Development and Assessment of a Dual-Mode, Noise-Immune Stethoscope for Combat Environments
ARMY MEDICAL MATERIEL AGENCY FORT DETRICK MD
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Future NATO operations will continue to take place in remote and austere environments far from fixed medical facilities. Not only is access to advanced medical technology lacking in such operational environments, but the use of certain basic medical devices can also be severely inhibited. The common acoustic stethoscope is rendered useless when ambient noise levels exceed 80-85 dBA. Noise cancelling electronic stethoscopes with mechanical impedance-matched transducer designs can extend the useful range up to 90 dBA. Unfortunately many operational environments exceed this threshold. The noise level in an air ambulance can reach 120 dBA, rendering even advanced electronic stethoscopes unusable. A need exists for a stethoscope that can detect heart and lung auscultation in the presence of fixed- and rotary-wing aircraft, as well as in ambulances and other operational environments where the ambient noise level precludes auscultation with a standard stethoscope. Possessing this capability can help prevent unnecessary loss of life by allowing combat medics to identify pneumothoraces and loss of intubation integrity conditions that would otherwise go undetected. This is basic medical care available in medical fixed facilities everywhere, but currently not available to our deployed medical personnel operating in high noise environments. The U.S. Army has partnered with Active Signal Technologies to develop a dual-mode noise-immune stethoscope NIS capable of operating in a standard electro-mechanical acoustic mode, or a unique Doppler mode. The Doppler mode allows auscultation in high-noise environments. Because even modern military vehicles do not produce acoustic energy at the ultrasound carrier frequencies of 2-3 MHz, the use of an ultrasound transmitterreceiver provides an essentially noise-free auscultation channel for the NIS.
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