141 - Todd Davenport - a deep dive into Post-Exertional Malaise (PEM)

Episode 141 of the Long Covid Podcast is a chat with the fabulous Todd Davenport - physio & exercise scientist specialing in Long Covid, MECFS & Post-exertional Malaise. We take a dive into PEM, some of the science behind it and some things that can help avoid & mitigate it.

Some useful links:
Bateman Horne crash care plan

Workwell Foundation Links:
"I Have ME/CFS or Long Covid What Do I Do Now?"

PEM Timecourse Fact Sheet

How Do I Obtain Disability Benefits (most useful for US listeners)

Why Should I Do a Two Day CPET?

Energy Saving Tips

Heart Rate Monitor Fact Sheet

Opposition to Graded Exercise Therapy Letter to Health Care Practitioners

Long Covid Physio:
Long Covid Physio video library multiple languages

Long Covid Physio International Forum Science of PESE

Renegade Research PENE as a Bioenergetic Health Con

For more information about Long Covid Breathing courses & workshops, please check out LongCovidBreathing.com

(music credit - Brock Hewitt, Rule of Life)

Transcript

Jackie Baxter  
Hello, and welcome to this episode of the long COVID Podcast. I am so excited to be joined tonight by Todd Davenport. And we are going to dive in to the mystical magical world of post exertional malaise, I'm sure other things as well. So a very, very warm welcome to the podcast today.

Todd Davenport  
Thank you. And I just wanted to say now that the recording is going, thank you for all that you've done in the manner of taking a very practical approach to identifying topics that are important for the community of people who are living with long COVID, and approaching them in a really personable way with really reliable folks that you've brought on to the podcast. So congratulations on what you've done. And thanks for having me as part of all that.

Jackie Baxter  
Oh, thank you so much. It's absolutely my pleasure. So would you mind just saying a little bit about yourself? And what it is that you do?

Todd Davenport  
Yeah, so I am a physiotherapist, we would maybe call it a physical therapist here in the US. So for some people that's strike one, first strike against me is that I'm a physio. And I'm a physic physiotherapy professor here in the United States at the University of the Pacific School of Health Sciences in Stockton, California, which is east of San Francisco, for folks who are wondering kind of where that is on the map. 

Todd Davenport  
I'm an Exercise Scientist. So that's strike two, for some people, because as we'll talk about, exercise, physical exertion is one of those types of exertion that makes people sometimes feel worse, who have long COVID. But I promise that I've tried to sort of learn a lot over over my time being a physio, almost 25 years Yikes. 

Todd Davenport  
And in my time, studying myalgic encephalomyelitis, and now long COVID for about 15 years, which is sounds like a lot of time to actually have saying it out loud. In order to really bring some good information about what physical exertion does to the body. You know, if you have a certain type of long COVID that mirrors myalgic encephalomyelitis that is called post exertional malaise, which would be the clinical Hallmark that we're going to talk about mostly today. And it take that those physiological insights to really try and understand what to what to do next.

Jackie Baxter  
And what did bring you into the world of you know, ME CFS originally, and obviously now we've added long COVID to that pile. But yeah, what sort of brought you into that world?

Todd Davenport  
Like everything a long story. My story started being an athlete, and being very curious about why athletes made mental mistakes when they were tired. I played basketball, I was wondering why people made decisions or sort of didn't execute certain fundamentals with fatigue as a factor. So when I got to college, I did my honours thesis on Exercise Science on doing neurocognitive games before and after a fatiguing bicycle task. 

Todd Davenport  
Interestingly enough, I chose my teammates from the swim team, who were very fit, and it took them a long time to get fatigued. So that was a learning lesson right there. We were there trying to get them fatigued for a long time. And then kind of rolled that experience into my experience into additional kind of preclinical experiences as a student, student athletic trainer, working with athletes, then as physiotherapy student, doing some work at our US national National Institutes of Health, looking into, you know, how we test people who have health conditions characterized by fatigue. 

Todd Davenport  
And then, you know, fast forward a few years when I joined University of the Pacific, I was sort of doing a Google search about who's in my neighborhood, I found this thing on campus called the Pacific fatigue lab. And I thought, well, you know, I mean, I've done some things with fatigue, you know, a little bit about it. And, of course, as is my habit just sort of wandered over there on an unannounced knocked on the door. 

Todd Davenport  
And thankfully, they opened it and there I met the Pacific fatigue lab team, Stacy Stephens, Dr. Mark van as Dr. Chris Snell, Jared Stevens, and have really worked with them ever since. That group has since kind of gone on and Stacy founded the workwell foundation. So, I continue on as a scientific adviser to the workflow foundation. So, that is that is my long and wandering path into this, this content area. 

