Personal Health Care Blood Pressure Monitor

Personal Health Care Blood Pressure Monitor

Abstract Personal Health Care Blood Pressure Monitor is based on the ratio algorithm of oscillometric method and it is used to measure vital parameters of Blood Pressure like Systolic, Diastolic, Mean and Pulse rate

This system is implemented using MSP430F169 .The detailed

description of this project is presented in this report.

1. Introduction Arterial blood pressure is the force exerted by the blood on an area of the wall of an artery as it is pushed through the circulatory system. During the course of the cardiac cycle, the arterial blood pressure is constantly changing. As the heart beats, the highest pressure in this cycle (systolic blood pressure) is recorded. Between beats, the lowest pressure (diastolic blood pressure) is recorded. The systolic number is always stated first and the diastolic number is listed second. For example: 122/76 (122 over 76); systolic = 122, diastolic =76.

NIBP measurement is realized by adopting ratio algorithm of oscillometric method. Basic process inflates the cuff until a certain pressure, then default the cuff slowly. If the pressure in the greater then the systolic pressure of the patient , we may consider that the blood flow in blood vessel is blocked .At this time no pulsation should exist in the blood vessel surrounded by the cuff start deflating the cuff when the cuff pressure less than systolic pressure blood flow party exists in the blood vessel. The pulsation will cause the cuff pressure to fluctuate within small range; that means an oscillating signal overlaps the pressure to signals. This oscillating signals increase with the decrease

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Personal Health Care Blood Pressure Monitor of the cuff pressure. When the cuff pressure reduces to a certain value the amplitude of the oscillation signal will decrease. It is because the decreasing cuff pressure because the attenuation effect of the subcutaneous tissue to pulsation increases. The attenuation effect will become obvious with the continuous decrease of cuff pressure and as a result the amplitude of oscillating signal will decrease even more obviously. Ratio algorithm is to take advantage of the ratio characteristic of these oscillating signals and as a result to measure blood pressure. It is based on the following theory when the cuff pressure is equal to diastolic pressure or systolic pressure, the ratio of the amplitude of the corresponding oscillating wave and the maximum amplitude among the oscillating waves is a relatively constant value. Therefore we can first find maximum amplitude; its corresponding pressure is the MEAN value. Accordingly we can find the amplitudes corresponding to systolic and diastolic pressure based on the specified ratio and further obtain the systolic and diastolic pressure. About this method it is very important to determine the ratio. Generally this ratio should be acquired after a number of experiments. In this sense, ratio method is a kind of experiential method.

2. Hardware Design Personal Health Care Blood Pressure Monitor is designed using MSP430F169

a) Why MSP430F169? 1. Low Supply-Voltage Range, 1.8 V . . . 3.6 V 2. Ultra low-Power Consumption 12-Bit A/D Converter With external Reference, Sample-andhold and Auto scan Feature Dual 12-Bit D/A Converters With Synchronization 3. 16-Bit Timer_A With Three Capture/Compare & PWM Registers 4. 16-Bit Timer_B With Three or Seven Capture/Compare-With-Shadow Registers 5. Brownout Detector 6. Bootstrap Loader 7. No External Programming Voltage Needed 8. Programmable Code Protection by Security Fuse 9. MSP430F169 60KB+256B Flash Memory,

b)Hardware Description The proposed System as following main units

1) Power Supply Unit The equipment is powered by 3xAA alkaline batteries, this 4.5V is converted to 5V using step-up regulator (TPS63002), 5V is use to power the Air pump, Pressure sensor, Solenoid valve and display unit further this voltage is converted into 3.3V using step down LDO regulator (TPS75633) it is used to power all the logic and micro controller circuits.

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Personal Health Care Blood Pressure Monitor 2) Processing Circuit The cuff pressure and oscillometric signal in the cuff pressure is acquired by the pressure sensor and its further process using low pass filter and amplifier section of processing circuit, which in turn feed into the ADC channel of microcontroller for the further processing.

3) Micro controller The heart of the circuit is MSP430F169 which acquires the processed signal from the cuff and it controls Air pump, Solenoid for successful process and measurement of blood pressure also two line (2 x16) alphanumeric LCD is used display the vital parameters.

c)Block Diagram

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Personal Health Care Blood Pressure Monitor

3.Software Design a) Flow chart Start

No C

If(Check key)

Yes Timer On

Motor Enable

Bleed Solenoid Enable

Start ADC function

If(ADC Flag) True

Yes

P

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No

Personal Health Care Blood Pressure Monitor

P Calculate the Cuff Pressure

Display Cuff Pressure

Check Cuff Pressure Max

No

Yes Motor Disable

No

Check flag osc on, Solenoid _on R

Yes

Check Cuff Pressure Is reduced

Yes Solenoid _Off Delay_ms Solenoid _On

P1

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No

Personal Health Care Blood Pressure Monitor

P1

Calculate OSC Signal

Check Cuff Pressure Min

NO

Yes Solenoid off,Timer Disable Calculate Mean, Systolic blood pressure is recorded, Diastolic blood pressure is recorded& Plus rate is recorded

