Proposed Standards and Guidance for Accessible Medical Instrumentation
Preface
Staff of the RERC-AMI from Marquette University and Human Spectrum Design joined the Human Factors Engineering (HFE) Committee of the Association for the Advancement of Medical Instrumentation (AAMI) in December 2005. At the time, the committee’s primary duty involved drafting a guidance document entitled: “Human Factors Design Guidelines for Medical Devices”, which included sections on various general and specific design topics that will soon become a national standard (i.e., ANSI/AAMI HE-75 anticipated in early 2008) once the formal review process is complete.
The RERC-AMI was primarily responsible for drafting the Accessibility Considerations section of the standard, which was generated and revised during an evolutionary process that involved numerous drafts until committee consensus was reached. Thus, several of the early drafts generated by the RERC-AMI included content that was later modified or deleted by the committee in order to make the Accessibility Considerations section more appropriate for the ANSI/AAMI national standard. But, because we feel strongly that a lot of the early material is important to share with interested stake holders, instead of letting the content go unpublished we decided to post this rich resource to our website. The material below comes from early drafts, and this information will continue to be revised without notice.
Introduction
Thise guidelines focus on addressing the needs of people with disabilities, who include medical patients and healthcare professionals of all specialties, and provides guidance for accommodating the variation inherent in any human population in the design of medical equipment. The goal is to make medical devices as accommodating of human diversity as possible in order to improve usability, access, performance and safety for all users.
The U.S. Census (2000) found that 1 in 5 persons over the age of 5 in the U.S. has a disability, although this proportion is probably low because many older adults do not consider themselves to be “disabled,” just aging. Importantly, it is also likely that the proportion of users of certain medical devices (e.g., patients who use equipment in the home) who have disabilities is well above one-fifth of expected users. Some people are born with disabilities, and some acquire them through accident or illness; some disabilities are temporary and may be related to the reason for presenting at a medical facility. For example, many patients who use medical devices (e.g., crutches, hospital beds, dialysis machines) have temporary or progressive functional limitations. Some disabilities are situational and may be exacerbated by poorly designed medical equipment. For example, in dim lighting, everyone has a visual impairment, which can make labels difficult to see; in noisy situations, everyone has a hearing impairment, which can make alarms difficult to hear or distinguish; and when the hands are full or gloved and wet, everyone has a manual limitation, which can make disposable packaging difficult to open.
Some healthcare professionals could be considered to have disabilities or activity limitations (although many deny it or at least would not use those labels). Some individuals enter the profession with disabilities, and others acquire them along the way. Of particular importance are those individuals who develop disabilities through repetitive stress injuries or traumatic incidents on the job, such as back injuries from patient handling and carpal tunnel syndrome from extended computer use. In addition, all professionals age and as they do, most will experience functional decrements including decreased near vision and some amount of hearing loss; arthritis is also common. An important fact is that overall the healthcare workforce is getting older. Increasing the employment of people with disabilities in the healthcare professions is a federally mandated goal, and this has special significance for certain professions such as nursing, in which there are both an aging workforce and a shortage of new workers entering the field. Every healthcare profession requires specific skill sets and ability profiles, so not everyone is a potential user of all equipment and many types of medical equipment do not need to be accessible to or usable by people with all disabilities. But in general, accessible medical device designs can help enable aging and injured providers to continue practicing medicine.
It is important to recognize that everyone is a medical patient – and that many medical patients have disabilities or activity limitations, either permanent or temporary. Because some medical devices are inaccessible, including some basic equipment such as examination tables, some patients with disabilities even avoid seeking medical care, which can aggravate primary conditions and cause secondary conditions. Accessible medical device designs can enable patients with disabilities to obtain the healthcare they need, and at the same time, can improve usability for most patients.
Accessibility is also a civil rights issue that has legal status. U.S. legislation that applies to medical device design includes the Americans with Disabilities Act ( ADA, 1990), Section 255 of the Telecommunications Act of 1996 (Section 255), and Section 508 of the Rehabilitation Act of 1973 as amended in 1998 (Section 508). The ADA prohibits discrimination against or segregation of people with disabilities in all public facilities, activities, programs, or services, including public hospitals and healthcare facilities. Section 255 requires that telecommunications products and services be accessible to and usable by people with disabilities, if readily achievable; and where it is not, devices and services must be compatible with peripheral devices and specialized customer premises equipment commonly used by people with disabilities. Section 508 requires Federal agencies to make their electronic and information technology (E&IT) accessible to people with disabilities; this law applies to all Federal agencies when they develop, procure, maintain, or use electronic and information technology. The US Access Board (http://www.access-board.gov) implements the regulations associated with these laws, and a design is considered accessible if it meets specific regulations.
