While inadequate medical device design is not always directly linked to medical device-related malfunctions, user studies indicate that insufficient training accounts for 70% to 90% of such errors. However, even if those responsible have been held accountable, other factors can still harm patients. One such factor is inadequate human-machine interface (HMI) design. Many malfunctions are hidden within routine medical procedures and the use of medical devices, causing disaster for unsuspecting doctors and patients. The HMI is the part of a medical device that has a direct relationship with the user. The quality of the HMI design directly impacts the reliability of the medical device and the safety of the patient.
1. The meaning of human-computer interface
The interface between a person and a product is called the "human-computer interface" (HCI). The HCI sits between the user and the product system, serving as the medium for transmitting and exchanging information between people and products. The product's interface exists within the information exchange between people and things; in fact, it can be said that any area where human-computer interaction exists falls under the category of interface design. Its connotations are extremely broad, reflecting the relationships between people.
The development of human-computer interface design theory has organically integrated theories from various related disciplines, continuously improving its basic concepts, theoretical system, and research methods, forming a comprehensive interdisciplinary field with an extremely wide range of research and applications. Human-computer interface science encompasses knowledge from computer technology, psychology, ergonomics, design art, sociology, and anthropology, involving disciplines such as computer science, industrial design, new media, psychology, sociology, and anthropology.
A human-machine interface (HMI) encompasses all human-interacting components of equipment during use, preparation for use (e.g., calibration, setup, and activation), or maintenance (e.g., repair and cleaning). It includes hardware controlling equipment operation such as switches, buttons, and knobs, as well as other components like indicator lights, displays, and audiovisual alarms. It also includes a set of logic that guides the system on how to respond to user commands, including how, when, and in what form information is fed back to the user. A crucial aspect of an HMI is determining which logical information display and control behaviors align with the user's capabilities, expectations, and most likely actions.
2. Human-Machine Interface Design for Medical Devices
2.1 Arrangement and design of control/display devices for medical devices
Many medical devices have large control consoles, rows of control buttons, and displays. Designers should consider the user's ability to quickly and effectively identify control, power, and display buttons; access and precisely set controls; accurately read display information; and link controls with relevant displays. A satisfactory design includes an effective combination of control and display functions, clear and unambiguous labeling, and very easy-to-operate buttons. Clear instructions and effective alarms are also important. Unfortunately, however, there are many examples of errors in control and display design. The design flaws mentioned below all occur in the design of a certain brand of anesthesia machine.
As shown in Figure 1, this anesthesia machine has a rotary switch below the oxygen inlet that can add 5L of oxygen per minute to the fresh air flow. This is for rapid oxygen replenishment in case of emergencies or power failure. However, the extra oxygen flow is not displayed on the electronic flow meter. Accidentally activating this switch can cause mild anesthesia, so more visible indicators, such as a display screen, should be provided.
As shown in Figure 2, this anesthesia machine has three main knobs for setting the ventilator mode. The setting is moved from the lower right to the left of the control panel, which doesn't conform to user habits. This is because most of us naturally look down and to the right when reading, just like when we read a book.
This example illustrates that seemingly minor design flaws can lead to very serious problems. Establishing relevant human factors guidelines for medical devices can reduce the occurrence of such problems. The following are design guidelines for human-machine interfaces in medical devices.
Ensure that all aspects of the design align with user expectations. Consider existing and established user habits.
When designing the work platform, control, and display components, they must be aligned with the user's capabilities. These capabilities include physical strength, dexterity, memory, vision, and hearing.
Carefully organize the arrangement of the control and display components, and ensure that the relevance between the controls and displays is very obvious. These conveniences can appropriately reduce the user's memory burden.
Determine the intensity of the auditory signals so that they are easily audible to users of medical devices. Also consider the effect of ambient noise.
Ensure the visual signal is strong enough for the user to receive it under various ambient lighting conditions. Similarly, light intensity and color differentiation can also help optimize recognition.
Ensure that the signage and display are easily visible from various angles and distances. Careful consideration should be given to the size, contrast, color, and depth of the label.
Ensure that abbreviations, labels, text, and acronyms are clearly indicated or displayed, and that the use of medical devices is consistent with the instructions in the user manual. Where possible, they should all conform to standard medical terminology.
The control switches and knobs should be designed to be consistent with the usage habits of the user group (this depends on user learning and existing medical device standards).
2.2 Software Design of Medical Devices
With numerous control and display components, users must identify and integrate a great deal of independent information. The current trend is to add more functionality to software to reduce the number of control and display components, but this also increases the user's burden in another way. As shown in Figure 3, there is too much input information on a small display screen. Although there are few control and display components on the panel, the large amount of information displayed places high demands on the user's memory. A large amount of information must be recalled sequentially, which may prevent the user from observing other related data simultaneously. Without sufficient prompts and indicators, users begin to get lost in the information system. Similarly, without accurate functional status feedback and prompts, users may misunderstand the displayed data or react incorrectly.
Many usage errors caused by software design are attributed to other related factors because these errors are difficult to recall and identify during analysis and correction. Similarly, software-related errors are often subtle. For example, inconvenient data entry steps can frustrate users, leading to errors that aren't directly caused by these poor input methods. Unclear command structures and abbreviations or omissions in menus can also cause serious errors. There are relevant design principles for overcoming these problems, as follows:
Maintain consistency in the use and design of headings, defaults, icons, and tables to avoid ambiguity.
