[HN Gopher] Excitable cells
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Excitable cells
Author : johannes_ne
Score : 249 points
Date : 2025-03-28 13:05 UTC (4 days ago)
(HTM) web link (jenevoldsen.com)
(TXT) w3m dump (jenevoldsen.com)
| samwho wrote:
| Absolutely fantastic. Well done!
| Kalabasa wrote:
| Learned about the heart today! Thank you!
|
| I wonder what other types of cells / tissues can be simulated by
| cellular automata?
| owenpalmer wrote:
| I was thinking the same thing. I need more simulations like
| this!
| agumonkey wrote:
| Anybody know similar article but about blood flow / hemorheology
| ?
| lofties wrote:
| Excellent article! Well written and the animations make it so
| much easier to understand. However I was unable to get the loops
| to go.
| samwho wrote:
| I was able to do it by clicking in a few places in quick
| succession evenly spread out.
| jcattle wrote:
| Try clicking in one place repeatadly and adjust clicks
| slightly to always go next to the fastest refractory cell
| possible. This works like a charm to induce arrhytmia
| leereeves wrote:
| I was able to consistently start a loop in one click by
| clicking on the edge between grey and white (slow and fast
| refractory) cells ASAP after a normal beat.
|
| If I'm fast enough, the wave can't spread to the grey cells so
| it only goes in direction around the red cells and starts a
| loop.
|
| (But you can't do this on the first image with a Defibrillate!
| button because there are no slow cells.)
| EncomLab wrote:
| As someone who lives with this reality moment to moment (thanks
| to a deeply bridged LAD coronary artery) it is interesting to see
| a visual representation of these effects.
| pscanf wrote:
| _Exciting_ simulations! :) And an excellent explanation.
|
| From time to time I get episodes of sudden tachycardia1. It's a
| very strange feeling: one second everything is fine, the next my
| heart jumps in my throat and starts beating at 230 bpm (not a
| typo). After a while, just as quickly as it came, the tachycardia
| goes away and I'm back at whatever HR I was before the trigger.
| If it doesn't go away by itself, breathing in deep and holding my
| breath typically does the trick. It's like a light switch! A bit
| scary, but also very fascinating.
|
| Thanks for explaining so well what goes on "under the hood"!
|
| 1
| https://en.wikipedia.org/wiki/Paroxysmal_supraventricular_ta...,
| I believe.
| papascrubs wrote:
| I have a similar condition. Mine is:
|
| https://www.mayoclinic.org/diseases-conditions/wolff-parkins...
|
| I have the same bouts of tachycardia. They are very
| intermittent, no real cause. And the same breath holding
| technique works for me. Very interesting stuff!
| papascrubs wrote:
| I have the same condition. I was diagnosed at a very younger
| age with Wolff-Parkinson-White syndrome. It might be worth
| looking into.
|
| https://www.mayoclinic.org/diseases-conditions/wolff-parkins...
| limaoscarjuliet wrote:
| With WPW you MUST NOT take beta blockers (AFAIR), it may kill
| you.
|
| I had just plain vanilla Afib and got ablation 2 years ago -
| best thing ever, cured instantly.
| pscanf wrote:
| Fortunately I don't think it's WPW in my case. Or at least,
| my cardiologist never mentioned it, so I assume it's some
| other condition that has similar symptoms.
| dcminter wrote:
| A couple of years ago I woke with a minor headache that I
| ignored for various reasons all day, then skipped lunch as I
| had an important meeting later and lots to do ahead of it, and
| the headache got progressively worse. Just before the meeting I
| felt nauseous, threw up, and then started having the feeling of
| palpitations in my chest. I've always had them from time to
| time - that feeling that ones heart has skipped a beat or taken
| a couple of extra ones - but this time it wasn't going away
| after a couple of beats.
|
| To cut a long story short, I went to hospital (instead of that
| meeting) and it turned out that it was atrial fibrillation and
| that while it feels medium terrifying it's not necessarily that
| big a deal.
