Masimo MightySat Review – Pulse Oximeter for Work and Play
Why look at the Masimo MightySat? Well after doing the recent review of the Garmin Fenix 5 Plus, it became apparent that one of the few benefits of the Fenix 5X Plus, over the regular Fenix 5 Plus is the addition of pulse oximetry. But this is not merely a random metric Garmin have decided to tack on to their uber watch. They are taking the concept particularly seriously. Sufficiently seriously, that they have paid approximately $50,000 in order to get the 5X Plus FDA approved as a medical grade pulse oximetry device! So when climbing at altitude (one of the few reasons why Fenix 5X Plus users might actually be able to use the kit) when your watch tells you that you are dying, it might be a good idea to pay attention!
While pulse oximetry might be an easy metric to understand, I have two pulse ox meters in my doctor’s bag (Paeds and adult) I thought it might be a worthwhile idea to talk about a publically available, FDA approved, Pulse Oximeter, and discuss what, if any benefit there is for the athlete in training
So with that in mind, here is my review of the Masimo MightySat Pulse Oximeter (written in the shadow of Garmin Fenix 5X Plus) Ok, price, that is the first hurdle here, why should you even look at a £270 pulse oximetry, when you can buy them on eBay of £6.99? Easy – accuracy, and validity.
Most of the time when I’m using my regular pulse oximeter at work, I need to ask a patient to place their hands flatly on a desk, or at least rest them on their legs, as movement can have a significant effect on the readings generated. Given that the Masimo MightySat is aimed as much at the home user as the medical professional, the engineers have gone to the trouble of adding in an algorithm to ensure that a medically useable result can be achieved even from a moving finger.
Also, rather than a single signal processor, as is found in most optical heart rate watches, the Masimo MightySat runs five signal processors in parallel in order to generate reading which is accurate to 2% for O2 saturation, and 3% for pulses when used on a finger you are not wildly waving around
Now I’m sure many of you will have already done the maths, which shows a 2.6% difference between the Sunnto 9 and the Masimo MightySat just looking at the pulse. Which is certainly a very reasonable reading for pulses. Now Masimo claims (crucial word there) that un-certified devices can be up to 30% out with their readings for sats and pulse… which is think is frankly a rather surprising claim, which I’d be inclined to take with a wrist watched sized serving of salt… especially as most of the sports watch manufacturers do NOT loudly proclaim what the accuracy on their optical devices is. So whilst it is highly likely this specialist device is MORE ACCURATE, I’m not sure how many devices are up to 30% out today
Masimo MightySat – Device Design
What is in the box? A fairly standard affair, manual including instructions on how to place the device on a finger (if you need instructions on that, I’m not entirely sure this is a device which you should be playing with!), lanyard, a nice little fluffy pouch to put the Masimo MightySat in, and finally a pair of AAA batteries
Although I was a touch miffed to find the AAA batteries in the box had corroded. Perhaps for a device costing over £250, getting some big name batteries such as Energiser, or Duracell was too much to hope for?
The screen of the Masimo MightySat is a 3cm OLED unit, which initially might sound quite swanky… however it is pretty much standard fare on the pulse oximetry units knocking around in most doctors surgeries today. HOWEVER what the Masimo MightySat does with its screen is a little bit more in detail, covering the five parameters which the device can record; along with pleth waveform, battery charge and Bluetooth connection status.
The unit has a floating hinge meaning that the top and bottom of the Masimo MightySat will move apart, as well to allow the larger finger to fit inside
On the business end of the unit is a flexible rubber covering and a battery cover release button. The rubber allows the finger to get a better seal with the unit, preventing stray light from coming in. Unfortunately, the nature of the rubber means that it really does attract muck, even in the little Masimo bag, so make sure you have some cleaning wipes on standby
If you press the battery button in the rubber, this allows the back of the device to pop off to insert the AAA batteries. Given that the Masimo MightySat has become part of my daily doctors kit bag, I’ve swapped over to using rechargeable Sanyo (Now Panasonic) Eneloop batteries, which tend to be better at holding their charge – 85% retention over one-year post charge
Opening up the Masimo MightySat you can see the red LED on the top of the device, and the sensor underneath, which compares to most of the optical HRM sensors normally discussed on this site which have the sensor and (green) LED on the same surface. A red led is needed specifically for oxygen saturation
So that is pretty much the Masimo MightySat in overview as a piece of hardware, but what is under the skin?
