Inogen One designers employed a simplified interface. Patients have just four classes of decisions to make about the device.

A graying population is placing a greater demand on home health care, and with it, the need for medical devices that can be operated independently and effectively by patients at home or while traveling. The home medical appliance industry is expected to grow to a $7.5 billion market by 2009, and increase by 8 percent annually for the next five years, according to "The U.S. Market for Home Care Products," a study released in June by Kalorama Information, New York, N.Y., a life sciences market research firm.

As these devices increasingly become a part of the American home, however, design engineers must pay closer attention to the user’s interface with the products. Design consideration must be given to "human factors," or the science of interactions between people and technology, including users’ abilities, limitations and operating environment.

The user’s ability to effectively operate a home medical device hinges on a number of factors including medical training and experience, language barriers, literacy, memory, learning ability, dexterity, vision and hearing.

De-emphasizing deficits

The NxStage System One eliminates the need for a dedicated electrical line and the 20 amp fuses associated with in-patient dialysis machines. It instead functions with a standard electrical outlet. The system also has no water requirement, and can be used at home or during travel.

Often it is necessary to solicit input from outside organizations that may represent the end user, for example, when targeting an elderly population, the Arthritis Foundation may be a good source. Input from the physical therapy or occupational therapy departments of local universities can also be of assistance when designing a home medical product that provides for ease of use.

The focus is to make products that are targeted to a population with dexterity, visual or cognitive deficits, that de-emphasize those deficits, in other words, the end product should not be seen as one that was designed for the disabled or elderly.

Large and widely spaced buttons are often used for better control, and to eliminate errors. Spoken commands can also be used when it is necessary to eliminate the need for physical manipulation of the controls, and minimization of the need for sustained pressure on the controls to accommodate finger or hand strength are also strategies that are often employed.

Close to 9 million Americans suffer from visual deficits severe enough to make it difficult for them to read an ordinary newspaper, and over half a million people are legally blind. Design strategies for this population include providing tactile landmarks on control surfaces and providing a voice mode for redundancy of visual information.

Mobilizing devices

The NxStage system employs single-button pushes to increase patients’ comfort level with the menu. The simplified interface has four key operating buttons.

Designed as a single solution oxygen concentrator that can be used at home or during travel, the Inogen One from Inogen, Goleta, Calif., supplants the need for an oxygen tank for people with chronic obstructive pulmonary disease. This segment of the population includes patients suffering from asthma and emphysema as well as other respiratory illnesses that result in a reduced capacity to exchange oxygen in the lungs. About 1.6 million U.S. patients use prescriptive oxygen to treat their respiratory illnesses.

By switching to a portable device, Inogen One has been able to reach an evolving COPD population, which is now being diagnosed earlier in life, living longer and is increasingly ambulatory, according to Geoffrey Deane, vice president of engineering for Inogen.

When creating the Inogen One, designers took into consideration what a typical day would be like for the oxygen user. Running out of oxygen is a major concern for COPD patients. Patients using a conventional oxygen tank have to constantly be aware of how much oxygen is in their cylinder, and anticipate how long they will be away from home. Unlike an oxygen tank, the Inogen One gives the user the ability to plug the product into a wall, accessory power outlet on a car or under-seat adapter on an airplane to regenerate oxygen through an oxygen concentrator, which uses a reversible chemical sorption process to separate oxygen from the air.

The Inogen One also operates on the premise of oxygen conserving, so it only delivers oxygen during the inhalation portion of the breath. The system comes packaged with two oxygen conserving devices — one embedded within the concentrator, and one that is used externally, called the Satellite Conserver. When a patient inhales, a very small vacuum pressure wave travels up the cannula and is sensed by a sensor in the OCD. When the OCD recognizes the pressure wave as a breath, it opens a dosing valve and emits a bolus of oxygen down the same tube. A tube of relatively short length, typically 7 ft., is used to maintain consistent function.

To provide for ease of setup tear down, the NxStage System One designers replaced the fluid circuit of the conventional system with a disposable cartridge.