|
| It went away after a couple of days (if it had lasted longer
| they'd have done "electroconversion" to try to get it back into
| the proper ryhythm artificially). Apparently the real danger of
| this is that it might cause a blood clot which in turn could
| cause a stroke, but it's unlikely to be an issue in the short
| term.
|
| They did put me on blood thinners and beta blockers between the
| occurrence and getting a full check up a month later, so I was
| _very_ calm when we rescheduled that meeting.
|
| Top tip: don't ignore a terrible headache; go to bed.
|
| Edit: PS I think my heart rate was just above 100bpm at rest
| (possibly 120?), which was unnerving enough, so I can imagine
| how much more scary 230bpm must feel! You definitely win.
| PaulHoule wrote:
| I fainted when I was an exercise class. I'd had too much to
| eat before then, my digestion was pretty slow then, also it
| was a crazy hot day in a building with a pool (high humidity)
| and an old HVAC system. Didn't help that I had a crush on the
| instructor and was trying even harder because of that.
|
| Woke up on the ground feeling very relaxed. Got a medical
| workup that checked a lot of things, they had me wear a
| Holter monitor for a month. In the last 30 minutes of the
| study period they caught five bad heartbeats of A-Fib when I
| was sleeping. Funny one of my evil twin's schemes went south
| around then and I (we?) were feeling really bad about it. My
| cardiologist told me that the threshold was one bad heartbeat
| so I have A-Fib and have a risk of strokes, he recommended
| that I take a baby aspirin as it has a mild blood thinning
| effect.
|
| Around the beginning of the next year I developed a deep vein
| thrombosis which got cleared up with Eliquis, a blood
| thinner. The emergency room referred me to my primary care
| doc who ran all sorts of tests and couldn't find a reason for
| the DVT so he decided to keep me on Eliquis indefinitely, the
| cardiologist figured that covered the A-Fib so I dropped the
| aspirin because the combination could cause excessive
| bleeding.
|
| I have one of those credit card Kardia EKGs and haven't seen
| an A-Fib episode yet. For the decade before I got that workup
| I did crazy amounts of cardio (helped me stay sane under
| incredible pressure) and around the time my evil twin was out
| I was getting up in the morning before sunrise, hiking 6
| miles, going to the gym during the day, going out in the
| evening and hiking another 6 miles. My cardiologist says I
| have "Athlete's heart" with an abnormally low resting heart
| rate (drops below 50 at night when I get a good night's rest)
| and I shouldn't do more than an hour of cardio a day, so I
| don't.
| pscanf wrote:
| Yeah, the first time it happened (about 15 years ago) I
| thought "that's it, I'm dead". Heart things are unnerving
| indeed! Best of luck with your AFib!
| TheJoeMan wrote:
| Do you drink a lot of caffeine? A family member had this
| occasionally with no family history of issues, and the
| cardiologist had them wear a portable EKG for a few days that
| synced with an Android phone, with not much results. Finally
| the family member cut down from 4 espresso shots a day to just
| 1 cup of brewed, and the issue hasn't returned.
| pscanf wrote:
| Yeah, several cups of tea per day. I also recently had that
| test done, but nothing emerged as nothing occurred during the
| 24 hours I was monitored. Just like I expected, actually, as
| fortunately those episodes are very rare for me, not enough
| to warrant drastic lifestyle changes. (I can't give up my
| tea! :D )
| leereeves wrote:
| I love this article. I had already learned all the facts in the
| article, but even so, the interactive animations helped me
| understand it better. Thank you.
| eknkc wrote:
| I have frequent ectopic beats that I feel as a flutter / heavy
| beat on my chest. The doc says it won't kill me but it is
| extremely uncomfortable at times. This has been a great material
| to learn about the inner workings of heart cells.
|
| BTW Here's an ECG from my Apple Watch showing 3 such beats (you
| can't miss them): https://link.ekin.dev/l1Vc3Gdf
|
| If you happen to have these, just get checked out by a
| cardiologist. They are almost always benign but the frequency /
| daily amount are reasons for concern.