Todd Davenport  
And as you point out, it you know, we've done some work with in particular cardiopulmonary exercise testing and specifically, today cardiopulmonary exercise testing to really try and understand the metabolic, the cardiac, the pulmonary consequences of physical exertion and people with ME. And have since rolled that work into long COVID as a subset, fairly sizable subset, of people with long COVID start to resemble people with ME.

Jackie Baxter  
Yeah. Because I think what, you know, someone like me who got long COVID. And what back in 2020, and, you know, suddenly was like, what fresh hell is this? And then, you know, we start noticing links between MECFS, long COVID, and other things as well, that have been around for much, much longer. 

Jackie Baxter  
And, you know, I think I had a couple of friends with ME, and I thought, oh, you know, I get it, and then you get it yourself. And you're like, oh, no, I didn't get that at all. Then you just you can't understand unless you've had that experience of it, I think. And I think, you know, the post exertional malaise kind of angle of it, as well is something that's very difficult to understand. 

Jackie Baxter  
You know, I think regular people, you know, they push themselves super hard, they go run a marathon, and they feel tired the next day, and like that is normal. But the idea of like, getting out of bed to brush your teeth, and that knocking you out for a week. That is something that is very hard to understand, unless you have actually had that experience of it. 

Jackie Baxter  
So maybe before we dive down the rabbit hole too far, can we just talk about what post exertional malaise actually is? And it's probably not just one thing, which is probably the hard thing about it, isn't it?

Todd Davenport  
It is and so as you so beautifully set up, I think the average person understands what fatigue is, the average person has been tired, whether they you know, physically over exerted, you know, they've over exerted over a period of time, not slept well. You know, when I tell people that I'm an exercise scientist and a physiotherapist that has been interested in chronic fatigue, just to kind of boil things down and try and use the popular parlance. The most common thing I hear is Oh, yeah, thanks for studying. I get tired too. 

Todd Davenport  
You're like, No, you don't know. No. This is not cup of coffee and a lie down, kind of fatigue. This is not, you know, back off on your training a little bit, the gym, you've been hitting it too hard. And you'll feel better. In fact, I've stopped saying that I'm interested in chronic fatigue just for that reason, because the focus on fatigue oversimplifies what post exertional malaise is. 

Todd Davenport  
And post exertional malaise is really a multi system, multi symptom, kind of just constellation of experiences that occur after exertion. So it's not just fatigue. And let's just talk about the fatigue since that's the one that people kind of know about. This is the feeling of zonked, the feeling of nothing left, the feeling of I cannot get out of bed or out of off this couch. My body will not let me do it. 

Todd Davenport  
I have worked with marathon runners who have post exertional malaise and they will tell you that the feeling of finishing a marathon and post exertional malaise are not equivalent feelings, that post exertional malaise is worse. And part of what makes it worse are the associated signs and symptoms that go along with this. 

Todd Davenport  
Cognitive dysfunction, which is very troubling because it limits short term memory and attention. It inhibits you know short kind of short term learning you know. There's also sleep impairment that goes with this, going asleep, staying asleep, quality of sleep once you are asleep. All crummy widespread body pains, numbness and tingling headaches, shortness of breath and palpitations, issues with with gastrointestinal that with digestion, maybe with genital urinary tract disturbances. 

Todd Davenport  
All of the signs and symptoms occur in response to some kind of an exposure and exertion - could be physical exertion which is you know, if you follow me on Twitter, if you listen to some of the other podcasts I've done, you'll hear me talk a lot about physical exertion because I'm a physio and I'm an Exercise scientist. 

Todd Davenport  
But that's not to discount the importance of cognitive exertion. Where even watching a video on a small screen, an iPad, a short video is enough to provoke signs and symptoms. Also, the exertions include environmental exertions, so environmental exposure, so, scents and smells and odors and chemicals, people can be oversensitive to those as well. So there's there's a whole host of exertions that kind of go into this post exertional malaise. 

Todd Davenport  
And I do want to point out that there are some folks that dispute this idea of malaise. Because first, it's sort of an old timey word that people don't really use anymore. And people think it runs the risk of underselling what this is, because malaise is sort of like just like feeling off because you're ill. 

Todd Davenport  
And so probably the conceptualization that best captures post exertional malaise is, doesn't even use that word. It's the international consensus criteria for myalgic encephalomyelitis, which was written in 2011. And it uses this term post exertional neuro immune exhaustion. 

