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, patient monitors and monitoring systems equipped with various microcomputers emerged. Hospital ward monitoring gradually shifted from manual clinical monitoring to remote monitoring using on-site monitors and systems. Especially since the 1990s, the development and application of network technology, multimedia technology, and information technology have fundamentally transformed hospital management methods, leading to rapid development of hospital information digitization. In some large comprehensive hospitals, a new model of "digital hospital" based on information technology and geared towards the 21st century has been proposed.
A digital hospital is an open, fully distributed hospital management information system model based on a local area network (LAN). It connects various departments within the hospital through computer networks, covering all aspects of a patient's hospital visit. The hospital monitoring system is a low-level distributed monitoring LAN within this inpatient management system. As early as the Seventh Five-Year Plan period, critical care patient monitoring systems were a national key project, resulting in some rudimentary bus-based distributed ward monitoring solutions. However, these so-called bus-based monitoring systems, using traditional serial communication protocols, could only achieve point-to-point communication. Even if multi-point communication was achieved through a "master" device, only one master device was allowed in this bus network, with all others being slave devices. Therefore, the nodes lacked interoperability and could not form a multi-master redundant system, resulting in poor system reliability. Furthermore, the nodes constituting the system were limited by the master device's load, leading to poor scalability. Therefore, traditional bus solutions lacked fully open distributed network capabilities. Fieldbus, a relatively new technology that first developed in the industrial control field in recent years, has not yet been applied to hospital ward monitoring. The application of fieldbus in a fully open distributed system for ward monitoring will have significant practical and innovative implications.
1. Development and Current Status of Distributed Monitoring Systems in Hospital Wards
Before the 1980s, when microcomputer technology was not yet prevalent in my country, hospital ward monitoring primarily relied on patients manually calling on-duty staff on foot. After the 1980s, various ward call intercom devices and systems emerged, allowing patients to call on-duty staff to request medical care. Subsequently, monitors and monitoring systems equipped with various microcomputers appeared. Initially, these systems generally used dedicated components, forming independent systems without interfaces to external systems, thus lacking remote monitoring capabilities. Therefore, how to interconnect these on-site monitoring instruments and independent monitoring systems to form a distributed hospital ward monitoring system network, enabling remote monitoring, has become a popular research topic in this field. With the rapid development and application of digital communication technology, serial communication technology, which is adapted to remote information transmission, has gradually matured and been widely used. Hospital ward monitoring systems have begun to introduce serial communication technology. By using on-site monitoring instruments and equipment distributed in various wards, real-time data acquisition of patients' physiological parameters is achieved. The data information is transmitted over long distances through a serial communication interface. With the help of a remote computer, medical staff analyze and process the data parameters to form patient medical orders, which are then transmitted to the on-duty nurses for clinical monitoring. At the same time, the on-duty nurses can also receive real-time monitoring requests and simple monitoring feedback from the patient in the duty room. This forms the so-called hospital ward distributed monitoring system.
The earliest serial communication protocol used was the RS-232 interface standard, and the system structure is shown in Figure 1. This system uses ordinary twisted-pair cable as the transmission medium to realize point-to-point communication between the central monitoring station and the bedside monitors of patients. The communication is simple and easy to implement. However, as the number of monitored patients increased, the number of network lines became too large. Moreover, because the RS-232 interface standard appeared relatively early, 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 TTL level, a level conversion circuit is required to connect to the TTL circuit.
(2) The transmission rate is low. In asynchronous transmission, the baud rate is 20Kbps.
(3) The interface uses one signal line and one signal return line to form a common ground transmission. This common ground transmission is prone to common mode interference, so it has weak noise interference resistance.
(4) The transmission distance is limited. The standard value for the maximum transmission distance is 50 feet, but 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, one of which is RS-485, which has been quickly applied in the field of ward monitoring. The system structure is shown in Figure 2.
In comparison, the RS485 serial communication interface has the function of communication between multiple points, and can be said to be a bus standard communication protocol. It has the following advantages:
(1) The RS-485 interface signal level is lower than that of RS-232, which is less likely to damage the chip of the interface circuit. Moreover, this level is compatible with TTL level, which can be easily connected to TTL circuit.
(2) The maximum data transmission rate of RS-485 is 10Mbps.
(3) The RS-485 interface uses a combination of balanced driver and differential receiver, which enhances the common-mode interference resistance, i.e., it has good noise interference resistance.
(4) The standard 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 on the bus, i.e., single-station capability. The RS-485 interface, on the other hand, allows up to 32 transceivers to be connected on the bus, i.e., multi-station capability. This allows users to easily establish a device network using a single RS-485 interface.
Although RS-485-based distributed bus systems offer many advantages over previous distributed systems, they still possess some inherent limitations compared to fully open distributed systems based on fieldbuses.
(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) No bus disconnection function. If the RS-485 transceiver on a certain node is short-circuited or a serious error occurs, the entire bus will not work properly.
