We can all think of products that drive us crazy. They range from video recorders that are confusing to program to rigid-plastic packages that require a struggle to remove the contents. These are daily annoyances, but when it comes to medical devices, the result of difficult or confusing operations can have profound consequences resulting in costly inefficiencies and dangerous outcomes.

The study of human factors is also referred to as usability or ergonomics. For medical devices, human factors centers attention on the “user interface,” who will use the device, and where it will be used.

Human factors engineering (HFE) requires a thorough knowledge of the device from unpackaging it to preparing, using, monitoring, and finally storing or disposing of it. HFE also considers the clinical situation and clinical environment. A human factors study should answer numerous crucial questions: Who will use the device and what is their experience with similar devices? How does the device fit within a surgical suite, catheter lab, exam room, or home? What are the traffic patterns of caregivers around the device and patient?

Comfort, ease-of-use, and familiarity with a medical product translate into a lower risk of making mistakes. Successful designs are developed with attention to these details along with the subtleties of human perception and decision making in critical circumstances.

What's the worst that could happen?

Along with a good risk management plan, human factors studies provide another means of determining and mitigating potential hazards.

It's not hard to see that small errors can lead to large consequences with accidental device misuse. To make matters worse, many factors affect the performance of individuals using medical devices. HFE must take those factors into consideration. A few examples include:

Perception is the individual and varying tactile, visual, and aural recognition of features on devices. Examples include the varied sensitivity to different audio frequencies, and color blindness.

Physical attributes are the great variety and combinations of height, weight, hand sizes, physical strengths, stamina, and manual dexterity among medical-device users. Grip sizes, and the size and spacing of controls are common examples of variables affected by people's physical attributes.

Cognitive acuities vary in aptitudes to types of learning and memory, and also vary in response to stress and physical fatigue. The intensity of concentration required for procedures as well as their duration can take a toll upon mental acuity.

Who we are and our relevant training and related experience varies with the types of users such as physicians, nurses, medical technicians, professional caregivers, and patients.

Impact of environment includes factors such as distracting environmental sounds and visual ‘noise’, space constraints, weather, and lighting.

These factors are one set of the variables that affect the use of medical devices. Another set considers the complexity and large quantity of functions that typify many medical devices.

For example, RF generators have numerous settings for each function of cutting, cauterizing, and ablating. Errors in entering multiple set-points and misreading output displays can lead to hazardous outcomes.

Product such as these make design-for-usability more important and challenging than ever before.

The FDA is also increasingly promoting the importance of HFE for medical devices. The agency cites numerous cases of injuries and deaths attributed to medical device usability problems. Although there are no FDA directives regarding human factors engineering, the agency has published a human factors-guidance document that says that “Medical device manufacturers are required to follow FDA's human factors guidance and regulations to help ensure safe use of these devices.”¹

Human factors practitioners

Human factors engineering is performed by professionals from diverse backgrounds including degreed human factors specialists, mechanical engineers, software engineers, psychologists, and cultural anthropologists among others. Industrial designers are also human factors practitioners and have a unique focus and skill set that is well suited to the human factors engineering of medical devices.

Industrial Design is the professional discipline of conceptualizing and developing aspects of manufactured products for users' perceptions and interactions. Objectives of industrial design include accommodating engineering and manufacturing needs while meeting user needs and wants. As such, the industrial designer can be considered an integrator of engineering and user-related features. Inherent in the discipline is designing for manufacturing concerns. By combining attention to these details, industrial designers create integrated products and systems that meet user needs and wants while incorporating helpful technology and planning for effective manufacturing methods.

Attention to human factors is an essential aspect of industrial design. Industrial designers think outside the product by working to understand the types of people who will use the products and placing emphasis on addressing the user-related aspects of products. Design for usability has become a major role of the industrial design profession. Variables such as size, shape and location of controls and grips, labeling, and angles of displays are all factors that industrial designers work with on a daily basis.

The difference in an industrial design approach for device development versus a purely human factors engineering approach is often a matter of degree of attention to the variables mentioned, and the amount of research and development allotted to properly address and implement them for effective, efficient, and safe usability.

The value of ongoing involvement

When industrial designers are effectively employed in the development of a medical device, they become an integral part of the team. Addressing user-needs means they conceptualize medical devices in early development stages to create housing designs and other device details which accommodate design requirements and engineering specifications such as component sizes, ventilation, and mobility. Therefore, it is crucial that they work directly with engineering and science teams to properly accommodate those concerns. Developing medical devices, however, is iterative work that must allow for revised requirements and evolving engineering decisions. This iterative nature makes it crucial to involve industrial designers throughout development so industrial design of the device can evolve and properly accommodate the maturing development.

Similarly, to develop effective human factors for medical devices, the human factors engineer must be involved in early research as well as an ongoing basis throughout the product development. As an example, if the height of a console changes as components change, the visibility of a display on the console may be impaired.

Industrial designer as human factors engineer

Including industrial design and human factors engineering throughout development of a medical device can provide significant return on investment. The user-centered focus of industrial designers makes them effective as human factors engineers. Industrial designers can be engaged to research and identify human factors concerns, develop solutions for them, and then combine the solutions into designs for the devices. In addition, when attuned to the engineering evolution of a project, the industrial designer can evaluate and revise design features as necessary to ensure that effectiveness for usability and safety concerns are not compromised.

Those involved in HFE can access many methods and tools for understanding and developing human factors recommendations for medical devices. Here's a partial list of such tools:

• Cognitive task analyses provide an analysis of the intended sequential use of a device and can highlight potential problems during each step.