Todd Davenport  
And it kind of gives this sense of the exhaustion piece, which kind of gets at the fatigue plus, that we were just talking about. And then also kind of starts to pull together some of the suspected underlying etiology of the signs and symptoms under the neurological system and the immune system. 

Todd Davenport  
So in post exertional neuro immune exhaustion, there is basically, there are several types to this. So how do you know you have this? The first is that you might have this really marked decline in your physical and cognitive capabilities in response to an exertion. The other is that the symptoms that follow reliably following exertion. 

Todd Davenport  
There are stages, there are levels to this, and we can link in the show notes, immediate post exertional malaise, short term and long term post exertional malaise, but there's generally a lag time involved of, of 24 to even 72 hours. And then there's a prolonged recovery period, and that often people have a decreased threshold for their physical and their mental performance. 

Todd Davenport  
And so those are the general aspects of post exertional neuro immune exhaustion that we call post exertional malaise. And honestly, we only call it that because everyone calls it that. And we have to find a common language. 

Jackie Baxter  
Yeah, and I guess it's, you know, you hear people talk about this all the time with brain fog is the one that often comes up where brain fog is a sort of like, a very friendly term for something that is not so friendly, and what it feels like. But it is the word that is used and people, I don't know if they understand it, but they certainly, you know, hear it. 

Jackie Baxter  
And I guess PEM and posted exertional malaise is kind of the same, isn't it? You know, where it doesn't quite give the scale of what it is. But is there anything that really could give the scale of what that is? You know, that that's kind of quite difficult, isn't it?

Todd Davenport  
Yeah, I don't know if there is, I don't know what it would be. Because here's the thing is, I'm always struck by how profoundly people need to fake being well, just to work with me as a healthcare practitioner. And some people have a really good poker face that. 

Todd Davenport  
I'm always gauging, you know, are the words getting in? Are the thoughts coming back reasonably, you know, associated or collected? Does it look like the person is just kind of fading out on me, you know, and they're, they're kind of have that 1000 mile stare past the camera past me. And so I'm always looking for nonverbals that are associated with an increase in cognitive function, but you're totally right. I don't know how we capture this in a word.

Jackie Baxter  
So we sort of learned to track this ourselves, you know, as we go through this experience, and okay, well, yesterday, I did this thing. And today, I'm feeling absolutely awful. And you start to make the links. Okay, well, this has happened before when I did that thing. And this happened. Okay. I think maybe I have PEMyou know, this, this is that, you know, you start to recognize those patterns. 

Jackie Baxter  
But yeah, what is physically going on in the body? When that happens? What do we know about that?

Todd Davenport  
There's so many things that are going on. So I'm going to just in the interest of time, and sort of sticking within the the confines of what I know the best. I'm going to talk about post exertional malaise as an energy production problem by the body. Post exertional malaise, as I mentioned, is a lot of things. It's an immune system problem. It's a circulatory problem. It is a hormonal problem. And a bunch of things that I'm leaving out, but, but it is at its core, also an energy production utilization problem. 

Todd Davenport  
And so I'm going to, I'm going to paraphrase a load of exercise physiology studies into a silly analogy that I like to use. And that's the analogy of the plug in hybrid car. So your body works like a plug in hybrid car, come to find out after all of this. So in a plug in hybrid car, you have two fuel sources, you have a gas motor, and you have a battery. 

Todd Davenport  
And the gas motor is great for things like you know, going freeway speeds and going up down hills and hauling people and gear in your car. And the battery is great for stop and go traffic, lower speed kind of city driving, so forth. And the gas motor can charge the battery, so you don't have to plug it in as much. So that's nice. 

Todd Davenport  
So this is similar to you know, your gas motor kind of being your aerobic metabolism. This is your long term energy system, it generates a lot of power for you. A lot of energy allows you to do prolonged things, allows you to do kind of higher intensity things. 

Todd Davenport  
And then you have your short term energy system, kind of your creatine phosphate, these are sort of your early kind of like lytic pathways, just metabolizing what's on hand in your muscle cells. And those are like your battery. 

Todd Davenport  
So let's imagine now that you're a plug in hybrid car, and that your gas motor doesn't work. Or that your gas motor is unreliable. So what do you lose? Well, you lose the ability to do prolonged things, you lose the ability to go up and down hills, higher intensity things, hauling people and gear, you also lose the ability to charge a battery. And so you over rely on the battery, leaving you potentially stuck at the side of the road, which is simulating a crash. 

Todd Davenport  
So you do all this work, you realize that a your body works just like other things that we've been engineered for our convenience. And so I want to acknowledge Dr. Chris Snell who introduced us to this analogy and that I've tried to kind of add to and refine over time. So now, what you do next is try to avoid overusing your battery. 