Patients do not always want to be within 7 ft. of the concentrator’s OCD, so Inogen duplicated the OCD functionality in a small accessory, called the Satellite Conserver. In this case, an up to 100-ft. tube may be attached between the concentrator and the satellite conserver, and a cannula of up to 7 ft. is attached to the Satellite Conserver. The concentrator’s OCD is then disabled and the dosing valve is continuously opened, allowing oxygen to flow down the 100-ft. tube, restricted only by the Satellite’s OCD. The Satellite provides the breath detection and oxygen dosing function, and the tubing acts as a small accumulator for oxygen product waiting to be delivered.

The Inogen One engineering team took several other factors into consideration when designing the device. One of the most significant was the consumer’s comfort level with using the device in public. To that end, they employed an organic form and shape, eliminating rigid corners and hard, flat surfaces on the device; instead incorporating curved surfaces to contain vibration and noise, as well as resist shock impact. The Inogen One’s noise concentrator operates at 35 dBA to 40 dBA, comparable to the noise level of a cooling fan on desktop computer, and quieter than the cooling fan on overhead projector.

Inogen One designers also employed a simplified interface. Patients have just four classes of decisions to make about the device: First, they can select the flow setting by depressing triangular shaped + and – buttons, which are raised and have lipped edges, allowing for tactile recognition for patients that suffer from degenerative vision. After each button press, the device emits a beep, the liquid crystal display back light is illuminated and the new flow setting is displayed on the LCD. The tactile design was extended to the remainder of the function keys, and all of the buttons and displays are located on the top of the concentrator, unobstructed from view.

Second, they can select the device’s power source by inserting a power cord into a DC input jack on the concentrator, or by inserting a battery in the battery slot. The power input jack is located near the top of the concentrator, and a co-axial barrel plug, which does not have orientation, was used to make insertion easier. The battery is "keyed," meaning that it has a shape that can only be inserted into the battery slot one way, and the battery slot has a handle for less dexterous users. When a power mode is changed on the concentrator, it emits a notification beep. Once a power mode is selected, an icon is displayed on the concentrator’s LCD indicating which power source is being used and the amount of power available. The LCD also shows the amount of battery time remaining, allowing users to better manage their time.

Third, users can select the OCD’s functional mode. The OCD can operate in several different schemes designed for different modes of use, for example, ambulation vs. sleep. The user depresses a button, marked "Mode," and the selected mode is displayed as an icon on the LCD. And lastly, they can elect to turn the device on or off by depressing the On/Off button. The system requires that the button be held depressed for a moment in order to turn the concentrator off, helping to avoid inadvertent shut-offs. The system also alerts the user when it is starting up or shutting down with a beep.

The device is operated by an on-board microprocessor, which constantly monitors system function, so the system can communicate a number of other informational items to the patient. For example, the device notifies the patient when the remaining battery power is getting low by beeping and lighting the backlight. It then provides text instruction on the LCD. When there is a system failure in the device, the patient is also notified with alerts: The device lights up multi-colored light emitting diodes, which convey different types of information, from errors (red), to notifications (yellow), and a flash each time a bolus is delivered by the onboard OCD (green). (A bolus is a concentrated volume of gas delivered medically to a patient as a dose. In this case, a pulse of oxygen, typically between 20 ml to 50 ml, delivered via the nasal cannula in response to the sensed onset of inhalation.)

Simplifying interface

The OmniPod Insulin Management System was designed for maximum discretion. It is worn directly on the skin, making it easy to wear the device under clothing. Also there is no tubing or pump to manage.

When designing the NxStage System One home hemodialysis system, engineers at NxStage Medical, Lawrence, Mass., wanted to eliminate all of the infrastructure requirements of conventional systems. To that end, they removed the requirements for a dedicated electrical line and the 20 amp circuit associated with the machine, and instead made the system function with the use of a standard electrical outlet by cutting the energy requirement to that of a typical light bulb. The system also requires no water and can be used at home or during travel, unlike conventional systems, in which a significant portion of the equipment itself is dedicated to preparing the water.

