Human Factors Engineering & Wearable Medical Devices
Wearables and Human Factors Engineering
Waking up to an alarm is universally known, understood, and even dreaded. Most of us wake up to an alarm every morning, but recent advancements sensor technology allow us to wake up to an alarm that reports a host of pertinent health data such as breathing rates, blood oxygenation, or sleep health. Further improvements in sensor technology may precipitate alerts throughout the day and could involve your healthcare provider altering medication dosing due to a health condition, proximity of exposure to hazardous materials, or even user pregnancy status.
Evolution of Wearables
Wearable medical devices, also referred to generally as “wearables”, have been integral to treatment and care of multiple health conditions for decades. Wearables have exhibited reliable and effective ways to enhance or amplify an individual’s own sensory input with hearing aids, track heart rate variability with smart watches, and even actuate a medication response with wearable autoinjectors. While wearable devices may encompass a variety of applications, this article pertains to any device that is worn by the user to measure biometric or health data or environmental data of the user’s surroundings. These wearable devices may be mobile cell phones, watches with embedded sensors, or simple sensors such as a pulse oximeter. The key component is that the user is able to wear the device on their person for a period of time. However, due to wearable sensors remote nature and long-term implementation, human factors plays a critical role in proper wearable use to maintain the validity of the data.
Advancements in sensors, batteries, and AI (artificial intelligence) integration have created a new realm of possibilities in the wearable space. These advancements have driven the success and widespread popularity of fitness trackers and have opened up the target population of these devices to a variety of user groups. The exponential growth in popularity of these fitness trackers indicate that 303 million wearable devices will be purchased in 2024 alone[1]. With respect to medical applications for personal use, these wearable devices have been applied to assist in diagnosis, tailor treatment options to the user’s medical profile, store and manage medical information, and increase efficiency of care. When the data is aggregated for predictive modeling, larger trends can be applied to validate applications such as biomarkers for disease onset or effectiveness of a medication regimen across a user group or patient population. With the recent expansion of the wearables market, there has been an increased need to work human factors considerations into the design process.
User-Centered Wearable Design
During the design and development of any product, user centered design should be the focus during each developmental phase which considers the needs and characteristics of each user group. When employing user centered design for wearables, the customization of wearable can be as detailed as the users themselves, and extensive considerations need to be accounted for in order for users to implement a wearable long-term. Many wearable developers aim to target certain markets, such as niche fitness enthusiasts, to guide the trajectory of this customization. A wearable’s design may vary greatly based on the user group characteristics and the considerations or limitations of use. A user may want to openly exhibit a wearable such as a fitness tracker, whereas others are specifically designed for discretion, like most hearing aids. It is imperative to conduct usability research iteratively during product design to ensure buy-in and adherence for wearable use in addition to proper operation and comprehension of the wearable’s functionality by the end user. Some general use considerations to take into account for each user group and use environment include:
Purpose/functionality of the wearable device,
Assistive or non-assistive. For example, hearing aids provide auditory assistance, whereas a fitness tracker simply records physiologic data.
Invasive or noninvasive nature of the wearable,
For example, a wearable insulin pump would be considered invasive since it breaks the skin, A fitness tracker worn on the wrist would be noninvasive.
Features to prevent (or alert the user to) accidental actuation or deactivation,
Wearable device lifespan,
Range of consequences that may occur from a use error consequence severity spectrum. For example, the consequences of battery death in a fitness tracker battery dies as compared to a Holter monitor (heart rate monitor which uses electrodes and a recording device to track your heart's rhythm for 24 to 72 hours).
A review of the human factors considerations for the design of wearable devices was presented at the Annual HFES proceedings in 2014. This review found 20 design principles that govern wearability of a device and the hardware and software the devices employ. There are 3 main themes within these 20 principles:
The ease of integrating the wearable into the user’s daily habits.
i.e. Aesthetics, comfort, fashion, wearability, subtlety.
The logistics of integrating the wearable into the user’s daily habits.
i.e. Resistance, reliability, ergonomics, obtrusiveness.
The ability of the wearable to provide the required and expected information.
i.e. Affordance, contextual awareness, customization, ease of use, intuitiveness, overload, privacy, responsiveness, satisfaction, simplicity, user friendliness.
Developers in the wearables space should ensure their design process encompasses these themes as these principles influence a user’s ability to effectively use the wearable(s) they employ.
A wearable’s functionality can encompass measurement of physiological (heart rate, blood pressure, body temperature, respiratory rate, electrodermal activity, surface brain activity), emotional fluctuations through skin temperature, and cognitive measures such as stress, concentration/attention, relaxation/meditation, and alertness. Other aspects of wearables that might influence human factors include placement of the wearable on the body, wearable battery lifespan, and wearable connectivity requirements. Intuitive user interfaces are vital to the proper use of a wearable device. If a pulse oximeter is placed incorrectly and cannot properly acquire pulse oxygenation data, a false negative may be sent to the user’s healthcare provider.
