Monitoring patient vital signs in their homes can lead to better health care at lower cost. However, designers must be ready to address a set of design challenges that are unique among medical devices.

Today’s increased quality of medical care comes with a price—higher costs. Remote diagnosis and treatment of illness is fast becoming the leading trend in the medical technology industry. Telemedicine promises increased health care quality while reducing costs. In particular, home health telemonitoring is a rapidly growing segment in both revenue and research & development funding.

Frost & Sullivan estimates the home telemonitoring market will see $260 million in sales in 2010, growing at 24% per year. Additionally, the American Recovery and Reinvestment Act of 2009 provides for $20 billion in R&D funding for new medical technologies, with telemonitoring prominently called out as one of the target technologies

Why Home Healthcare?

Regular automated monitoring of patient vital signs can alert health care professionals to emerging problems so that medical intervention can take place early, when it is typically the more effective and less costly.

Home telemonitoring is used for managing a variety of conditions. For example, patients with congestive heart failure can have their weight monitored. A sudden spike in weight can indicate fluid buildup due to a worsening condition. If caught early, treatment is more likely to be easily managed and hospitalizations reduced.

Patients with diabetes can be monitored to make sure they regularly check their blood glucose levels and maintain these levels within a healthy range. Detected problems lead to a discussion with the patient on ways to improve their diet. Stable blood glucose control has been demonstrated to greatly reduce grave complications of diabetes, such as heart disease and blindness.

Unexplained fainting spells and other symptoms may indicate transient cardiac problems, which can be difficult to diagnose because they may occur irregularly, e.g. for only a few moments every few months. By wearing a small electrocardiograph device that continuously sends data for review, medical professionals will catch patients having any cardiac problems in real time.

Telemonitoring: Systems View

Figure 1: Block diagram of a typical home telemonitoring system. Data from a number of sensors in the home is aggregated and held by the base station, and eventually transmitted to the data center for storage and review.

In a typical telemonitoring system (Figure 1), a patient generally uses various physician-prescribed devices as necessary, such as a blood pressure cuff and glucose meter to monitor their specific conditions—we’ll generically refer to these as sensors.

Different patients are prescribed different sensors as appropriate to their specific needs. Sensors transmit collected data, either wirelessly or via cable, to a base station in the home. The base station, in turn, aggregates this data and regularly transmits it back to a central location for storage and analysis. In some implementations, patient questionnaires may also be sent to the base station, and results transmitted back.

For designers and manufacturers, home health telemonitoring systems occupy a unique niche. They are medical devices rigorously regulated by the FDA. However, this market segment, in certain respects, is a hybrid between medical devices and consumer products because end-users include patients and others, not just medical professionals. As a result, as insurance reimbursement for home telemonitoring evolves, these devices are more cost-sensitive than most other medical devices. Production volumes are typically higher than they are for most medical devices but lower than for typical consumer devices.

The “medical device” consists of more than just electronics in an enclosure—it includes a complex infrastructure featuring local- and wide-area networking, a sophisticated back-end database, analysis software used by medical professionals and so forth. Creating these devices presents several challenges that the designer must deal with.

The Product Experience

Engineers and designers who develop medical devices are typically accustomed to addressing the needs of well-educated and expert medical professionals. Medical professionals have an important role in home telemonitoring, but two other constituencies must also be considered: the patients and the installers.

Patients include people who may have a high school education or less and are typically older and often have disabilities including visual and hearing impairment, and cognitive issues.

Installers and/or technical support are the individuals who will get the system up and functioning in the patient’s home. Background and training of these people may vary greatly here, ranging from medical professionals to dedicated installation technicians. In some cases, the patient or family may perform the installation.

The case for a successful user experience is made stronger by the FDA’s growing emphasis on human factors as a key element in device design—in a growing number of cases, product recalls have been initiated solely due to a confusing design that makes errors likely. The general approach for success here is to follow a human-centered design and be empathetic to the users. Basic design principles include:

  • Delivering a user experience that integrates into the typical behaviors and environment of the end user. By lowering the effort required to adopt a device, users are more likely to stay in compliance and the device is better able to deliver the intended benefits.
  • Providing timely feedback and status indication. Multi-sensory feedback is crucial for many elderly users because of their degrading physiological functions. “Quick and at a glance” status screens are also highly desirable to people who need to constantly monitor their health condition.
  • Testing with users early and frequently throughout the development process. Even the best design intent can sometimes create adverse effects. The only proven approach for reducing/minimizing design errors is to prototype the design and take it to the users for feedback.