Jackie Baxter  
And you know the analogies, they're great, because they're putting it into a sort of a situation that people understand. You know, and that makes it relatable to understand what's going on in your own body. And for someone else to understand what's going on with you, like a friend or a family member or employer or whoever it is that you're trying to kind of explain what is going on. 

Jackie Baxter  
And they don't get it. Because why would they, and you're trying to find this language to explain it in something that they will understand. And that's very difficult to do, because there's sort of limited crossover for someone who hasn't had that experience. So I think that's great. I think that's very relatable, even if they're not mechanics, will kind of understand the sort of the basics of how the car work.

Todd Davenport  
Yeah. Oh, gosh, I am not a mechanic. So if you probe any farther on how a plug in hybrid car works, I would be unsuccessful, would not be the person to help.

Jackie Baxter  
Um, so you mentioned earlier that post exertional malaise can show up in people from sort of 24 hours to 72 hours ish. And it's different in different people. I think it's different in different circumstances. You know, there's definitely been times where I thought I got away with it, and then got hit 12 hours later and was like *laughs* dammit. So, do we know why the time lag is different in different people? Is there any kind of knowledge on that?

Todd Davenport  
You know, not totally sure. But I would suspect that it has to do with some of the underlying and bioenergetic impairments that we see in people with post exertional malaise. And that some of the chemicals, this is kind of the biochemical take now, some of the chemicals that are used in the cycle of creating energy molecules become depleted. And I think it has to do with the relative depletion and timing of recovery of some of those. 

Todd Davenport  
Now, obviously, we're taking a very narrow view just for the purposes of sort of time and convenience and the limitations of your guest. And there probably are other systemic impairments that also are associated with that, are involved in that time lag. So the short answer is I'm not sure. 

Todd Davenport  
But again, as we think about post exertional malaise is lots of things. But among those things, an energy production problem probably has something to do with those chemicals being in short supply and how quickly they can become recovered or regenerated.

Jackie Baxter  
Of course, because no system in the body is working in isolation, as it's connected to everything else. And everyone's makeup of all of those systems and how they interact with each other is going to be very different. And it's probably going to be different on different days as well.

Todd Davenport  
Absolutely. So as we think about the whole person, you know, putting my clinical hat on for a minute, really, the only constant with post exertional malaise is variation. Variation between people, variation between days, variation between months, variation between different phases of a recovery process, and so forth. So it's, there's just a lot of variation. 

Jackie Baxter  
Yeah, and I think this is one of the frustrations, isn't it, because even within your limitations that you are having to come to terms with having, it's not like it's always the same. It's like, Okay, on this day, I can do that. But on that day, I can do half of that. And then two weeks later, I might be able to do a bit more, but then a month after that, I'm right back down the bottom again. And it's like, you know, I can't work with this.

Todd Davenport  
Yeah, exactly. So it's a little bit like trying to nail jello to the wall, it's just not gonna work very well. It's just gonna slide down and do its own thing. And, you know, from a clinical perspective is very similar, because even with clinicians who work with people who have chronic health conditions, there's sort of like some general linearity to a plan, but there's just when you're working with someone who has post exertional malaise, that linearity goes out the window. So everyone's trying to nail different different flavors of jello to the wall and to try and figure out the patterns and how things work. 

Todd Davenport  
But the think the overall, the unifying theme, is to try and figure out your capacity, try and figure out where that gas motor kicks in. At what level of exertion that is, and how much of that gas motor you can depend on for how long and then try and stay within that. Now, Dr. Leonard Jason, a few years ago called this the energy envelope, which is a common term that people use to try and figure out what that capacity is, really. 

Todd Davenport  
All the energy envelope beans is to try and figure out what your resources are on a given day. And then to stay within those resources. And, you know, allocating a certain portion of those resources if you can, to almost bank for yourself. So not constantly redlining, you know, to the very edge of what you can do, but to sort of try and maintain a little bit for the benefit of your own recovery. 

Todd Davenport  
Which is, which is hard, because now, what you're trying to do is you're trying to sell people on number one doing less, which I'll make an additional comment about in a moment. The second thing that you're trying to sell people on is, you're going to have them stopped short of their capacity, even if they feel good, just to kind of give themselves permission to feel good later. 

Todd Davenport  
But I want to go back to this idea of, of doing nothing. Staying in your energy envelope, or what we might call pacing, is far from doing nothing. It's balancing activities with rest, and it takes a lot of planning. It takes a lot of figuring where you are now, where you've been, where you're going to be, what you have to do. It takes a lot of prioritizing. 