• Formal usability testing

• Focus groups with potential users who have valid input to a proposed device

• User interviews and questionnaires

• Anthropometric research can provide data for variables such as hand sizes and standing and sitting heights so that controls, handles, and displays locations can be optimized

• Review of training videos for predicate or other related devices can help provide insight into how similar devices are used and potential operational issues

• Physical human factors study models or mock-ups

• Observational analyses and ethnographic studies such as direct interaction with the intended medical users and observing prototypes or related devices in actual use (e.g. observing surgical procedures) can provide great insight into crucial human factors variables

Industrial designers that work on medical devices are typically experienced with many of these tools. In addition to user-centered research, mock-ups are particularly useful. These can be an expedient and cost-effective way to evaluate and refine human factors before development advances to costly prototypes. Here are a few examples of factors evaluated and refined using mockups:

• Display and touch panel sizes and placement. Mock-ups allow optimizing their visibility and reach.

• Sizes and location of controls. Mock-ups allow evaluation of ease-of-access and intuitive sequential use, and prevention of accidental or premature actuations.

• Hand positions for grips and mechanical operations. Mock-ups let testers optimize them to prevent or minimize strain and fatigue.

• Force levels required by users to activate controls or move components. Mock-ups can provide a means of identifying and measuring appropriate activation forces.

Qualifying human factors resources

When selecting an industrial designer or other resource for human factors engineering, it is advisable for the medical-device manufacturer to learn about their candidates' qualifications by asking questions regarding their experience and proficiency with various human factors engineering methods. In general, the device manufacturer can ask for specific examples of candidates' experience with HFE. These can initiate discussions and an understanding of whether a candidate is qualified to conduct human factors engineering for your needs. Ask candidates:

• How they have effectively researched and developed human factors solutions for other devices? Can they provide examples?

• Have they conducted usability studies?

• Have candidates conducted or planned user interviews or focus groups?

• What types of mock-ups has the candidate created to qualify and refine human factors? How long did these take and what costs were involved?

• Have they performed task analyses, and what were the benefits of such studies?

• What human factors methods would they recommend for your device?

• How have their human factors engineering endeavors benefited the resulting products and their customers?

As industrial design has matured from its inception in the first half of 20th century, emphasis has evolved from merging artistic forms into manufacturable products, and now to an emphasis that focuses on ease-of-use. This includes the integration of many controls and functions that exemplify today's products.

Putting design principles to work

The development of a new cardiac catheter device shows HFE at work. The device (pictured below) has a handle that requires six discrete control actions and must be operated by only one hand. Numerous controls make intuitive use a key design goal. Additional goals include optimizing the access of controls (the handle rotates during use), and providing safety features for all controls because accidentally operating any of them at the wrong time can result in patient injury, or halting the procedure and resuming with a new device. Also, when moving from one control to another, it is important to minimize hand movement because that may be adversely transferred to the distal end of the catheter.

Working with the customer allowed creating a multi-faceted approach to develop the device's human factors. For example, the design team:

• Created a detailed task analysis to understand and identify proper sequences and human factors concerns during each sequence

• Conducted initial interviews with physicians that use similar devices

• Observed a working prototype in a preclinical animal study

• Sketched human factors design concepts

• Modeled selected concepts quickly in mock-ups of foam

• Reviewed the mock-ups in roundtable discussions

• Refined human factors concepts with illustrations

• Prototyped three concept models (with a Polyjet RP machine) and included moving controls

• Interviewed 12 physicians individually for feedback regarding the three models

• Consolidated concepts into one design based on the physicians' feedback and rapidly prototyped a new model for their review

• Let human factors involvement continue during integration of the control mechanisms into the handle design and during preclinical studies that will use prototypes of the resulting design.

To date, this human factors program has been highly successful to determine qualified decisions for product requirements and direction for the industrial design and engineering of the device.

A few relevant standards

Medical device developers including industrial designers and human factors engineers should be aware of these FDA and ISO standards.

ISO 14971-1:2007 Medical Devices - Application of Risk Management to Medical Devices (per FDA site www.fda.gov/cdrh/humanfactors/resource-manufac.html#3) This document says human factors studies can be used to determine a device's ease-of-use and assess the extent of user comprehension and compliance to instructions and warnings for their safe and effective use. The standard was released in 2000 and amended in 2003 and 2007.

2001, ANSI/AAMI HE74:2001, “Human Factors Design Process for Medical Devices” is an FDA recognized guidance document.

2003 (amended in 2006) IEC 60601-1-8, Ed. 1, Medical Electrical Equipment - Part 1-8: General Requirements for Safety - Collateral Standard: Alarm Systems - Requirements, Tests and Guidelines - General Requirements and Guidelines for Alarm Systems in Medical Equipment.

Additional documents likely to be recognized by the FDA:

2007, IEC 62366, Application of Usability Engineering to Medical Devices

2008, AAMI HE75 — 3ed. Human factors engineering — Design of medical devices (Draft). This revision of the AAMI HE48:1993 is a comprehensive guide and reference for human factors engineering. In its draft state it is currently nearly 600 pages.

References for further reading

1. FDA CDRH website http://www.fda.gov/cdrh/humanfactors/resource-manufac.html

2. Overview of the FDA's New Human Factors Program Plan: Implications for the Medical Industry, Peter B. Carstensen, CDRH, Updated December 3, 1996