The Age-Old Stethoscope Goes High-Tech

Bob Michaels
Medical Design Excellence Awards 2010 Coverage

Everyone is familiar with the stethoscope—the archetypal medical gizmo that doctors drape around their necks and hold against patients’ chests on countless TV shows, not to mention in real life. But that old workhorse of medical professionals everywhere has gotten a modern makeover—it’s gone digital.

An electronic device used to listen to patients’ body sounds for diagnostic support, the Littmann Model 3200 stethoscope from 3M (St. Paul, MN) is unlike the stethoscopes of old. Featuring on-board recording capability, the instrument enables clinicians to record sounds for peer review or teaching purposes. It works in conjunction with StethAssist heart and lung sound-visualization software from Zargis Medical (Stamford, CT) and the Zargis Cardioscan cardiac diagnostic support software, which communicates with a PC via a Bluetooth wireless channel. By playing back original sounds recorded by the stethoscope or replicating them through headphones, the PC now allows doctors to listen carefully to their patients’ hearts.

“Doctors’ ability to perform auscultation—the act of listening to the internal sounds of the body—has been declining in part because of reliance on advanced technology such as echocardiograms,” explains Tim Chismar, a technical service engineer at 3M. The new stethoscope aids doctors in performing auscultation to help them differentiate between real and apparent heart anomalies and reduce their reliance on echocardiograms. However, to overcome the inherent difficulty in performing chest auscultation using traditional, nonelectronic stethoscopes, the Littmann device amplifies body sounds of interest and reduces distracting ambient noise.

The auscultation skills acquired by physicians through experience are augmented by the computer-aided technology provided by the Cardioscan software, Chismar says. With the assistance of a voice-guided protocol, this software enables physicians to record heart sounds. It also helps healthcare professionals to establish good clinical practice by directing them to record heart sounds from standard sites on the chest in a fixed, repeatable sequence. In addition, the protocol establishes the connection between individual recordings and their associated location on the chest, retaining information that is essential to clinical diagnosis.

Designed for exclusive use with the Littmann 3200, Cardioscan uses algorithms that detect suspected heart murmurs, remarks John Kallassy, CEO of Zargis. “This software helps differentiate whether a murmur is innocent or pathological and whether or not further testing is needed,” he says. “We do that by looking at the characteristics of the murmur.”

Heart-sound analysis can be challenging because everyone’s heart is different, Kallassy notes. “Hence, analysis algorithms must recognize acoustically different heart sounds as being the same, while distinguishing the first heart sound from the second and murmurs from background noise.” Cardioscan achieves this using signal-processing methods that exploit time-frequency analysis and statistical modeling methods.

Featuring a chrome-plated metal housing that reduces ambient noise while minimizing frictional noise created by the user’s fingers, the device was designed by Bang & Olufsen Medicom (B&O Medicom; Struer, Denmark). “We designed and built the stethoscope based on inputs from 3M,” comments Carsten Pedersen, project manager at B&O Medicom. “That involved industrial design, mechanical and electronic design, and firmware development, including the Bluetooth wireless interface.”

Because B&O Medicom developed the first digital electronic stethoscope for 3M in 2001, it was well qualified to meet the challenges involved in making the new model. “One challenge was to minimize the size and weight of the device, which uses a relatively large AA battery to support the Bluetooth communications,” Pedersen says. “Another was to install a Bluetooth antenna inside the metal chassis while ensuring the required range of wireless transmission.” This capability was achieved by making the antenna an integrated part of the PCB in the chest piece of the stethoscope and shaping it to achieve uniform reception all around the chest piece.

“Nearly every physician today has access to PCs that are powerful enough to run sophisticated algorithms,” Kallassy concludes. “It made sense for us to marshal the power of computing to assist the healthcare professional’s ears in understanding and making more sense out of physiological sounds.”