Medical electronics: from hospital and clinic to the home

Applications for home health technologies include chronic disease management, mental health services, post-operative care, independent senior living, weight loss, fitness, wellness and beyond. Home healthcare is currently booming because of factors such as ageing populations, increasing healthcare costs, and demand for access to healthcare resources in remote and rural areas. For many years to come, we will continue to observe an increase in medical electronics going into the home.

Medical electronics designed for a home environment versus a hospital setting have different requirements in terms of performance, feature sets, power consumption, portability, connectivity, and cost, which is covered in this article.

Size and Cost
Consumer medical electronics being used at the patient’s home share some features common to other consumer electronics. Size and cost become more important factors in determining whether a product can succeed in the market. The first practical electrocardiogram (ECG) machine, invented by Willem Einthoven 100 years ago, weighed 600 lbs and required five people to operate it. The patient had to submerge his arms and legs into glass electrode jars containing large volumes of a sodium chloride solution.

Today a patient can comfortably wear a portable (ECG) monitor at home or while moving around because it is lightweight (only a few ounces) and small. For example, a 12-lead ECG monitor in hospital typically comes with an ECG cart that can roll around for mobility, while a 12-lead ECG monitor for home use typically shrinks to handheld size that can be carried around in the pocket.

Using highly integrated solutions is one way to reduce size and cost. Today, many blood pressure monitors and blood glucose meters are single-chip solutions based on ultra-low power, 16-bit MSP430 microcontroller units (MCUs) with an integrated analog front-end (AFE), interfaces, real-time clock (RTC) and liquid crystal display (LCD) controller.

Additionally, devices like the ADS1298 (Figure 1), an ADC with an integrated ECG front-end, combine all common AFE requirements for an ECG system, from the low-noise programmable gain amplifiers, eight high-resolution delta-sigma ADCs, to the right leg drive amplifier, lead-off detection and respiration-impedance measurement. As a result, component cost and size can be significantly reduced, as compared to discrete implementations.

Figure 1: Complete AFE for ECG system using the ADS1298.
(Click on image to enlarge)

Ease of Use
Equipment user capability can differ greatly due to age or physical limitation. Optimizing ease of use reduces incorrect usage, as well as encourages better and wider adoption of medical technologies. Features like voice prompt, touch screen, graphical user interface, fewer wires and simple, big buttons can enrich the user experience dramatically.

Touch screen technologies play a prominent role in consumer electronics because they allow intuitive and fast interaction between users and devices. For a relatively small screen size, resistive touch screen is the most cost-effective technology, although it offers less resolution than capacitive touch screens. Resistive touch screens are preferred for medical electronics because they stand up better to liquids, chemicals and other contaminations.

Moreover, it responds to a touch from anything: finger, glove, hard or soft stylus. Five-wire resistive touch screens can increase durability over four-wire solutions because the electrodes are on the bottom layer and the top layer acts only as a voltage measuring probe. This allows the touch screen to continue working properly – even when damaged or scratched.

Connectivity
Connectivity is an essential function of home healthcare devices. A blood-pressure monitor may be connected to a computer via universal serial bus (USB) to upload and track historical records. A fitness watch may be connected to a social network website via Wi-Fi™ so the user can share his data with family and friends. A telehealth monitor may be connected to various personal health devices via Bluetooth® while at the same time being connected via a wireless network so that the doctor can monitor the patient’s status real time.

There are many factors to consider when choosing the appropriate network protocols. These include the number of devices in the network, network topology, communications range, power consumption requirements, and interoperability with other systems or devices. USB is the most commonly used wired protocol between devices and hubs.

Given its established prevalence in various types of electronics, it is not surprising that Bluetooth® was the first wired communications standard certified by the Continua Health Alliance, an industry consortium dedicated to establishing a system of interoperable personal healthcare solutions. Bluetooth low energy is a newer protocol that consumes only a fraction of that consumed by Bluetooth, and is poised to gain momentum during the next few years. This, of course, will depend on how quickly profiles become available and a comprehensive ecosystem is put into place.

Other standard and proprietary wireless protocols such as Zigbee® and ANT/ANT+™ are alternative options for personal area networks (PAN) and local area networks (LAN).

For local area network (LAN) applications, while Wi-Fi and wireless medical telemetry services (WMTS) are both being deployed by hospitals, Wi-Fi is the standard most widely implemented in residential homes. Wired communications such as broadband and plain old telephone service (POTS) are commonly used as well. Additionally, wireless communications provide a neat solution when Internet or access points are not available.

A combination of wired and wireless interfaces may be integrated, depending on the situation and targeted customers. For example, elderly people may not be technically savvy enough to configure Wi-Fi access or pair Bluetooth devices. Therefore, installation cost must be included in the total solution cost, if technical assistance needs to be provided. A built-in wireless modem may be the easiest solution for this group of users.

