A brief introduction to the concept
Defibrillators show the future direction of health care. This device has become an important life-saving technology, but only a few years ago, only hospitals and ambulances were equipped, and only trained medical professionals would use it. Some people are still skeptical about the function of defibrillators. Imagine if a colleague suddenly covered his chest and fell to the ground, what would the untrained staff do? It must be to run to the cabinet, smash the glass, take out the defibrillator’s “Quick Start Guide”, and quickly browse to learn about the connection, control and preventive measures. At the same time, the patient is still suffering from pain on the ground. At the same time, the rescuer’s mind flashed with countless similar scenes from medical dramas, in which doctors usually defibrillate themselves or nurses rather than patients. But in reality, it is not so dramatic, medical technology has been out of the hospital and into the workplace and people’s daily life.
Defibrillators in the workplace
This kind of defibrillator will explain to the users who have never used the defibrillator how to use it, and how to use the monitor and lead switch correctly. The machine will then determine the appropriate amount of electricity according to the patient’s condition to prevent the novice from injuring himself when rescuing the patient. When emergency medical staff arrive, they can connect to the defibrillator and download the data stored in it, so that the data can be brought back to the hospital for doctors to view and analyze.
Development direction of medical and health care equipment
The above story shows the prospects and challenges of home electronic health care technology. Medical equipment is no longer limited to clinical application, but more and more into people’s daily life. Such devices include: Health AIDS (such as a calorie calculator app on a mobile phone or a heart rate monitor on a treadmill), life sustaining infusion pumps, vital signs monitors for long-term data recording, and emergency equipment (such as defibrillators). In order to bring medical monitoring and medication equipment into the family, they should have the following characteristics:
1. Portability: small power, low power consumption, easy to carry for elderly patients (attachment: power technology helps the whole people mobile medical).
2. Intelligent: the equipment can ensure the correctness of its configuration according to the monitoring information obtained, so as to complete the target task or give a reminder when emergency treatment is needed.
3. Safety: the safety design of the equipment must reach the level of the old products provided in the hospital, so as to ensure the safety of the untrained personnel when using the equipment.
4. Connectivity: easy to program, update and read data. These devices must be able to connect to non-medical devices, such as commercial networked computers, in order to communicate with telemedicine facilities.
The innovation of medical and health care equipment requires more attention to security, and the degree of attention is at least no less than that of electronic devices currently used in hospitals. Security includes many aspects. The device must be able to judge for itself whether the connection is correct and the condition of the patient. The device must be able to prevent misoperation or malicious tampering. For privacy requirements, the device must store and transmit patient data in a secure manner. In addition, the equipment must have good electrical safety to ensure that there will be no circuit failure when connecting with non-medical communication equipment or other household appliances, so as to prevent high-voltage or leakage current from flowing into the human body. Electrical safety is largely ensured by isolation. After the implementation of electrical isolation, the power supply is electrically isolated from the power supply loop or other medical equipment (such as defibrillators and other devices that generate high voltage). The second half of this paper will focus on how to realize the security isolation of medical devices, especially those used in non clinical environment.
In medical application, patients are easily injured by electrical equipment. Under this protective layer of skin, body fluids are mainly composed of saline containing blood and cytoplasm. Salt water is a good conductor of electricity, while skin is a good insulator when dry. Medical devices that try to monitor the interior of the body use large areas of electrodes and conductive glue to reduce skin resistance. This means that any unplanned signals on these medical devices can easily generate electric currents, which can flow through the patient’s body, disrupt the nervous system and affect the function of organs such as the heart. When designing electronic medical equipment with electrical safety, these important electrical safety requirements are part of iec60601 medical safety standard. Even if it looks like a very ordinary application like the heart rate monitor on fitness equipment, it must comply with the isolation specification to ensure safety. Life threatening equipment must meet stricter standards.
Ensure that the equipment is not affected by harmful power supply and control grounding
The main sources of electronic signals in the power grid are out of plan. Medical applications must be able to block AC Leakage on 50 Hz to 60 Hz lines and current transients due to lightning strikes, switching noise, or line faults. This is not for medical devices; however, medical devices are more demanding in this regard, and the amount of leakage current depends on how the device is connected to the patient.
The connection between the device and the patient must also be isolated to prevent the device from using other connections as another circuit when the patient uses multiple medical devices, resulting in abnormal current direction. In addition, if the patient has access to any equipment (such as a home appliance or metal bedstead) connected to the building’s safe ground, the current must not pass through that path. Insulation for patients requires two separate insulation systems, or a single system proven to be equivalent to two separate systems. This is called dual patient protection isolation, or 2mopp for short. The difficulty lies in ensuring the safety of communication and power supply of domestic medical equipment. Next, we will focus on the communication interface.
How to achieve isolation requirements for electronic equipment
Typical home electronic medical devices need to communicate with other medical devices or existing home electronic facilities, which should meet the privacy and security requirements to ensure that the information is not intercepted or damaged, but also comply with the leakage and security requirements of iec60601 standard. In general, electrical connections need to provide dual patient protection and should normally meet the following conditions: rated withstand voltage of 4KV, very low capacitive leakage and defibrillation resistance rating.
Electrical safety requirements can be achieved by the following methods.
Radio frequency communication
The first method is to communicate over radio frequency links (such as low-power Bluetooth or ZigBee standards), which can completely avoid electrical connections. A battery powered medical device with a non-conductive enclosure can meet all isolation requirements. The advantage of Bluetooth is that most laptops and smart phones provide this function, so the device can be connected to realize data recording or remote control. The ZigBee interface needs additional interface hardware to communicate with non-medical network devices such as home laptops. For monitors with low data transmission rate and inconvenient connection, this method is more ideal.
