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How Pulse Oximeters Work (2015)
- progre 6y agoSince the site is hugged to death, why not check out Technology Connections video instead: https://youtu.be/4pZZ5AEEmek https://youtu.be/4pZZ5AEEmek
- d1str0 6y agoExcellent video and excellent creator!
- herbstein 6y agoTechnology Connections is such a good channel that mixes humor and in-depth looks at things people only kind know a little bit about.
- Tokkemon 6y agoWas going to send this link, but alas you already did. Alec is so good at this and I'm a proud Patron of his work. It's always really well done and thoughtful.
- dvt 6y agoWent to a party last weekend where the host used a pulse oximeter (and thermometer) on everyone. Blood O2 level is apparently a leading indicator of COVID-19. Pretty cool stuff. The inner workings of it are actually quite simple as well, pretty amazing that it works as well as it does.
- popotamonga 6y agoI discovered i have a problem with one. Every one else who tried it had 98-100 all the time. I had < 94 no mater what
- brain5ide 6y agoWhat problem if you don't mind? I have a Garmin that says I'm 94ish, though it's accuracy is questionable. Haven't had a chance to test with a proper one.
- asveikau 6y agoI thought I recall reading that 94 is not dangerous or abnormal, and 90 is when you should get checked out.
- alkonaut 6y agoThis is something that is still not quite understood by doctors. I take my kid (Who has a respiratory condition) to hospital at 90. In my experience if you are in hospital with oxygen because of a respiratory illness, the oxygen would probably be given once you dip below 92-93 assuming they know you have a respiratory condition. Not because that’s the danger level but because they want to be able to tweak the O2 if you fall even lower. Doctors then usually instruct nurses to adjust the flow so saturation stays in the 90-95 range. People at high altitude or in airplane cabins can be at 70% for hours without even noticing. Meanwhile someone having a dip from 90 to 80 with pneumonia might be gasping for air.
- el_don_almighty 6y agoHN is the new /.
- d1str0 6y agoFeel free to make a new HN that caters perfectly to you.
- ChrisGranger 6y agoI think the parent was referring to the Slashdot effect of knocking small websites offline. https://en.wikipedia.org/wiki/Slashdot_effect https://en.wikipedia.org/wiki/Slashdot_effect
- rcar 6y agocached: https://webcache.googleusercontent.com/search?q=cache:Gs1gDy7I1WkJ:https://www.howequipmentworks.com/pulse_oximeter/+&cd=1&hl=en&ct=clnk&gl=us https://webcache.googleusercontent.com/search?q=cache:Gs1gDy...
- behnamoh 6y ago"Error establishing a database connection"
- deleted 6y ago[deleted]
- Fabricio20 6y agoTechnology Connections [0] also has a great video about these awesome devices, although not that much in-depth in comparison to this website. [0]: https://www.youtube.com/watch?v=4pZZ5AEEmek https://www.youtube.com/watch?v=4pZZ5AEEmek
- linsomniac 6y agoAgreed, watched that a few weeks ago and enjoyed it.
- ravedave5 6y agoSuch a great channel and good explanation.
- maxfan8 6y agoHere is the WBM archive of it: https://web.archive.org/web/20200708064647/https://www.howequipmentworks.com/pulse_oximeter/ https://web.archive.org/web/20200708064647/https://www.howeq... (for those who can't access the original site due to it being hugged to death)
- ornel 6y agoI measured myself at home in Mexico City and got 93%. I got kind of worried, knowing people sick with COVID-19 can have very low saturation levels without realising it. Then I remembered I was standing at about 2200 m above sea level. Lots of unexpected weirdness happens at high altutude
- amelius 6y agoSo was it really your oxygen saturation level, or was the measurement flawed?
- alecmg 6y agoeven holding your breath for couple seconds will tank saturation, so pretty likely high altitude will do the same until your breathing adjusts to compensate
- Engineering-MD 6y agoIt shouldn’t effect your oxygen saturation’s at all. Respiration is driven by raised CO2 not drops in oxygen in the healthy (COPD is the classic example of where low oxygen levels drive respiratory effort)
- peripitea 6y agoI know I replied to a different comment of yours, but this paper also illustrates how this point, while matching common medical wisdom, is not necessarily correct when accounting for altitude: https://www.thelancet.com/journals/langlo/article/PIIS2214-109X(19)30543-1/fulltext https://www.thelancet.com/journals/langlo/article/PIIS2214-1... (Summary: Healthy children at higher altitude breathe more rapidly.)