Todd Davenport  
And resting actually takes a heck of a lot of work for people. Resting is not an easy thing to do. This is not like chill out and watch trashy TV. This is usually somewhere between being awake and being asleep, because you're trying to minimize cognitive exertion, tends to be pretty boring, tends to be very isolating. And it's just hard. 

Todd Davenport  
So as a clinician, a lot of what I do is try and help people sort through their pacing plans, and try and figure out where this energy envelope is and strategies to stay within it. You know, again, balancing activity with rest, but also managing things like isolation and trying to manage things like boredom, and trying to manage things like frustration because this is really hard stuff to do. So, oftentimes, you know people say pacing as being something less, but it actually turns out to be a boatload of work. 

Jackie Baxter  
Yeah, definitely. And I think, yeah, balance is something that I've really started to appreciate in my life on the other side, is that yeah, it's great to have those days where you do all the things, but actually, you need to balance that out. Actually, you know, someone told me back a couple of years ago that pacing was a skill for life. And I was just like, No, I'm looking forward to never having to pace again. 

Jackie Baxter  
And now I'm thinking, you know, it's a totally different thing, you know, when you don't have something like long COVID, but it is something that's still sort of useful to hang on to, in some ways, I think might be an umbrella sort of overriding kind of thing, rather than maybe more specifically.

Todd Davenport  
Yeah, you know, long COVID is new, so we're still trying to get a handle on it. And so I just sort of assumed that pacing is a life skill, I couldn't agree more strongly. I would say, it's just a core competency of living with long COVID. And it's the thing that I teach first, people may come and ask me, I want to exercise. How do I exercise. Well, how's your pacing? What's pacing? Okay, we're starting there first. So we're gonna back up a few steps. 

Todd Davenport  
And just kind of make sure that people understand the potential warning signs of overdoing and have a plan for what happens if they overdo. So those are really, really important things. I think of my clinical practice with people who have long COVID, and who are trying to manage despite post exertional malaise, is being more along the lines of a health coaching model. 

Todd Davenport  
Now, health coaching, is, you know, trying to help people make a behavior change that we commonly think of like as, like more exercise. But I'm thinking less exercise, and I'm thinking more pacing, and striving towards this balance, and how people can best achieve that balance. 

Todd Davenport  
Now, some folks who have, you know, maybe less severe involvement, there's a little more capacity to have a balance. But there are some people who are severe, very severe who their balance is rolling in bed. And that's it, or making it to a trip to the bathroom. So that balance looks very different. And the capacity for that balance looks very different in people. 

Todd Davenport  
So I don't want to give the sense that, you know, one size fits all because remember, the whole idea here is that variability is the only constant. 

Jackie Baxter  
Yeah, absolutely. And, like what you were saying a moment ago about the warning signs, I think that was something that was like a total lightbulb moment for me, because, you know, I would do a thing, crash, do a thing crash. And then when I started to notice, okay, what does it feel like, just before I go over the edge, and then when I started to notice what that kind of felt like, 

Jackie Baxter  
Okay, this is the moment where I can stop, maybe I can intervene, maybe I can do some breathing, maybe I can lay down whatever that looked like. And not all the time, because I wasn't always very good at it. And sometimes you're not able to stop, you know, if you're in a car and you're in a traffic jam, you can't just, you know, close your eyes and lay down. But you know, being much more aware of what that felt like. 

Jackie Baxter  
And what I could do was huge for me, because there's so much about what you can't do when you're unwell with something like this, you know, it's can't, can't, can't, can't can't. And then once you find the can, it's like, okay, I have this tiny, tiny bit of control sometimes, and yeah, for me personally, that was absolutely massive.

Todd Davenport  
Yeah, we're always trying so this, this balance of activity with rest is prioritized based on the person who's living with long COVID. As a clinician, ideally, I don't go in with goals for people, people set their own goals. And if we're fortunate to have this situation where people have a little more energy, and it's very common that you know, people do improve with pacing. 

Todd Davenport  
There's always a limit, there's always a system to work within, that's different for every patient, but people do improve with adherence to a pacing program. In fact, there was a nice study that was put out just recently in people with Long COVID suggesting that pacing can be beneficial, and that you know, greater adherence to a pacing program is predictive of better outcomes. 

Todd Davenport  
But you know, what you do with that energy is up to you, it shouldn't be up to your clinician. So, if you're working with a clinician that wants you to, hey, you're feeling better, hop on the bike. Well, we know that in people with post exertional malaise, the acute responses to exercise or abnormal, the response to graded exercise has not been favorable, not been favorable enough for it to be favored in clinical practice guidelines. So it's not. 

