by Randy Frank, Contributing Editor
The technology to make wireless health/medical systems is a reality.
With health and fitness increasingly important to a growing number of people, wireless sensing of human activity and physiology is soaring. Market research firm IHS projects that shipments of sensors used in wearable electronic devices will rise by a factor of seven from 2013 through 2019, expanding from 67 million in 2013 to 466 million units in 2019.
Smartphones contain many of these sensors, and smartwatches will add to the volume. With the wearers as the interpreter and implementer of any changes that the data suggests or requires, what does it take to go beyond the physical fitness craze and really address serious medical problems?
The Medical MEMS and Sensors 2015 Annual Conference and Exhibition last year in Santa Clara, Calif., investigated advances and challenges in this area. Recognizing the rapid growth in the sensors in wearables market, Uli Chettipally, MD, MPH and Emergency Physician at Kaiser Permanente said, “Even more exciting to watch is the transition of wearables from a health and fitness accessory into a clinically useful tool; a tool that will be able to predict, diagnose and monitor disease processes.”
While a sensor or sensors provide the starting point for the analysis, wireless technology and software are required for a useful sensing node or system.
One good turn
One of the existing medical tools, the Leaf Patient Monitoring System, addresses bed sores, or more officially pressure ulcers, caused by the lack of motion in bedridden patients, including those who are paralyzed, sedated and comatose. Receiving U.S. FDA clearance in August 2013, the system addresses a serious medical problem. For those unfamiliar with the issue, U.S. Dept. of Health and Human Services’ Agency for Healthcare Research and Quality Research shows that pressure ulcers cost the nation’s healthcare system more than $11B per year.
To reduce that cost, the Leaf system uses a tri-axial accelerometer to accurately monitor the patient’s position and movement and wirelessly communicates the data for action by a caregiver. Mounted on the patient’s chest, the disposable sensor provides alerts for the need to turn the patient and confirms that action. It also ensures that sufficient tissue depressurization occurs between turns to prevent pressure ulcers.
Other sensors in the patient-mounted module include: a phototransistor to measure ambient light levels and turn on the device when the packaging and/or adhesive liner is removed; and a capacitive contact sensor to detect when it is attached to skin and sense when it is removed from skin.
The wireless sensing module communicates up to 75 ft to a relay antenna—but placing antennas every 25 ft is recommended. A proprietary mesh network that conforms to the physical layer of the IEEE 802.15.4 wireless standard is used for the 2.4-GHz wireless data transmission.
A server and software complete the system with either a central monitoring station or a mobile device receiving the data transmissions.
Measuring acceleration rates that are typically well below 5 g, the microelectromechanical system (MEMS) accelerometer has the capability to wake up for certain events and then transmit data. Since the measurement system uses a mesh network, if one receiver fails to communicate for whatever reason, the redundancy allows successful signal transmission.
According to Mark Weckworth, COO of Leaf Healthcare, “We generally put one of our relay antennas in each patient’s room. It makes sure that the sensor on the patient’s body can generally talk to more than one receiver.”
The mesh networking routing algorithms in the Leaf system are very sophisticated and proprietary.
“We’ve created our own software stack from scratch,” said Weckworth. “Because of that, our system is much more manageable and flexible.”
Achieving system design goals is critical for any project and the Leaf patient monitoring system is no exception.
“The thing that was really important for us in the design of this system was the ability for us to go into these facilities, set the system up very quickly and inexpensively without encumbering the hospital’s IT infrastructure or interfering with it, or if the hospital wanted to for us not to interact with their RF systems at all. And then once we leave, to support the system easily and conveniently from a remote location,” said Weckworth.
The success of achieving this goal is that Leaf can offer a hospital a free trial installation to overcome any hesitation to experience its effectiveness in preventing bedsores.
Improved heart rate measurements
With its recently introduced AS7000 biosensor, ams, an Austria company that designs and manufactures high-performance sensors and analog ICs, expects that designers can replace the electro-cardiogram (ECG) chest strap and obtain reliable and useful ECG readings from a wrist or arm-mounted sensor in lifestyle, fitness and health monitoring applications.
Targeting wearable devices that are worn constantly (at rest and when exercising), the AS7000 sensing system is a highly integrated optical sensor module with software to provide very high accuracy optical heart rate measurements (HRM) and heart rate variation (HRV) readings.
The AS7000 uses an HRM method called photoplethysmography (PPG), which measures the pulse rate by sampling light modulated by the expansion and contraction of blood vessels. While other optical schemes provide raw PPG readings, the AS7000 has a digital processor to implement ams developed algorithms that convert the PPG readings into digital HRM and HRV values.
