Design of fully open distributed monitoring system for hospital wards based on fieldbus

0. Introduction

In the early 1980s, with the rapid development of many new technologies such as sensor detection technology, analog and digital communication technology, computer application technology, and microelectronics technology, monitors and monitoring systems with various microcomputers came into being. Hospital ward monitoring has gradually shifted from manual clinical monitoring to remote monitoring using on-site monitors and monitoring systems. Especially since the 1990s, the development and application of network technology, multimedia technology, and information technology have led to a fundamental change in hospital management methods, which has led to the rapid development of hospital information digitization. In some large comprehensive hospitals, a new model of " digital hospital " based on information technology and facing the 21st century has been proposed.

The so-called digital hospital is an open, fully open, distributed hospital management information system model based on a local area network . It connects the scattered departments of the hospital through a computer network, covering all aspects of the patient's visit to the hospital. The hospital monitoring system is a bottom-level distributed monitoring local area network in the inpatient management system. As early as the Seventh Five-Year Plan period, the critical patient monitoring system was a national key project, and some initial bus distributed ward monitoring solutions were produced one after another. However, these so-called bus-type monitoring systems, because they all use traditional serial communication protocols, can only achieve point-to-point communication. Even if the system can achieve multi-point communication through the "Master" device, only one master device is allowed in this bus network, and the rest are all slave devices. Therefore, the nodes are not interoperable, and a multi-master redundant system cannot be formed, and the system reliability is poor. In addition, the nodes that constitute the system are limited by the load of the master device and have poor scalability, so traditional bus solutions do not have the performance of a fully open distributed network. As a new technology that has first developed in the field of industrial control in recent years, fieldbus has not yet been applied to the field of hospital ward monitoring. The application of fieldbus in the fully open distributed system of ward monitoring will have very important practical innovative significance.

1. Development and current status of hospital ward distributed monitoring systems

Before the 1980s, microelectronic computer technology had not yet emerged in my country, and hospital ward monitoring mainly relied on manual walking to call the attendant to monitor patients. After the 1980s, various ward call intercom devices and systems began to appear, in which patients called the attendant to request medical care. Since then, monitors and monitoring systems with various microcomputers have appeared. At first, such monitoring systems generally used special devices to form an independent system, did not provide an interface with the external system, and could not perform remote monitoring. Therefore, how to interconnect these on-site monitoring instruments and independent monitoring systems to form a hospital ward monitoring distributed system network and realize remote monitoring has become a hot research topic in this field. With the rapid development and application of digital communication technology, serial communication technology adapted to remote information transmission has gradually matured and been widely used. Hospital ward monitoring system has begun to introduce serial communication technology, using on-site monitoring instruments and equipment distributed in various wards to realize real-time data collection of patient physiological parameters, and transmit data information over long distances through serial communication interfaces. With the help of remote computers, medical staff analyze and process data parameters to form patient medical order information, which is then transmitted to nurses on duty to perform clinical monitoring on patients. At the same time, nurses on duty can also obtain real-time monitoring request information and simple monitoring feedback information from patients in the duty room, thus forming the so-called hospital ward distributed monitoring system.

The first serial communication protocol used was the RS-232 interface standard. The system structure is shown in Figure 1. The system uses a general twisted pair as the transmission medium to achieve point-to-point communication between the central monitoring station and the patient's bedside monitor. The communication is simple and easy to implement. However, as the number of monitored patients increases, the entire system has too many networking lines, and because the RS-232 interface standard appeared earlier, there are some shortcomings in communication, mainly the following four points:

(1) The signal level of the interface is high, which can easily damage the chip of the interface circuit. Also, because it is incompatible with the TTL level, a level conversion circuit is required to connect it to the TTL circuit.

(2) The transmission rate is low. In asynchronous transmission, the baud rate is 20Kbps.

(3) The interface uses a signal line and a signal return line to form a common ground transmission form. This common ground transmission is prone to common mode interference, so the anti-noise interference capability is weak.

