Orthostatic intolerance with tachycardia (postural tachycardia syndrome) and without (hypocapnic cerebral hypoperfusion) represent a spectrum of the s

[Violeta]

https://www.frontiersin.org/journals/neurology/articles/10.3389/fneur.2024.1476918/full

Spectrum of chronic orthostatic intolerance without orthostatic hypotension includes postural tachycardia syndrome (POTS), with orthostatic tachycardia and hypocapnic cerebral hypoperfusion (HYCH), without orthostatic tachycardia. This study compared autonomic, cerebrovascular, and neuropathic features of POTS and HYCH.

With respect to hypocapnic cerebral hypoperfusion:

In essence, when someone with hypocapnic cerebral hypoperfusion stands up, their body may not be able to regulate blood flow to the brain effectively, leading to reduced oxygen and nutrient delivery to the brain and causing the symptoms of orthostatic intolerance.
(Low CO2 levels in the blood cause the blood vessels in the brain to narrow, reducing blood flow.)

With respect to hypocapnia:
Carbon dioxide is an important side product of the citric acid cycle (Krebs cycle).

Physiology, Carbon Dioxide Transport​

https://www.ncbi.nlm.nih.gov/sites/...oxide is an important,may be acute or chronic.
Oxygen delivery and carbon dioxide removal intrinsically link through processes described by the Bohr and Haldane effects.

 

[Violeta]

From Ray Peat's article, Altitude and Mortality

Breathing too much oxygen displaces too much carbon dioxide, provoking an increase in lactic acid; too much lactate displaces both oxygen and carbon dioxide.

 

[Violeta]

I did not know about Cort's article about hypocapnia.
Haven't read it yet.

https://www.healthrising.org/blog/2022/03/10/hypocapnia-chronic-fatigue-syndrome-pots/

 

[cfs since 1998]

Yes, this paper by Novak & Systrom is very good. It shows you can have autonomic dysfunction even with a "normal" tilt table test done using conventional methods.