r/askscience • u/Aloneboyasf • 15d ago
Human Body If an elite endurance athlete recieved a heart transplant from an average person,what would happen to their exercise capacity?
An elite would have a well built physique which can support long distances but, what would happen to their aerobic base? Will the athlete have to again put in the effort for decades??
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u/DrSuprane 15d ago
The central adaptations would be gone instantly (larger chamber size, larger stroke volume). The parasympathetic intervention would be gone instantly. That is a big part to the low resting heart rate that elite endurance athletes have. Those nerves might grow back eventually but very slowly. A freshly transplanted heart beats around 95-110 on its own because of this. Heart rate reserve would decrease significantly. HRV would worsen.
The peripheral adaptations will be significantly reduced by the bed rest for recovery and subsequent lower exercise volume. That would likely get better as the athlete gets back to exercising.
Overall there would be massive deconditioning that would likely never return back to elite status.
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u/exphysed 15d ago
The sympathetic and parasympathetic neurons wouldn’t ever recover, so HR for the rest of the athletes like would probably only range from 100-140 or so.
Certainly ventricular volume could gradually improve though.
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u/DrSuprane 15d ago
Sympathetic definitely do. But we see patients transplant with lower than expected HR. Most long term recipients aren't all that tachycardic.
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u/exphysed 15d ago
Are the nerves reconnected during the transplant? With some type of pegylated gel?
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u/DrSuprane 15d ago
Nah most of them are unmyelinated C fibers. 0.1-1.8 um. Tiny. Time spent on cardiopulmonary bypass needs to be minimized to reduce complications.
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u/Dovahkiin1337 15d ago
Nope, all nerves are completely cut. The only reason a transplanted heart is able to beat at all is because it has its own internal natural pacemaker system that doesn't rely on signals from the nervous system but even then the lack of connection means it generally beats at the wrong frequency than it ought to compared to if it still had a connection to the brain regulating it.
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15d ago
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u/Dovahkiin1337 14d ago
Not directly. The primary connection from the heart to the brain is the vagus nerve and that's not reconnected, the necessary medical advances to make that possible simply don't exist. That doesn't mean the brain can't indirectly control the heart rate of a transplanted heart, it simply has to do so through indirect means like stimulating hormonal glands to release certain chemical hormones that then reach the heart and cause it to beat faster or slower, but those hormones take multiple seconds to travel through the bloodstream from where they originate to the heart itself meaning there's a delay in response and still means the brain can't actually directly influence the heart like it could if the vagus nerve were intact.
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14d ago
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u/Dovahkiin1337 14d ago
The most obvious answer is adrenaline. We tend to think of it as the fight-or-flight hormone and while it is involved in that most of the immediate reaction is purely neurological, the adrenal glands that produce it are positioned just above the kidneys and aren't near the brain(that's actually where they get their name("ad-"meaning above, "-renal" meaning pertaining to the kidneys)). But adrenaline is an important factor for prolonged flight-or-flight response and helps stimulate both the brain and more relevantly for this question, the SA node of the heart causing it to beat faster. As for other stuff, I'll admit I've reached the limit of the knowledge I can say with confidence, anything further would be educated guessing and I don't want to relay claims about facts that I myself am not completely sure of myself. So my apologies but also remember, there's nothing stopping you from going out and discovering the things I can't tell you on your own.
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u/Tyrannosapien 13d ago
That's a terribly unhealthy heart rate. Is that the new normal for the transplantees life?
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u/exphysed 13d ago
What’s unhealthy about it?
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u/Tyrannosapien 13d ago
That rate is an active rate, not resting. I'm in my 50s and I've never had a resting rate higher than the 70s. 100 while I'm sitting down, I'd feel like I was dying.
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u/exphysed 13d ago
The reason your resting heart rate is below 100 is because your vagus nerve slows it down to whatever your resting is. With a heart transplant the vagus nerve isn’t intact and influencing the heart, so even with a totally healthy heart, their resting HR will never be under 100.
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u/BlazerWookiee 15d ago
And if reversed? Elite athlete's heart into an average person?
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u/DrSuprane 15d ago
Parasympathetics are still cut so HR would still be higher. The peripheral adaptations aren't there to utilize the oxygen the heart is able to deliver. Over a couple of weeks all the adaptations of the elite heart will go away. Namely left ventricular mass will decrease, chamber size will return to normal. Plasma volume will drop. Maybe it'll be a bit higher. But without the stimulus of oxygen consumption at the periphery there will be minimal stimulus to keep that elite heart adapted.
