Effect Measure

High tech stethoscope

I had to laugh when I saw this piece in New Scientist. It’s about a new high tech ultrasound stethoscope supposedly immune to background noise.

The stethoscope is a useful tool for quickly diagnosing damage to the heart or lungs, which many victims of traumatic injuries can suffer. But they can be difficult to use when background noise reaches about 80 decibels ? the same as a busy street. These surrounding sounds can then drown out audio information that is crucial to an accurate diagnosis.

Street noise, nothing. How about the ground floor of an inner city hospital of some repute in a ward of 40 women with beds side-by-side, the windows open in the summer, no screens and pile drivers in the background. Not a third world hospital, either. This was the old New York Bellevue Ground B, living out its last years as the “new” Bellevue was being built around it. Hence the pile drivers.

I did some of my training there, using a trusty Littman stethoscope which I was given for free by some drug company (since I can’t remember which one they didn’t get their money’s worth). It was a good stethoscope but I’m not sure I ever heard “the low rumble of mitral stenosis” even in a quiet examining room, and you can bet I never heard it on Ground B. It was quite a wild place. I still remember coming into the ward about 2 am to see one of my colleagues trying to take a history from a new admit. He had his stethoscope on the patient’s ears (the patient was hard of hearing) and he was yelling into the bell, “How often do you shit?”

The new improved high tech model is said to work even with background noise up to 120 dB, roughly twice the sound intensity of the previous limit. Instead of “listening” to vibrations caused by a beating heart, however, it sends an ultrasound pulse into the body and picks up the reflections. Since the heart wall moves back and forth during contractions, the device uses the Doppler shift which it then converts into sound. It’s also not quite so convenient. You have to use a gel between the sensor and the patient and you have to use noise canceling headphones.

It isn’t clear this will work so well in a vibrating vehicle or helicopter or if the patient is moving. Using a sensor that detects movement and converts it into sound but now there is a new kind of background “noise,” movement noise. The Doppler shift information is also different than the sound produced by the heart or arteries from pulsation, so it may become a specialist device for trained operators or a way to get only the crudest information, like heart rate, in super noisy environments. Still no “low murmur of mitral stenosis.”

Meanwhile the problem of trying to hear heart sounds in the midst of hospital construction has been solved. Now we just have to deal with getting rid of hospitals.


  1. #1 Alan
    December 5, 2006

    Wouldn’t it be similar to an echocardiogram? Except that instead of conveying information visually, it would convey it aurally. It might be more productive to work on making echo machines cheaper and more portable, and to train non-cardiologists in their use.

  2. #2 revere
    December 5, 2006

    Alan: NIce observation. Somehow, though, I don’t think this is going to catch on (famous last words; wait and see and someone 50 years from now will reprint this with exclamation marks about the device that changed medical science forever).

  3. #3 epifreek
    December 5, 2006

    There is also a new more “ordinary” stethoscope, which blocks out background noise and could be worn by healthcare workers wearing powered air-purifying respirators (which make noise) as might be the case in an influenza pandemic.

  4. #4 M. Randolph Kruger
    December 6, 2006

    Geez Revere, the bloody thing is supposed to be able to cancel out more noise than the monitors at LAX airport? They go off at 100 and they send you a nice bill when you fly too close to them. So, you are supposed to be able to hear the stenosis but not the 747 that just blew past your ass? Uh-huh. Reverse cancellation with noise against noise from recognition, then reverse noise playing back cancels it. But do you really want someone whose ears are getting whacked from two different noise sources doing a diagnosis on you?

  5. #5 Edmund
    December 7, 2006

    Wow. 120 dB is really loud. I absolutely can’t tolerate being around 110 without earplugs, and of course 120 is 10 times louder than that.

    This might be better off as a proof-of-concept device rather than something which has a lot of practical applications.