Ensure users are informed of the current status of medical devices in real time.
Provide timely and clear feedback during user actions.
User prompts, menus, and other information should guide users to consider the most important steps, rather than leaving them "stuck."
Provide users with sufficient resources when errors occur, and offer clear guidance on correction and repair.
Avoid providing unformatted, dense, or overly simplistic information, as this will confuse users and overburden them.
Use acceptable symbols, icons, colors, and defaults to convey information effectively, economically, and quickly.
When simple hardware solutions are available, avoid over-reliance on software. For example, a single button can provide timely and effective functionality.
Dedicated display sections should be provided for highly important information. In such cases, other data should not be displayed in these sections.
2.3 Component Assembly Design of Medical Devices
Currently, many different manufacturers produce components for the same medical device. Various types of wires, tubes, interfaces, and valves are available on the market. Different types of components often look very similar but are difficult to fit together, leading to poor contact or incorrect installation. Figure 4 illustrates how similar ports can confuse users and cause incorrect connections. In fact, these incidents can often be prevented through design. It is crucial that components and accessories of medical devices be treated as part of the system, not as isolated elements, during user studies, testing, and simulations. Relevant design guidelines are as follows:
Wiring, pipes, joints, valves, and other hardware should be very easy to install and connect. With proper design, improper installation should be impossible or very difficult, or easily detected and corrected.
User instructions should be easy to understand, and warnings should be clearly stated.
If a hazard cannot be addressed by design, colors and other markings should help users correctly connect components or install parts.
Circuit contacts should be protected (e.g., with insulating wrapping of conductors) to prevent leakage, short circuits, etc.
Components and parts should be labeled so that faulty parts can be replaced quickly.
2.4 Alarm Design for Medical Devices
Alarms and related warnings are used to alert users to the patient's condition and the status of the medical equipment itself; this seemingly straightforward function is often complex. In many environments, alarms sound simultaneously or intermittently from one or more medical devices, making them difficult to distinguish and easily distracting for healthcare workers. Alarms may be perceived as unpleasant or part of the background noise. They can also cause stress for users. Ambient noise and numerous visual displays often mask specific sound and auditory signals, and loud alarms can drown out others. Electromagnetic interference, electrostatic effects, or alarm oversensitivity often cause false alarms. Therefore, testing alarms in various environments is crucial. The following design principles apply to alarm design:
When designing and testing alarms, consider the environment in which they will be used and other medical devices that will be used with them.
Ensure that audiovisual alarms and other critical alarms are included in the design requirements.
Carefully consider the effects of oversensitivity, electromagnetic interference, and other electrostatic effects on the alarm.
The alarm should be positioned so that it is within or outside the visual and auditory range of the average user.
Ensure that the brightness and color contrast of the alarm are sufficient to be detected in different lighting environments.
When using codes (such as colors), they should correspond to the user's established usage habits.
Ensure that the alarms in the design are different from each other, and if possible, also different from the alarms on other medical devices used at the same time.
Ensure alerts are triggered promptly when critical issues occur. It's crucial that alerts help pinpoint the source of the problem.
Consider prioritizing critical alarms. Critical alarms should have more visual and auditory signals.
Setting an alarm can temporarily silence them.
Alarms should have visual cues, indicating the status and mechanisms to determine the cause of the alarm.
3. Other elements of the human-machine interface for medical devices
3.1 Scale, Intensity, and Angle
The work platform, seating, and control console that connect to medical devices should be user-friendly. Anthropometric data is crucial for medical device design; controls should be easily accessible, and seating should be highly comfortable. Anthropometric data is widely used in the design of anesthesia workstations, dental workbenches, and other medical devices, and it's also applied to many home medical devices, such as wheelchairs. In these designs, portability, compactness, and simplicity are paramount. Understanding both clinical and home environments is also essential.
Important but difficult to understand are the biomechanical aspects of tools, including hammers, dental instruments and tools, control handles, keyboards, and other instruments requiring actual sensitivity or force/repetitive movement. For example, a type of commonly used medical instrument shown in Figure 5 has very high requirements for size and strength. Surgeons and dentists often need to use instruments in confined spaces, and the problems that arise may not only be related to sensitivity and force, but also to visibility and the coordination with other instruments.
3.2 Changes in usage
Designers are often encouraged to create unique and distinctive products. However, this can impact user experience and training in healthcare settings, as doctors and nurses are accustomed to specific operating patterns for equipment. For instance, when two devices appear similar but require different operating methods, established habits for one device can conflict with the other. This can lead to errors caused by similar product operation. For example, swapping the ON/OFF switch on two very similar medical devices often results in users unconsciously repeating the same rotary switch operation when switching between devices. The same problem frequently occurs during the redesign or refurbishment of medical devices. This discussion is not to discourage innovation but rather to advocate that designers carefully assess the impact of changing user habits on the human-machine interface.
4. Conclusion
The discussion of numerous design flaws in medical devices aims to emphasize the importance of adhering to design principles. Good human-machine interface (HMI) design in medical devices can reduce user-related accidents and increase the versatility of medical device products. However, few medical devices on the market currently have HMI designs that are comprehensively considered. Therefore, it is necessary to adhere to detailed design principles in all aspects of interface design to minimize medical accidents.