While some industries depend on “separate but equal” alternative designs to achieve accessibility (e.g., separate, accessible toilet stalls in public restrooms to comply with the ADA), this approach is generally not economically viable in healthcare when serving diverse user populations. To cite an extreme example, no facility is going to have a special, accessible MRI machine that is used only for patients who use wheelchairs. The most logical and cost-effective solution is to have equipment that can serve the needs of the most diverse possible group of patients in a single unit that may have optional components or modes of use.
This approach of designing for people with all kinds of disabilities and everyone else at the same time has several names, such as universal design, inclusive design, design for all, or transgenerational design. Regardless of the name it is given, the goal is the same. In healthcare, the goal is to optimize medical device usability for as large and diverse a potential user population – whether lay or professional users – as is technologically practicable (readily achievable) and financially feasible.
It is not possible to design medical devices to suit absolutely every individual in every potential situation, but designers can usually get closer to this ideal than is true for many current equipment designs, and small design changes can make big differences in usability. When direct access is impossible, medical equipment needs to offer indirect access by being compatible with auxiliary “assistive” equipment that is either available to all (such as a magnifying device) or supplied by the individual user (such as reading glasses or a screen reader). Awareness of such options can influence the design process. Accessibility solutions often rely on multi-modal interfaces, which can end up adding complexity to devices; but in general, good use of human factors principles can enhance device accessibility as well as usability.
The guidance that follows is intended to provide extensions of other sections in HE-75 that directly relate to designing for users with a diversity of abilities. For most medical devices, the effective application of human factors practices will be synergistic with enhancing accessibility as long as designers recognize and include individuals with disabilities as potential device users in all stages of the usability evaluation process. Approaches are available for usability testing that systematically address accessibility by embedding inclusive design concepts into protocols, identifying access barriers and use error events for users with diverse abilities, and integrating post-activity questionnaires into the process (Winters et al., 2006b).
Scope
This section provides general guidance based on existing federal legislation, and on a consensus document called the Principles of Universal Design. This section does not include detailed descriptions of causes or types of functional limitations and disabilities, human skills and abilities (or disabilities) (see Section on Basic Abilities), or environmental access (see Section on Environmental Concerns). Specific guidance is then provided for patient support surfaces, weight scales, and healthcare applications of web-based information technologies.
Design Considerations
What are the most important general aspects of designing medical devices to be accessible for people with disabilities? In practice, this requires that devices accommodate the widest possible diversity and range of human abilities. This section presents a summary of various strategies for providing accommodation, including direct access through universal design, multimodal interfaces and alternative formats, and indirect access through commonly used assistive technologies (e.g., text-to-speech screen reader, pointing device, and wheelchair) and the interface requirements associated with use of such technologies in conjunction with medical devices.
Table 1 provides some self-reported disability incidences (for male and female U.S. populations) and some examples of functional limitations that may affect the design of medical devices. Table 2 summarizes information on the functions and types of interfaces needed for some commonly used assistive technologies. Table 3 provides a useful classification scheme for delineating between types of sensorimotor, interface, and device modes. Note that there are three primary sensory modes, each of which represents varying degrees of ability. For example, a reasonable accommodation for an individual who is blind may be different than for a person with a specific type of partial visual limitation. Such degrees of ability are also true for motor abilities such as manual control and speech production. Also note that many interface modes are inherently multimodal; for instance, a “control” device such as a keyboard has a tactile component (e.g., excursion and stiffness of keys), plus a visual component (labeling and motion of keys), and an audio component (sound associated with key depression or retraction).