Device Communications

There are many brands and models of sensors for measuring vital signs (blood pressure cuffs, scales, etc.) that support wired or wireless connectivity. Unfortunately, the market is quite fragmented with regard to means of communication. USB, RS-232, Bluetooth and proprietary wired and wireless technologies are all in widespread use. This poses a challenge to the designer of the base station that receives, aggregates and forwards measurement.

Fortunately, there is a growing effort toward standardizing the communications methods used by these devices. The Continua Alliance is an association of roughly 200 manufacturers of medical devices and supporting industries (contract design, software, electronic components, pharmaceutical, etc.), with a mission: “To establish a system of interoperable personal telehealth solutions that fosters independence and empowers people and organizations to better manage health and wellness.”

Figure 2: Classes of devices defined in the Continua design guidelines.

As part of its mission, Continua has developed standard protocols for communications between monitoring equipment and base stations. These protocols utilize USB and wireless Bluetooth, ZigBee and Bluetooth Low Energy technologies to support interoperability. For example, any base station that supports the Continua standard on Bluetooth should be able to operate with any peripheral that supports that standard. Continua adoption continues to ramp up with about 15 devices certified to date. The Continua design standards are ambitious and broad, including local- and wide-area communications in a number of usage cases. Figure 2 and Figure 3 demonstrate the Continua model of interconnectivity.

One of the most challenging pieces of the home telehealth game is transmitting data from the base station to the central monitoring station. A variety of communication technologies can be used, including telephone modem, Internet (via Wi-Fi or Ethernet) and cellular modem. No single technology will work in all situations so designs should support multiple technologies. Care must be taken to ensure reliability as well as adherence to privacy standards such as the Health Insurance Portability and Accountability Act (HIPAA).

Controlling Cost

As in many areas of medicine, insurance reimbursement for telemonitoring lags somewhat behind the technology. For this reason, controlling device costs is critical; there are several strategies that can be helpful here.

Figure 3: Interconnectivity between Continua device classes.

Particularly in the medical device world, bringing a product to market is often thought of as a two-step process—first design the product, then move to manufacturing. However, close collaboration between the designers and manufacturing during the development process can lead to important cost savings. Most obviously, this helps to ensure easy manufacturability, which translates into lower unit costs and higher reliability. Also, using a manufacturer’s supply chain resources during the design phase to negotiate volume component costs, before design-in, can lead to less obvious but potentially very substantial cost savings. For example, a manufacturer’s buyers can work with multiple vendors and distributors to obtain pricing for, say, Bluetooth modules, prior to a part being selected and designed in.

As with all medical devices, obtaining commitments on the extended availability of components is critical—the need to switch to a new part once manufacturing commences not only requires a change in design, it also requires a new round of verification testing. However, a conundrum exists in that the lowest-priced parts are often those that become obsolete the soonest. In many cases, it makes sense to use commercially manufactured modules that implement higher level functions rather than going with a “from scratch” approach. Some module manufacturers provide value through using low-cost parts yet guaranteeing availability for as long as 10 years by internally managing any changes due to part obsolescence. Since changes are managed within the module, they have little or no effect on the rest of the device and reduce the need for redesign and reverification.

System Complexity and Verification

In the case of a home telemonitoring system, the “medical device” is much more than a box that rolls out of the factory. Rather, it consists of many subsystems, often from many vendors.Various sensors and communications technologies may be employed for different patient installations. Computers and telecommunications equipment make up part of the picture, and these may need to be upgraded or otherwise altered over time, e.g., as bug-fix patches are released by a software manufacturer.

As these are FDA-controlled systems, the manufacturer of telehealth systems must ensure proper verification testing, and this can be a challenge that is not often appreciated in advance. Given the number of combinations of devices that can be used, and the regularity in which it may be necessary to change out at least some hardware and/or software, the testing burden can quickly become a very substantial chore. It’s best to craft a modular design and verification test strategy from the start of system design, so when the inevitable changes occur, testing is isolated as much as possible to only those parts that change.

Logic PD
Minneapolis, MN,
(612) 672-9495.

Continua Alliance
Beaverton, OR.
(503) 619-0867.