readout and functional electronics for intracranial pressure icp sensor

8/10/2019 Readout and Functional Electronics for Intracranial Pressure Icp Sensor

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Proceedings of the 2nd

International Conference on Current Trends in Engineering and Management ICCTEM -2014

17 19, July 2014, Mysore, Karnataka, India

32

READOUT AND FUNCTIONAL ELECTRONICS FOR INTRACRANIAL

PRESSURE (ICP) SENSOR

Aravind G1, Dr. C.R.Venugopal

2, Vijay Mishra

3

1Dept. of ECE, SJCE, Mysore, India

2HOD,Dept. of ECE, SJCE, Mysore, India3CeNSE, Indian Institute of Science(IISC), Bangalore, India

ABSTRACT

Intracranial Pressure (ICP) is the combination of the pressure exerted by the brain

tissue, blood and cerebral spinal fluid (CSF). Continuous monitoring of ICP data has evolved into an

indispensable diagnosis tool in the current medical scenario. The main advantage of continuous

monitoring of ICP is that it prevents the blind prophylactic treatment of ICP, avoiding

unnecessary administration of the ICP lowering therapies which in turn can be dangerous at times.

This work involves electrical characterization of intracranial pressure(ICP) sensor developed

at CeNSE, IISC and its comparison with a commercially available similar sensor. The sensitivity of

these sensors are measured and analyzed for different configuration of associated network bridge.

Using commercially available similar sensor available in the market we have proposed a new idea

for intra-cranial pressure(ICP) monitoring in the cranial vault, along with the temperature. First part

consists of our new proposed model for ICP monitoring along with temperature. In the second part

we have tried to emulate our new proposed model using commercially available sensor for

different pressure as well as temperature values. Electronics part consisting of opamps in

different configurations, has been designed and tested several times, inorder to condition the low

output voltage of sensor. Finally MSP430 microcontroller has been programmed to accept the output

of signal conditioning board and display it on the output devices. Programming is done using

Embedded C language. IDE tool used is code composer studio(CCS).

Keywords: Commercially Available Sensor, Emulation, Pressure Sensor, Piezoresistor, ICP,

Wheatstone Bridge.

1. INTRODUCTION

Intracranial Pressure (ICP) is the combination of the pressure exerted by the brain tissue,

blood, and cerebral spinal fluid (CSF) [1]. The normal range of this pressure is 0 10 mm of Hg [2].

INTERNATIONAL JOURNAL OF ELECTRONICS AND

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Volume 5, Issue 8, August (2014), pp. 32-45

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I A E M E


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Continuous monitoring of ICP, sometimes for a few days, is crucial in diagnosing and treating

patients with severe head injuries.

1.1 Problem statementPresent ICP monitoring devices available in market focuses only on monitoring pressure

inside the cranium that houses the brain. Simultaneous monitoring of intracranial temperature (ICT)is also desirable and has not been covered by the existing systems.

Accurate knowledge of cerebral temperature is assuming increasing importance, because

its manipulation is employed more frequently for cerebral protection. Recent work has confirmed

that body temperature and brain temperature may differ significantly. Hence, brain temperature

monitoring is essential if one is trying to improve outcome by lowering brain temperature. ICP

monitoring is very crucial especially during head injuries.

1.2 Objective

The main objective of this project is to develop an embedded system for the ICP sensor and

to perform electrical characterization of the ICP sensor, which has been designed and developed at

CeNSE, IISC.

The work involves programming of microcontroller to read the sensor output and display iton output devices. This project has challenges like setting up the calibration setup and implementing

the sensor practically. It involves application of electronics and microcontroller programming skills,

calibration and testing of the sensors. The purpose of Intracranial Pressure (ICP) monitoring is to

trend the pressure inside the cranial vault. The pressure readings determine the interventions

necessary to prevent secondary brain injury, which can lead to permanent brain damage and

even death. If the intracranial pressure is in the range of 20 to 25 mmHg, therapeutic interventions,

medical and/or surgical, should be initiated. This is because as the ICP increases, it gradually

becomes more difficult for the blood to be pumped to the head to perfuse the brain tissue.