| elric wrote:
| Many (most?) people get ectopic beats, but the threshold for
| noticing them seems to differ. Being stressed/anxious makes
| them more noticeable. There's a self-reinforcing feedback loop:
| the more you notice them & worry about them, the easier you
| will notice them ...
|
| The thing about arrhythmias is that they can only cause damage
| while they're happening, but ectopics are only a problem for a
| single beat, which is not going to impact your oxygenation or
| blood pressure or anything else. Even a bunch of them every day
| won't cause any damage.
| UncleOxidant wrote:
| > Many (most?) people get ectopic beats, but the threshold
| for noticing them seems to differ.
|
| This. Some of us have very high levels of proprioception. I
| can feel my pulse just by sitting quietly - I don't need to
| put my finger on my wrist to take it. Same with ectopic
| beats, I definitely feel them. And I find that there's a
| cycle to it - as you say there's a feedback loop: feel
| ectopic beat, become anxious, more ectopic beats, more
| anxious, etc. Then I have to try to actively forget about
| them. During those feedback times I'll have many ectopic
| beats / day (many per hour, even), but then some days later
| I'll realize I haven't had any for a while and I might go for
| weeks without noticing any.
| eknkc wrote:
| Apparently everyone gets them but the burden (% of beats
| being screwed up) is important. A high burden for prolonged
| periods means damage accumulation.
|
| I had 2 24 hour monitors and one caught 700 eptopic beats in
| a day. Another couple months later, 15.000 in a day. The
| second one was a concern for the cardiologist. She ordered a
| couple more tests, started beta blockers asked for diet
| changes.
|
| I still have a high burden as I can feel them but whatever..
| rdegges wrote:
| I had something similar for many years (triggered by an episode
| of afib brought-on by triggering my vagus nerve). The one thing
| that has helped me fully get rid of these (after YEARS of
| trial-and-error) was getting onto beta blockers (Propranolol).
|
| These have COMPLETELY gotten rid of my ectopic beats and also
| helped me deal with the health anxiety.
|
| If you ever want to talk, feel free to hit me up (contact info
| in profile).
| grumpy-de-sre wrote:
| Propranolol is such an underrated drug, or at-least it was
| when I first started using it twenty years ago (initially for
| hand tremors but I found it did more than settle just my
| hands). Glad others have been discovering its usefulness over
| the years.
|
| I think they've even recently found use in cancer therapy
| [1].
|
| Sir James Black the pharmacologist who developed it is an
| absolute legend [2].
|
| 1. https://www.tandfonline.com/doi/full/10.1080/2162402X.2023
| .2...
|
| 2. https://www.youtube.com/watch?v=ZPe0sLghRBQ&list=PLVV0r6Cm
| Es...
| UncleOxidant wrote:
| > an episode of afib brought-on by triggering my vagus nerve
|
| I get ectopic beats when I've got trapped gas in the stomach.
| Sounds weird, but generally when I get them I realize I need
| to stand up (because I've usually been sitting with bad
| posture which leads to the trapped gas) and have a large
| belch and then it calms down. I mentioned this to my doc and
| he said it was Roemheld syndrome (
| https://en.wikipedia.org/wiki/Roemheld_syndrome ) which is
| vagus nerve-related.
| eknkc wrote:
| Yeah, I've been on propranolol and then metoprolol but they
| don't seem to do much in terms of reducing ectopics.
| Currently on metoprolol though.
|
| I've had an echo, stress ecg and then a ct angiogram.
| Everything is physically fine so at this point I mostly
| ignore them cause at least I know they are not an immediate
| danger.
|
| Thanks!
| throwaway7783 wrote:
| Daily dose of magnesium supplements has made it tolerable for
| me, when beta blockers (carvedilol) didn't help much.
| ggambetta wrote:
| I had some of those, verified by ECG. Cut down on coffee a bit,
| they went away.
