09 January 2021

Music from the dorsalis pedis

Arguably the most interesting item I bookmarked during my blogcation, as reported by the New England Journal of Medicine -
A 65-year-old man who had previously undergone bilateral hip arthroplasty presented with a dislocated hip after a fall. When a handheld Doppler device used to assess the pulses in his feet was placed on the dorsalis pedis, it picked up music in addition to the pulse, as shown in a video.
The article at the link was outside the paywall initially; I don't know whether it will remain so.  In the audio at the gif, the music is clearly a broadcast by a radio station.  The staff at the hospital tried using other Dopplers, all of which gave the same result, so it was not a Doppler malfunction.  They then checked other patients' pulses, but heard no music, so the phenomenon appears to be somehow caused by this patient's prosthesis.  I like when they pan the camera to show him smiling about everything at the end.

Addendum:  The app Shazam identified the music in the gif as “Gracias Por Tu Amor” by Banda El Recodo De Cruz Lizárraga.


  1. Of course, paywalled now, and my university access delays full-text for three months.

    I'd be interested to see if they moved the patient, and then used the same doppler. There are a number of phenomena that can result in radio waves being intercepted and made audible by non-radio equipment, and sometimes it can be highly dependent on the location due to various natural and artificial environmental effects. Typically it involves unintentional capacitances and inductances in the processing/preamplification portions - especially when followed by high amplification factors.

    I'm sure many of us have heard stories about people picking up radio on their braces, and these are likely apocryphal, but I once recorded what is known in obscure technical music jargon as "a bitchin' face-melter of a guitar solo" using a wah-wah pedal, and picked up some local radio loud and clear. We (the band) never identified the song, but we kept it in the recording, reversing the audio so it becomes a "derivative work" rather than you know, plagiarism. It's actually a pretty common problem with wah pedals and other guitar effects, and there are various ways of combating it with varied effects.

    I really want to read the article. If I get my hands on it and I'm still curious, I'll report back.

  2. AM radio is easy to demodulate if you just have a diode. Semiconductors form with "bad" connections between different conductors, such as the interface between a needle point and a chunk of certain minerals, which are used in old school crystal radios. I've read of creating a diode using the surface of a razor blade which has some sort of surface treatment. I remember as a kid, we accidentally picked up a radio station while plugging in a speaker to our Apple 2 computer. The only requirements are that the station is significantly louder than the others so that you don't need a tuning circuit and you just rectify the raw radio waves in the air to an audio signal.
    The fact that the song was a Spanish language one doesn't surprise me as there are a lot of strong AM stations broadcast from Mexico.
    (This would not work at all for FM stations. That's too complicated)

  3. in the '60s I could get San Francisco on my toaster.

  4. Reminds me of Lucille Ball's radio receptive dental fillings.


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