Factors that will affect TILT tests patients may have forgotten about:
Postural hypoperfusion in the brain will arouse the CNS and thus this is why you feel worse sitting up because you have a horrible mixture of your brain being half asleep and your brain becoming alert something is wrong, which further attenuates sympathetic nervous drive. In addition Hyperadrenergic POTS patients will produce excess epinephrine upright Vs supine (laying flat) and thus feel even more 'nervous' than POTS patients with other forms of Dysautonomia. This then leads to TILT tests becoming abnormal, or less abnormal than when in a more calm state at home (less sensory input, less anxiety). For example:
Dysautonomia anxiety falsely elevates 'resting' supine (flat) HR during TILT procedure affecting results:
Expectation anxiety due to Dysautonomia will release excess epinephrine and thus elevate Bp and Pulse. What is important to remember is then your Laying Flat PR will be falsely elevated, and likely not change much when they tilt you up. If you were calm, and had a resting PR of 60-90 then of course when tilted, your PR will go up to maybe 110-160 when they tilt you depending on how bad you are on the day.
Cardiac output increases with stress, and will make your TILT test falsely better:
Stress increases cardiac output as your heart pump goes up, increased cardiac output when testing for POTS is the last thing you want, as the results will not be as bad, as if you were calm and relaxed when TILTED. If you are anxious, your cardiac output will increase the blood flow to your brain also, which isn't like this at home when you are calm and feel more dopey/stoned/faint. Again, the most ideal situation is to be totally calm when having these tests done. How on earth you do this with Hyperadrenergic POTS I don't know. Befriend the staff beforehand? Visit the centre beforehand? Won't work really to be honest.
Cardiac output increasing from stress wakes your brain up - again hidden when at home, but present on TILT:
If you have POTS you may be aware that at home, calm you are totally stoned and off your face and can hardly string a sentence together. Have an emergency and get an adrenaline rush, and if chest pain/tachy/sob doesn't consume you, you may feel unusually alive. This can be infuriating when sitting in ER when you think to yourself, wait a second, my BP at home chilled out isn't 150/92, more like 114/75. The stress of waiting in ER, even if the emergency is over, is why you are more 'with it', because your brain is getting more blood than usual as your heart is pumping stronger due to stress. Again, this can stop tests they give you, showing up as bad as they are when rested, when your circulation is much less maximised. Talking of which....
Don't fill up on water before a TILT test as you normally do at home:
Hydration levels affect the TILT test. Ideally, take it dehydrated in the morning, so book it at 9-11am and don't drink anything from midnight if possible (most of us drink a lot before bed, as dehydration makes us terribly worse). The more full of water you are (we always drink a lot when going out as we feel so faint too), will maximise your blood volume and blood flow, this will make your TILT test better than it would be, if done in the opposite setting.
This is why the OP and we all feel better lying flat, your circulation is far less 'aroused' by your CNS. All of your energy requirements (very important this) are dialed down when laying flat, all of the signals to your brain also. Sitting up with Dysautonomia is a huge stress on the body. This is why sitting up in a doctors office, even if you don't have chest pain/tachy is a nightmare as your brain is pleading you to lay flat but you can't. You may have also noticed when you're forced to sit upright, then afterwards you crash and become profoundly weaker. This again is because your energy that runs your CNS has been totally expended and there is nothing left. It is here you will probably notice a flair in Dysautonomic symptoms when you think to yourself, wait a second at 10 am I was chatting to my doctor sitting in a chair (albeit stressed as I had to get to the hospital) and by 3pm I can barely speak or move and must go lay down in bed, or lay down flat on the sofa as my brain is totally smashed.
Drug/Medication Issue on TILT:
*Taking Diazepam or a CNS suppressor to 'stay calm' will definitely affect your test. In addition, Diazepam and similar can actually cause tachycardia creating a false impression for the technologist that you are nervous at rest before the test, when it's a side effect of the drug!
*Taking beta blockers, or Ivabradine will lower your resting HR and make it look like you don't have POTS anymore.
All of these factors can affect a TILT table test, and so it's best to have it done 'raw' or 'naked' (not literally), yet doing this in patients who are ultra nervous (due to POTS) can be very challenging.