This blog post was written to highlight some of the potential risks involved with smart-watch pulse oximeter devices, if they become widely available. This post was deliberately written in a somewhat alarmist style to bring these issues to the fore. I hope the concerns raised in this blog post are addressed by manufacturers of such devices, so as to ensure that people use pulse oximetry information from smartwatches in a calm and safe manner. - Lewis
Disclaimer added: 22/11/2017.
24/09/18. Garmin have recently launched a smartwatch with pulse oximeter capability: the ‘fenix 5X Plus’, which reads out pulse oximeter AND altitude. This seems to be a sensible solution to the smart-watch blood oxygen monitoring problem. They have also released the lower-cost ‘Vivo smart 4’ which does not seem to have an altitude sensor. Thanks to commenter ‘Ozzy’ for bringing this new wearable information to my attention. I hope everyone enjoys their new gadgets.
A mystery red LED…
Analysis of Apple’s smart-watch hardware has revealed a deactivated red LED sitting idle in the smart watch. Why put this waste of space into this tiny device if you are not going to use it? Speculation has reasonably guessed that this red LED would be used for measurements of blood-oxygen levels, but for some unknown reason Apple have not activated it. Some mundane speculation suggests that Apple may be waiting on FDA approval, or may be trying to improve the accuracy of this tech. However, I have a much more dramatic reason why Apple haven’t activated this little red light. It involves airplanes, it involves international panic, and it involves avoiding multiple massive lawsuits.
The nightmare scenario….
Imagine this: a few months from now, a big company – let’s call them ‘FruityTech Inc.’ - launch their brand-new smart-watch with a new must-have feature: real-time measurement of blood oxygen levels. They sell this feature of blood-oxygen monitoring as being beneficial for exercise monitoring or for keeping an eye on oxygen level drops due to sleep apnoea [see Dong Chin Joi et al., 2016]. What FruityTech Inc. haven’t realised is that their new feature would likely cause widespread panic on the world’s airplanes and likely leave them with a few BIG lawsuits. It would play out something like this:
As an on-trend technology aficionado, you attend the launch of the FruityTech Inc. smart-watch in New York. This new model has the neat feature of measuring your blood oxygen levels. You buy the smart-watch, strap it on, and do some basic tinkering until satisfied with the various settings. Happily, your blood-oxygen level is 98%, which you are told is within the normal range of 95-100% at sea level. You board a routine passenger flight back home. You have your FruityTech Inc. smart-watch on your wrist. Sitting on the runway, you glance around and noticed that that quite a few other tech-savvy international jet-setter passengers have brand new FruityTech Inc. smart-watches too. You check your blood oxygen-levels, and you are still at 98%. Perfect.
The cabin is pressurised and your plane takes off.
About five minutes into the flight you glance at your new smartwatch and you notice that your blood oxygen is now 94%... 93% … 92%.... 91%.... 90%.... what’s going on? Is your smart watch faulty?
You ask one of the other nearby passengers what their smart-watch is reading. They noticed blood oxygen is dropping too… this person is at 87%!
Someone nearby jokes that they hope the plane’s oxygen level is okay. You call the airline attendant and ask if everything is okay with the oxygen system. They reply “of course”. Another passenger overhears this, and starts to panic.
Before you know it, everyone on the plane is worried about oxygen levels, with quite a few passengers panicking. With on-board wifi, someone sends a tweet about the oxygen systems on their plane failing. The story goes global.
Reports come in of the same phenomena happening in dozens of flights. panicked passengers. Some flights land soon after take-off due to the sheer number of agitated passengers. Upon landing, passengers are relieved when the cabin is de-pressurised and their blood-oxygen levels return to the normal range. No one is physically hurt, but the panic has been extremely costly.
It doesn’t take long for people to figure out what’s happened. Medical professionals and airline industry insiders chime-in, but by then it’s too late. FruityTech Inc. has multiple lawsuits for stress and causing needless panic on its hands from both the airline industry and from private individuals.
So what happened in our hypothetical scenario? It’s all down to the cabin pressure in airplanes and human physiology.
Throughout any commercial flight, all passengers breathe the usual atmospheric mix of 21% Oxygen, 78% Nitrogen, and 1% other stuff. However, at cruising altitude a passenger plane cabin is pressurised to the equivalent of a high mountain where the air is thinner than at sea level. This means that whilst 21% of the air is still vitally required Oxygen, there is physically less air! In fact, it is equivalent to roughly 15% Oxygen at sea level. Unknown to most passengers this drop in available oxygen causes everyone’s blood-oxygen levels to drop by between 5 and 15% for the duration of the flight [see Humphries et al., 2005].
This low blood-oxygen levels (known to medical professionals as acute mild hypoxia) is normally uneventful because a blood oxygen drop of this level is inconsequential for healthy people just sitting around. Some passengers with respiratory conditions may require supplementary oxygen, but that’s about it. Crucially everyone is blissfully unaware of their low blood oxygen levels.
The problem is that when multiple passengers have a smart-watch telling them that their blood-oxygen levels are dropping in real-time. One smart-watch could be faulty. But all of them failing… well that could easily be misinterpreted as the oxygen levels in the cabin dropping.
Our imaginary -yet likely – scenario shows what a minefield smart-watches and other wearable health-monitoring technology is.
What this means….
Various large technology companies have probably had planned to include a blood-oxygen measurement feature in their smart-watches until somebody quietly figured out the scenario presented in this blog. There would be a big liability risk to any smart-watch manufacturer which includes blood-oxygen measurements. The lawyers would never allow it.
Basically: I doubt we will never see a sensible company incorporate blood-oxygen measurements into their smart-watches.
About the author: Lewis MacKenzie is a biophysicist with a PhD in measuring blood oxygen levels.
1. Choi, Dong Jin, Moon Sik Choi, and Soon Ju Kang. "A wearable device platform for the estimation of sleep quality using simultaneously motion tracking and pulse oximetry." 2016 IEEE International Conference on Consumer Electronics (ICCE). IEEE, 2016.
2. Humphreys, S., Deyermond, R., Bali, I., Stevenson, M. and Fee, J.P.H., 2005. “The effect of high altitude commercial air travel on oxygen saturation”. Anaesthesia, 60(5), pp.458-460.