(3) There is no caching function in the hardware;
(4) The data communication method is command-response, which results in poor system flexibility;
(5) When the RS-485 bus is idle, it needs to maintain a fixed current on the bus, which affects the lifespan and power consumption of the device.
(6) In an RS-485 bus network, devices can only communicate with each other through a “Master” device. However, only one Master device is allowed in such a bus network, and all the others are Slave devices. Therefore, the nodes are not interoperable and cannot form a multi-master redundant system, 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 interconnected communication network system.
2. Characteristics of fieldbus technology and its advantages in a fully open distributed monitoring system for hospital wards.
Due to the shortcomings of traditional bus systems, we analyzed the characteristics of fieldbus technology, which has been developed and matured in the field of automation over the years, and introduced it into hospital ward monitoring to form a fully open distributed monitoring system for hospital wards. This system can effectively overcome the limitations of traditional bus systems.
The shortcomings of traditional bus systems.
Fieldbus, developed internationally in the late 1980s and early 1990s, provides network services according to the ISO/OSI international standards organization's Open Systems Interconnection model. It is a fully distributed, fully digital, intelligent, bidirectional, multi-variable, multi-point, and multi-station communication system used between field instruments and control systems and control rooms. Fieldbus systems have the following technical characteristics:
(1) System Openness: An open system refers to a system with an open communication protocol, allowing interconnection and information exchange between devices from different manufacturers. Fieldbus developers aim to establish a unified, open system for the factory's underlying network. Here, "open" refers to the consistency and openness of relevant standards, emphasizing consensus and compliance. An open system can connect to any other device or system that adheres to the same standards. A fieldbus network with bus functionality must be open; an open system gives users the right to integrate the system. Users can combine products from different suppliers into systems of any size according to their needs and considerations.
(2) Interoperability and Interoperability Interoperability here refers to the ability to transmit and communicate information between interconnected devices and systems, enabling point-to-point and point-to-multipoint digital communication. Interoperability means that devices with similar performance from different manufacturers can be interchanged to achieve interoperability.
(3) The intelligence and functional autonomy of the field equipment It distributes the functions of sensing measurement, compensation calculation, engineering quantity processing and control to the field equipment. The basic functions of automatic control can be completed by the field equipment alone, and the operating status of the equipment can be diagnosed at any time.
(4) Highly Distributed System Structure: Since the field devices themselves can perform the basic functions of automatic control, the fieldbus has formed a new fully distributed control system architecture. This fundamentally changes the existing DCS distributed control system architecture that combines centralized and decentralized approaches, simplifies the system structure, and improves reliability.
(5) Adaptability to field environment Working at the front end of field equipment, as the bottom layer of the factory network, the fieldbus is designed specifically for working in the field environment. It can support twisted pair, coaxial cable, optical cable, radio frequency, infrared, power line, etc., has strong anti-interference ability, can use two-wire system to realize power transmission and communication, and can meet intrinsic safety explosion-proof requirements, etc.
In the modern operation and management of large and medium-sized hospitals, networks will become a crucial infrastructure connecting various departments within the hospital and facilitating information exchange with the outside world. A complete and efficient hospital operation and management information network system plays a vital role in the modernization, informatization, and intelligentization of hospital operation and management, and in improving the efficiency of patient monitoring and management. The monitoring system in hospital wards is a subsystem of the hospital management information network. Therefore, the monitoring and nursing care of each ward is best suited to utilize a fieldbus to construct a local area network (LAN), enabling real-time and reliable communication between doctors, nurses, and patients. Furthermore, the intelligent use of on-site medical, diagnostic, and monitoring equipment in the wards can automate patient care monitoring. Moreover, due to the aforementioned characteristics of fieldbus, especially the simplified structure of the fieldbus system, it demonstrates superiority in the design, installation, normal operation, and maintenance of hospital ward monitoring systems.
(1) Saves on hardware quantity and investment;
(2) Saves installation costs;
(3) Saves on maintenance costs;
(4) Users have a high degree of initiative in system integration;
(5) Improved the accuracy and reliability of the system;
(6) The design is simple and easy to refactor;
3. A model of a fully open distributed monitoring system for hospital wards based on CAN bus and its hardware and software components.
CAN is currently the only fieldbus approved as an international standard, and it has the following basic characteristics:
(1) The CAN protocol follows the ISO/OSI model and adopts a three-layer structure of physical layer, data link layer and application layer.
(2) The communication rate of CAN is 5Kbps/10km, 1Mbps/40m, and the number of nodes can reach 110. The transmission medium can be twisted pair, optical fiber, etc.
(3) CAN signal transmission uses a short frame structure, with each frame containing 8 effective bytes. This results in short transmission time and a low probability of interference. Furthermore, when a CAN node experiences a serious error, CAN has an automatic node shutdown function, automatically severing its connection to the bus, ensuring that other nodes on the bus and their communication are unaffected. Therefore, it has strong anti-interference capabilities.
(4) CAN nodes use point-to-point, point-to-multipoint, and broadcast methods to send and receive data, enabling a fully distributed multi-machine system without master-slave distinction.