(4) The transmission distance is limited. The standard maximum transmission distance is 50 feet, and in practice it can only be used for about 50 meters.

In response to the shortcomings of RS-232, some new interface standards have emerged. RS-485 is one of them and has been quickly applied in the field of ward monitoring. The system structure is shown in Figure 2.

Relatively speaking, the RS485 serial communication interface has the function of multi-point communication, which can be said to be a bus standard communication protocol. It has the following advantages:

(1) The signal level of the RS-485 interface is lower than that of RS-232, which is less likely to damage the chip of the interface circuit. In addition, the signal level is compatible with the TTL level and can be easily connected to the TTL circuit.

(2) The maximum data transmission rate of RS-485 is 10Mbps.

(3) The RS-485 interface uses a combination of a balanced driver and a differential receiver, which has enhanced common-mode interference resistance, that is, good noise interference resistance.

(4) The maximum transmission distance of the RS-485 interface is 4000 feet, but it can actually reach 3000 meters. In addition, the RS-232 interface only allows one transceiver to be connected to the bus, which is a single-station capability. The RS-485 interface allows up to 32 transceivers to be connected to the bus. That is, it has multi-station capability, so users can easily establish a device network using a single RS-485 interface.

Although the distributed bus system composed of RS-485 has many advantages over the previous distributed systems , it still has some insurmountable defects compared with the fully open distributed system composed of fieldbus :

(1) The hardware has weak error detection, error correction, and error location capabilities, and the system's own monitoring and maintenance functions are poor;

(2) There is no bus disconnection function. Once the RS-485 transceiver on a node is short-circuited or a serious error occurs, the entire bus will not work properly;

(3) There is no cache function in the hardware;

(4) The data communication method is command-response, resulting in poor system flexibility;

(5) The RS-485 bus needs to maintain a fixed current on the bus when idle, which affects the life and power consumption of the device.

(6) The devices in the RS-485 bus network can only communicate with each other through the "master" device. However, this bus network only allows one master device, and the rest are all slave devices. Therefore, the nodes are not interoperable, and a multi-master redundant system cannot be formed, resulting in poor system reliability.

(7) The RS-485 bus does not have the characteristics of an open Internet and cannot form a fully open distributed Internet communication network system.

2. Features of fieldbus technology and its advantages in fully open distributed monitoring systems in hospital wards

Due to the shortcomings of the traditional bus system, we analyzed the characteristics of the mature field bus technology that has been developed and applied in the field of automatic control for many years, introduced it into the hospital ward monitoring, and formed a fully open distributed monitoring system for the hospital ward, which can well overcome the shortcomings of the traditional bus system.

The shortcomings of the system bus system.

Fieldbus was developed internationally in the late 1980s and early 1990s. It provides network services in accordance with the open system interconnection model of the ISO/OSI international standard organization. It is a fully decentralized, fully digital, intelligent, bidirectional, multi-variable, multi-point, and multi-station communication system used between field instruments and control systems and control rooms. The fieldbus system has the following technical characteristics:

(1) Openness of the system An open system means that the communication protocol is open, and the equipment of different manufacturers can be interconnected and exchange information. Fieldbus developers are committed to establishing an open system with a unified factory bottom network. The openness here refers to the consistency and openness of relevant standards, emphasizing the consensus and compliance with standards. An open system can be connected to any other equipment or system that complies with the same standards. A fieldbus network with bus function must be open; an open system gives the right to system integration to the user. Users can combine products from different suppliers into a system of any size according to their needs and considerations.

(2) Interoperability and interoperability Interoperability here refers to the realization of information transmission and communication between interconnected devices and systems, and can implement point-to-point and point-to-multipoint digital communication. Interoperability means that devices with similar performance from different manufacturers can be interchangeable and interoperable.

(3) Intelligence and functional autonomy of field equipment: It distributes functions such as sensor measurement, compensation calculation, engineering quantity processing and control to field equipment. The basic functions of automatic control can be completed by field equipment alone, and the operating status of the equipment can be diagnosed at any time.