The NxStage system instead uses a pre-made sterile dialysate in bags, where traditional machines need to take tap water and to turn it into dialysate. The water requirement for a conventional system is at least 150 l a day. System One weighs about 70 lbs. to 75 lbs. and uses about three to four 5-l bags of dialysate per day. By contrast, an alternative home dialysis system requires water processing and weighs about 300 lbs.

To provide for ease of setup and tear down, System One designers replaced the fluid circuit of the conventional system with a disposable cartridge. The cartridge not only makes the system easy to load and unload, but also eliminates the majority of the maintenance generally associated with dialysis machines.

Because much of the dialysis patient population tends to be 65 and older, the design team chose to use a switch pad with low-depth menus. The system employs single-button pushes to increase patients’ comfort level with the menu. The simplified interface has four key operating buttons that control starting and stopping treatment, adding fluid and a mute function for alarms that signal the user if something has gone wrong with the system, for example, if there is air in the lines. Users of NxStage System One only need to know how to prime the system, connect it, run the treatment, rinse back their blood and resolve alarms to operate the system.

Discretely designed

Health Buddy from Health Hero is about the size of a small answering machine, and has a large backlit LCD, which communicates with patients in several languages, using four buttons to select information from a list. The design team chose blue buttons and a white look and feel to make device resemble a kitchen appliance.

The OmniPod Insulin Management System is designed to "enable" more people with insulin-requiring diabetes to manage their insulin through continuous subcutaneous insulin infusion. Only 5 percent of insulin-requiring diabetes patients use CSII, despite research that demonstrates the advantages of the therapy, according to Jeff Smith, vice president of marketing and business development for Insulet, Bedford, Mass. To help change that, the company identified the barriers to CSII use for insulin patients and designed its OmniPod system to address those barriers.

The system has no tubing that can catch, snag, disconnect and interrupt insulin delivery and eliminates the "tether" that conventional insulin pumps require between the pumping device and the infusion site by integrating the tubing, infusion set, inserter, insulin reservoir, power supply and pump into one Pod that attaches directly on the body. A Personal Diabetes Manager that programs and monitors the OmniPod also contains a blood glucose meter.

Conventional insulin pumps require a user to manually insert an introducer needle under the skin, then remove the introducer needle leaving a small plastic cannula for delivery of subcutaneous insulin. The OmniPod System automates this process with a push of a button on the PDM. In a fraction of a second the introducer needle is inserted, then withdrawn, leaving the cannula in place. The user never sees the "sharp" associated with the insertion process as it is drawn back into the pod.

The shape of the OmniPod was designed for maximum discretion, making it easy to wear the device under clothing, and there is no tubing or pump to manage. The PDM was designed with a large viewing screen and back light, making it easier to see the information displayed for users who sometimes suffer from vision problems associated with diabetes. The adhesive that attaches directly to the skin was bonded to the OmniPod in a manner that lets the device "float" on the skin, reducing stress and pulling on the skin.

The PDM has an icon-based menu that makes it intuitive to use. The PDM also uses sentences to reduce complexity, for example: “Do you want to activate a Pod now? Yes or No?” The user interface includes a food database that assists in the calculation of carbohydrates, integrating the insulin delivery, blood glucose monitoring and carbohydrate intake data in one source.

Appliance/patient relationship

The primary feature of HeartStart from Philips Medical Systems is its ready-to-go mode of operation. Previous defibrillators required users to open electrode pads, plug them into the device, and various other aspects of preparation. The HeartStart is preconnected — all the user has to do is pull a handle and then use it.

The Health Buddy from Health Hero, Mountainview, Calif., is an in-home health assistant, or hub, where patients go everyday to educate themselves, modify their behavior and communicate with their healthcare team, which can include a cardiologist, pharmacist, nurse and any number of other health practitioners. The system also collects vital sign information.

The device has a personal design that makes it look like more of a kitchen appliance than a medical one. It is about the size of a small answering machine, and has a large backlit LCD, which communicates with patients in several languages, using four buttons to select information from a list. There are also several numerical controls for inputting information. The design team chose blue buttons and a white look and feel to make device resemble a kitchen appliance.