Ronald Tingl, biosensors senior marketing manager for the Advanced Optical Solutions Div. at ams, said, “Medical applications will probably require continuous (24/7), longer term (weeks), medical-grade certified measurement of vital signs. Vital signs to be measured will likely include accurate HRM, HRV, respiration rate, SpO2 [peripheral capillary oxygen saturation], skin resistivity and skin temperature, to start with.”
With the ams AS7000 biosensor, all of these can be measured but additional steps must be taken.
Tingl points out that to achieve reliable, highly accurate data, it is important to ensure that measurements are performed correctly. This requires proper location on the body, optimal opto-mechanical design and a convenient form factor that can be worn 24 hours per day. As a result, the use of small, convenient wristbands or patches on the upper arm is probably preferred over smart watches.
“In a second step, software is needed to turn the individual vital signs into meaningful, actionable data for the user and the doctor,” said Tingl. “To give an example, you could use all of the above info except SpO2 to do a stress measurement application including feedback to reduce stress. Another set of parameters including SpO2 could be used to provide information on sleep apnea or COPD [chronic obstructive pulmonary disease].”
To simplify designing an end product with the AS7000 biosensor, ams offers an HRM/HRV wristband demonstration kit containing a fitness band-mounted AS7000. An ams-developed heart rate app provides digital HRM and HRV readings for real-time logging of measured data.
Targeting medical applications
Manufacturers of sensors that do not make systems can help medical system designers by understanding their requirements. For example, Merit Sensor’s LP series ultra-low pressure sensors target sleep apnea systems and other medical measuring requirements, including: air flow (spirometers, ventilator), gas flow/pressure (respiratory) and air pressure (nebulizers). The fully compensated, digital (I2C) output sensors are easily used in wireless medical sensing applications and have an accuracy of ± 2.5%.
According to Rick Russell, president of Merit Sensor Systems, “To successfully address medical applications beyond simple health fitness monitoring, a device manufacturer must provide a benefit that does more than count steps and calculate burned calories. Monitoring blood pressure, for example, would not only offer a benefit but could save a life. This requires the full understanding of government regulations and the need for a sensor algorithm that will correctly diagnose a condition without the use of cumbersome wires and patches.”
The ultimate wearable
The ultimate wearable is an implanted device. Obviously, implanting a sensor system within a patient has many challenges.
One company that has addressed those challenges is Integrated Sensing Systems. ISS is not a sensor company that has a focus on medical applications, but a medical device company. That makes it quite different.
“We are an FDA registered medical device manufacturer,” said Dr. Nader Najafi, president and CEO. “We are ISO 13485 certified for quite a few years and actually we do the entire manufacturing of the implantable device.”
For chronic patient management, ISS’ Titan Wireless Implantable Hemodynamic Monitor (WIHM) uses a MEMS capacitive pressure sensor designed and manufactured by ISS that receives radio frequency (RF) signals from its antenna and does not require batteries. An external Readout Unit (ROU) provides RF power signal (of microwatts) to and receives the RF pressure signal from the antenna of the sensor and converts the sensor signals into digital values. For tele-powering, the ROU is about 8 in. from the implanted sensor during the readings.
Najafi explains that placing an implantable in the pulmonary artery on the right side of the heart, a rather normal procedure, is a much more meaningful hemodynamic parameter than external blood pressure monitoring.
“But the most important hemodynamic parameter is the pressures of the left side of the heart because it clearly shows the state of the heart, particularly for heart failure or arrhythmias,” he said.
Designed to monitor the filling pressure, heart rate, rhythm and pressure waveforms of the left side of the heart, the Titan system addresses long-term management of congestive heart problems in operating room and intensive care unit situations, as well as during one, three and six month follow-up visits. The left filling pressure, the pressure it takes for the left atrial pressure to equal the left ventricle pressure, is not adversely affected by other common health problems, such as a pulmonary embolism, making it a preferred location for heart pressure measurements.
The preferred location and accurate data from a wireless implant may be able to cut the cost impact of heart failure.
“Today, NIH [the U.S. National Institute of Health] calls congestive heart failure a new epidemic in the U.S.,” said Najafi. “Depending on which report you read, between 20 to 40 cents of every dollar that the Center for Medicare and Medicaid Services spends is on heart failure. That’s the number one cost for medical healthcare.”
With Titan sensor monitoring, patients showed shorter duration of some types of post-surgery medical problems in the ICU, improvement in certain heart functions and a reduced rate of re-hospitalization—all based on optimal medication.
Whether the sensing device is worn internally or externally, sophisticated applications of advanced sensors, software and wireless data transmission will change the way doctors and medical care providers analyze and treat diseases. In some cases, the sensor will be used in high volume, more common healthcare and fitness applications as well.
ams
www.ams.com
Integrated Sensing Systems
www.mems-iss.com
Leaf Healthcare
www.leafhealthcare.com
Merit Medical
www.meritsensor.com