- Engineering-MD 6y agoI’ll be honest, a lot if the portable oxygen saturation monitors seem to report slightly out of range readings. It often picks up after a few minutes, I suspect they are calibrated poorly tbh. 94-98% is the desired range.
- DangerousPie 6y agoDoes anybody have any suggestions for how to check whether a pulse oximeter actually works properly? I bought one online from a not particularly trustworthy shop. I have never seen it show any value other than 99%. How can I figure out whether it actually does anything and doesn't just show 99% no matter what?
- mturmon 6y agoI purchased a relatively cheap one from Amazon a couple of months ago. Less than $50, I believe. I tried some simple stuff when it arrived. I believe I was able to get it to swing within the 94-99% range by holding my breath and by deliberate, deep breathing, over the span of just a minute or two. It definitely was not pegged at 99%. The changes were surprisingly fast. My wife was able to get the same response. If it matters, I'm at about 500 feet above sea level (not high-altitude at all).
- deleted 6y ago[deleted]
- DangerousPie 6y agoHow long did you hold your breath for?
- mturmon 6y agoPerhaps 30 seconds? It was uncomfortable but not a big strain. I see someone nearby saying 2-3 minutes. For me, it was not that long!
- mancerayder 6y agoI bought one a few days ago (weird coincidence), from Amazon for around $35 at the advice of a friend. Skeptical also, my 97% level upped to 98-99 with deep breathing, and then I held my breath as long as I could possibly do it and it dropped to about 93-94. That's obviously not a confirmation that it's calibrated or trustworthy, but at least it shows a relative measure that seems real in both directions of oxygen saturdation. Surely if I have a drop due to illness I should notice, even if the number isn't exact.
- wlesieutre 6y agoSpeculated to be included in the Apple Watch S6 this fall. https://9to5mac.com/2020/03/08/apple-watch-blood-oxygen-saturation/ https://9to5mac.com/2020/03/08/apple-watch-blood-oxygen-satu... At the time they reported that there were mentions of it in an iOS 14 leak, but it wasn't clear if it would be a software update to existing watches (somehow able to detect it with existing heartrate hardware) or in a watch hardware revision. Since it wasn't mentioned in the watchOS news at WWDC, looks like it'll be new hardware. Either that or the code they found in iOS 14 was related to the health app and support for 3rd party oximiters, but that's not how the 9to5 post frames it so best I can do is take their word for it.
- deadmutex 6y agoIIRC, Fitbit has products on the market that has them. Works both on iOS and Android. https://www.wearable-technologies.com/2020/01/fitbit-adds-blood-oxygen-monitoring-spo2-in-its-versa-charge-and-ionic-device/ https://www.wearable-technologies.com/2020/01/fitbit-adds-bl...
- stygiansonic 6y agoGarmin also has them on several devices: https://support.garmin.com/en-US/?faq=SK2Y9a9aBp5D6n4sXmPBG7 https://support.garmin.com/en-US/?faq=SK2Y9a9aBp5D6n4sXmPBG7
- dghughes 6y agoGarmin seems to be highly inaccurate at measuring oxygen and the devices take a very long time compared to a finger oximeter. I get 93% but a cheap Walmart finger oximeter shows me at 99%.
- VectorLock 6y agoWow they finally did it. After the hardware being there for _years_ they managed to get around to enabling the software. I already jettisoned them for Garmin after waiting so long.
- dmitrygr 6y agoIt is really grating that all the visualizations are wrong. Blue is shorter wavelength than red. Infrared is longer wavelength than red. Every single image is wrong. :(
- alister 6y agoThe author explains his visualization as follows: One is a red light, which has a wavelength of approximately 650 nm. The other is an infrared light, which has a wavelength of 950 nm. (Throughout our description, we will show the infrared light in light blue. In reality, infrared light is invisible to the human eye.)