The decision to use a wearable can be a personal and may be considered risky due to privacy concerns. A large concern is the sensitivity of health data and the potential for piracy of the control of certain devices. From fertility trackers to cardiac pacemakers, devices contain and process sensitive health information that could be compromised or manipulated by hackers to elicit an adverse response for the user. If a user does not fully comprehend the security interface of a device, their data and/or health may be compromised. When wearable devices pose a risk if their data is compromised, security features must be intuitive enough for all user groups to understand and control and should be considered an important part of a human factors evaluation.
User understanding of the device and its functionality can be enhanced through a variety of feedback modalities such as visual, auditory, haptic, and (less reliable) olfactory mechanisms. The spectrum of use errors for wearable devices could range from a minor inconvenience for a fitness tracker to an adverse cardiac event if a Holter monitor does not properly indicate and alert the user or medical staff to the occurrence of a cardiac event. Safe and effective use hinges on both user comprehension of the product and the inherent awareness of the level of their understanding. A user may operate a wearable correctly without realizing it and achieve the proper results, or they may operate the wearable incorrectly but remain unaware of the error(s) incurred which may result in invalid data being recorded.
Human Factors Testing Strategies for Wearables
When preparing for early human factors testing for wearables products, human factors professionals apply the user-centered design considerations mentioned above as a guide for tasks to evaluate for performance and device use and to the human factors considerations presented at HFES in 2014. For example:
Wearable connectivity, battery and lifespan – This relates the logistics of integrating the wearable into the user’s daily habits. Does the device need to be charged? Can it be worn in the shower? Is there an indicator if and when the battery dies or the overall device becomes nonfunctional? Certain wearable injectors would have the additional factor of medication lifespan to consider.
Human factors approach: Evaluate the user’s understanding of battery levels and device connectivity during a training session or during a typical knowledge task assessment after a familiarization period with the device.
Sampling rate – This relates to the ability of the wearable to provide the required and expected information to the user (and potentially their healthcare provider). How often is the wearable device designed to detect a signal? How often the device is logging the signal acquired to the cloud?
A common issue is that users do not understand that if the device is not set up properly to push data to the cloud once the device itself reaches its data capacity, the data will be overwritten and lost. If this lost data segment included a period of atrial fibrillation, serious consequences might occur.
Human factors approach: Conduct follow up phone interviews with participants at intervals specific to the device’s sampling rate to confirm their understanding of device communication and ensure a fluid data set is acquired.
Formative testing
Goal: Evaluate the user’s understanding of the device and instructional interface(s).
From this formative evaluation, developers can isolate common use errors and points of confusion in order fine tune instructional materials to enhance user understanding and ensure proper device use.
If a user needs to monitor their blood pressure for 2 consecutive months, and the device’s battery only lasts a week, periodic interviews with the user to ensure their understanding of when the device battery has died could be advised. Even if the user understands and implements proper battery charging procedures, other aspects of the device such as proper communication with the associated smartphone application would need to be assessed.
Based on user understanding of the UI during formative testing, multiple aspects of the UI may need to be updated to alert users of a malfunction. If substantial device and instructional design materials require alteration, consider conducting additional formative testing to ensure the updates mitigated risk.
Regulatory Considerations for Wearables
Regulatory considerations for wearables have developed over the years to account for increasing mobility of medical devices and their connectivity to other medical hardware and software. The FDA has issued multiple policy directives on Mobile Medical Applications in 2013, 2015, and most recently published the Policy for Device Software Functions and Mobile Medical Applications in September of 2019. This most recent directive does not specifically define or mention the term wearables. However, a broader tactic is applied to the concept of wearables, and the regulatory approach taken by the FDA is aligned with their procedures to apply oversight if and when the product in question poses a risk to patient safety if malfunction or misuse were to occur. Software and mobile application developers are encouraged to adhere to the Quality System regulations defined in 21 CFR part 820, including good manufacturing practice for the design and development of medical devices. Software functions (typically mobile applications) which are the focus on the FDA’s regulatory oversight are listed in Appendix C of the 2019 aforementioned guidance and include software that:
Transforms a mobile platform into a regulated medical device,
Connects to an existing device type for purposes of controlling its operation, function, or energy source,
Is used in active patient monitoring to analyze patient-specific medical device data.