Health Buddy is designed mostly for elderly patients with one or more chronic diseases, but can be used by children as well with modified commands. Health Hero actually sponsored a project in New York City, where children 14 and younger used the product, and they interacted with the device as well as elderly users, according to Geoffrey Clapp, senior technical officer for Health Hero.

Nevertheless, with the elderly user in mind, Health Hero made the Health Buddy a very simple question/answer device for a population that many times is not computer savvy. In working with elderly diabetics, who had lost parts of their fingers or extremities due to diabetic ulcers, or their fingers trembled so much that they had to press the buttons with their knuckles, the design team also took into account size of the buttons and the amount of spacing between the buttons. By holding to four large, widely spaced buttons, the design team also provided for ease of use for consumers with arthritis.

Health Hero additionally learned during the design process that the trust relationship between a patient and their device was key to its success. By using proper nouns instead of referring to the user as “patient,” and carefully wording questions, they found the trust relationship between the device and test groups increased. That trust relationship resulted in an over 67 percent reduction in hospitalization among the appliance’s users, Clapp says.

Testing iterations

The case of the Philip’s Medical Systems’ HeartStart is bright red on the outside with a reminder to call emergency services.

When thinking of the design for their HeartStart Home Defibrillator, Philips Medical Systems’ engineers noted that the system would be used very infrequently. Consequently, they had to ensure that the product would be ready to use when an emergency came. The HeartStart has extensive self-testing built into the device: It wakes itself every day to run self tests, checking its pads and batteries. If there are problems, it tells the user in their native language what the problems are and how to correct them. Philips Medical Systems, Andover, Mass., also noted that the person that would be using the system would likely be a family member, so the design team focused on creating features to calm the user down.

Natural sounding, professionally recorded voice prompting was used and color schemes for the system are task specific. The case is bright red on the outside with a reminder to call emergency services, however, once opened, the color pallet changes with a calming blue-grey interior. The remainder of the scheme is focused on the system’s primary features. For example, the start handle is a calming pastel green, drawing visual attention to the first device that has to be used to proceed with the rescue.

The design team provided for ease of use by relying on familiar mechanical metaphors. For example, to activate the device, the user pulls a handle that looks similar to a fire alarm handle, which is labeled the same way as a fire alarm —"pull."

The primary feature of HeartStart is its ready-to-go mode of operation. Previous defibrillators required users to open electrode pads, plug them into the device, and various other aspects of preparation. The HeartStart is preconnected — all the user has to do is pull a handle and then use it. The design team did extensive testing across all expected users, including the elderly. They found that the elderly had problems opening packaged products, particularly the foil for defibrillation pads.

The team therefore placed the defibrillation pads in a plastic container with a foil lid that is very much like a yogurt container, and found that the foil was much easier for the elderly to manage than the than tear-off tops that were on previous products. They then modified adhesive liner on the pads to make it easier to pull the liner from the pad. Testing was key to Philip’s design methodology, senior research scientist for Philips Medical Systems David Snyder says. Philips took their designs, built prototypes, mounted remote control computers inside of the devices so they could control mockups from a remote location, and then took their prototypes to anticipated user groups in shopping centers, medical centers, nursing homes and senior centers to interact with the test groups. They put the users through mock rescue scenarios with no training and recorded it with video.

"We looked at places where people failed, where they did very well, and we went back to the drawing board, iterated the product, and went back out and did testing again. One of the key realizations that came out of that experience was that whatever voice prompts we put in, there were going to be a small number of people who got stuck," Snyder says, and notes that to combat that problem the team added a system capability that allows the device to see where the user is in their resuscitation attempt. If the user does not complete a certain task, the system will give him or her more information, or speak the command in a different way. Users cannot move onto another task until the one they are on is complete.

"Those kind of features really come from the design iteration with users. Those are things you cannot do from a theoretical basis, you really have to go out and try it with customers and see how they respond, and go back and modify the product to address the issues you find."