- dmitrygr 6y agoi mean this, for example: https://web.archive.org/web/20191230203925im_/https://www.howequipmentworks.com/wp-content/uploads/2015/01/wave_show.gif https://web.archive.org/web/20191230203925im_/https://www.ho...
- wtallis 6y agoThe fact that those curves don't even come close to resembling sine waves seems more wrong to me, and really helps drive home the fact that the diagram was made in MS Paint with little regard for accuracy.
- hakcermani 6y agoThe blue color is being used for infrared so the wavelength is right. The author could have used a '-- red' for infrared rather than blue to be less confusing.
- amiga_500 6y agoDoes anyone know the degradation in blood oxygen levels under moderate exercise for a person who is fairly health (not athlete but slim, does regular exercise)? I had covid, so bought one of these, and I'm now building my way back to being able to jog, after months of shortness of breath. I would like to be able to understand what level my blood oxygen %, for a normal, healthy person, would drop to when say jogging.
- spaetzleesser 6y agoMine doesn’t drop much during exercise.
- amiga_500 6y agoDefine much, please. I believe getting near 90% at rest means it's time to think about an ER visit.
- peripitea 6y agoFrom what I understand, this is more because having that low of oxygen at rest is highly likely to be a symptom of a deeper problem, not because the 90% oxygen by itself is a huge imminent problem. Afaik you can go days/weeks at that level and be mostly fine if you are otherwise healthy. For example, this paper suggests that some people who live at high altitudes have perpetual SpO2 of <90%: https://www.thelancet.com/journals/langlo/article/PIIS2214-109X(19)30543-1/fulltext https://www.thelancet.com/journals/langlo/article/PIIS2214-1.... For those of us living near sea level, temporary drops below 90% should be ok if you are otherwise healthy (up to a certain point of course), because as someone else in the thread suggested, they will rebound to >=95% as soon as you return to rest/normal breathing. (Disclaimer: I'm not a medical expert, but have had to study breathing a fair amount. Happy to have corrections from anyone with more knowledge on this!)
- pps43 6y agoIf I really push during my 5k run, pulse oxymeter shows around 85%. Not sure how much to trust it, as soon as I stop it climbs back up. Unclear if it's due to vibrations, or my lungs catching up.
- oehtXRwMkIs 6y agoFun fact about pulse oximeters: in California EMTs are regulated so strictly that it is illegal for them to use a pulse oximeter as it is deemed "invasive". So if anyone is experiencing a medical emergency that could successfully be delayed following the algorithm involving checking blood O2, they better hope the EMT is experienced/lucky enough to suspect low O2 or that there's a paramedic or nurse on board. It's definitely one of those laws that aren't really enforced but it's weird that in California EMTs have to break the law to do basic screening.
- dreamcompiler 6y agoThis is a very weird law. In NM, basic EMTs can use a pulse/ox, insert blind airways, inject narcan and epinephrine, administer nitroglycerine, attach an ECG monitor, and do half a dozen other things more invasive than a pulse/ox.
- seehafer 6y agoWonder where they got that definition of "invasive" because it surely wasn't in a medical textbook.
- tomjakubowski 6y agoCitation please? Page two of LA County Health Services's "EMT Scope of Practice" document lists pulse oximetry as part of the basic diagnostic process for EMTs. This would seem curious if state regulations forbid that. http://file.lacounty.gov/SDSInter/dhs/206315_802.pdf http://file.lacounty.gov/SDSInter/dhs/206315_802.pdf
- oehtXRwMkIs 6y agoThat's LA, here's California: https://emsa.ca.gov/wp-content/uploads/sites/71/2017/10/Scope-of-Practice-Documents-Current.12.11.18.pdf https://emsa.ca.gov/wp-content/uploads/sites/71/2017/10/Scop... EMTs in California are indeed allowed to use it, I must have learned something that was county specific, not state wide. My apologies.
- dreamcompiler 6y agoFWIW some Samsung phones (and probably others) have this functionality built in. I've tested mine and I consistently get readings within 1 point of my gold-standard Nonin pulse oximeter.
- leetrout 6y agoIt's always interesting to me how much of a hivemind the internet has and how many coincidences there are. Just last night I dug out my cheapo pulse oximeter and checked everyone in my house to get a baseline. I then googled how they work and read pretty much the same thing.
