Normal vitals is not a diagnosis

This paper studied ME/CFS patients using Doppler echography to measure actual cerebral blood flow, not just velocity, during head-up tilt testing. The results were direct and hard to dismiss. Cerebral blood flow was significantly reduced in ME/CFS patients during tilt compared to healthy controls, with reductions proportional to the severity of the condition. Mild ME/CFS patients showed reductions of around 22%. Severe patients showed reductions exceeding 30%.

The critical finding for testing standards is in the subgroup analysis. A subset of ME/CFS patients did not meet standard criteria for POTS, because heart rate did not rise by 30 beats per minute. Another subset did not meet criteria for orthostatic hypotension, because systolic blood pressure did not fall by 20 mmHg. By the conventional diagnostic framework, these patients would have passed a standard tilt test. And yet their cerebral blood flow during tilt was measurably and significantly reduced compared to controls.

The paper demonstrates that orthostatic physiology and standard diagnostic criteria for POTS and OH are measuring different things. Standard criteria measure whether a particular compensatory response, tachycardia or hypotension, crosses a threshold. They do not measure what is actually happening in the brain during orthostatic stress. A patient can fail to meet POTS criteria and fail to meet OH criteria and still be experiencing significant cerebral hypoperfusion every time they stand up.

For patients who have been told their tilt table test was normal, this paper provides direct evidence that a normal tilt by standard criteria is not the same as a normal cerebral response to upright posture. They are measuring different things. Only one of them correlates with the symptoms patients report.