Abstract: the design of a portable electronic blood pressure monitor continuous ambulatory blood pressure meter. Blood pressure measurement using the oscillometric method, using ATmegal6 microcontroller as the core, realize the A / D conversion, timing measurement, data storage, serial communication, LCD display and other functions, can be used as casual blood pressure meter, can continuously 24 hours a day to dynamic monitoring of blood pressure and pulse need.
Keywords: portable; ambulatory blood pressure; ATmegal6; oscillometric method
With the popularity of portable medical devices, which are often used with electronic sphygmomanometer. But the other similar products in the market is only applicable to casual blood pressure, for some disease diagnosis requires 24 hour ambulatory blood pressure monitoring patient, such products cannot meet the needs of. And for a family or a patient, often need to casual blood pressure, but sometimes also need monitoring of 24 hours ambulatory blood pressure, if only to meet the need of dynamic blood pressure monitoring market and production dynamic blood pressure meter, is bound to some waste resources. Based on the above requirements, according to the basic principle of market of electronic sphygmomanometer, to design a dynamic blood pressure monitoring and design of portable electronic blood pressure casual blood pressure meter.
1 design theory
1.1 blood pressure measurement and the 24 hours ambulatory blood pressure monitoring
At present, the use of measuring blood pressure mercury blood general hospital, doctors can use a stethoscope to hear different voices of arteries, to determine the values of systolic and diastolic blood pressure, this is Co Pyinfa; but the most electronic sphygmomanometer is generally used oscillometric method. The measuring principle of oscillometric method cf..
We usually measure blood pressure are even measured blood pressure (Clinic Bloodpressure, CBP). Casual blood pressure limitation, it can only represent the measured blood pressure condition at that time, some people in measurement due to feelings of tension or mood swings caused by high blood pressure readings. Ambulatory blood pressure monitoring (Ambulatory Bloodpressure Monitoring, ABPM) is a 24 hours a day, every 15 ~ 30 min or optional interval for automatic noninvasive blood pressure measurement and recording method. The circadian rhythm of blood pressure in human body typical "Shuangfeng Valley", namely, wake up in the morning blood pressure gradually increased, appeared first peaks in the morning 6:00 to 8:00, then the blood pressure tends to be stable, at 4:00 ~ 6:00 showed second peaks, night sleep, blood pressure decreased gradually, the night 2:00 to 3:00 to a minimum. The circadian rhythm of blood pressure is normal or not is a good indicator to judge the severity of hypertension, blood pressure fluctuations in the level and trend of ambulatory blood pressure monitoring can reflect the patient all day, providing valuable information to assess the hypertension and cardiovascular function.
1.2 the overall scheme design
Ambulatory blood pressure monitoring, is based on the original electronic sphygmomanometer, add new functions: automatic sphygmomanometer cuff inflation and deflation timing to make; can adjust the automatic blood pressure measurement time interval, the general setting for every 15 ~ 30 min records 1 times, in order to minimize interference with daily activities and sleep at night can be adjusted according to actual needs, time intervals, such as every 30 min record 1 times during the day, at night than during the day recording time interval can be set to the appropriate extension, recorded every 60 min 1; can automatically display the systolic pressure, diastolic pressure, mean arterial blood pressure and pulse rate; increase the RS-232 serial communication, convenient display of dynamic blood pressure the curve in the computer software platform; whenever you press the START button, immediately start with test, and can automatically supplement measurement in the measurement of failure; 4 day 5 standard alkaline batteries (1.5 V per day) in low voltage power supply, automatic alarm, replace the battery from the breakpoint on measurement.
The overall block diagram of the device, as shown in Figure L, micro controller to control air inflated to a certain pressure to the cuff value (such as 180 mmHg), to ensure that more than systolic blood pressure, the flow control valve block, and then from 3 to 5 mmHg rate of ladder deflation. The bleeding process, pressure sensor to the cuff pressure signals into electric signals, signal through the low pass filter, pulse signal obtained the cuff of the static pressure signal and the very weak, all the way to the microcontroller pin of ADC0, is used to convert the cuff pressure signal (weak pulse oscillation signal can be ignored) into blood pressure value; another way through filter, get the pulse oscillation signal, the amplifier were sent to the MCU ADCl and AINl pins, used to measure the pulse oscillation signal amplitude and signal pulse through the comparator get the standard to calculate the pulse rate, when the detected systolic, diastolic and mean blood pressure, open the valve, so that the cuff all deflation, a measurement process, and the measurement results to save, display. The whole measuring process is controlled by micro controller and complete all kinds of computing. The main part of the diagram below respectively in detail.
2 system hardware circuit design
2.1 simulation circuit
The 2.1.1 signal acquisition unit
Blood pressure measuring range is generally 0 ~ 200 mmHg, the silicon pressure sensor MPX5050GP of Motorola company, with its internal temperature compensated and amplifier output function, can be directly connected with the MCU interface, the use is very convenient. MPX5050GP pressure sensor has the characteristics as follows:
(1) in the 0 ° C to 85 ° C maximum error range is 2.5%;
(2) the temperature compensation range: -40 ~ +125 ℃;
(3) pressure measurement range: O ~ 50 kPa (0 ~ 375 mmHg);
(4) supply voltage: 5 V (4.75 ~ 5.25);
(5) the full-scale output: 4.7 V;
(6) the zero bias voltage: 0.2 V;
(7) the sensitivity: 90 mV / kPa, reaction time 1 ms.
This design uses the monolithic integrated circuit A / D conversion |
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