Table 1: Some self-reported causes of disability among 41.2 million adults (age 18 and older) in the United States in 1999 and some possible functional limitations associated with each disability |
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Cause of Disability |
Total (%) |
Men (%) |
Women (%) |
Some Possible Functional Limitations |
Arthritis or Rheumatism |
17.5 |
11 |
22.4 |
Joint stiffness, joint contracture/deformity, joint pain, muscle weakness, joint weakness/instability (Arthritis Foundation) |
Back or Spine Problem |
16.5 |
16.3 |
16.6 |
Back stiffness, pain, limited side/forward reaching/bending |
Deafness or Hearing Problem |
4.4 |
4.4 |
2.6 |
Loss of ability to hear specific tones, inability to perceive sounds |
Limb/extremity stiffness |
4.2 |
4.2 |
3.9 |
Loss of fine and/or gross motor control, limited joint range of motion |
Mental/emotional problem |
3.7 |
3.7 |
3.5 |
Difficulty concentrating, indecisiveness, slowed or fuzzy thinking |
Diabetes |
3.4 |
3.4 |
3.4 |
Decreased tactile sensation, vision loss, hearing loss, limb loss, decreased mobility |
Blindness/vision problems |
3.3 |
3.3. |
3.1 |
Blurred vision, cloudy vision, double vision, difficulty with color discrimination, loss of central vision |
Stroke |
2.8 |
2.8 |
2.4 |
Dysphasia, loss of sensation, visual deficits, joint contractures, spasticity, muscle weakness or atrophy, changes in muscle strength, tone and response, loss fine and/or gross motor control, upper extremity flexion synergy patterns (Thorn et al., 2006; Shumway-Cook and Wollacott, 2000) |
Broken bone/fracture |
2.1 |
2.1 |
2.2 |
Limited strength, limited mobility, reaching difficulty |
Mental retardation |
2 |
2 |
1.4 |
Limited memory, |
Cancer |
1.9 |
1.9 |
2.1 |
Fatigue |
Head/spinal cord injury |
1.1 |
1.6 |
0.7 |
Limited memory, paralysis, spasticity, limited mobility |
Learning disability |
1 |
1.4 |
0.6 |
Reading difficulties, limited memory |
Alzheimer/senility/dementia |
0.9 |
0.6 |
1 |
Short term memory loss, speech impairment |
Paralysis |
0.8 |
1 |
0.6 |
Limited mobility, reaching difficulty, skin pressure sensitivity |
Missing limbs |
0.7 |
1.2 |
-- |
Balance, dexterity |
Epilepsy |
0.5 |
0.9 |
-- |
Seizures |
From CDC, 2001, Prevalence of Disabilities and Associated Health Conditions Among Adults-United States, 1999. MMWR 2001: 50(7): 120-125. |
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Table 2: Examples of assistive technologies (AT) that a designer may need to interface with to provide indirect access to the device, or to accommodate for when providing direct access. |
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Assistive Technology |
Function |
Interface |
Text Telephone (TTY/TDD) |
Enables users who are deaf, hard of hearing, or have speech limitations to communicate via telephone by typing and reading messages instead of talking and listening (or sometimes with intermediary voice relay operator). Letters typed into the machine are turned into electrical signals that travel over regular telephone lines, and are converted back into letters that appear on a display screen and/or are printed on paper. |
May include phone jack, keyboard with 20 to 30 character keys, display screen, ring indicator (flashing light), telephone modem, printer |
American Sign Language (ASL) |
Enables users to communicate using signs made with the hands and other movements, including facial expressions and postures of the body. |
Requires clear line of sight; if remote, must include visual display, may include tactile display for individuals who are deaf-blind |
Braille |
Enables users who are blind (and deaf-blind) to read by touching with their fingers an array of raised dots that represent letters, numbers, and punctuation. |
Tactile labeling, consider user reach range to such labels |
Screen Reader |
Converts text into synthesized speech so users can listen and navigate through software content. The user can allow the screen reader to read everything from top to bottom, or one line at a time, or use the tab key to navigate from link to link, from one heading to the next, from one frame to the next, or by other methods. |
Requires software, audio display, text based content |
Magnification |
Enables displayed information, such as that on a computer screen, self-contained monitor or a control, to be readable by a person who has low vision. |
Consider approach space, clear line of sight, software or physical magnifier (may be carried by the user or embedded in the product) |
Voice recognition/activation software |
Enables use of voice commands as an input mode to devices. Two categories: systems with limited vocabulary that are intended for many users, and systems that use learning algorithms and involve training that are customized to a specific user. |
Requires user speech, microphone, software, compatible operating system; may involve a visual and/or audio display |
Cane, crutches, walker |
Facilitates user balance while standing or walking |
Consider approach space, reach space, one- or no-hand operation of controls, grab bar for balance aid and/or AT storage during medical device use |
Guide cane |
