Tiny lung-heart ‘super sensor’ combines stethoscope, accelerometer
The hermetically-sealed high-precision 2-mm x 2-mm MEMS vibration sensor can acquire wideband (DC to 12-kHz) mechano-acoustic physiological signals and – when positioned on the chest wall – enable simultaneous monitoring of multiple health factors associated with the cardiopulmonary system including heart and respiratory rate, heart sounds, lung sounds, and body motion and position of an individual. Such a device, say the researchers, could enable a future socially distanced health monitor.
“Right now, medicine looks to EKGs (electrocardiograms) for information on the heart, but EKGs only measure electrical impulses,” says Farrokh Ayazi, Ken Byers Professor at Georgia Tech’s School of Electrical and Computer Engineering. “The heart is a mechanical system with muscles pumping and valves opening and shutting, and it sends out a signature of sounds and motions, which an EKG does not detect. EKGs also say nothing about lung function.”
The chip – an accelerometer contact microphone – involves two finely manufactured layers of silicon, which overlay each other separated by the space of 270 nanometers – about 0.000001 inches. They carry a minute voltage that fluctuates in response to vibrations from bodily motions and sounds, creating readable electronic outputs.
In human testing, say the researchers, the chip has recorded a variety of signals from the mechanical workings of the lungs and the heart with clarity – signals that often escape meaningful detection by current medical technology. In addition, the device detects vibrations that enter the chip from inside the body while keeping out distracting noise from outside the body’s core, such as airborne sounds.
“If it rubs on my skin or shirt, it doesn’t hear the friction,” says Ayazi, “but the device is very sensitive to sounds coming at it from inside the body, so it picks up useful vibrations even through clothing.”
The device records signals in sync, potentially offering the big picture of a patient’s heart and lung health. For the study, say the researchers, they successfully recorded a “gallop” – a faint third sound after the “lub-dub” of the heartbeat that are normally elusive clues of heart failure.
The experimental device is currently battery powered and uses a second chip for signal conditioning to translate the sensor chip’s signals into patterned read-outs. Three sensors or more could be inserted into a chest band that would triangulate health signals to locate their sources.
The high-resolution, quantified data produced by the chip, say the researchers, may be able to be used in future research to match to pathologies in order to identify them.
“We are working already to collect significantly more data matched with pathologies,” says Ayazi. “We envision algorithms in the future that may enable a broad array of clinical readings.”
Someday, say the researchers, a device may pinpoint an emerging heart valve flaw by turbulence it produces in the bloodstream or identify a cancerous lesion by faint crackling sounds in a lung. For more, see “Precision wearable accelerometer contact microphones for longitudinal monitoring of mechano-acoustic cardiopulmonary signals.”
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