New devices leverage high-performance, low-cost sensing technologies and signal processing to develop radically new ways to non-invasively address medical-instrumentation challenges.
We've seen lots of activities in "wearables" and personal health/wellness devices of many types in the past year, with more to come. These small units can track pulse and respiration, cardiac waveforms, blood oxygen saturation (SpO2) level, and more.
All of the well-deserved attention that these useful medical and fitness products are getting, however, may be obscuring a bigger picture. Engineers, researchers, and scientists are combining advanced sensor types and technologies — along with complex analog and digital signal processing — to provide new insights into a variety of medical issues and to do so in a low- or no-risk, non-invasive way. A trio of recent stories showing such developments in prototype or evaluation stage was very revealing in showing the nature and sophistication of some of these developments via projects done as entries for a reputable design contest as well as university research.
For example, it's often vital to measure blood pressure, and there are many units that are fully autonomous: They pump up the cuff, release the pressure, capture the output signal from the cuff, and then apply signal-processing algorithms to extract the needed results on systolic and diastolic pressure — not a trivial task, given the range of pressure signals, unavoidable non-electrical noise on the signal, and other distortions. Then think about the challenge of continuously measuring blood pressure in real time without a need to stop, inflate, and deflate, which would be useful for ongoing monitoring.
That's the challenge that Bold Diagnostics, LLC, addressed as the winner of Tech Briefs "Create the Future 2016" contest in the medical category. The company's Continuous Wearable Blood Pressure Monitor uses Differential Pulse Arrival Time (DPAT) technology, which uses the fact that the pulse wave generated by the heart's contracting arrives at the right arm before the left arm because of an inherent delay created by the anatomy of the aortic arch.
This difference in arrival times is an indicator of blood pressure (Figure 1). Using this approach, they claim that they were able to achieve a strong correlation (±5 mm Hg) between the DPAT method and conventional testing of blood pressure in comparison to control measurements (Figure 2).
Figure 1. Differential Pulse Arrival Time makes use of a small but measurable difference in heart-pulse arrival time at each arm, which is a function of pressure and the result of different transit distances for each path to the path traveled by the blood. Source: NASA Tech Briefs.
Figure 2: Controlled tests on the DPAT-based approach show close matching for both systolic and diastolic readings with the standard approach. Source: NASA Tech Briefs.
Another interesting entry and winner of an Honorable Mention citation was the Apnosystems Infant Care System (ICS), a therapeutic wearable for babies. This small, wearable system is designed to continuously monitor the SpO2 level of infants at risk (via optical pulse oximetry) to determine if they have stopped breathing due to their unstable airway conditions or other medical issues (Figure 3). If the system determines that SpO2 has dropped so low that this has occurred, immediate intervention is needed to prevent the serious consequences of lack of oxygen, including brain damage. Then, in addition to sending a Bluetooth-based alert to a smart phone, the system automatically provides mild, non-harmful transcutaneous electrical nervous stimulation — a small electrical "tingle" — which will rouse the infant and restart automatic breathing.
Figure 3. This small unit measures SpO2, which is closely related to breathing activity, and immediately stimulates the baby with small electrical current if the level falls below a threshold value; it also sends a smartphone alert. Source: NASA Tech Briefs.
It's worth looking at the Top 100 entrants and the Grand Prize and Category winners to get a good sense of the range of innovation and "out-of-the-box" work being done; it’s very thought-provoking and even somewhat inspiring.
Of course, there are many innovations that are unrelated to contest entries; many of them are being done at universities. For example, ear infections are common but often misdiagnosed, with a roughly 50/50 right/wrong assessment; in fact, it's often the physician's experience and judgment based on various symptoms that is used to make the final determination. The reason is that the conventional visible-light otoscope used for viewing within the ear can’t penetrate deeply enough into the tissues to show the buildup of fluid behind the eardrum.
To overcome this problem, a team at MIT developed and is field testing a new kind of otoscope that uses shortwave infrared light SWIR rather than visible light and can penetrate much deeper (Figure 4, see "A new eye on the middle ear" and "Using the shortwave infrared to image middle ear pathologies." Although this is more complicated and expensive than a standard unit, the difference is modest with today's electro-optical technology; it can hopefully provide a more accurate assessment than the standard method, which is only slightly better than a guess.
The shape of the ear canal and location of the eardrum (tympanic membrane) makes it difficult to see and assess fluid on the other side (left); the image as seen through a standard otoscope as well as when using SWIR-based imaging (right). Source: BiOptics World.
Instead of just improving on what has been done, these innovations in medical test and measurement look at new ways to collect sensor-based data and act on it. They do this by using and combining transducers that go beyond the standard approaches and adding signal-processing algorithms, which transformed this data into useful insight. Measuring multiple parameters such as pressure, IR, temperature, and others is also becoming a common approach as the cost of these sensors, as well as their size and power needs, decreases while their performance increases.
Have you seen any similar non-invasive, relatively low-cost, small-sized medical instrumentation that impressed you? Or have you worked on any of these designs?