(4) Highly decentralized system structure Since the field equipment itself can complete the basic functions of automatic control, the fieldbus has formed a new architecture of a fully distributed control system. It fundamentally changes the existing DCS centralized and decentralized distributed control system, simplifies the system structure, and improves reliability.

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(5) Adaptability to the field environment: It works at the front end of the field equipment. As the field bus at the bottom layer of the factory network, it is designed specifically for working in the field environment. It can support twisted pair, coaxial cable, optical cable, radio frequency, infrared, power line, etc. It has strong anti-interference ability, can use a two-wire system to realize power transmission and communication, and can meet the requirements of intrinsic safety and explosion-proof.

In the process of modern large and medium-sized hospital operation and management, the network will become an important infrastructure to connect various departments within the hospital and exchange information with the outside. A complete and efficient hospital operation and management information network system plays a very important role in the modernization of hospital operation and management, and in improving the efficiency of hospital monitoring and management. The monitoring system of hospital wards belongs to a subsystem of the hospital management information network. Therefore, the monitoring and nursing of each ward in the hospital is most suitable for using the fieldbus to form the underlying local area network, so as to realize real-time and reliable communication between doctors, nurses and patients, and to realize the automation of patient care monitoring by using the intelligent medical, diagnostic, monitoring and other equipment on site in the ward. Moreover, due to the above characteristics of the fieldbus, especially the simplification of the fieldbus system structure, it has superiority in the design, installation, normal operation and maintenance of the hospital ward monitoring system .

(1) Save hardware quantity and investment;

(2) Save installation costs;

(3) Save maintenance costs;

(4) Users have a high degree of system integration initiative;

(5) Improved the accuracy and reliability of the system;

(6) Simple design and easy to refactor;

3. Hospital ward fully open distributed monitoring system model based on CAN bus and its software and hardware composition

CAN is the only field bus approved as an international standard. It has the following basic characteristics:

(1) The CAN protocol follows the ISO/OSI model and adopts a three-layer structure consisting of the physical layer, data link layer, and application layer.

(2) The communication rate of CAN is: 5Kbps/10km, 1Mbps/40m, the number of nodes can reach 110, and the transmission medium can be twisted pair, optical fiber, etc.

(3) CAN uses a short frame structure for signal transmission, with 8 valid bytes in each frame. This shortens the transmission time and reduces the probability of interference. In addition, when a serious error occurs in a CAN node, CAN has the function of automatically shutting down the node and automatically cutting off the connection with the bus, so that other nodes on the bus and their communications are not affected. Therefore, it has a strong anti-interference ability.

(4) CAN nodes use point-to-point, point-to-multipoint and broadcast methods to send and receive data, which can realize a fully distributed multi-machine system without the distinction between master and slave.

(5) CAN uses non-destructive bus arbitration technology.

(6) CAN can support explosion-proof areas.

Therefore, CAN (Controller Area Network) bus is recognized as one of the most promising field buses . Usually, the intelligent measurement and control system based on CAN bus is shown in Figure 3:

According to the characteristics of ward monitoring: generally, at least one central monitoring station is required, where the doctor in charge of monitoring is responsible for overall monitoring, and then each floor is set up with a nurse duty room to conduct real-time monitoring and nursing of the beds in charge, as well as on-site online monitoring of the beds in each ward. Therefore, the entire monitoring system can be divided into three levels: management level - monitoring level - on-site level. The system structure based on CAN bus is shown in Figure 4:

It consists of a host monitoring PC as the management level (in the office of the attending physician), nurse intelligent monitoring nodes as the monitoring level (in the nurse duty room in each corridor, assuming m-story corridors), and bed on-site measurement and control nodes as the on-site level (ward beds, assuming n beds).

The following is a brief introduction to the system hardware and software components:

1. Hardware Design

1. Central monitoring PC

Basic hardware composition: PC + CAN bus communication interface adapter card

CAN bus communication

The interface adapter card quickly transmits the data and control parameters in the PC to the specified CAN network node. At the same time, the collected data of each CAN network node is transmitted to the PC for further analysis and processing. The structural block diagram of the CAN bus communication interface adapter card is shown in Figure 5.

