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I was innocently reading my mail today when I ran across this:

http://www.medpagetoday.com/Blogs/IltifatHusain/61146

There are some problems with this article. I had trouble finding a link either in this, things linked to by this to the article which found problems in the previous app, "Instant Blood Pressure", to the Johns Hopkins article describing an attempt to validate the app by people not connected to the app. So, you know, google.

http://www.hopkinsmedicine.org/news/media/releases/popular_blood_pressure_app_misses_the_mark

App failed to detect most of the participants in the study who had high blood pressure, incorrectly saying they had normal blood pressure (using 140/90 as the cutoff, in case you were wondering).

The initial article I read had the perspective that, duh, of course this won't work, which honestly I initially did not have any problem with. But alas, as with a lot of bad rhetoric, the more the author went on, the more suspicious I became of that assumption. Helpfully, a word is supplied! photoplethysmography

Anyone who has ever been around a woman in labor, or any other poor unfortunate being continuously monitored by machines that go "beep" knows just how evil continuous blood pressure monitoring is. It disrupts focus, the ability to sleep and I still think it isn't good for the nerves distal to the cuff, I don't really care what anyone says. And can running a cuff that often be good for blood pressure walls? Can it? Really? (See what I mean about assumptions?) If you could take something along the lines of a pulse oximeter (which while obnoxious, is much more readily ignored than an automated cuff going off every fifteen minutes or whatever) and a microphone taped to your chest and use that instead, I am pretty sure we'd all just LOVE that, amirite?

But is it _real_? Sure, there are at least some scammy apps out there (surprise). And sure, there is going to come a day where we probably should actually do some enforcement on scammy apps that amount to some form of health care fraud.

But can cuffless photoplethysmography actually _work_?

It's not looking good, if people are resorting to things like this:

https://www.ncbi.nlm.nih.gov/pubmed/26736283

On the other hand, this:

https://www.ncbi.nlm.nih.gov/pubmed/26040284

I'm inclined to agree with the general thrust of this one: interesting possibilities, but not ready for clinical use yet.

https://www.researchgate.net/publication/237060099_Innovative_continuous_non-invasive_cuffless_blood_pressure_monitoring_based_on_photoplethysmography_technology

I hadn't realized that people had been working on this stuff for as long as they have, nor did I know there were commercial cuffless products out there already. Also, OMG the things they do to validate _non-invasive_ systems.

https://www.ncbi.nlm.nih.gov/pubmed/12131075

I can only hope that pigtail catheter was in the aortic arch for some other reason; the idea that they put one in to do this bicycle stress test is a little horrifying.

Oh, and while I focused exclusively on the BP aspects of photoplethysmography, one or more of the apps made other claims as well. If you are wondering about the ability to detect cholesterol non-invasively, well, I haven't found anything about using a camera, microphone and computing power that will do that, but I did find this:

http://www.prevu.com/English/pts/intro.html

ETA: I did find this, which seems sketchy at best:

http://www.inderscienceonline.com/doi/abs/10.1504/IJMEI.2012.048384

Also, there are people working on using impedance, which I'm pretty skeptical of. And a while back, people working trying to use IR as well. For the whole non-invasive cholesterol thing.

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