Todd Davenport  
And so I would almost prefer, you know, people, if you had it in you to go do something, let's find out what that looks like for you, sort of in what duration? And what intensity makes sense? What are the warning signs of overdoing. And so it becomes a greater conversation. 

Todd Davenport  
So I would just be aware of the clinician who has you hop on the treadmill, because you're having a good day, because it's a slippery slope towards an intervention that doesn't help, potentially harms, and does not put you in the middle of the decision making about how best to spend your energy.

Jackie Baxter  
Yeah, and you know, what I think like, what is important to people, it's going to differ depending on the person, you know, some people, you know, Exercise and Movement is a very important part of their life. So maybe they do want to spend some of their energy going for a walk, or, you know, whatever that movement is going to look like for them. 

Jackie Baxter  
Whereas, you know, you mentioned earlier, all the different types of energy, you know, your cognitive, your physical, your emotional, your, whatever, the ones where, you know, and actually, for some people, maybe it's going to spend some time with their family, or, you know, watching their kids at the play park or reading a book, or, you know, whatever that is. 

Jackie Baxter  
And I think, as you say, that's got to be down to the person. I think it's important that they understand that all of these things do take energy. But ultimately, what they decide to spend their energy on, it shouldn't really be pre prescribed by someone who isn't them. 

Jackie Baxter  
You mentioned earlier, I think the CPET, I think one of the many kind of frustrations with something like long COVID Is the subjectiveness of it. You know, you could you go to your doctor, and you say I have these symptoms, and they don't show up in any tests, you know, and some doctors will say, Okay, well, I'm going to believe you. And let's look into what we can do. And some doctors will not. 

Jackie Baxter  
And the same is true with some employers and some family members as well. You know, if there's nothing coming up in your tests, then well, maybe they're crazy, maybe they're making it up, maybe they're not as ill as they think. And the post exertional malaise thing is obviously a whole extra thing on top of that, because it's not, this is showing up for me now. It's if I do this thing, now, this is going to show up down the line in 24 hours, in 48 hours. So is the CPET a way that we can sort of use to measure this in some way?

Todd Davenport  
It is and to kind of get a little bit into the CPET. But without getting too technical, just kind of a challenge. But I will do my best. Think stationary bike. We have a person on a stationary bike with a mask and a tube connected to a computer. And the bike has electronic brakes on it so we can make the pedals harder and easier to maneuver. 

Todd Davenport  
And there's a whole setup and you know, there's EKG monitors on your chest and so forth. So there's kind of a lot, it's a whole thing. But you know, the long the short of a cardiopulmonary exercise test, at least in this regard is that you pedal on the cycle ergometer, stationary bike, and it gets progressively harder during the task. Every minute, it gets a little harder. 

Todd Davenport  
And while you're pedaling, you're breathing into the mask and the tube. And we are collecting the breath, running the breath through the computer. And we're analyzing the amount of oxygen and carbon dioxide in your breath. And from that data, plotting, basically the composition of oxygen and carbon dioxide in your breath, we can determine when your body starts to shift away from using oxygen to burn fats and sugars. 

Todd Davenport  
And so we call that the ventilatory anaerobic threshold. That's usually the point during exercise, that you start to lose your breath. And you know, as the exercise gets harder, you're not going to exercise that much longer after you've lost start to lose your breath. You'll have to stop and over and over time exercise intensities above losing your breath start to kind of defeat the process of burning fats and sugars using oxygen. 

Todd Davenport  
Free oxygen radicals and lactate and all this all these chemicals come in and just start to gum up that process. It doesn't work very well. So it's there's physiological reasons why it's hard to exercise above that level for very long. So we basically are looking for, you know, some maximal test criteria, and we do that on one day. 

Todd Davenport  
And then 24 hours later, because remember, there's a lag time here in terms of post exertional symptoms and signs, we do another cardiopulmonary maximal cardiopulmonary exercise test when the person is in the post exertional state. And so that measurement is more reflective of a person's post exertional physiology, than the first one where they walked in the door. 

Todd Davenport  
So, so normally what we see in someone who's say they're out of shape, right here, I could get to the gym. And I don't, but that's a conversation for a different podcast, why the physio is not exercising. But normally, even though my markers on the first test might be low, suggesting that I'm deconditioned, I will be able to repeat those same markers on the second day. 

Todd Davenport  
Or I might be able to even increase my performance a little bit because I have had the experience of the first CPET, I have learned like a little some bounce, little biomechanical efficiencies, there's some motor learning that happens. And so I might even be able to actually increase my measurements. 