Main functions: Receive, process and save monitoring information from each duty room and bed. Specific functional features are as follows:

a) The large screen can simultaneously display data graphs and charts of different monitoring parameters collected from multiple points on site;

b) Large capacity disk to record monitoring information;

c) It has monitoring sound and light alarm function;

d) Full Chinese software interface;

e) Computer-aided analysis and diagnosis function;

f) It has the function of networking and communication with other subsystems of the hospital;

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2. Nurse Intelligent Monitoring Node

The hardware structure block diagram of the nurse intelligent monitoring node is shown in Figure 6. As can be seen from the figure, it consists of two parts: a microcontroller PAC87C591 with on-chip CAN (a powerful 8-bit microcontroller with an integrated CAN controller inside the chip, which can provide hardware support for the network node to connect to the PC, and also has other functions such as A/D conversion circuit inside), and a human-computer interaction interface.

Main functions of the node:

a) Receive and execute patient medical advice information from the central monitoring PC;

b) Receive remote monitoring request signals from monitored patients in real time

c) Record and upload the monitoring log of the monitored patients to the central monitoring PC;

3. On-site measurement and control nodes of hospital beds

The structural block diagram of the bed field measurement and control node is shown in Figure 7. It mainly includes three parts: MCU89C52, CAN controller SJA1000 chip and field sensor interface.

Main functions of the node:

a) Collect and upload real-time monitoring parameters of patients (including patient temperature, blood pressure, heart rate, respiration, etc.);

b) Sending a patient monitoring request signal;

c) In response to the control signal sent by the upper monitoring station, the automatic execution unit performs corresponding operations;

2. Software Design

The software design adopts a structured programming scheme, which has good modularity, modifiability and portability. The entire system software design is divided into three parts, namely:

1. Central monitoring PC interface adapter card software design

It is written in VC++6.0 object-oriented visual high-level language based on Windows 98 platform, with system

Functional modules include parameter (such as baud rate, output control, message identification and shielding, etc.) setting, monitoring status setting, data sending and receiving, local status query, node status query, real-time alarm and interrupt receiving data management. The software function module is shown in Figure 8. The host computer first initializes the CAN bus adapter card and itself, and then sends a command to notify a specific node to send data to the CAN bus. After conversion by the CAN bus adapter card, the central monitoring PC will perform corresponding processing according to the actual situation. The command is sent to each node in a timed round-robin manner, and the data is received in an interrupt manner.

The second is the driver of the PCL-841 CAN card. The manufacturer provides a complete DLL driver function library for the PCL-841 card. When using VC++6.0 for development, you must first connect the DLL library to the development environment, and then you can call the functions in the library. The library function call needs to follow a certain process, as shown in Figure 9:

2. Intelligent monitoring node software design

The intelligent monitoring node software consists of three parts: initialization, data transmission and interrupt processing. It mainly completes two tasks: one is to receive the monitoring request signal and control algorithm of the on-site monitoring node; the other is to transmit the node status and data information to the host computer when the central monitoring PC requests data. The node main program flow chart is shown in Figure 10:

3. On-site measurement and control node software design

The main function of the on-site measurement and control node software is to complete the on-site patient physiological parameter sensing collection and data fusion and the automatic control of on-site medical equipment, while realizing digital communication with the central monitoring PC and other intelligent monitoring nodes.

4. Conclusion

Fieldbus is increasingly being accepted by more and more fields with its leading advantages, mature technology and good cost performance. The author believes that the application of fieldbus in hospital ward monitoring system to form a fully open distributed system local area network will surely lay the foundation for the new concept of " digital hospital " in the 21st century. In addition, with the intelligence of various medical devices and monitoring instruments and the popularization of network technology, home telemedicine (including health care) is an inevitable trend in the development of the medical industry. Therefore, the remote home health monitoring system will further provide a broader application prospect for the application of fieldbus in this field.