Display Mean, Systolic,Diastolic&Plus Rate Buzzer On Stop Process Go to Start

C

Low Power Mode

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R

Personal Health Care Blood Pressure Monitor b) Program Details Inflate 1. Update the cuff pressure value every 3 msec. 2. If Cuff Pressure is greater than the inflate pressure and less then the maximum possible pressure. 2.1. Stop the motor 2.2. Set the delay flag 3. If pressure exceeds the maximum possible cuff pressure 3.1. Default the cuff pressure 3.2. Set the error “Cuff over pressure “

Deflate 1. Update the cuff pressure every 3msec.

2. Read the oscillation signal after every 10 msec. 2.1. Record the average of the oscillation signal to get the relative baseline. 2.2. Take continuous average of 10 oscillation signal readings for waveform analysis. 2.3. While rising, record the rising peak amplitude. 2.4. When falling started, 2.4.1.Stop the peak-to-peak time recording timer. 2.4.2.Record the time. 2.4.3.Reinitialize the timer. 2.4.4.Start the timer for the next peak-to-peak time. 2.5. While falling, record the falling peak amplitude. 2.6. When rising started, 2.6.1.Record the falling edge time. 2.6.2.Check if the previous pulse is in correct heart rate time and the amplitude of the pulse is greater than or equal to the approximate baseline. 2.6.2.1.

Record the pulse for analysis

2.6.2.2.

If two pulses are recorded, analyze the pulses to get the correct peak at that cuff pressure.

2.6.2.3.

Check if the two pulses match in amplitude (+- 50) and falling edge time (+- 75).

2.6.2.4.

Record the average of the two pulses for the envelope data.

2.6.2.5.

Store the peak-to-peak time (or the pulse time) for heart rate Calculation.

2.6.2.6

Check the envelope – online analysis.

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Personal Health Care Blood Pressure Monitor 2.6.2.7

First peak should always be less than the specific envelope start peak, else re-inflate the cuff to 30mmHg (Adult Mode) more than the previous maximum inflate pressure.

2.6.2.8

Calculate the mean using the online envelope data.

2.6.2.9

Calculate the online threshold after the Mean A trial Pressure is got.

2.6.2.10

If one reading is got below the threshold line, release the air in the cuff.

3

If no pulse is available for the max peak-to-peak time, enable deflate to the next step.

4

If one pulse is got, then no pulse is available until the max peak-to-peak time, enable deflate to the next step.

5

If the total process time exceeds the specified limit, 5.1 Deflate the cuff pressure. 5.2 Set an error code – “Exceeded measurement time limit”

6

Deflate to the next step; analyze the pulses again for the envelope readings.

Release cuff air: 1. If any error is set or any point is got below the threshold line, 1.1. Release the air, by opening the solenoid valve. 1.2. Filter the envelope to remove the small notches. 1.3. Calculate the systole, mean and diastole using the envelope data based on the Linear Regression formula. 1.4. Check the systole, mean and diastole validity depending on the limits. 1.5. Calculate the heart rate (pulse rate). 1.6. Calculate the baseline. 1.7. Display the readings if no error is set, else display the corresponding higher priority error code. 1.8 If switch is pressed, 2 times, restart the process.

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Personal Health Care Blood Pressure Monitor Summary Personal Health Care Blood Pressure Monitor is constructed with the help of ultra low power MSP430F169 and it is used to determine blood pressure parameters & pulse rate with considerable accuracy which will aid the user to determine haemo-dynamic status in order to monitor their health conditions in the comfort of their homes. This device is portable and it is powered by using 3xAA alkaline battery.

Reference 1. MSP430F169 Data Sheet - SLAS368D 2. MSP430X1XX Family User Guide - SLAU049F 3. Integrated Silicon Pressure Sensor On-Chip Signal Conditioned, Temperature Compensated and Calibrated MPX5050 MPXV5050G SERIES 4. High efficient single inductor buck-boost converter with 1.8-a Switches (TPS63002)-SLVS5l0A 5. Low-noise, high PSRR, RF 200-ma Low-dropout linear regulators (TPS75633)- SBVS054E 6. LinCOMS Precision Quad Operational Amplifiers(TLC274)–SL0S092D 7. SN74LVC4245A Octal Bus Transceiver And 3.3v To 5 V With 3 State Outputs (SN74LVC4245A) –SCA5375H 8. Micro SIZE , Signal-Supply CMOS Operational Amplifiers(OPA337) –SBOS077B

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