The Wearable I am Most Excited About
Respiratory wearables are coming in force and I am here for it
Source: NIH
Some readers are probably surprised that I am more excited about respiratory rate wearables than continuous lactate monitors, but when you understand physiology, you quickly understand the value of knowing respiratory rate accurately. Ironically, respiratory rate may well give us the information most people will want to use continuous lactate monitor for; understanding intensity of exercise.
Why is Respiratory Rate so Helpful
Illness
As a doctor in training, the question arose often enough that I remember it well; “what is the most sensitive vital sign to deterioration of a patient?” Given the low profile of respiratory rate in the general population when compared to temperature or heart rate, there weren’t many who answered correctly when first posed the question. The answer being, of course; respiratory rate. The caveat or warning to us was always to check for ourselves (count the rise and fall of the chest over a minute) because of some shortcuts that were taken at times (do 10 seconds and multiple by 6 for instance). These short cuts are probably not so impactful when your number is higher (like pulse rate) but with lowish numbers, the error compounds.
So we arrive at respiratory rate being very sensitive to illness and deterioration of patients who are ill, but what about in those who aren’t quite “ill” or in the performance space?
Wellness
It turns out, respiratory rate is not just sensitive to illness, but shows good sensitivity (though it can be hard to detect) to many aspect of physiological stress. That could be mild, early exposure to a virus perhaps, psychological or emotional stress (these would likely be much better than what is currently on the market measuring ‘stress’ or similar through the day).
Performance
As I alluded to in the introduction, many people in the performance space use lactate to understand intensity of exercise, in fact the only exercise “zones” with any physiological basis use points that can be demarcated by lactate (that’s right, there are 3 physiological zones, and that “zone 2” you’ve been reading about is actually high zone 1, it’s a mess). The reason these zones can be demarcated is there are differences in physiology that are visible between these intensities, which as mentioned, show differences in lactate. BUT, crucially, also show differences in respiratory rate! In fact these thresholds between the zones are sometimes called ventilatory thresholds.
A Quick Respiratory Physiology Lesson
Fundamentally all of the above is explained by the below reaction that I can still draw in my sleep thanks to my preclinical medical school training.
Effectively what this boils down to is that we can compensate for changes in hydrogen ions (read acid) and bicarbonate (read base) via changes to respiratory rate (increasing of which will mean a reduction in CO2 as we ‘blow it off’) . This is important because we need to maintain a narrow physiological range of pH (fun fact this stands for “potential hydrogen” - makes sense now right), so we need ways to adjust our physiology. We can also adapt more chronically via changes in bicarbonate in the body. We won’t get into acute vs chronic here or drivers of the change ie respiratory (left side of the reaction) vs metabolic (right side of it), but know it’s a well designed system that can adapt well.
The take home here is: we can adapt to changes in acid/base status to maintain pH - much of this adaptation at least as we can track it and in the acute time window is via changes in respiratory rate.
So my bullishness on the utility of respiratory rate should, hopefully, be both apparent and understandable by now - that is, provided it is well measured. Enter ‘wearables’, a label for any number of sensors and devices that can be worn that provide us data.
Wearables
Something that is absolutely crucial to understand when talking about wearables is that there is a huge difference between what is measured and what is inferred or estimated. Generally they report both as though they’re no different, but the level of accuracy and certainty of these things differs significantly (Marco Altini has covered this concept nicely in his writing here).
As an example, things like watches, rings and bracelets/bands MEASURE; pulse rate (via changes in light), movement (via accelerometers) and some will measure temperature. They then use this data to ESTIMATE; respiratory rate, steps and sleep. This is why you may find walking whilst carrying something contributes 0 steps to your step count whilst grating, hand grinding coffee or something else similar yields many for example.
So, as with taking respiratory rate in the hospital, where estimates (count breaths taken in 10 secs and multiple by 6 for example) can be problematic, the same can be said for wearables.
But isn’t this an article about how excited you are about a wearable?
Yes, we have finally arrived! A new(ish) group of wearables has hit the market, targeting respiratory rate as their key measure! And for these I am excited!
Challenges for Wearables
As an avid user, and someone who’s worked in the industry there are some common challenges for wearables. It is not enough to be accurate, unfortunately for companies. Many factors can impact success (or failure), some of which are difficult to solve and others of which are even out of the control of the companies.
Let’s look at a few:
Timing - not often talked about, but timing is key. I think the timing is right for these companies, provided they have the runway for a few years before a significant uptake (more on adoption phases here). If they had hit the market 5 years ago, I think they may have struggled to gain traction with consumers.
Form factor - they are currently in shirts, which I think is a pretty smart design. That said, I have a feeling IF they can solve for a smaller form factors (perhaps similar to what we see from GPS companies in sports) they may see more success, though I could be wrong here. One battle here will be keeping data quality if form factor is changed. The other challenge here may be the impact that something like this has on breathing mechanics (no I am not talking about the Hawthorne Effect but this can be significant in wearable use), I am talking about recent research on sports bras showing they could impair respiratory function (something anyone who goes ‘rucking’ probably experiences too).
Integration - Table stakes these days in the industry is integration and to a high level. These companies (or at least the successful ones) will probably be the one(s) that can build integration into other tracking devices and platforms the quickest. If they can get their data written to .FIT (the file type for exercise activities exported or sync’d from your favourite sports watch etc) and displayed live as a data field on your bike computer, GPS watch etc, they will go a long way to success. Or perhaps, if they don’t manage this quick enough, they will not see the uptake they’re hoping for. This may seem easy but I can assure you it is not. Not because it is technically difficult, but because it is a lot of work, and this work continues with every update from any device (this is what is called ‘tech debt’ and it can kill a company with a small team of engineers).
Utility - This boils down in many ways to what in the industry is called ‘UX’ (user experience). If these are difficult to use, uncomfortable or do not integrate well, the UX will be poor and retention will suffer if people start using them at all. Similarly, if there is no integration as mentioned above, then the data will not be in context - making interpretation very difficult and the data much less useful. One note here, is that some companies want to keep their data (it is after all a valuable commodity) and not send it everywhere. In this case, pulling all other data sources into their ecosystem is usually their strategy. This is a similar lift from the engineering side of things, but adds friction for the user too (now you’re asking them. to change where they have been interacting with their data to!).
So despite some significant challenges, I am appropriately excited about where respiratory rate related wearables will head. There are currently a few on the market, all in the form factor of shirts as I understand things, which is probably why I have been hesitant on uptake myself. That said, this article has given me the nudge required to do some more research into which to use and perhaps try them one out.
References
Gerald Norman Pho, Nina Thigpen, Shyamal Patel, Hal Tily; Feasibility of Measuring Physiological Responses to Breakthrough Infections and COVID-19 Vaccine Using a Wearable Ring Sensor. Digit Biomark 20 December 2023; 7 (1): 1–6. https://doi.org/10.1159/000528874
Massimiliano de Zambotti, Cathy Goldstein, Jesse Cook, Luca Menghini, Marco Altini, Philip Cheng, Rebecca Robillard, State of the science and recommendations for using wearable technology in sleep and circadian research, Sleep, 2023;, zsad325, https://doi.org/10.1093/sleep/zsad325
Kipp S, Leahy MG, Sheel AW. Sports Bra Restriction on Respiratory Mechanics during Exercise. Med Sci Sports Exerc. 2024 Feb 5. doi: 10.1249/MSS.0000000000003403. Epub ahead of print. PMID: 38350462.