- jacquesm 6y agoThis is more a function of how many people read HN than anything else. On a population that large in a crowd of technically inclined people there's bound to be somebody who in the space of 24 hours researched how oximeters work. I read the same article a few months ago.
- leetrout 6y agoTrue
- bdcravens 6y agoThe most painful thing I've experienced medically was an arterial blood draw to measure my o2 sat levels. (They numb your inner wrist with novocaine then go in with a giant needle to the artery deep in there. If it's that painful numb, I can't imagine what it'd be like otherwise. And each time it was no more accurate than the pulse oximeter.
- joshgel 6y agoMost of the time we don’t numb patients to be honest. I’ve had it done to me, we practiced on each other in Med school. It is painful, but I suspect the Novocain you got didn’t work because it’s the artery that’s painful not the skin. But it does give you different information than a pulse ox. For example, people can have respiratory failure from too low oxygen (captured on a pulse ox), but also from top high CO2 (not measured on pulse ox). It also gives a measure of acid-base status, which can be thrown off for a variety of reasons (usually renal or respiratory). It is used somewhat too much in my opinion but can be life saving in some situations.
- dialamac 6y agoAn Pulse Ox and ABG are not interchangeable exams, with the ABG giving a lot more data about respiratory and metabolic derangements. A pulse ox can also be outright fooled such as in cases of carbon monoxide poisoning or essentially wrong in other poisoning. Also for a wrist ABG there’s no reason to use a giant needle. A 23g is usually fine, length is usually not an issue as the artery is actually quite superficial. For reference, an 18 gauge is the smallest that might be considered “large”. And the sizes are bigger as the number gets smaller.
- sirius87 6y agoWow! that was a fantastic, insightful read. did not know the pleth was of note.
- dghughes 6y agoThe problem with pulse oximeters is the people who need them often can't use them. Yes I know it's not meant as a medical device. My dad has COPD and IPF but he can't use the SPO2 meter on the Samsung phone I gave him (and Samsung disabled the SPO2 function for Canada). A Garmin VivoSmart 4 can't give a decent reading on him or me and it takes forever. Part of the problem is blood flow dad's fingers are ice cold due to his condition. My dad uses a cheap oximeter from Walmart it works better than anything else. It's the type that clips over a finger it's fast and seems to be accurate. I'd like to get a wristband or watch that has a good SPO2 meter but nothing seems to exist.
- vwcx 6y agoCan anyone recommend an inexpensive fingertip oximeter?
- exhilaration 6y agoBack in April, I bought this unit and sent it to my wife's family in New Jersey. I spent some time googling what to get; I found several discussions on Reddit where doctors and med students agreed that the "Zacurate" units reliably matched their hospital units. https://www.amazon.com/Zacurate-Fingertip-Oximeter-Saturation-Batteries/dp/B01HSAG8BE https://www.amazon.com/Zacurate-Fingertip-Oximeter-Saturatio...
- danieltrembath 6y agoThe Royal Melbourne hospital in Australia is using pulse oximeters to manage COVID positive patients in their own homes. The program was setup in March this year to manage a large number of patients remotely (cost/safety). The patients take their own measurements with a pulse oximeter and digital thermometer (both off the shelf consumer items). The person is prompted via SMS and submit their vitals via website. A software system orchestrates all of this and alerts patients and clinicians to anyone with worrying numbers. This keeps beds free at the hospital, but still gets the small percentage of patients back to hospital that get really sick. It also does all the other boring monitoring and administrative work needed when you're checking up on lots of real people. Full disclosure. I worked on this project. A version has been open sourced and if you're a hospital or other medical service you're welcome to use our work. We're publishing improvements as we go. https://github.com/rmhcovid/txtmon https://github.com/rmhcovid/txtmon https://www.thermh.org.au/news/royal-melbourne-hospital-implements-virtual-monitoring https://www.thermh.org.au/news/royal-melbourne-hospital-impl... Using simple standalone devices and a low-coding platform already in use by hospitals (REDCap) the whole project was crash-built in a couple of weeks and is saving lives. That platform has many shortcomings (messier even than Excel), but there's various medical/privacy rules that make more traditional development unattractive for quickly prototyping. It's been a rewarding project to work on despite many frustrations.
