Blundur (“to doze” in Icelandic) is a non-invasive sensor to quantify respiratory effort during sleep, developed together with the Kempenhaeghe sleep institute.
In 60 seconds
A sleep apnea is a chronic disorder where the body repeatedly stops breathing during sleep. It’s estimated to affect 300.000 people in the Netherlands. The most reliable method to distinguish more complex types of apneas is by using respiratory effort. The current reference method to quantify respiratory effort is by means of inserting a catheter into the oesophagus. This method is uncomfortable for patients and sometimes poorly tolerated. Less invasive alternatives like thoracic belts, do not meet the requirements with regards to signal quality and reliability.
Kempenhaeghe, the largest sleep institute in the Netherlands, was working on a non-invasive sensor to quantify respiratory effort from the outside of the trachea, using a pressure transducer.
“In theory this method has a lot of potential, in practice it’s seriously hampered by the device-patient interface.”
In this project, I developed a patient-device interface that is both comfortable and stable and can be used reliably during a sleep study. I started the project by creating a data logger so I could test different iterations of the design during the night. Kempenhaeghe mentioned their interest in doing more measurements at home, therefore the last part of the project was spent on creating a home-monitoring solution.
Watch the project video below:
To define the requirements for the final design, I discussed the goals for the project with the team at Kempenhaeghe and conducted a contextual inquiry to learn more about the context in which the sensor would be used.
Kempenhaeghe's goal was to have a well-functioning prototype to start early with clinical validation. For safety and to reduce the requirements for a clinical trial it was decided to keep electronics away from the body. In addition, it was decided to make use of rapid manufacturing services to easily be able to order prototypes.
An important insight from the contextual inquiry is that sensors are applied hours before the actual sleep study. Therefore it should be possible to connect and disconnect the sensor comfortably from the data acquisition system.
Based on these requirements I started a process of testing and validation by collecting data about the sensor response.
I decided to start the process by creating a data collection circuit to quickly validate different iterations of the sensor system during the night. The circuit utilizes a low-pass filter, amplifies and converts the analog signal from bipolar to unipolar before saving the sensor signal with a timestamp to an SD card.
On the left, you see Kempenhaeghe's original design for the patient device interface. Due to the protrusion, the contact area is small and constant counterpressure is given on the double-sided tape. My initial proposal was to create a flexible surface area as can be seen on the right. The flexible surface follows the skin, increasing the contact area and distributing forces better.
I started by experimenting with silicone rubber and scrap materials but wasn't getting an airtight seal. Then I learned about tracheostoma patches used for laryngectomy patients. Laryngectomy patients breathe using an opening in their neck, at the same location as Kempenhaeghe's proposed sensor. The tracheostoma patches are used to hold air filters and voice prostheses using an airtight seal.
Using some scrap materials I created a quick proof of concept to validate with the data collection system. While testing during the day I got good results for up to an hour. This approach seemed promising.
The graph below shows how the sensor response changes for normal breathing on the left and obstructed breathing on the right. Obstructed breathing is simulated by breathing through a straw. Breathing with an obstruction results in higher and wider peaks because it takes more effort and time to obtain enough oxygen.
The first test results were promising, using the tracheostoma patches I was able to get an airtight seal for longer periods of time. Based on these results I designed and 3D printed a custom connector, using this connector I was able to collect data during a full night of sleep. Based on testing with multiple people, several adjustments were made. The connection to the tubing was put on an angle to create a strain relief and a luer-lock was added to comfortably attach and detach the tubing.
An illustration of the proposed solution using tracheostoma patches.
After developing the sensor into a stable design that is easy to apply, the last part of the project was spent on developing a home-monitoring solution.
“We’ll start with comparing the different sensor technologies in a clinical setting, but the intention of these kinds of technologies is that they potentially could be applied in the home situation.”
Kempenhaeghe showed interest in home-monitoring, to gain longer-term sleep data of patient in a “natural environment.” For me it was an opportunity to continue exploring product design and prototyping. The goal was to find a balance between a medical and consumer product that would fit in the home of a patient. Because the physician needs to be able to quickly explain and hand-over the device for home-monitoring after consulting, the focus was on making the device plug and play.
The prototype was created by stacking lasercutted parts together, filling and a lot of sanding to get a smooth surface. The top is created by layering magohany veneer and cutting/engraving it using a lasercutter.
The goal of the home-monitoring solution is to make it very easy to start a measurement. The device directly start collecting data when you plug it in. A small led on the back of the device will start pulsing to your breathing, to reassure that the sensor is properly applied to the skin. The LED is only visible when connecting the sensor and will not annoy users during the night.
Below some of the productphoto's shot at the end of the project:
With my designs and research data I went back to Kempenhaeghe to evaluate the project and discuss future opportunities. The team of Kempenhaeghe responded very positively.
“Since the solution is so simple and non-invasive, we are quickly able to start testing with patients. With consent of the patient, we are able to add the sensor to the polysomnography study quite easily.”
“We didn’t dare to dream of such a solution! I have high expectations!”
After finishing the project, Kempenhaeghe started testing the sensor with multiple patients with positive results. They are currently working on the scientific validation of the sensor. To be continued!
Dutch Design Week
Blundur was part of Mind the Step 2015, an exhibition in one of the large venues of the Dutch Design Week, the Klokgebouw. See the picture below.
I hope you enjoyed this project.
How about looking at another one below?!