Another challenge device makers may encounter is coexistence between multiple wireless technologies. One example is simultaneous operation of Wi-Fi and Bluetooth, where both use the same 2.4-GHz frequency band even though their transmission protocols are quite different. Bluetooth operation in a system cuts the available bandwidth for Wi-Fi by at least a third.

This is reduced even further by protocol overhead and timing, especially in modes designed for saving power. When a Wi-Fi router cannot establish a connection through acknowledgement, the link may time out and be closed. Similarly, when Bluetooth scans for available devices on power-up, too much interruption can cause the link to fail. Using a combo solution that integrates multiple radios into one chip can address this challenge.

For example, the WL1271 (Figure 2) provides intelligent, seamless coordination in the time domain at the media access control (MAC) layer. It enables sharing the same antenna and antenna filter by both Wi-Fi and Bluetooth, reducing component counts and circuit board space.

Figure 2: A combination solution integrating Wi-Fi and Bluetooth protocols.
(Click on image to enlarge)

Portability
Portability is enabled by integration, batteries and wireless communications. Extending battery run time is a common design goal of all portable electronics. Using AA and AAA batteries are common in medical electronics because they are readily available and can supply power to the devices immediately. However, when wireless communications are integrated into the system, these standard batteries may not last long enough so rechargeable batteries should be considered.

Battery charge management solutions with power path management (Figure 3) ensure that the device can be used as soon as external power is plugged in, even when the battery is deeply discharged. Furthermore, with a direct power path from the external input to the system, battery charging and discharging cycles are reduced and, therefore, battery cycle life is improved. Another key factor affecting battery longevity is thermal design. Reducing system heat dissipation and isolating the battery slows down battery degradation.

Figure 3: Battery charge solution with integrated power path management.

For applications where battery power availability is critical, accurate battery fuel gauging is an important function. This tells you precisely how much capacity or usage time remains, prompting users to charge the device before it runs out of power. Unlike traditional coulomb counting methods, Impedance Track™ technology eliminates battery learning cycles and offers 99 percent accuracy, regardless of battery age.

Security and Safety
Counterfeit accessories and improper operation can cause security and safety concerns when using medical devices, especially in a home environment where users are not supervised or professionally trained. Radio frequency identification (RFID) and authentication technologies can help authenticate peripheral parts for system safety.

The healthcare industry is using RFID for many and varied applications, from medical asset tracking to calibration functions. Particularly noteworthy are pharmaceutical companies that have been successfully using RFID technologies to combat counterfeit and compromised drugs.

In the RFID authentication approach, a digital signature is generated and locked into the tag’s memory for each label or package. A digital signature can be read by authenticated RFID readers to validate the tagged product as it moves through the supply chain, provided the reader is supplied with the appropriate manufacturer public key to read the signature. Using standards-based public key technology, digital signatures and data encryption helps to ensure the signature’s authenticity and, consequently, the authenticity of the tag itself.

RFID tags are ultra low-cost and very small, and the antenna can be made into flexible shapes. These features make it easy to authenticate a variety of peripheral parts. For example, a tiny RFID tag with a round antenna can fit perfectly on a cable so that the system can authenticate the legitimate cable before operation is enabled.

Another solution is to use an authentication integrated circuit (IC). The most basic authentication scheme is identification (ID) authentication. However, it may be possible for the ID to be captured and replicated by counterfeiters. The challenge and response-based authentication is much more robust, and the security is even enhanced with sophisticated algorithms such as SHA-1/HMAC, which has been used for years to authenticate Internet transactions for virtual private networks (VPNs), banking, and digital certificates.

To authenticate a peripheral part such as a battery pack, the host generates a random challenge based on encrypted device ID and a secret key. The authentication device then responds with a digest value. If the value matches the host’s calculation, the battery pack is authenticated.

Summary
We looked into the design considerations of medical electronics for home use in five aspects: size and cost, ease of use, connectivity, portability, and security and safety. Highly integrated solutions reduce board size and total solution cost. Features such as touch screen and voice prompt enable user-friendly human-machine interface. Wired and wireless connectivity technologies connect medical devices to computers, gateways, websites and remote locations.

Good battery management techniques can lead to longer battery run time, which ensures better portability. RFID technology and various authentication schemes can be used to ensure legitimate parts are being used for security and safety. It is important to understand both the design risks in the system as well as the risk introduced by the use environment and the end user when considering the design trade-offs of any solution.

References

• Download TI’s Medical Applications Guides: click here.
• For TI’s wireless solutions that enable smart sensors, click here and here