Heart Rate Variability means the delay between different types of heart beats, by the way.
Simply speaking, they looked at whether cognitive problems are caused by something to do with our heart and circulation rather than something or things mis-firing in our brains on their own.
They found that although people with CFS were as accurate in those tasks as people without CFS, they were much slower at carrying them out. That’s the Brain Fog we experience.
They also found that after a thinking challenge was carried out by a person with CFS there was a correlation between the speed or slowness they took in the challenge and various differences they observed in HRV.
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