In 2018, Apple Watch Series 4 was cleared by the FDA as a Class 2 medical device with EKG and fall detection capabilities[2]. Since this breakthrough, multiple other products have become available to track a variety of biometrics, and the demand for remote health monitoring with the current pandemic has dramatically increased. In June of 2020, the FDA issued additional information on Remote or Wearable Patient Monitoring Devices Emergency Use Authorizations to facilitate this demand.
Digital Health Center of Excellence
The recent initiation of the Digital Health Center of Excellence (DHCoE) from the CDRH to align and coordinate the regulatory approach of the FDA to digital health is a major initiative to advance healthcare by encouraging high-quality digital health innovations. While the DHCoE will support the FDA’s procedures for digital health review, the DHCoE will not be directly responsible for marketing authorization decisions. The objectives of the DHCoE and how they tie in with one another are illustrated in Figure 1[3].
Figure 1: Digital Health Center of Excellence comprehensive approach for advancing and realizing the potential of digital health.
The DHCoE is currently in Phase 1 of their evolutionary plan for the Fall of 2020. Phase 2 will continue through 2021 and consist development of strategic partnerships and resources, assembling advisory groups, and build out the community for the DHCoE to implement measures of digital health. Considering the current pandemic, the phased approach will evolve with the lens of public health playing a larger role in the current health environment as compared to a pre-pandemic atmosphere. With the phased rollout of this Center of Excellence, further guidance is expected, and additional opportunities may become available as the scope of this venture develops.
Monitoring of health outcomes during COVID-19
The onset and development of the COVID-19 pandemic has greatly increased the need for reliable, remote mechanisms of healthcare and symptom monitoring. There are several examples of wearables that have been implemented to track and even predict the onset of COVID-19 prior to symptoms becoming detectable to the user. For example, Philips[4] has a wireless wearable biosensor that monitors COVID-19 symptoms while an individual is in the hospital. In addition, in May the US military solicited proposals[5] to “to develop a wearable diagnostic capability for the pre‐/very early‐symptomatic detection of COVID‐19 infection” and committed 25 million dollars to be used across 10 projects. Fitbit was one company who received funding for this endeavor[6].
This pandemic-driven push toward remote health monitoring for the general public has implications for the future of wearable devices. With wearables being so widely embraced, long-term longitudinal tracking of physiological health data will broaden our understanding of health and the human body and create avenues for future medical developments in the wearable space. Focusing these advancements with user-centered design as a priority will ensure: 1) the data collected is accurate, 2) valuable contributions to the data set for that wearable which may enhance the medical community’s understanding of the breadth and depth of a particular biometric, and 3) contribute to further insights about the habits and metrics of the user.
Stay tuned for next month’s newsletter when we discuss 2020 in review!
[1] https://www.fierceelectronics.com/electronics/incredible-rise-wearable?mkt_tok=eyJpIjoiWXpCaE5URTNNMlppTldFdyIsInQiOiI2TmlTMlJTTEt3K29RbmtIMGV5SnhnQjlFaFpWcmUxeDR3YmtIbk5qT3AraStaWWVJRGtza0RrSFhLZ25Ya09XK1g3bHppSjdPVEdXelRkN0dGSlJDZzY5alNDNzlFTXdtK1JTT3BDbGw4MEZMUTd4emZ6c0QzNUlETzlWYWFrOG1JUFdOY211enlBUkVTVU9XRzNqUFE9PSJ9&mrkid=53370691
[2] https://www.forbes.com/sites/jeanbaptiste/2018/09/14/apple-watch-4-is-now-an-fda-class-2-medical-device-detects-falls-irregular-heart-rhythm/?sh=1b0667532071
[3] https://www.fda.gov/medical-devices/digital-health-center-excellence/about-digital-health-center-excellence
[4] https://www.mddionline.com/covid-19/philips-wins-regulatory-nod-clinical-surveillance-biosensor
[5] https://beta.sam.gov/opp/0afc4ee652694b7d9c5bc2a9209cb65d/view?index=opp&naics=541&page=2
[6] https://www.nextgov.com/emerging-tech/2020/10/army-picks-fitbit-develop-wearable-presymptom-covid-19-detectors/169689/
About the Author:
Lauren Jensen, PhD
Dr. Lauren Jensen, PhD, is a Biomedical Engineer and Human Factors Consultant with Agilis Consulting Group, LLC. Lauren is experienced in applying human factors principles to the design, evaluation and validation of medical devices and products. Prior to joining Agilis Consulting Group, Lauren worked in the startup space in Austin, TX engineering wearable medical products, and competed as a top ten finalist for the NASA iTech Cycle III for innovative technologies. During her PhD at Tulane University School of Medicine, Lauren developed and validated a therapeutic wearable to reduce surgeon tremor and fatigue in the OR.