| the_arun wrote:
| Trying to understand Author's education. Have they done both
| Medicine & Engineering? Looking at their articles & github, they
| are sound in electro physiology, Anaesthesiology & software.
| Great intersection of knowledge.
| mjamesaustin wrote:
| I don't know the author, but I will note that my cardiologist
| got an Electrical Engineering degree before going to medical
| school and views it as a huge advantage when dealing with the
| heart.
| johannes_ne wrote:
| Thank you all for the interest in the article and the kind
| feedback.
|
| I'm a medical doctor with an interest in engineering and
| coding. My PhD was quite focused on signal analysis and coding,
| and my supervisor is a medical engineer.
| fraserphysics wrote:
| I am reworking the analysis of ECGs from an old contest, and I
| want help from an expert.
|
| In 2000 the Computers in Cardiology challenge (CINC2000) provided
| ECGs from sleep studies of 70 patients and asked contestants to
| identify obstructive sleep apnea based on those ECGs. I was on
| the team that won.
|
| Now I am reworking the problem for the second edition of a book
| (see https://www.fraserphysics.com/book.pdf), and I see great
| variety in those ECGs (see
| https://www.fraserphysics.com/all_ecgs.pdf). I suspect that some
| of that variety is due to lead placement, and some is due to
| pathology, but I'm not sure.
|
| Is anyone here willing to help me out?
| dheera wrote:
| Oh this is interesting. Thanks!
|
| I've survived ventricular fibrillation 3 times and have an
| implanted ICD. I never really understood why delivering high
| voltage shocks is that effective, and always have anxiety about
| "the time it won't work"
| mjamesaustin wrote:
| As someone who had their life upended last year upon discovering
| I had AVNRT, this article is much appreciated. I'm still trying
| to understand the root cause of my arrhythmia, because two
| ablations and one daily medication later and I still have regular
| episodes.
|
| It's wild how many different types of arrhythmia there are, and
| how they can be connected to many other systems in the body. It
| seems like mine might be related to my nervous system.
| PaulHoule wrote:
| I'm rarely intimidated by a textbook but I was intimidated by a
| set of cardiology books I saw at the vet school. The topological
| structure of waves in the heart is
|
| https://en.wikipedia.org/wiki/Spiral_wave
|
| because cardiac cells circle around a loop with phase from 0 to
| 2p, contrast that the usual oscillator which has position p and
| momentum q. An oscillation in that space can rotate around the
| center and look like a phase but it's also possible to go right
| through the center, whereas for cardiac excitations the p
| variable is on the unit circle. This astonishing book covers the
| topology of this kind of thing:
|
| https://archive.org/details/geometryofbiolog0000winf/page/n9...
|
| particularly the cases where you have just one phase (e.g. jet
| lag or cell division or plant phenology) but it applies as well
| to those spiral waves where every element in the medium has a
| phase.
| randerson wrote:
| I had a benign irregular heartbeat (Premature Ventricular
| Contractions) for half my life. During one checkup the
| cardiologist said my heart had become enlarged to compensate, and
| if I wanted an energy boost I should get an ablation surgery.
|
| The ablation was quite the experience as I was kept conscious
| throughout (and I felt euphoric thanks to the painkillers). A
| team of students carefully threaded a wire in through my femoral
| artery, guided it up to the inside of the heart and zapped the
| problematic cells. I could actually feel the moment they fixed
| it. One moment my rhythm was irregular, the next it was regular.
| They then ran a series of stress tests that included injecting me
| with something that pushed my heart rate above 200 bpm. That was
| uncomfortable. I was back to my normal routine 24 hours later and
| I did indeed have more energy.
| johannes_ne wrote:
| Thank you for all the kind responses.
|
| I also want to make a similar article, where I calculate an ECG
| for the simulation, and then make and explain the changes
| necessary to make the ECG look realistic. A main challenge will
| be that the depolarization has to happen very fast relative to
| the repolarization, which may be computationally difficult for a
| cell-based simulation.
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