Why is POTS an autonomic disorder? How does an increase in orthostatic heart rate correlate with a failure, or dysfunction, of the autonomic nervous system? I've been doing research for weeks about dysautonomia and I understand the details of the ANS involvement in orthostatic hypotension, but I can't understand how POTS relates to autonomic dysfunction. I've found plenty of resources on POTS, but I just haven't found one that explains it in a way that I can fully understand. Could someone please try to explain this to me?
My easy "surface answer" is just a "definitional" one. Control of body functions like blood pressure, heart rate, etc. is by definition performed by the autonomic system. When the body's response to a certain stimuli serves to harm the organism rather than benefit it... this is defined as a dysfunction. Therefore, harmful responses evident in body functions such as heart rate are by definition an "autonomic dysregulation" or "dysautonomia"... *provided* they are via expression of autonomic activities themselves rather than some other specific defect like a heart conduction problem, a hormone level imbalance (like Addison's), simple dehydration, etc.
But in reality it's fuzzier because there are multiple causes of POTS, some of which are unknown or theoretical. Who knows, perhaps some peoples' POTS is actually from a non neurological kidney dysfunction (and their autonomic nervous system is intact). But what would happen then is that specific cause would be separated out from POTS and isolated (like the other known diseases that cause POTS symptoms but are not POTS).
Also, it can be helpful to focus on some of the specific causes that are somewhat pinned down. A classic one to look at is NET (NorepinEphrine Transport enzyme) deficiency... where there is virtually no norepinephrine and dopamine is being used instead... being substituted *in* the autonomic nervous and neurohormonal system itself. Or look at "peripheral denervation" where POTS is at least partially caused by a lack of response in the vascular bed due to "simple failure" of nerve conduction. Or consider cases of head injury where lesions might be visible in brain regions known to be associated with autonomic function. So basically, the *known* causes of POTS are true autonomic disorders (as near as can be discerned)... and the unknown and theoretical causes get to "tag along" for now even if they may not be caused by isolated damage to the autonomic nervous system itself.
Also, "baroreflex" failure or hypersensitivity is suspected for some... which is an "autonomic" sensor & problem. And other "hypersensitivities" within heart or vascular sensors are theorized as well... including cases where POTS people do NOT have any orthostatic hypotension (even having a hypertension) yet DO have the big pulse increase (and related symptom cluster). I think denervation of the kidney can be a cause (particularly a neuronal cause of chronic hypovolemia) though I might be blurring with another condition other than POTS... not sure (maybe Parkinsons?)
But if your confusion has to do with the fact that the name POTS focuses on the tachycardia... while in many cases the tachycardia is a "healthy" autonomic response to postural hypotension... I can see reason for confusion. However, ultimately the causes are autonomic... or theorized to be at least... or at the very least the autonomic system is integral in amplifying the underlying problem (like hypovolemia) into the symptoms that make up the syndrome.
When you stand up, your autonomic nerves are supposed to get a message to tighten your blood vessels to compensate for gravity pulling your blood to the ground. If the vessels don't tighten, you don't get as much blood to your heart, so your brain thinks "Ahh! We're running out of blood! Must pump more blood through!" and sends a message to your autonomic nerves telling the heart to beat faster in order to move more blood through. However, the blood is still down in your legs, so beating faster doesn't do any good. Then your brain totally freaks out, because nothing it's doing is fixing the problem. Also, since your blood is all down in your legs, there's none in your brain, so your brain starts being stupid, and eventually loses enough blood that you pass out. Once you're flat, the blood starts flowing back up to your heart and brain, and you're okay again.
Thank you for your responses. I guess I'm still confused about how POTS relates to "continuous" symptoms, as opposed to symptoms that emerge only after standing up.
When I stand up, my vision and hearing goes away, I feel faint, nauseous, and have other pre-syncope symptoms. If I start walking right after I stand up, the symptoms come and go very quickly... within seconds. I guess that's from my muscles moving the blood from my legs?
