advantages
• System Architecture
• Our Objectives
• Timeline and Division of work
• Conclusions

7
Background

• In vivo-Latin for within the living
• Experimentations are done using a whole, living
  organism
• In vivo monitoring is critical for developing
  effective treatments

8
Background (Contd.)

• Long-Term Implantable Blood Pressure Monitoring
  System
• Wireless Battery less In VIVO Blood
  PressureSensing Micro system

9
Outline

• Current blood pressure sensors in use
• Background
• Long-Term Implantable Blood Pressure Monitoring
  System and Advantages
• Wireless Battery less In VIVO Blood
  PressureSensing Micro system and Advantages
• System Architecture
• Our Objectives
• Timeline and Division of work
• Conclusions

10
Long-Term Implantable Blood Pressure Monitoring
System

• The system employs an instrumented elastic cuff,
  wound around a blood vessel
• Operates in a linear diameter v.s. pressure
  region of the vessel for real time blood pressure
  monitoring
• The elastic cuff is made of soft bio-compatible
  rubber, filled with bio-compatible insulating
  fluid with an immersed MEMS pressure sensor
• The MEMS sensor detects the vessel blood pressure
  wave form with a constant scaling factor,
  independent of the cuff bias pressure exerting on
  the vessel.

11
Implantable blood pressure monitoring system
MEMS sensor
Insulating Liquid
Vein
Cuff
12
Advantages

• This technique avoids vessel insertion
• Also substantially minimizes vessel movement
  restriction due to the soft cuff elasticity
  
• Attractive for minimizing long-term adverse
  biological effects

13
Outline

• Current blood pressure sensors in use
• Background
• Long-Term Implantable Blood Pressure Monitoring
  System and Advantages
• Wireless Battery less In VIVO Blood
  PressureSensing Micro system and Advantages
• System Architecture
• Our Objectives
• Timeline and Division of work
• Conclusions

14
Wireless Battery less In VIVO Blood
PressureSensing Micro system

• Wireless powering and data telemetry are also
  incorporated in the micro system
• This eliminates the need of external wire
  connections and any bulky battery
• The micro system can be used to obtain reliable
  measurements without suffering from stress
  induced distortion

15
Wireless Battery less In VIVO Blood
PressureSensing Micro system
16
Outline

• Current blood pressure sensors in use
• Background
• Long-Term Implantable Blood Pressure Monitoring
  System and Advantages
• Wireless Battery less In VIVO Blood
  PressureSensing Micro system and Advantages
• System Architecture
• Our Objectives
• Timeline and Division of work
• Conclusions

17
Microsystem architecture
18
The in vivo blood pressure sensor inside an
actual lab rat
19
Outline

• Current blood pressure sensors in use
• Background
• Long-Term Implantable Blood Pressure Monitoring
  System and Advantages
• Wireless Battery less In VIVO Blood
  PressureSensing Micro system and Advantages
• System Architecture
• Our Objectives
• Timeline and Division of work
• Conclusions

20
Our Objectives

• The sensor specified in the background exhibits
  increased noise levels
• The transmitter of the same dissipated a 80 of
  the system power
• Our objectives are
• a) To design a similar sensor which exhibits
  less noise levels
• b) To design a better and more power efficient
  transmitter for the sensor

21
Objective 1

• To find a solution which exhibits less noise
  levels
• We began by investigating the reason for the high
  noise levels in the current design

22
Reason for noise

• Animal body vapor penetration into the device
• Affect the functioning of the electrical
  connections within the sensor.

23
The damage caused

• The high impedance node can be highly sensitive
  to vapor penetration
• Electrical connections between the sensor
  diaphragm and IC chip

24
Solution proposed

• Protection for moisture penetration is required
  for the sensor diaphragm as well as the
  electrical connections between the sensor
  diaphragm and IC chip.

25
Solution proposed (Contd.)

• A passivation layer, such as silicon dioxide
  (SiO2) and silicon nitride (Si3N4), can be
  deposited on the top of diaphragm.
• An encapsulant material with strong moisture
  resistance can be used to protect the bond wires
  between the sensor and IC before applying
  silicone passivation layer.

26
Objective 2

• To design a better and more power efficient
  transmitter for the sensor
• In the microsystem, an oscillator based FSK
  transmitter was employed for data telemetry
• This transmitter was on throughout and hence
  resulted in 80 power dissipation

27
Solution

• To use a transmitter operating with a low duty
  cycle
• One can also use a transmitter with an increased
  bandwidth

28
Numerical Calculations

• If the sampling frequency is 2 kHz, with data
  rate of 48 kbps, corresponding bit rate is 24 per
  0.5 ms
• This is the current specification for the system

29
Numerical Calculations (Contd.)

• Instead if we the transmitter is designed to be
  on for 0.05 ms and off for the remaining 0.45 ms
• This results in one order magnitude power
  reduction at increased data rate of 480 kbps
• This corresponds to 72 overall system power
  reduction

30
Outline

• Current blood pressure sensors in use
• Background
• Long-Term Implantable Blood Pressure Monitoring
  System and Advantages
• Wireless Battery less In VIVO Blood
  PressureSensing Micro system and Advantages
• System Architecture
• Our Objectives
• Timeline and Division of work
• Conclusions

31
Timelines
February March April May
Research project topic and preparation for report 1
Report 1
Objective 1
Presentation 2
Objective 2
Final Report
32
Division of Work

• First Objective
• To design a similar sensor which exhibits less
  noise levels-A. Pillai
• Second Objective
• To design a better and more power efficient
  transmitter for the sensor-D. Nair

33
Conclusions

• A review of current in-vivo blood pressure
  sensors was presented in this review study
• We identified the potential problems with
  existing solutions
• We have proposed two solutions that will enhance
  the performance of the current design

34
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