1.3 MotivationFigure 1.1 shows typical brain sites used for ICP measurement, such as intraventricular drain,

intraparenchymal probe, sub-arachnoid probe, epidural probe.Intra cranial contents are:

Brain - 80 to 85%

Cerebrospinal Fluid(CSF) - 8 to 12%

Cerebral Blood Volume - 5 to 8%

Figure 1.1:The typical brain sites used for ICP measurement


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As the cranial vault is essentially a closed, fixed bony box, its volume is constant. This

volume is described by the Monro-Kellie doctrine, proposed in the early part of the 19th century:

Intracranial (constant) = Brain + CSF + Blood + Mass lesion

As all these components are fluids and non-compressible, once the cranial vault is filled, it'spressure rises dramatically. This intracranial pressure (ICP) rise can then lead to interruption of

cerebral blood flow by reducing the cerebral perfusion pressure. As an intracranial mass lesion or

oedematous brain expands, some compensation is possible as cerebrospinal fluid (CSF) and blood

move into the spinal canal and extracranial vasculature respectively. Beyond this point, further

compensation is impossible and ICP rises dramatically [4].

1.4 Scope of the projectSimultaneous monitoring of ICP and ICT(Intra cranial temperature) is not reported anywhere

else. ICT is equally important to monitor in case of serious head injuries. Simultaneously monitoring

of pressure and temperature by suitable electronic processing of electrical signals coming out of the

sensor is done here. In this project ICP monitoring systems has been set up at laboratory conditions

to provide an virtual environment to sense the ICP and ICT through sensor.

1.5 Organization of the reportThe framework of the project is described as follows:

1- IntroductionThis chapter gives a brief introduction about the project work, project objectives, motivation

for the project, scope and organization of the project report.

2- Sensors used in our experiment

This chapter deals with different types of sensors used in this project and its electrical

characterization.

3- Functional electronics

This section deals with the hardware part of the project.

2. SENSORS USED IN OUR EXPERIMENT

A sensor is a device, which responds to an input quantity by generating a functionally related

output usually in the form of an electrical or optical signal. Sensor's sensitivity indicates how much

the sensor's output changes when the measured quantity changes. For instance, if the mercury in a

thermometer moves 1 cm when the temperature changes by 1 C, the sensitivity is 1 cm/C.

In this project we are using three sensors:-

ICP sensor- Designed and developed at CeNSE IISC.

Commercially available sensor

Emulated sensor- This sensor tries to emulate the behavior of ICP sensor by using

commercially available sensor.

2.1 Piezoresistive pressure sensor

Piezoresistivity is the change of resistance of a material when it is submitted to stress.

Typically, pressure is measured by monitoring its effect on a specifically designed mechanical


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structure, referred to as the sensing element. The application of pressure to the sensing element

causes a change in shape, and the resulting deflection (or strain) in the material can be used to

determine the magnitude of the pressure. Piezoresistive pressure sensor's design includes two basic

elements. They are thin elastic diaphragm and piezoresistive material. The diaphragm is fixed around

the edges, with a trace wire on the surface. The wire is made of a piezoresistive material. When a

pressure is applied to the back of the diaphragm, the diaphragm (and the wire on it) deform,changing the resistance of the wire. By measuring the resistance of the wire, we can measure the

pressure causing the deformation. The sensitivity of the sensor depends on the piezoresistive

material. Schematic of a sensor is as shown in Figure. 2.1.

Figure 2.1:Cross sectional schematic of pressure sensor

Here L and H correspond to length and thickness of the diaphragm respectively. Silicon

based pressure sensors have been widely used for industrial and biomedical electronics [8]. In this

design, Silicon nitride is used as diaphragm material and polysilicon is used as piezoresistive

material.

2.2 ICP sensorThis ICP sensor model has been designed and developed as IISC, Bangalore. In this design,

silicon nitride is used as diaphragm material and polysilicon is used as piezoresistive material. Atpresent, in the market we can find sensors which can only sense ICP. Simultaneous monitoring of

ICP and ICT(Intra cranial temperature) is not reported anywhere else. ICT is equally important to

monitor in case of serious head injuries. Simultaneously monitoring of pressure and temperature by

suitable electronic processing of electrical signals coming out of the sensor is done here. Therefore

the main objective of the sensor is to sense intracranial pressure as well as intracranial temperature.

The top views of ICP sensor is shown in figure 2.2. The figure 2.3 shows the side view of ICP

packaged sensor. The resistor which is on the diaphragm is sensitive to both temperature as well as

pressure. The resistor which is outside the diaphragm is sensitive to only temperature.