(5) CAN uses non-destructive bus arbitration technology.
(6) CAN can support explosion-proof areas
Therefore, the CAN (Controller Area Network) bus is widely recognized as one of the most promising fieldbuses. A typical intelligent measurement and control system based on the CAN bus is shown in Figure 3.
Based on the characteristics of ward monitoring, it generally requires at least one central monitoring station for overall monitoring by the attending physician, nurses' duty rooms on each floor for real-time monitoring and care of their assigned beds, and on-site online monitoring of patients' beds in each ward. Therefore, the entire monitoring system can be divided into three levels: management level, monitoring level, and on-site level. The system structure based on the CAN bus is shown in Figure 4.
It consists of a host monitoring PC as the management level (in the attending physician's office), a nurse intelligent monitoring node as the monitoring level (in the nurses' duty rooms in each corridor, assuming m floors), and a bedside monitoring and control node as the field level (in the wards and beds, assuming n beds).
The following is a brief introduction to the hardware and software components of the system:
Hardware Design
1. Central monitoring PC
Basic hardware components: PC + CAN bus communication interface adapter card
CAN bus communication
The interface adapter card rapidly transmits data and control parameters from the PC to the designated CAN network node. Simultaneously, it transmits the data collected by each CAN network node to the PC for further analysis and processing. The block diagram of the CAN bus communication interface adapter card is shown in Figure 5.
Main functions: Receive, process, and save monitoring information from various duty rooms and beds. 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 disks record monitoring information;
c) It has a monitoring audible and visual alarm function;
d) Fully Chinese software interface;
e) Computer-aided analysis and diagnostic functions;
f) It has the ability to network and communicate with other subsystems of the hospital;
2. Intelligent monitoring node for nurses
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 PAC87C591 microcontroller with on-chip CAN (a powerful 8-bit microcontroller that integrates a CAN controller on the chip, providing hardware support for network nodes to connect to PCs, and also includes A/D conversion circuits and other functions) and a human-machine interface.
Node main functions:
a) Receive and execute patient medical orders transmitted from the central monitoring PC;
b) Receive remote monitoring request signals from the monitored patients in real time.
c) Record and upload the monitoring logs of the patients under your care to the central monitoring PC;
3. On-site monitoring and control nodes at hospital beds
The structural block diagram of the on-site monitoring and control node for the hospital bed is shown in Figure 7. It mainly consists of three parts: an MCU89C52, a CAN controller SJA1000 chip, and on-site sensor interfaces.
Node main functions:
a) Collect and upload real-time monitoring parameters of patients (including patient temperature, blood pressure, heart rate, respiration, etc.);
b) Send a patient monitoring request signal;
c) In response to control signals sent by the upper monitoring station, the automatic execution unit performs corresponding operations;
II. Software Design
The software design adopts a structured programming approach, exhibiting good modularity, modifiability, and portability. The entire system software design is divided into three main parts:
1. Software design for the interface adapter card of the central monitoring PC
Written in VC++ 6.0, an object-oriented visual high-level language based on the Windows 98 platform, it has a system...
The software includes functional modules for setting parameters (such as baud rate, output control, message identification and masking), monitoring status settings, data transmission and reception, local status query, node status query, real-time alarm, and interrupt data reception management. The software functional modules are shown in Figure 8. The host computer first initializes the CAN bus adapter card and itself, then sends commands to specific nodes to send data to the CAN bus. After conversion by the CAN bus adapter card, the data is processed by the central monitoring PC according to the actual situation. Commands are sent to each node using a timed polling method, while data is received using an interrupt method.
Secondly, there's the driver for the PCL-841 CAN card. The manufacturer provides a complete DLL driver function library for the PCL-841 card. When developing with VC++ 6.0, you first need to link this DLL library into the development environment, and then you can call the functions in the library. The library function calls need 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 handling. It primarily performs two tasks: first, receiving monitoring request signals and control algorithms from field monitoring nodes; second, transmitting node status and data information to the host computer when the central monitoring PC requests data. The node's main program flowchart is shown in Figure 10.
3. On-site monitoring and control node software design
The main function of the on-site monitoring and control node software is to complete the sensing and acquisition of physiological parameters of patients on-site and data fusion, as well as the automatic control of on-site medical equipment, and to realize digital communication with the central monitoring PC and other intelligent monitoring nodes.
4. Conclusion
Fieldbus technology, with its leading advantages, mature technology, and excellent cost-effectiveness, is increasingly being accepted by more and more fields. The author believes that the application of fieldbus in hospital ward monitoring systems, forming a fully open and distributed local area network, will inevitably lay the foundation for the new concept of the "digital hospital" for the 21st century. Furthermore, with the increasing intelligence of various medical devices and monitoring instruments, and the widespread adoption of network technology, home telemedicine (including health care) is an inevitable trend in the development of the medical industry. Therefore, remote home health monitoring systems will further provide broader application prospects for fieldbus in this field.
