April 1, 2007 A new ultrasound stethoscope ignores outside noise, allowing medics to hear life-saving sounds inside the body. Developed by electrical engineers, the device exploits the Doppler effect as it sends an ultrasound wave into the body. The change in frequency is converted into sound that medics can hear, with a clean, audible signal.
The roar of a fire truck ... the whine of ambulance sirens ... MedEVAC helicopters overhead. They're first at an accident scene, but they're also loud -- making some emergencies too noisy for paramedics and doctors to listen to a patient's vital signs with a stethoscope.
"You can't hear lung sounds. You can't hear heart sounds inside of a running helicopter," Donald Lehman, a flight paramedic with the Maryland State Police in Pikesville, tells DBIS.
William Bernhard, an anesthesiologist and Master Flight Surgeon with the U.S. Army in Perryville, Md., says traditional stethoscopes do not work well because of all the outside noise that interferes with the sounds they're trying to listen to. Now a new, ultrasound stethoscope ignores outside noise, allowing medics to hear life-saving sounds inside the body.
"It's extremely helpful because it's the only thing out there on the market that will work," Bernhard tells DBIS.
Developed by electrical engineers, the device sends an ultrasound wave into the body. When it hits moving organs -- like the heart or lungs -- it bounces back at a different frequency, called the Doppler effect. This change in frequency is converted into sound that medics can hear.
"The exciting thing now is that we have a simple, hand-held device and can be used in these very high noise environments and gives a very, very clean, audible signal," Electrical Engineer Adrian Houtsma, of the U.S. Army Aeromedical Research Laboratory (USAARL), tells DBIS.
The new device is being field tested for the Army, where loud war zones make a standard stethoscope useless ... helping save lives one sound at a time.
Researchers like Houtsma are in the process of obtaining FDA approval for the device and are working to make sure it doesn't generate signals that interfere with aircraft or other equipment. It will first be manufactured to sell to the armed forces and could cost between $250 and $700.
The traditional stethoscope has hardly changed since its invention in the 1800s by French inventor and physician Rený Thýophile Hyacinthe Laýnnec.
BACKGROUND: A new type of stethoscope relies on ultrasound to enable doctors to hear the sounds of the body in extremely loud situations, such as during the transportation of patients in MedEVAC helicopters, or wounded soldiers in Blackhawk helicopters.
HOW IT WORKS: These new ultrasound models transmit a sound signal into the patient's body. This sound is reflected back to the stethoscope at a slightly different frequency because it bounces off the internal organs, changing the sound wave patterný essentially, the Doppler effect. The difference in frequencies between the transmitted sound wave and the returning sound wave received by the instrument can be computed to determine the motion of the internal organs. This difference in frequency is then converted into audible sound. Ultrasound stethoscopes produce a markedly different sound than conventional ones. An acoustic stethoscope yields a 'lub-dub' sound from a heartbeat with the first beat being the strongest. An ultrasound stethoscope yields a 'ta-da-ta' pattern with the second beat being the strongest.
THE PROBLEM: Traditional stethoscopes transmit and amplify sound within the range of human hearing: from 20 hertz to 20,000 hertz. Most body sound, such as that of the heart and lungs, fall into the 100 to 200 hertz range. Current acoustic stethoscopes detect and amplify vibrations that allow doctors to hear the heart and lungs better. However, they become difficult to use around 80 decibels -- a noise level comparable to an alarm clock or a busy street -- and are useless above 90 decibels. Modern electronic stethoscopes improved that threshold to 95 decibels by replacing the earpieces with loudspeaker inserts, which provide a better seal over the ear canal. They also have electrical cables instead of the conventional tubing, decreasing acoustic noise. But this is still not sufficient to make the instruments useful in very noisy environments. The ultrasound stethoscope is nearly impervious to loud noise and can make accurate readings at noise levels up to 120 decibels, similar to the volume experienced in the front row at a rock concert.
THE DOPPLER EFFECT: Both sound waves and light waves exhibit the Doppler Effect. Just as a train whistle will sound higher as it approaches a platform and then become lower in pitch as it moves away, light emitted by a moving object is perceived to increase in frequency (a blue shift) if it is moving toward the observer; if the object is moving away from us, it will be shifted toward the red end of the spectrum.
The Acoustical Society of America contributed to the information contained in the TV portion of this report.
Editor's Note: This article is not intended to provide medical advice, diagnosis or treatment.