Figure 2.2:Top profiles of ICP sensor


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Figure 2.3:Side profile of ICP packaged sensor

2.2.1 Pressure calibration

Practically, inorder to apply a constant pressure to the sensor we have used

sphygmomanometer at the input side of ICP monitoring system. The pressure was applied in steps of

40mmHg ranging from 0-160mmHg.

Figure 2.4:Hardware setup of ICP sensor for pressure calibration

Table 1:Tabulated results for ICP sensor

Sensitivity is 7.13 V/mmHg

Sensitivity=(Difference between any two bridge output voltage) / Number of divisions

= (1.3419 - 1.0981) / 40 = 0.007135

Sensitivity is 7.135 V/oC

Pressure in mm Hg Bridge O/P in mV Difference

0 1.3419

40 1.0981 -0.2438

80 0.8127 -0.2854

120 0.5513 -0.2614

160 0.3076 -0.2437


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Bridge output(millivolts) v/s Pressure(mmHg)

Figure 2.5:Bridge output voltage variation for different pressure values in ICP sensor.

The circuit is completed by balancing the bridge. The pressure is applied in steps of 40mmHg

ranging from 0-160mmHg. The changes in the bridge output voltage values are observed with the

increase in pressure and the results are tabulated (Table 1). The complete hardware setup of balanced

bridge for pressure calibration in ICP sensor is as shown in figure 2.4. The changes in the bridgeoutput voltage values of wheatstone bridge for different pressure values is shown in the figure 2.5.

We can notice a decreasing voltage as pressure increases. The result shows that the sensitivity of our

ICP sensor is 7.13 V/mmHg. This shows that it is not very much sensitive to applied pressure.

2.2.2 Temperature calibration

Similar to pressure calibration, complete the circuit by adding two external resistors to from a

full bridge configuration. This complete setup is kept in a Hot-Cold chamber. Hot cold chamber is an

electronic device which is consists of a air tight vacuum chamber. The chamber can be adjusted to

any temperature ranging from -200 to +200 degree celcius. The components are place in that

chamber and different temperatures are applied, inorder to study the behavior of the components.

Here in this case, the ICP sensor is balanced through Wheatstone bridge and placed in this Hot-Cold

chamber. The sensor is kept inside the Hot-Cold chamber and the other two resistors of Wheatstonebridge is kept outside the chamber. We have used resistance pots to balance the bridge. The pots are

kept outside the Hot-Cold chamber inorder to prevent the pot resistance variation affecting the bridge

output. The complete setup of ICP sensor for temperature calibration is shown in figure 2.6.

Figure 2.6:Hardware setup of ICP sensor for temperature calibration


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Table 2:Tabulated result for ICP sensor

Temperature in deg celcius Bridge O/P in mv Difference

0 3.7354

10 3.9047 0.1693

20 4.1019 0.1972

30 4.3857 0.283840 4.5498 0.1641

Sensitivity is 0.02838 mV/oC

Bridge output v/s Temperature

Figure 2.7:Bridge output voltage variation for different temperature values

The sensor is tested for different temperatures ranging for 0 degree celcius to 40 degree

celcius in steps of 10 degree celcius. Bridge output voltages at different temperatures are tabulated

(Table 2). Calculate the bridge output voltage for per degree celcius change in temperature. Shown in

figure 2.7.

2.3 Commercially available sensor

The P161 is a ultraminiature silicon piezoresistive pressure sensor die that is suitable formonitoring pressure from the tip of a catheter. This sensor is offered in a miniature 1150 X 725 m

die. When excited with an AC or DC voltage source, it produces a milli voltage output that is

proportional to input pressure [9]. It is half bridge design, where external resistors are needed to

complete a full bridge configuration. Below figure 2.8 shows commercially available sensor

schematic diagrams: Complete the full bridge by inserting two 800 external resistors, closely

matched to minimize offset error. i.e. the built in resistors are of 800. So external resistors of 800

each are used to balance the wheatstone bridge. The dimension of the sensor is given by (l:w:h)

:1150m X 725 m X 170m.

Figure 2.8:Commercially available sensor schematic diagram


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2.3.1 Pressure calibrationThe complete hardware setup of balanced bridge for pressure calibration in commercially

available sensor is as shown in figure 2.9. The resistance of resistor R32 on commercially available

sensor increases with pressure. On the other hand, resistance of resistor R12 decreases with pressure.

