Continuous Cardiorespiratory Monitoring for People with Cystic Fibrosis
Researchers from Byteflies and Rainbow Babies and Children’s Hospital at University Hospitals Cleveland Medical Center set out to answer the question:
Can a Byteflies Sensor Dot monitor relevant cardiorespiratory parameters in people with Cystic Fibrosis (CF) and could this lead to improvements in the standard of care?
That question is not an easy one to answer as we need to determine if Sensor Dot:
- Can measure relevant sample-level¹ physiologic and behavioral signals;
- Is user-friendly enough for home use and is compatible with clinical workflows; and
- Can derive meaningful physiologic and behavioral patterns (digital measures) that correlate with relevant outcomes in CF.
Most of these questions were treading uncharted territory so we ran a pilot study to obtain preliminary answers, which will hopefully lead to a more formal validation study in the future.
This article summarizes the main findings of that pilot study but first a couple of housekeeping notes:
- Our pilot study was not intended to generate a definitive answer to any of these questions. It was an expedition to evaluate if we were even asking the right questions. Therefore, this work was not peer-reviewed but rather published as a preprint on medRxiv. A full-length paper is embedded at the end of this post.
- The study protocol is available on clinicaltrials.gov.
- In addition to Byteflies and Rainbow Babies and Children’s hospital, researchers from Case Western Reserve University, Indiana University, Hasselt University, and Cystic Fibrosis Europe participated in analyzing the data and authoring the paper.
¹ Sample-level denotes the raw data we can extract from a sensor, such as electrocardiogram data which was sampled at 125 times/second.
Table of Contents
- Why are wearable devices important for people with CF?
- Is Byteflies Sensor Dot the right tool for the job?
- Conclusion
- Full Paper
Why are wearable devices important for people with CF?
Cystic Fibrosis (CF) is a genetic disorder that affects multiple organs but primarily the lungs (the CF Wikipedia page is a good place to learn more). Unfortunately, a cure does not exist (yet!) and people with CF require lifelong specialized care.
The CF Foundation recommends that people with CF visit their care center at least four times a year and perform at least two pulmonary function tests (PFTs) per year (more on that later). And that is assuming they are otherwise in good health. Between these visits, as with many chronic conditions, little objective data on people’s lung function, other symptoms, and quality of life is available. More specifically, pulmonary exacerbations (PEx) are a frequent source of hospitalization. Early detection and treatment of PEx are especially important to prevent long-term problems.
Knowing that, having an unobtrusive wearable home-use device to monitor for PEx or other signs that indicate the need for a hospitalization could lead to earlier intervention, and – over time – a better understanding of that person’s health trajectory, which is incredibly valuable information for any care team to have.
Is Byteflies Sensor Dot the right tool for the job?
For this study, we used a prototype version of Sensor Dot that can record the following sample-level signals:
- Electocardiography (ECG)
- Bio-impedance (bioZ)
- Accelerometer in 3-dimensions
From those sample-level signals, we could derive the following digital measures:
- Heart rate (HR) in beats-per-minute
- Respiratory rate (RR) in breaths-per-minute
- Activity index as a measure of total activity
- Number of coughs
Sensor Dot was placed on the chest and connected to two standard ECG electrodes as shown in the figure below. After a measurement, a Sensor Dot is placed back on the Docking Station which sends the collected data to the Byteflies Cloud.
If you are interested in the technical details of how the signals were recorded and the digital measures derived, please see the full paper at the end of this post.
In total, 26 people with CF who had a scheduled clinic appointment participated in the study. They all performed a pulmonary function test (PFT) which assesses lung function. Based on the outcome of the PFT, participants were divided into three severity categories (MILD, MODERATE, and SEVERE).
After that necessary setting the stage, back to our original questions:
1. Can Sensor Dot measure relevant signals?
The figure below shows a 22 h trace of the digital measures highlighted above (heart rate, respiratory rate, activity index, and number of coughs) for a 53-year-old male in the MODERATE severity category. We can make a couple of observations:
- Heart rate (top graph) goes up with increases in activity index (bottom graph), as expected, and reached a maximum value of 132 BPM.
