Evergreen
Senior Member (Voting Rights)
They don't say that 40% have excessive orthostatic tachycardia. They say that 3/17 (17.6%) HVs had that. 7/17 (41%) HVs had symptoms - this would be any symptom at all reported during the head-up tilt test, which could be unconnected with the test, or they may have only counted prodromal symptoms like dizziness, nausea, blurred vision, odd sensation in chest, maybe neck pain as symptoms.If someone naturally has to do things to prevent themselves from fainting in everyday life, I would argue they should not be a control in a ME/CFS or POTS study. Perhaps it is a function of my youth, but I have met very few people in the general population (far less than the 40% here) who have significant orthostatic symptoms. I think we need some clarification on what criteria they are using for "excessive orthostatic tachycardia" but there is no way that 40% of the population has POTS.
I think the reason you don't meet people with significant orthostatic symptoms is that normal life prevents them even in those who would have a surprise positive tilt test. You're walking around, you're sitting but moving your arms etc. So it tends to happen to a small number of people in more unusual situations like a long wait in a queue on a hot day, or standing in a choir, or standing or sitting still in a church. My sister used to faint with exercise for a few years as a teenager. She has absolutely no orthostatic symptoms as an adult. She would definitely qualify as a healthy control. Who knows what would happen on a tilt.
Looking back I've always had OI issues, I just didn't know what they were. I knew that I felt crap if I had a bath or got in a jacuzzi or played tennis (picking up the balls and lots of standing around, I think) or stood on the train in the morning. All easily sidestepped. I would have been a healthy control until I got ME/CFS. I'm now someone with really debilitating OI that does not get easily captured in these tests. I've had a negative 20 minute tilt and a positive-at-32-minute tilt. In real life can I stand still for 32 minutes? No, not even close, standing still at all is problematic. Sitting still is problematic. My guess is that the stress of the testing situation is enough to counteract what my BP would otherwise do - a bit like white coat hypertension in the doctor's surgery vs 24-hour BP monitoring at home (the latter also misses my issues). Or that, as @Jonathan Edwards has pointed out, the problems ME/CFS people without POTS have with being upright may not be not about blood pressure and heart rate.
Edited to change "are" to "may not be" in final sentence to accurately report my understanding of JE's view.
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