Figure 2.9:Hardware setup of balanced bridge for pressure calibration

We have used resistance pots to balance the bridge, as variable resistances can be appliedthrough the resistance pots. Apply pressure to the sensor through sphygmomanometer and tabulate

the bridge output voltage for different pressure values (Table 3). Calculate bridge output voltage for

per mmHg pressure variation. Refer figure 2.10.

Table 3:Tabulation for commercially available sensor


This commercially available sensor is not sensitive to temperature, so we are not performing

temperature calibration, only pressure calibration is done here. The sensitivity of commercially

available sensor is 58.08 V/mmHg.


Figure 2.10:Bridge output voltage of commercially available sensor for different pressure

Pressure in mm Hg Bridge output in mV Difference

0 -4.9185

40 -3.000 1.9185

80 -0.7066 2.2934

120 1.580 2.2446

160 3.8612 2.3232


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2.3.2 Emulating ICP sensor using commercially available sensorIn ICP sensor, the resistance of resistor which is on diaphragm decreases with pressure and

resistance of the resistor outside the diaphragm increases with pressure. Therefore we have selected

R12 of commercially available sensor for calibration.

Emulation: R12 from commercially available sensor and a fixed resistor of same value are

connected in series. This combination forms the ICP sensor model, as it has one resistor is on thediaphragm and the other one outside the diaphragm, shown in figure 2.11. below.

Figure 2.11:Hardware setup for emulating ICP model

2.3.3 Pressure calibration

Complete the circuit by adding two external resistors to from a full bridge configuration.

Tabulate the bridge output voltage for different pressure values (Table 4). Calculate bridge output

voltage for per mmHg pressure variation, figure 2.12.

Table 4:Tabulation for emulated model



Figure 2.12:Bridge output voltage of emulated hardware setup against different pressure

Pressure in mm Hg Bridge output in mV Difference

0 4.885140 4.2335 -0.6516

80 3.4356 -0.7979

120 2.4978 -0.9378

160 1.5969 -0.9009


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2.3.4 Temperature calibrationInorder to apply a constant temperature to the sensor we are using an instrument known as

"Hot Cold chamber". Here, the Hot-Cold chamber is considered as a prototype of cranial vault.

Therefore sensor to be tested is placed inside this chamber and the bridge balancing is done outside

the chamber.

Similar to pressure calibration, complete the circuit by adding two external resistors to from afull bridge configuration. This complete setup is kept in a Hot-Cold chamber, figure 2.13. The sensor

is tested for different temperatures ranging for 0 degree celcius to 40 degree celcius in steps of 10

degree celcius. Bridge output voltage at different temperatures is tabulated (Table 5). Calculate the

bridge output voltage for per degree celcius change in temperature. Shown in figure 2.14.

Figure 2.13:Hardware setup for emulating ICP model using commercially available sensor for

temperature calibration

Table 5:Tabulation for emulated model

Sensitivity is 2.01373 millivolts/C

At room temperature: Bridge output voltage=9.4104 millivolts.

Bridge output(millivolts) v/s Temperature(C)

Figure 2.14:Bridge output voltage of emulated hardware setup against different temperature

Temperature in deg celcius Bridge O/P in mv Difference

0 -40.808

10 -20.671 20.1373

20 -0.9886 19.6828

30 17.1053 18.093940 35.2352 18.1299


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2.3.5 Comparison of results

2.3.5.1 Pressure calibration

Sensors Sensitivity of balanced bridge output

ICP sensor 7.13 V/mmHg

Emulated sensor 28.042 V/mmHgCommercially available sensor 58.42 V/mmHg

2.3.5.2 Temperature calibration

Sensors Sensitivity of balanced bridge output

ICP sensor 0.02838 millivolts/oC

Emulated sensor 2.03853 millivolts/oC

The sensitivity of the ICP sensor developed at IISC is too less as compared to the emulated

sensor and commercially available sensor. Emulated and commercially available sensors are almost

four and eight times sensitive to pressure than ICP sensor respectively.

3. FUNCTIONAL ELECTRONICS

3.1 Block diagram of the systemThe output of the balanced Wheatstone bridge will be in milli-volts. This voltage is very

small for further processing. Therefore it should be conditioned before applying to MSP430

microcontroller. Then, the output of the microcontroller is given output devices. Complete block

diagram of the system is shown in figure 3.1.