Todd Davenport  
In people with ME, or the ME subtype of long COVID, people who people living with long COVID and post exertional malaise, they are not able to repeat the first test results on the second day, the second test results are lower. And what's more important, most important here, is that the results are most striking at that point where you start to lose your breath during exercise. 

Todd Davenport  
What we call the ventilatory anaerobic threshold, that we have found by plotting your oxygen and carbon dioxide in your breath. You cannot fake that. You can't fake your Yeah, I guess maybe you could, but you'd have to take a ton of physiology, and be a really be very specific about that. So it's very, very difficult to fake, we'll say it's impossible. 

Todd Davenport  
And so the test to sub maximal exertion, people use less oxygen at that point, and they put out less workload than the first test. Again, this sort of unthinkable circumstance. And so what does this mean? Well, people don't generally like to function over the exertion where they lose their breath. It's uncomfortable, you know, like, I'm climbing stairs, I'm glad when I reached the top step, because my muscles are burning, and I've started to lose my breath. I'm not game for another flight. 

Todd Davenport  
But so people don't generally function for very long above that, that point at which they lose their breath. And if you have less oxygen that you burn, and less work output, after you've already exerted, that sounds like a crash. That sounds like a crash, because ultimately, your functional ceiling, your functional metabolic ceiling has dropped, and you can do less. 

Todd Davenport  
So now, whereas maybe on the first day, you're here, the second day, you're down here. And so the first day, you may have all these activities you could do. But now on the second day, you have all these activities you can do down here, but all these activities that you can't do. And so that's that's ultimately the utility of a two day cardiopulmonary exercise test. 

Todd Davenport  
Now, it's not without challenges, because we are aiming to provoke post exertional malaise. That's sort of how the test works. It relies on people to come to a clinic, you know, it requires a lot of specialized setup, commitment to keeping your equipment current and lots of good stuff so that even peoplewho run well known research centers aren't really set up to do this. So there's only only a few places around that can do it, and do it well. 

Todd Davenport  
But I will say that it's kind of the gold standard against which a lot of these other studies revealing differences between people with long COVID and ME. And controls can be assessed. So it's not like we don't have a measurement, we do have a measurement. It's just not ideal for a lot of people for a number of reasons. And many of these differences between, you know, sort of people with long COVID and healthy participants. People are calling them potential biomarkers. 

Todd Davenport  
You know, like, I don't think there's a day that goes by that the B word isn't used. We have a new biomarker for long COVID. But yet we don't have an approved way to diagnose it. And so probably the way this is going to go is that most of these new technologies should be compared against a two day cardiopulmonary exercise test in order to really understand. And you know, there are some challenges with that, that research design setup, but it is the best of what we have. 

Jackie Baxter  
Yeah, and I think, like you say, there's the sort of eternal quest for biomarkers for something to prove in like data, to show how bad you're feeling. Because it's people with long COVID, and I'm sure the same for ME, chronic fatigue, you know, they have no doubt in their mind how bad they feel, it's having to prove - if that's even the right word - to other people, how bad they feel. Which is kind of a sad state of affairs when sick people are having to prove that they're sick. 

Jackie Baxter  
But at the same time, I suppose from a research and clinical perspective, if you can actually find something where you can see in the data, okay, that's a healthy person, that's a person with long COVID, that's different, it kind of gives you somewhere to go. Okay, now, I can stick a pin in that, and maybe work out what I can do kind of thing. So I suppose there is more than one side to the, quote unquote, proving?

Todd Davenport  
Yeah, for sure. And I think you're exactly right, it would be great to have a blood test, it would be great to scan something and have it be definitive, we're just not there. That's not to say that there haven't been a raft of studies that have turned up some potentially very meaningful differences in how people living with long COVID, how their bodies work. But we just haven't boiled that down into the test that allows us to differentiate people with long COVID versus, you know, people who are out of shape, like me.

Jackie Baxter  
You know, there's different subtypes of long COVID. And, you know, there's all sorts of chat into what they are and how they are different and how they present differently. But, you know, if we're looking for the, you know, the one test, you know, the one thing of blood tests that says, Yes, you have long COVID. I mean, maybe that's not practical if there's so many different types of long COVID. You know, you mentioned the sort of ME subtype of long COVID. And that is absolutely one of them. But, you know, within, you know, you've still got loads of others, and they're probably all overlapping in some way as well.

Todd Davenport  
Yeah, I agree with you. At the end of the day, there's going to be some splitting apart of subgroups. What I hope we don't do is challenge the legitimacy via diagnosis based on the membership in a subgroup. That's not where we need to go with this. Trying to maintain a unified front. 