- elif 6y agoThank you for sharing this. In the program guide it says a temperature reading of > 42 degrees or an oxygen saturation of < 90 are the thresholds for a MET call. Is there a basis for these specific values or are they general approximations?
- danieltrembath 6y agoChosen by the emergency doctors who headed the project. Sats being the more important. Those are default thresholds, but each they can be overridden per-patient. As I understand it there is a lot of communication going between emergency teams and specialists around the world and the odd pre-publication paper. This work has come out of the RMH's emergency department. Full credit goes to Dr Martin Dutch who's idea the whole thing was. As best I know he came to the idea (tracking sats via cheap electronics to spot risky covid patients) quite early, and independently. He also built an initial prototype. I'm a developer who was brought in to build it out into a working system during the first phase of Australia's covid outbreak. PS: If you're thinking about using the system, it's worth having a read through the redcap_design_overview.md documentation. Building something like this in a research-survey tool was not easy and there's plenty of things in the design that will be head-scratchers when seen for the first time. Now that the model is proven we'll hopefully build out a 'real' version of it at some point. We're happy to assist where we can to see other hospitals (particularly resource-constrained ones) pick it up. The operating costs are very low (a server + sms gateway cost). The hospital has also open sourced some other covid tools developed this year.
- sohkamyung 6y agoOff-topic, but an inventor of the Pulse Oximeter recently passed away [1]: "Takuo Aoyagi, a Japanese engineer whose pioneering work in the 1970s led to the modern pulse oximeter, a lifesaving device that clips on a finger and shows the level of oxygen in the blood and that has become a critical tool in the fight against the novel coronavirus, died on April 18 in Tokyo. He was 84." [1] https://www.nytimes.com/2020/05/01/science/takuo-aoyagi-an-inventor-of-the-pulse-oximeter-dies-at-84.html https://www.nytimes.com/2020/05/01/science/takuo-aoyagi-an-i...
- nerdbaggy 6y agoIt’s weird, when I have a pulse oximeter on my finger and a blood pressure cuff on and it’s rather inflated I get electrical feeling shocks up my arm. The both have to be on the same arm. No idea what it is, probably a pinched nerve.
- bookofjoe 6y agoLikely ulnar nerve compression just above the elbow by the inflated blood pressure cuff. (retired M.D. here)
- nerdbaggy 6y agoThat makes sense thanks! I see that you were an anesthesiologist, now I can finally asked this question that I’ve always wanted too! When under general anesthesia why do they put you on opioids? I read that if not people would still react to the pain? Like would the scream and cry just not know they were doing that?
- bookofjoe 6y agoOpioids are a component of so-called "balanced" general anesthesia (GA). Over my 38 years in practice (1977-2015) and some 25,000-30,000 cases, probably 95% were GA and the remainder regional/I.V. sedation. Of the GA's, I estimate I used IV opioids in 95%. My drug of choice was fentanyl: fast and relatively short acting, easily titrated to response. Along with fentanyl, I routinely used diazepam or Versed (I started in 1977 and Versed didn't become available until 1985), and skeletal muscle relaxants for endotracheal intubation and skeletal immobility. Induction of GA was with sodium thiopental (1977-1989), thereafter Propofol. Having said that, know that by the time I retired, I was in a small minority of anesthesiologists (most older like myself) who trained when balanced anesthesia was standard. Today an overwhelming majority of anesthesiologists use only inhalation agents for GA and do not give opioids intraop. Inhalation GA often does not require skeletal muscle relaxants (depending on the surgical site), and if a patient is "light," they will react by moving and show increases in heart rate and blood pressure. Diff'rent strokes. FWIW, I am one of very few anesthesiologists with extended time in practice who have never been sued. >Like would they scream and cry, just not know they were doing that? Awareness under anesthesia is a whole different subject of considerable importance.
- acidburnNSA 6y agoSO is an internal medicine doctor. When covid was ramping up at first and we thought there would be beds in school gyms and stuff the first thing she did was get a pulse oximeter off the internet.
- jacquesm 6y agoWhat a fantastic, no nonsense and well researched article this is. I read it a couple of months ago and was very much impressed.