Figure 3.1:Block diagram of the system

3.2 ICP monitoring system

Practically in-order to apply a constant pressure to the sensor, we have used

sphygmomanometer and a pressure transducer tester DPM1B from Fluke Biomedical at the input

side. Functioning of this meter is to provide the pressure as well as measure it. One important

thing to be noted here is that we must make sure that the sphygmomanometer is leakage free. i.e.

there should not be any leakage in the sphygmomanometer inorder to read a correct pressure.

3.3 Signal conditioning boardThe figure 3.2 shows the signal conditioning board. This part has been designed and tested at

systems lab, IISC. The sensitivity of the pressure sensor being developed in IISC is about

7.13V/mmHg. It is very difficult to transmit this small signal directly into ADC for computation as

for even 100 mmHg output would be 0.713mV which is a very small signal and ADC even with 10

bits resolution isnt able to digitize it without adding the noise component. Thus an additional

circuitry is required which will be able to condition the signal for accurate pressure readings as well

as extract the temperature data from the pressure signal. This circuitry forms the part of this analog

front end. The circuit level diagram shown in the figure 3.2 is the representation of the analog front

ICP

monitoring

system

Signal

conditioning

board

MSP430 Output unit


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end design. The ICP resistors are denoted by R3 and R4. R4 resistor is on the diaphragm and the one

which is outside diaphragm is denoted by R3.

Figure 3.2:Signal conditioning board

The R3 resistor varies with only temperature, whereas R4 resistor varies with temperature aswell as pressure. Therefore the differential signal obtained at one end of bridge varies with

temperature as well as pressure(INPUT1) and the differential obtained signal at the other end varies

with only temperature(INPUT2). Then these signals are fed to dedicated Instrumentation

amplifiers(IA1 and IA2) for the Pressure and temperature extraction.

3.3.1 Pressure extraction pathThe differential signal, INPUT1 is a function of both temperature and pressure, and the

differential signal, INPUT2 is a function of only temperature. The pressure extraction path is via IA1

and OP2.

Initially, before applying to IA1, the differential signal, INPUT1 is passed through a voltage

follower inorder to match the input impedance of junction PCB output and analog signal

conditioning input.At room constant temperature the INPUT1 signal varies according to the applied pressure to

the sensor. As temperature being a common mode signal in both INPUT1 and INPUT2, they get

cancelled out and only pressure and offset voltage appears at the output of IA1. Now if by any

chance the output of IA1 is negative, we can negate this by adding a reference voltage using OP2,

which act as a summing amplifier with inputs coming from the output stage of IA1 and a constant

reference voltage coming from reference generating path. Thus output is scaled as well as amplified

by this stage.


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Ideally at 0 mmHg pressure the bridge output should be 0 volts. But practically we observe

some finite voltage at 0 mmHg pressure. This bridge output voltage at 0 mmHg pressure is known as

Offset voltage. Therefore the output at pressure extraction path consists of (pressure + offset)

voltage. While programming the microcontroller we should equate this offset value to zero in order

to display correct pressure values on output devices.

3.3.2 Temperature extraction path

Inorder to apply a constant temperature to the sensor we are using an instrument known as

"Hot Cold chamber". Here, the Hot-Cold chamber is considered as a prototype of cranial vault.

Therefore sensor to be tested is placed inside this chamber and the bridge balancing is done outside

the chamber.

Sensor is exposed to different temperatures, ranging from 0 to 40 degree celcius in steps 10

degrees. The bridge output voltage for each temperature variation are noted and results are tabulated.

The differential signal, INPUT2 is a function of only temperature and the temperature extraction path

is via IA2 and OP3. Initially, before applying to IA2, the differential signal, INPUT2 is passed

through a voltage follower inorder to match the input impedance of junction PCB output and analog

signal conditioning input.

One half of the differential signal is taken and it is provided to the instrumentation amplifier(IA2), the other signal which is fed to IA2 is a reference voltage generated by the reference

generating circuit. Wheatstone bridge also acts as a voltage divider and will divide the voltage

according to the resistor arms, thus the output of one of the differential arm can be nearly

predicted and modified depending on the changes observed in the excitation voltages. With

this arrangement temperature data is preserved from getting cancelled as it is present only in

one end and other end is constant voltage. Thus the single ended voltage at the output of

IA2 contains a component of the temperature experienced by the system which is extracted.

