For more than 200 years, the stethoscope has been one of the medical profession’s most useful tools. However, high noise levels can make the use of a stethoscope nearly impossible, creating challenges for medical professionals treating patients in busy emergency departments, surgical wards, ambulances, helicopters, and airplanes.
“For example, when an injured soldier is being evacuated by helicopter, it is often necessary for a medic to listen to chest sounds to decide if the soldier’s lung has collapsed, because a collapsed lung requires an immediate tracheotomy,” says Rajesh Rajamani, a professor in the Department of Mechanical Engineering. “Currently, it’s not possible to use a stethoscope on military evacuation helicopters because of extremely high noise levels. Proper medical relief of collapsed lungs could significantly reduce the number of preventable deaths on the battlefield.”
In a recent project, Rajamani and doctoral candidate Garrett Nelson designed a custom-instrumented stethoscope using a novel adaptive acoustic control system. By combining active noise cancellation with passive acoustic shielding, their approach makes it possible to successfully use a stethoscope in noisy, high-vibration transportation settings.
They began their project by measuring the quality of the noise levels on a Black Hawk helicopter, noting that the noise had both an acoustic and vibrational component. “Previous studies have relied on the use of a reference microphone for active noise control, and we realized that this method is incapable of successfully capturing noise transmitted structurally through vibrations,” says Nelson, now a postdoctoral appointee with Sandia National Laboratories.
Next, the research team simulated the vibration and acoustic noise environment of a Black Hawk helicopter using a laboratory test platform and tested the active noise-control capability of their customized stethoscope equipped with a reference accelerometer. Then, they compared those test results with tests of a microphone-based system.
“In the frequency range critical for the measurement of heart and lung sounds, our proposed system was capable of providing significantly superior performance to a microphone-based system—making the use of a stethoscope possible for the first time in this military aircraft environment,” says Rajamani.
Their work was funded by the US Army and 3M’s Infection Prevention Division.