Masimo MightySat – Specifications
- Weight: 73g
- Battery Life: Approx 1800 spot checks (so 15hrs when used at 30secs per check)
- Dimensions: 7.4 cm x 4.1 cm x 3.0 cm
- Communications: BlueTooth
Ok because of the nature of this product, accuracy does become an issue. Particularly depending on the use case – i.e. if sat still, or moving, so what are those accuracies?
- pO2 Accuracy Range 70–100%
- No Motion 2%
- Motion 3%
- Low Perfusion 2%
- PR Accuracy Range 25–240 bpm
- No Motion 3 bpm
- Motion 5bpm
- Low Perfusion 3 bpm
One thing which might be worthwhile considering – especially when devices like the Garmin Fenix 5x Plus are touting SpO2 readings, is that the Masimo MightySat will work down to 5 Deg C – so keep it warm on that mountain climb
Masimo MightySat Metrics
I was a touch perturbed when I read over the biomarkers which the Masimo MightySat could measure. Not least because whilst I have worked in ITU, which is a department which can just about measure everything which matters on the human body – I didn’t recognise PVI or Pleth Variability Index…
Then I saw the small logo at the bottom stating that PVI is a registered, proprietary measurement and I relaxed! Frequently, but not always, proprietary measures you’ve not heard of, which have not managed to break through to critical mass or widespread knowledge due to question over the utility
Never the less, I thought an overview of the five different measures of the Masimo MightySat might perhaps be useful – so here you go!
- Oxygen Saturation (SpO2)Run of the mill sat, used in doctors surgeries, and hospitals across the country – literally the oxygen level in the arterial blood. Will be affected by the ability of your body to move blood around, such as issues with your heart, or the ability to get oxygen INTO your blood, such as issues with your lungs, or altitude.
- NOTE anaemia, will NOT affect this statistic. If a normal persons blood has 1 million red blood cells in 1cm3, if each cell is carrying the maximum oxygen they can, the SpO2 will read 100%. If that same person is anaemia, and only has half a million red blood cells, if all are still carrying maximum oxygen, then the level will still read 100%.
- From an athlete perspective, climbers and hikers will find a benefit from O2 sats and respiration rate to gauge how they are acclimatising – (paper here). I’m on a medical expedition to Everest base camp in 2019 and will be interested to record my sats over the trip
- Pulse Rate (PR)Simply put – your heart rate. The number of contractions your heart goes through in one minute. This can be used as a surrogate marker for fitness, relating heart rate to workload the body is under
- Perfusion Index (PI)How well the blood is flowing through your finger. Useful when the SpO2 is reading low, helping to assess why. Is it because the patient has a really bad lung infection, or more simply their fingers are REALLY cold.
- Pleth Variability IndexThe variation in perfusion index over your breathing cycle. Changes in PVI may indicate changes in hydration, breathing effort, perfusion, or other factors.
- For best readings, this should be measured with the athlete lying down, as PVi is the difference in the pressure versus fluid in the chest cavity – by performing reading lying down, it ensures that all readings are done in similar conditions
- Respiratory Rate (RRp)Again, simply the number of breaths you take each minute
- Only a minor function on the Masimo MighytSat, but for me as a doctor, it is VERY useful as manual checking of resp rate has a few issues
- It is not a continuous measurement
- Observer error is common
- Inefficient use of staff time
- But how does an optical device looking at your pulse measure how quickly you are breathing?? – new word to me – photoplethysmography!
Basically using optically derived pulse measurements to determine volume change in an organ (lungs) – So here is the science on how pulse rate can be affected by breathing:
Basically, the heart rate fluctuates slightly in along with your respiration rate. Slight rises in HR occurring on inhalation and decreasing on exhalation. Using this data, the Masimo MighytSat can derive an estimated respiratory rate. Estimated, as this is calculated, rather than measured using an algorithm to compare the inputted data against a baseline for respiratory rate, studies on the underlying technology have an accuracy to within about two breaths.