Now if by any chance the output of IA2 is negative, we can negate this by adding a reference

voltage using OP2, which act as a summing amplifier with inputs coming from the output stage of

IA2 and a constant reference voltage coming from reference generating path. Thus output is scaled as

well as amplified by this stage.

3.4 MSP430 Microcontroller

MSP430 is 16 bit micro controller with a Von Neuman architecture. It has 16 bit address bus

and 16 bit data bus. Registers are 16 bit wide. CPU is often described as a RISC. The output of signal

conditioning board is given to the ADC of MSP430 microcontroller. The controller is programmed

to accept the analog values and display its respective decimal values on the LCD display unit.

CONCLUSION AND FUTURE WORK

Basically, the project work involves electrical characterization of intracranial pressure(ICP)

sensor developed at CeNSE, IISC and its comparison with a commercially available similar sensor.

The sensitivity of these sensors are measured and analyzed for different configuration of associated

network bridge. Using commercially available similar sensor available in the market we have

proposed a new idea for intra-cranial pressure(ICP) monitoring in the cranial vault, along with the

temperature. The sensitivity of commercially available sensor and ICP sensor has been tested and

verified at different temperatures and pressures.

The electrical characterization results shows that the sensitivity of the ICP sensor developed

at IISC is too less as compared to the commercially available sensor. So inorder to know the range of

sensitiveness of ICP sensor we tried to emulate the ICP sensor model using commercially available

sensor.


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After analyzing and comparing the electrical characterization results we have noticed that the

sensitivity of the ICP sensor developed at IISC is too less as compared to the emulated sensor and

commercially available sensor. The sensitivity variation is almost 1:4:8 between ICP sensor,

Emulated ICP model and Commercially available sensors respectively. That is, our ICP sensor is

four times less sensitive and eight times less sensitive as compared to emulated model and

commercially available sensors respectively.Electronics required for the intracranial pressure monitor has been designed and tested

several times. MSP430 microcontroller has been successfully programmed to extract the sensor

output and display it on output devices. Software part consists of embedded system programing.

Program is written in Embedded C language and the IDE tool used is CCS(code composer studio).

In future, our aim is to develop an ICP sensor whose sensitivity is as close to emulated

sensor. Inorder to increase the sensitivity of the present ICP sensor a new idea has been proposed and

the development of that new ICP sensor is under progress. As soon as it is designed it will be tested

and verified at different temperatures and pressures.

REFERENCES

[1]

Overview of Adult Intracranial Pressure (ICP) Management & Monitoring Systems, OrlandoRegional Healthcare, Education & Development.

[2] Normal & Abnormal Intracardiac Pressures by Lancashire & South Cumbria Cardiac

Network.

[3] Journal of Cerebral Blood Flow & Metabolism (1999) 19, 762770; doi:10.1097/00004647-

199907000-00006.

[4] http://www.trauma.org/archive/neuro/icp.html.

[5] Intracranial pressure monitoring for traumatic brain injury in the modern era by Llewellyn C

Padayachy, Anthony A Figaji, M R Bullock.

[6] Intracranial Pressure Monitoring by Gaurav Guta MD; Chief Editor: Jonathan P Miller.

[7] Chih-Tang Peng1, Ji-Cheng Lin1, Chun-Te Lin1, Kuo-Ning Chiang2. Investigation of

Thermal Effect of Packaged CMOS Compatible Pressure Sensor, in Proc of IMECE2002,

ASME International Mechanical Engineering Congress & Exposition. November 17-22,2002, New Orleans, Louisiana.

[8] Vidhya Balaji and K.N. Bhat CeNSE IISC.A Comparison of Burst Strength and Linearity of

Pressure Sensors having Thin Diaphragms of Different Shapes.

[9] http://www.ge-mcs.com/en/pressure-mems/mems-elementsdevices/p161.html.

[10] http://www.allaboutcircuits.com/vol_3/chpt_8/10.html.

[11] MSP430 Microcontroller Basics, author John H Davies.

[12] Using Code Composer Studio IDE with MSP430, a quick start guide by Vu Tuan Than, Rene

Beuchat.

[13] http://www.ti.com/product/msp430g2553.

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