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DSP-based non-invasive variceal pressure measurement system

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Esophageal variceal bleeding in patients with portal hypertension is the most dangerous complications, about one-third of patients will eventually bleeding [1 ~ 2]. If you can determine out of this one-third of bleeding in patients with early preventive treatment can reduce medical costs and treatment of their own risks. Pressure of esophageal varices is considered to predict esophageal variceal bleeding the most important reference indicator [3].

Control and detection system is the core of the entire system, determines the noninvasive manometry of esophageal varices system's main performance and indicators. Now, with the development of high-speed digital signal processor mature and widely used to provide high-performance digital control system is possible [6].

DSP-based non-invasive variceal pressure measurement system

A system architecture

Noninvasive manometry of esophageal varices main part of the system are:

(1) airflow occur, adjustment and air pressure detection part;

(2) The next bit machine parts: the main sample of the gas sensor signals received by conditioning, analog / digital conversion, calculation and, based on results issued by the appropriate PWM wave to the motor driver chip to control the pump speed in order to obtain the required gas air pressure; while the relevant data transmitted to host computer and receive a host computer issued by the control signal;

(3) Host Computer software components: that part of the collection, through the relevant algorithms and correction of data are processed and, based on the results of handling the next-bit machine controller parameters, or running adjustments, while achieving real-time monitoring and data, graphical display of .

The system block diagram shown in Figure 1.

DSP-based non-invasive variceal pressure measurement system

2 System Hardware Design

Gas Road, part of the structure shown in Figure 2. Close to the gas-sensing probe measured the vessel wall by the pressure of its veins, leading to changes in atmospheric pressure gas path parts. Here selected Honeywell 40PC series pressure sensors to detect the pressure change. 40PC series pressure sensor using a single silicon chip original design, all temperature compensation, output zero / full-scale correction, zoom and other functions concentrated in a silicon. The sensor operating voltage of 5V, the output voltage range from 4V, from 0.5 to 4.5V. At room temperature accuracy of 0.2%.

Pressure sensor into a pressure value is between 0.5 ~ 4.5V signal is followed by the dsp chip TMS320F2407 pressure signals to realize real-time acquisition and motor control. The chip has dual 10-bit analog / digital converter module, can achieve high-precision sampling. Pairs of data collected through the relevant algorithms to deal with the amendment and, based on results issued by the event manager control of PWM wave-power device off, in order to control the motor speed [5], in order to achieve part of the entire gas path pressure of the closed-loop control and adjustments [4] [6]. At the same time, the application of the chip serial communication interface (SCI) will be after the acquisition and processing of data through the RS232 serial bus passed to the host computer [4 ~ 5], and to graphically display real-time changes in venous pressure curve. DSP chip can also be ready to receive the adjustment host computer to send signals to the relevant parameters or running on-line adjustments.

DC motor speed control methods are voltage speed, the armature speed and the weak magnetic resistor string speed and so on, in the rated speed (called the base speed) the following string of resistors with voltage regulator, or governor, in the base rate used for more than a weak Magnetic speed. According to the characteristics of control, using pulse width modulation (PWM) variable speed method. PWM formula is as follows:

Uav = (ton / T) Us = αUs (1)

Formula, ton - switch each connected to time;

T - switch off the work cycle;

α - duty cycle.

By equation (1) shows that changing the pulse duty cycle, the average voltage across motor also changed, and therefore motor speed has also been brought under control.

DSP-based non-invasive variceal pressure measurement system

In recent years, with the microelectronics and power electronics technology, the field of DC motor control of the intelligent power integrated circuits (SmartPower IC), by such chips have the flexibility to constitute a small, high-reliable operation of the PWM servo system. For example, pairs of H-bridge power IC LMDl8200 is a comparison of a typical version of the chip. Figure 3 is to use the power of integrated circuits LMDl8200 build motor control system schematic.

3 System Software Design

DSP to complete the entire system, a large number of software features. To accomplish these functions, in addition to the core of the TMS320F2407 is used, but also full use of many of the TMS320F2407-chip peripheral modules such as A / D module, the event processor module, watchdog and real-time interrupt module, etc. [4 ~ 5 ]. The main part of the program be achieved by using external interrupt cycles of data acquisition, computing control and data transmission. Interrupt service routine in software algorithms of the most important component. DSP starts to initialize the first operation, including setting all interrupt vectors as well as DSP-PLL phase-locked clock module settings to enable the internal module clock frequency meet the requirement; then DSP is idle, waiting for the occurrence of interrupts, once the interrupt occurs, then runs the appropriate interrupt service routine, processing is complete DSP idle, waiting for another interrupt from occurring [6].

Host Computer software modules interface with Windows Windows-style, according to the operator with the relevant norms of customary arrangements for each step of the strict operation, at the same time cater for the various components of models and charts, to chart such as an intuitive way to show the test results after treatment , and real-time display of key parameters of the situation; for each individual test data and results will be stored in a particular database can be remote login and access, after the completion of each test will be automatically generated report file.

DSP-based non-invasive variceal pressure measurement system

4 Experimental results

Xiangya School of Medicine according to different authors carried out a detailed in vitro experiments and animal experiments, access to a wealth of valuable experimental data. In order to puncture manometry as a standard, in the original adherent manometry Department conducted a puncture manometry of esophageal varices, and these two methods to compare the data obtained (as shown in Table 1), has been puncture manometry adherent and non-invasive manometry diagram shown in Figure 4. Where, Y = 3.144 +0.931 x, a linear relationship between two sets of data.

Table 1 Standard puncture manometry manometry results compared with the adherent

Puncture manometry values mmHg Adherent manometry values mmHg
2 4
3 5
4 6
5 6
9 11
12 14
13 16

The system is structured, compact design, reliable, accurate determination of varicose vein pressure, in the clinical assessment of risk of bleeding esophageal varices has a good application value.

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