If you’d like it in infographic form, here is a screen grab from the above paper
Masimo MightySat – User Manual
The manual for the MightySat is available HERE
Masimo MightySat- Using the Device
There is no setup other than downloading the Masimo Personal Health app to your device.
The app is relatively straightforward, autodetecting the nearest Masimo MighytSat and then allowing you to see your data on a larger screen.
If you are recording your data remotely, such as when doing a workout, with your phone on a nearby table, the Bluetooth symbol in the top of the Masimo MighytSat will confirm that you have an active connection to your phone
When connected to the app, you can view either view your readings as an instant display, a time-displaced graph, or as serial readings
Having explained above what the five metrics mean, realistically for most people, they will be interesting, but not astonishingly useful from a training perspective. What however might be more useful is the heart rate recovery function within the app. Intended, as the name suggests, to see how quickly your heart rate drops after completing an exercise
While the app will tell you what these mean, the data doesn’t seem particularly useful at the high end. I need to be cautious saying this, but I’m not exactly unfit, but at the same time I know PLENTY of people on Zwift who will hand me my ass in a race, so just being in the top part of this bar is not massively helpful to me.
What is perhaps more useful is the Pleth Variability Index, as this can be used as an indicator of stress, hydration and fatigue, giving you an idea about whether you are overtraining – something I have been known to do in the past. We’ve all had those days where we just don’t have the get up and go, keeping an eye on variations from your baseline can indicate if it is worthwhile to give the turbo / treadmill a miss today.
If you want to get a little deeper into the science, there is some evidence to suggest the SpO2 could be useful in monitoring particularly hard training sessions – The National Athletic Trainers Association put out an interesting paper in 2012 showing that an athlete really pushing themselves to generate hypoxic tissue may be able to see a drop in oxygen levels as low as 92-93%, whilst this might sound alarming, it is actually normal. In turn, monitoring sats before training sessions also gives an idea as to how recovered an athlete is – e.g an SpO2 of 97% would suggest biologically prepared for an intense workout, or race level output, especially when it comes to running rather than cycling. As triathletes have been shown to induce greater hypoxia (reduced oxygen in tissues) in the run portion of their event, compared to the bike (Paper).
Masimo MightySat – Conclusion
With a list price of £279, the Masimo MightySat isn’t exactly cheap, especially when you compare it to Garmin’s Fenix 5X Plus. Even though the Fenix 5X plus does have FDA approval, that only requires accuracy to within 3.5%, as we’ve seen above the Masimo MightySat is accurate to within 2%.
Now that might sound like splitting hairs, but if you are a professional athlete, and let’s be frank that is really who is going to be getting the most use out of something of this calibre, a 1.5% difference in SpO2 is actually quite a lot, potentially sufficient to alter a days training plan
With both devices, you really need to collect a two-week baseline of data, so that you can understand what is your typical, and thus what is abnormal for you. Given the wrist mounting and 7-day recording from the Fenix 5x Plus, it will certainly be easier to get a baseline from a device you wear 24/7, but would the four additional biomarkers in the Masimo MightySat out way that ease of recording. Just possibly.
Again the issue about the benefit of the data comes back to usability. SpO2 alone is going to be useful, and potentially mid-ride SpO2 even more so, however, the additional data, such as pleth variability on the Masimo MightySat may provid3 yourself or your coach with a better overall picture of the effect of your training.
As a medic, the accuracy of the Masimo MightySat has displaced my older pulse monitor out of my doctor’s bag easily. But let’s be clear, if you are an athlete considering the Masimo MightySat, then you are looking to get every single benefit you can out on the track. Yes, the weekend warrior may see a small advantage regarding better optimising training, but then you have to ask yourself is the price of entry sufficient for the benefit you’ll gain? Only your wallet can tell you that.
For most people, currently the Fenix 5 X plus will provide an exciting curio in terms of oxygen saturation, but if you are determined to get the most out of your training, then the Masimo MightySat will have the edge – but then that might only be as you are running with a lighter wallet!
3/5 TG mark. Useful, but really a toy for the top tier athletes.