- Resting HR appears to be elevated (~ 80 BPM during the sleep phase).
- Resting respiratory rate is around 16–17 BrPM and goes up to 20–21 BrPM during the day.
- Two coughs were detected (dashed marker on middle graph; more on that later).
- Activity is low throughout the day because this person was staying overnight in the hospital.
These longitudinal overviews are interesting, especially if you consider the possibility to track these vital signs over extended periods of time to evaluate long-term trends but that was beyond the scope of our pilot. What is even more interesting is to examine if some of these vital signs correlate with CF severity as used in routine clinical care. More on that in section 3!
2. Is Sensor Dot user-friendly enough for home use and is it compatible with clinical workflows?
Any evaluation of an innovative technology would be grossly incomplete without also checking its future users are happy with the form factor and functionality. Especially during the initial stages of development so that changes can still be made to the design if necessary.
Importantly, users in this context not only refers to patients, but also the professionals in their care team. They have differing but complementary requirements that need to be satisfied to make a digital medicine tool successful.
This pilot study was run inside the hospital, which gave us an opportunity to evaluate Sensor Dot in the hands of healthcare professionals. And of course, the patients themselves were asked for feedback (24 people filled out the survey after using Sensor Dot). This feedback was overall very positive (see figure below), but it is important to note that we only assessed usability over short stretches of time (1 day at the most) and in the hospital.
3. Can Sensor Dot derive meaningful digital measures that correlate with relevant outcomes in CF?
As mentioned earlier, the group of participants (26) were divided into MILD, MODERATE, and SEVERE categories based on their PFT results. We evaluated if the digital measures that we recorded with Sensor Dot correlated with these severity categories. We made the following observations (see Figure 4 in the full paper for details):
- The heart rate of individuals in the SEVERE group was increased, especially when people were active.
- Some participants were admitted to the hospital for a PEx (inpatients), whereas others came in for routine check-ups (outpatients). When evaluating the average δHR, which is the difference between the heart rate during activity and at rest, the δHR in the inpatient group is higher than the outpatients for all severity categories. This indicates that we may be able to capture the cardiorespiratory effects of a PEx in the HR response to physical activity.
- At rest, respiratory rate in the SEVERE group was increased.
- We counted coughs with a very experimental technique. The details are in the full paper but briefly: we exploited the fact that the accelerometer in a Sensor Dot is placed on the chest. Consequently, a cough results in a transient pattern on the accelerometer. Because this is a proof-of-concept technique, we asked participants to self-report the number of times they coughed, and these numbers correlated quite well with the calculated numbers. In addition, the inpatients coughed on average ~10 times, while for the outpatients this was ~5 times. Since many PEx are associated with an increase in coughing, this is not a surprising observation but the fact that we can detect this trend with Sensor Dot is potentially interesting for longer-term home monitoring where self-reported monitoring is simply not practical.
Summarized, our observations are as follows:
Conclusion
We ran a pilot study with Sensor Dot to assess if it can monitor relevant cardiorespiratory parameters in people with CF, and if this could potentially lead to improvements in the standard of care. Although our results are preliminary, they provide us with a first guideline on which parts of the wearable system – from hardware to data processing and visualization – need to be improved to make it fit-for-purpose for CF and other chronic respiratory conditions, such as Chronic Obstructive Pulmonary Disease (COPD).
Development processes for medical wearables can be long as they require very thorough validation. The more stakeholders that are involved early in the development process, the better all performance and usability requirements can be considered.
Case in point, the wired electrodes used for this pilot study have since been replaced with next-gen cardiorespiratory patches (stay tuned for more information!).
Because this was a pilot study, it has a couple of limitations:
- The recordings were short (23 h long at most) and not yet done at the patient’s home.
- The study was exploratory and therefore not powered to produce conclusive evidence for the digital measures and their potential correlation with CF severity.
- Self-reported number of coughs are known to be inaccurate. To develop an accurate algorithm for cough counting, a much better reference standard should be used.