I fit the diagnostic criteria for POTS (my heart rate increases 40bpm), but I'm right on the borderline of orthostatic hypotension as well. My blood pressure drops about 15/10 mmHg. I've been doing research trying to figure out what's going on and I understand that when I stand up, for some reason my blood pressure falls, which makes my heart beat faster to try to compensate for the sudden drop in BP. But how does this relate to symptoms such as fatigue? I have had chronic fatigue for 6 years and none of the doctors I've seen can figure out what's wrong.
I've never seen a doctor specifically for my orthostatic intolerance because I never even knew that this wasn't normal. I'm 21 now, and I've had orthostatic intolerance symptoms since I was a little kid. I remember being 6 or 7 years old and having pre-syncope symptoms when I stood up, as well as other symptoms that I now suspect are related to autonomic issues. When I saw a neurologist last year he told me that my BP and heart rate weren't normal when I went from supine to standing, but he never said anything more about it and he didn't make it seem like a big deal.
So that's when I started doing research about this whole thing because my main goal is to find a reason for my severe fatigue. For a while I was thinking that I finally found out what's wrong with me, but now I'm kind of stuck because I can't seem to understand how POTS is related to generalized symptoms such as fatigue, pain, headaches, etc.
Migraines are really common with POTS. Migraines occur when the vessels in your brain constrict and then relax all of a sudden. Just as your body can't adjust your vessels to the change in posture, it also has trouble adjusting those in the brain.
I have a couple ideas on the fatigue. At first, I thought mine was just because I wasn't getting enough blood to the brain, and I'm sure that contributes. Now it turns out that the reason I have dysautonomia in the first place is that an autoimmune disease has destroyed the autonomic nerves. It takes time for my autoimmune medication to start working, but I am having more days where the fatigue lets up. Autoimmune diseases all cause really severe fatigue. It feels like when you have a really bad Flu and all you can do is sleep. Not sure if that's the case for you, but it might be worth looking into.
That's a great point about the continuous symptoms. The definition of POTS focuses on a specific outward sign and cluster of general symptoms but doesn't offer much explanation or connection between them. The bottom line is that nobody knows how it all works together... certainly not fully. The syndrome definition accommodates multiple causes, mysterious causes, crossover with other syndromes, etc. All of that really confuses things.
I'm afraid you are describing an understandable response. A bit of a hallelujah feeling when you find a condition that matches and describes you really well... followed by a bit of disappointment when it ends up not having such clear answers itself. It's not the end of the road for investigating stuff... but it is unlikely to be as simple as a quick blood test and a yes/no answer... more like trial-and-error treatments which will hopefully get back a lot of your functionality. There is a lot of crossover with CFS and even Fibromyalgia (even IBS for some). This facilitates some benefit when research or treatment from one category comes up it can be brought in to others sometimes. I consider myself a CFS-P sort (which is even used by some researchers... the P standing for POTS).
This is s54, I was having technical troubles with my other account and I had to create a new one.
supineallthetime, sorry it took me such a long time to get back on MedHelp to be able to thank you for your help!
Thank you for asking this question. It's really helping me to understand things. After more than 20 yrs of random and full-on false diagnoses, I've recently been told I have hypermobility syndrome and autonomic dysfunction of which I need further clarification of the latter - Am off to national neuro hospital soonish.
Anyways...I've saved this page as I really value the question and wonderful answers. Thanks so much
Hey there, thanks for your good wishes... Arh yes I thought that I may have Lyme, so went to a Lyme specialist who seemed far more focussed on other things (plus I was too skin sensitve and having psuedo seizures for any blood to be taken)...he was really pulling away from this as a diagnosis, so i need to take myself off the Lyme forum.
I'm now trying to see if it is indeed POTS that I have, or another autonomic dysfuction...as I have soooo many other neuro symptoms. And, lol, what is it with medical people saying "hmmm it's compicated" lol...really? oh that's news to me lol!!
Thanks for your explanation on POTS...it really helped me.
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