Todd Davenport  
It is hard sometimes among folks with lived experience, and the researchers who work with them. Because how we allocate research funding is through a mechanism of splitting people apart to try and find the most granular commonality that we possibly can. So you know, if this was cancer research, we're not just giving money for cancer researchers, we're giving money for specific types of cancer, we have programs for different different types. And so I don't think we're ever gonna get away from that. 

Jackie Baxter  
Yeah, the sort of practicalities and logistics and stuff is so difficult, I guess. Yeah, 

Todd Davenport  
totally. 

Jackie Baxter  
So we talked about pacing earlier. And that is, you know, a huge strategy. Are there any other sort of strategies or things, for want of a better word, that you would sort of suggest for firstly, avoiding post exertional malaise in the first place, and then you know, what to do, when we inevitably do get hit by it? What would you do to sort of minimize it, and maybe work through it as quickly and painlessly as possible. And obviously, it's not possible to be completely painless.

Todd Davenport  
It's, it's really hard. So the basics of a crash care plan are something that as a clinician, I try and sort out pretty early on with people. So you know, things like resting, laying on your back with your feet up can help increase the amount of blood going to your heart that can, you know, ameliorate some of the issues that some folks tend to have about post exertional malaise and regulation of their heart rates. 

Todd Davenport  
Also, using compression, especially lower extremity, like compression and compression of your tummy. The abdominal region tends to be pretty important, basically squeezing that blood up to in the manner of sort of Circulatory Support. Hydration, using salt, salt supplements, electrolyte drinks, because you know, people with ME have been documented to have a lower plasma volume. So again, this is more Circulatory Support stuff. 

Todd Davenport  
And I would say, you know, again, just sort of developing this sense of what are those symptoms that are sort of my key limiting symptoms, or my key symptoms that I know that I'm entering a crash, like this is starting to go sideways. And I need to change things here. As well as the activities that tend to bring them on. 

Todd Davenport  
So there are some things that you can do, you know, in the manner of sort of interventions and obviously any medications that you find helpful during a crash that have been prescribed by a physician, all together as this crash care plan, and then just really sort of getting to know yourself and sort of where you sit, where you're situated within the variability that is post exertional malaise

Jackie Baxter  
Yeah, I can't remember who it was, but there was someone who described something like long COVID as kind of having to relearn your new body. And I think, you know, some of the things that are likely to trigger and those warning signs that are also important, and anything that you can do to intervene and breathing was always my go to. 

Jackie Baxter  
If I noticed my breath starting to speed up, that would be me going. Yeah, absolutely. Now is the time where I need to stop, I need to lay down, I need to do some breathing. And, you know, obviously, breathing is kind of my wheelhouse. But you know, there are many, many other strategies as well.

Todd Davenport  
Yeah. And there's a whole thing we can say about, you know, therapeutic breathing, you know that that's a good point.

Jackie Baxter  
But yeah, absolutely. As you as you say, and I think, having that prepared before it happens, I think as well. Because when you're in that moment, when you are sort of spiraling down into that crash, and you're sort of past the point of no return, you don't have the brain capacity to think, ah, what do I do here? 

Jackie Baxter  
I'm a huge fan of lists. So I developed a list, and I had my, I can't remember what I called it, but it was my crash list. And then you know, when that happened, these were the things that I tried, and not all of them worked all the time. But you know they were there on paper for me when it did happen. So at least I had something to refer to, rather than sort of just laying there going, Oh, my goodness, this is horrendous. At least I had  something that I could try. I guess,

Todd Davenport  
Maybe something that we can link in the shownotes is the Bateman Horne centers crash care plan that folks might find useful because it really does sort of lead through what are the things to have on hand, you know, who are the people that may need to be contacted, having basic medical information together if someone needs to advocate for you. It's a very nicely constructed document that you can fill out. And let's make sure to have that available that might be helpful for folks.

Jackie Baxter  
Yeah, absolutely. Yeah. Because then even if you do need to just hand it off to somebody else and say, This is the stuff what needs done. Here's the list. And you have that knowledge that someone's got you as well, I suppose. Because in that moment, it is very scary when you're heading down that hole, so to speak. 

Jackie Baxter  
Thank you so much for joining me. It's been an absolute pleasure. And yeah, I think we need to come back and do round two, at some point when we have the capacity. So yeah, thank you so much for giving up your time

Todd Davenport  
Thank you and your listeners for having me. This has been fun. Hopefully it's been helpful information.

Transcribed by https://otter.ai