Army medics and civilian paramedics often have to function in difficult surroundings. Noise, for example, can be a major hindrance in the diagnostic process, when the patient's heartbeat is barely audible above ambient noise. This could be during medical evacuation from a battlefield by helicopter, or when dealing with non-military medical emergencies on a highway, or at a noisy public event. Conventional passive acoustic stethoscopes work fine as long as the ambient noise levels are under 80-85 decibels (comparable to a busy city street). Unfortunately, once levels reach 90 decibels effective auscultation is not possible. Modern electronic stethoscopes have raised the maximum tolerable noise-level to between 90 and 95 decibels with the help of earphones, effective sound insulation, and optimized sensor design. But they do not go far enough.

     However, help could be at hand in the form of the noise-immune stethoscope that deploys ultrasound-imaging technology. This device ensures the sound produced by the heart or lungs can be clearly detected above environmental noise, regardless of intensity.

     Work on this stethoscope was conducted by Adrian Houtsma, a former MIT researcher and emeritus professor of acoustics from the Technical University of Eindhoven in the Netherlands, and Ian Curry, both of the US Army Aeromedical Research Laboratory (USAARL) in Alabama, together with John Sewell and William Bernhard of Active Signal Technologies in Maryland.

     The project to find a more effective stethoscope was born out of a medical need identified by the US Army. The first hour after sustaining an injury-the 'critical hour'-is when diagnosis and treatment must take place if combat casualties are to stand a good chance of survival and early recovery. Auscultation is an important diagnostic tool for assessing the condition of the heart muscle, valves and major arteries. In addition, auscultation of the lungs is invaluable when confirming the placement of endotracheal tubes, or to diagnose such conditions as a collapsed lung, asthma or pulmonary edema. Unfortunately, these patients are often transported by helicopter where noise levels prohibit the use of traditional stethoscopes.