Enables users to detect their environment while moving through space; for example a person who is blind tapping for spatial orientation and object detection |
Consider approach space, shapes of devices near floor may be tapped |
Headstick, mouthstick, dowel |
Enables users to activate buttons and keys without use of fingers. Often held in the mouth or strapped to the forehead or hand splint. |
Buttons and keys should be flat or preferably, concave. |
Assistive listening system |
Used to transmit sound as directly as possible to a transducer in the ear of a user who is hard of hearing. |
Small personal amplifier, microphone, extension cord. |
Lift equipment |
Generally used to transfer an individual from one support surface, such as a wheelchair, onto another, such as an exam chair. Includes a controller and mechanical interface (with a surface that supports the individual in a sitting or lying position. |
May be portable, ceiling- or wall-mounted, etc., but in all cases the occupant, perhaps with aid, must be placed into the lift, the controls must be operated, and the occupant must safely exit the lift. |
Wheelchair, scooter |
Enables users with limited mobility to move through the environment without bearing weight on their legs. |
Consider clear path of travel, approach space, reach space |
Table 3: Categories of sensory, interface and device “modes” |
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Sensorimotor Modes and Key Categories of Functional Limitations Associated with Each |
Interface Modes |
Device Modes |
Vision (Visuomotor) Blindness Partial sight Visuomotor limitation Colorvision limitation Hearing Deafness Hearing limitation Touching/Manual Loss of sensation, motor Partial sensation, motor Biomechanical loss or joint contracture Gross sensorimotor, reaching Fine sensorimotor, dexterity Speaking |
Input Control buttons, knobs Keyboard Mouse pointer (e.g., standard, roller-ball, touchpad, force-pointer) Touch screen Joystick Microphone/Speech recognition Head/mouth pointer Output Display/captions Dial, gauge Magnifier Audio/speakers Volume control Vibration
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Conceptual modes associated with device use, often associated with grouping of functions, that a user should be able to easily understand, and switch between, in the process of using the device.
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Finally, it is useful to introduce the concept of “roles” to help define the scope of intended users of medical devices. As long as product designers clearly identify the roles of the individuals who are expected to use their products, additional considerations for accessibility may be unnecessary because certain roles may require certain abilities (e.g., vision and fine motor control for performing traditional surgery). Borrowing from terminology associated with the Health Level Seven (HL7) medical informatics standard (see http://www.hl7.org) that is used for both health information exchange and reimbursement, an “entity” in a “role” “participates” in an “act.” An “entity” only exists in the context of being associated with a “role,” and here “entities” include people and devices. Key “roles” for medical device users are practitioners and patients, which each have attributes within the HL7 system. Devices and individuals are only connected by virtue of their participation via “roles,” whereas the “role” of a medical device generally involves safe and effective use by an individual (or individuals) “participating” in a specific “role,” and furthermore, perhaps within the context of a specific environment. Finally, it is the individual in a role who may have a disability, and once the roles for device use are defined then it should be recognized that it is likely that even those persons who are capable and trained to participate as users are likely to have a diversity of abilities (particularly as they age); this helps define the scope of intended users.
Guidelines
There are many ways to design products to be accessible, and strategies that improve usability and sometimes accessibility are integrated throughout this standard. General guidance here, Section 3.1, is based both on adapting aspects of existing guidelines to medical devices and on considerations of universal design principles. Specific guidance, Section 3.2, provides guidance on accessible design approaches for specific types of medical equipment, some based on research (and often closely related to other sections of this standard) and some based on technical specifications developed for the implementation of federal legislation.
General Guidance
Three general approaches are described:
- Guidance on medical device access for individuals with disabilities based on multimodal interface design, and on the conceptual framework used in the U.S. Access Board’s regulations for Section 508 of the Rehabilitation Act, Section 255 of the Telecommunications Act, and the Americans with Disabilities Act.
- Guidelines based on the universal design principles and inclusive design strategies, as applied to the design of medical devices.
- Guidelines on strategies for enhancing accessibility when integrating telecommunications capabilities into home and mobile medical devices.