The disadvantage of radio frequency communication is that this type of link is easy to be interfered by radio frequency source and easily tampered with maliciously. Because the signal is transmitted in the air, it is necessary to encrypt the data according to the medical privacy law to prevent the data from being intercepted. For simple devices, this method will consume a lot of application resources. Establishing such connections also requires knowledge, which is not easy for elderly patients. Although RF communication meets all security requirements, its stability makes it less suitable for life-threatening applications. However, the mobility of wireless technology makes it the preferred communication mode.
Some applications of this approach include patches with built-in monitors and blood glucose meters that automatically record data. In order to ensure the safety of users, these devices do not need to be connected at any time.
If data integrity and stability are required, wired interface is the best choice. High speed data transmission can be realized by using wired interface, and there is almost no error. At the same time, the power supply can be provided by connecting with the interface. The common interface is USB, RS-232 or RS-485. The wired interface is stable and reliable enough to be used for data recording, providing critical control information to life sustaining applications and updating device programs. USB is the only standard interface for PC and mobile phone. However, this interface must meet the strict isolation requirements of iec60601. The common practice is to design the device as a non isolated interface, and it can only be used when the device is not in contact with the patient. For example, when using the device, the USB port can be placed under the cover plate, which can block the USB connector when the device is working. The advantage of this configuration is low cost, but the disadvantage is that it cannot be monitored in real time, and it is not suitable for applications where the connection between the device and the patient cannot be easily removed. Therefore, this method is very suitable for devices that do not need continuous connection to patients, but it is not suitable for devices such as infusion pumps that enter the patient’s body and must be used in the clinical environment.
Another type of mechanical interlock is used for field deployed defibrillators. The defibrillator’s shell is directly equipped with a network interface. Once the defibrillator is placed in the shell, it will be connected and charged by itself. In addition, the device will regularly self diagnose, check the battery condition and report the status data through the network. When using the defibrillator, it must be removed from the housing to cut off the network and power connections. The last type of mechanical interlock is the removable memory element. Similar to the SD card in a digital camera, after the data is written into the memory card, the memory card is taken out and read in a separate reader. Finally, the data will be sent to where it is needed. This is the most laborious method, because patients may not be required to do these things themselves.
The most reliable way to realize communication is to use wired isolation interface. It has the stability of wired interface, and can provide power through the built-in isolated DC-DC converter. It supports high-speed upload and download, and can be used when the device is connected to the patient. The wired interface does not need to encrypt the data, which reduces the processor overhead. Software maintenance can also be completed while the equipment is running. The interface can also be set up to realize real-time remote monitoring under high data transmission rate. For example, if patients need regular review, doctors can remotely obtain ECG information of patients. In general, the isolation of these interfaces depends on optical couplers and other devices, but these devices have certain limitations in transmission speed and poor integration ability. However, medical grade Digital Isolators do not have these limitations, so they are gradually replacing optical couplers in new applications.
The communication interface mentioned in the “mechanical interlock” section of this paper can be isolated by suitable digital isolators. For many years, RS-232 and RS-485 have been the main interface types of isolated medical communication. They are compatible with ADI’s adum2201 and other products, and meet the requirements of 2mopp medical rated performance in iec60601 standard. Unfortunately, these interfaces are not used by non-medical electronic devices. As a result, USB has become the most widely used interface. Adum4160 has realized USB isolation, and also has 2mopp anti defibrillation protection function. It is being designed for infusion pumps, defibrillators, noninvasive blood glucose meters and a variety of clinical patient monitors. It can be directly connected with non-medical grade PC for real-time monitoring. At the same time, its connection still has sufficient anti fibrillation ability and complies with relevant leakage specifications. Even in the system using wireless communication, USB port is provided for software maintenance and battery charging. Since there is always a need to connect USB, port isolation is performed for security reasons. The disadvantage of wired interface is poor mobility.
The defibrillator in Figure 1 has several different interfaces and uses a variety of isolation techniques, so it is an excellent example of checking isolated communication interfaces. The device must use ECG to monitor the patient’s heart activity to determine whether defibrillation is needed. The ECG data path must be isolated from the high voltage portion of the defibrillator so that sensitive ECG Electronics will not fuse when shock is applied to the patient. Isolation can be achieved internally by isolating gate drivers and digital isolators. The device can also be integrated with Ethernet interface. When the equipment is idle in the wall mounted box, it can receive the status monitoring through the Ethernet interface. The Ethernet interface is mechanically interlocked, so it cannot be used when the defibrillator is removed from the external wall mounted box. Similarly, the battery charging system is also connected to the wall mounted outer box and interlocked. The last function that needs to be isolated is the communication port, which allows ECG and defibrillation data to be downloaded for doctors to view and analyze. This connection generally isolates the USB interface, so data can be obtained without disconnecting the device from the patient.
Medical monitors and treatment equipment are gradually breaking the inevitable relationship between the clinical environment and the provision of medical care. These devices greatly improve people’s quality of life, so that people can receive high-quality treatment and monitoring at home. The perfect mobile monitoring and treatment drug delivery system can analyze human needs in real time and give drugs accurately in real time. For example, insulin infusion pump can imitate the human body’s insulin response, so as to better manage the disease of non bedridden patients. Through the new technology, patients who are temporarily unable to go to the hospital or clinic can also transfer their monitoring data to the hospital which is a few hours away from home. The heart monitor can also detect the condition before the patient has symptoms.
Medical information must be transmitted between medical equipment, doctors and equipment maintenance units. Working parameters such as the dosage of the drug must be transmitted to the device. It must be ensured that the firmware of the device is the latest version. At the same time, a variety of methods must be used to maintain the electrical safety of the equipment. All isolation methods discussed in this paper are suitable for household or clinical health care equipment which need high safety and reliability. The most appropriate isolation method can be selected according to the specific needs of specific applications.