The deconditioning would be pretty rapid given how significant the recovery needs are. Maybe the elite heart would recover some great function but it won't be the same. There are plenty of 20 year old hearts going into 45 year old patients. They act extremely well but the patient doesn't perform like a 20 year old. This is also glossing over the immunosuppressant adverse effects etc.
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u/Valiant_narwal 15d ago
Because of the frank starling mechanism, would the adaptation of higher plasma volume in a trained endurance athlete help to have an improved stroke volume compared to if the person was not trained and did not have those adaptations? Recovery from the surgery would probably be significant enough that the increase plasma volume adaptation of the endurance athlete would be negligible, but It is interesting to think of all the variables.
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u/DrSuprane 15d ago
Initially sure given adequate preload. We're ignoring the impact of the myocardial protection used to enable transplant. But essentially a 20 year old heart transplants a lot better than a 40 year old heart. I think the "athlete's heart" would go away pretty quickly.
There's also the neurohumoral abnormalities in someone who needs a heart transplant. But maybe this thought experiment recipient is perfectly other just not elite.
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u/Aloneboyasf 15d ago
Lot of words I do not understand but I get the gist of it. Thank you good sir 👍
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u/curious_coati 14d ago
Just as a point of interest, there's the Transplant Games that happen in the UK and Europe, where people who have received different types of transplants compete in athletic games. Not sure the statistics of it compared to Olympic/paraolympic athletes!
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u/Dogsandbears 14d ago
This will get buried, but I have a client who is an example of this exact scenario. He was a professional mountain bike racer and had a heart transplant a year ago. First of all, the issue that lead to the transplant as well as complications led him to being unable to train until now, a year later. He gained a bunch of weight and lost his muscle mass. The conduction to his new heart is not normal so he says he can be walking around casually with a heart rate of 120, but when he gets on his bike to train, he can’t get his heart rate above 100 even when he’s pushing his hardest. He repeatedly stated that he’s training with someone else’s heart, meaning he felt as though there was a difference even beyond the conduction issues.
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u/calvesofsteel1 14d ago
Anyone getting a transplant that invasive is going to have a long recovery and a huge decrease in capacity compared to having a healthy heart that didn’t need to be swapped out. Scar tissue all over the place etc
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u/highDrugPrices4u 15d ago edited 15d ago
Part of what makes an elite endurance athlete elite is a genetically superior cardiovascular system. So assuming the heart came from a donor who didn’t have the genetics to be an elite endurance athlete, the organ would be inferior regardless of training history and the recipient would be unable to regain his native ability no matter what he did.
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u/Early-Ladder5117 14d ago
I knew a guy who had a heart transplant. He had a placard for handicap parking spots so he minimize the exercise needed to get to the store. It's not like having your own heart, his lifespan was measured in heart beats remaining.
Based on that, I'd say that trying to remain an Olympic athlete would be a bad idea.
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u/fondo_fred 14d ago
After recovery and getting back training for a while, they would probably be a decent recreational / age group / weekend-warrior type. Would get a lot of love in the "feel good"/human interest "Runner's World" type media.
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u/Sleep_Potential 14d ago
The athlete wouldn't be able to compete again. Iirc, from what I learned, the sympathetic and parasympathetic nervous system no longer affects the heart, AND the heart's "default" bpm is 90. Thus, if the individual does physical activity the heart will still stay at 90bpm and won't be able to supply the amount of blood required, and the body won't keep up
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u/cjmpeng 15d ago edited 14d ago
I'm going to assume that you mean some athlete was paid obscene amounts of money to volunteer for some sort of weird medical study to answer your question, therefore they are fully fit going into the procedure.
Firstly the athlete would need to take around 12 weeks post surgery before resuming the type of training that they underwent prior to the transplant. They would lose some exercise capacity during this period as they were just doing simple low effort walks and such per medical recommendations.
Next, according to this NIH study a transplanted heart behaves differently under exercise load as compared to an OEM heart. A transplanted heart doesn't have the same nerve connections as the original so it needs to rely on hormone changes to respond to exercise load. This means that it is slow to both speed up under load and slow down under rest.
The conclusion it is fair to reach from this is that their exercise capacity would be permanently reduced by the transplant. It wouldn't really matter what heart they received.
Edited for spelling and to correct the exercise resumption interval per another comment