Influence of end-tidal CO<sub>2</sub> on cerebral blood flow during orthostatic stress in controls and adults with myalgic encephalomyelitis/chronic fatigue syndrome. — CFSMEATLAS
Influence of end-tidal CO2 on cerebral blood flow during orthostatic stress in controls and adults with myalgic encephalomyelitis/chronic fatigue syndrome.
van Campen, C Linda M C, Rowe, Peter C, Verheugt, Freek W A et al. · Physiological reports · 2023 · DOI
Quick Summary
This study looked at how carbon dioxide (CO2) levels in the blood affect blood flow to the brain when people stand up or tilt on a table. Researchers compared 535 women with ME/CFS to 34 healthy women. They found that CO2 does affect brain blood flow in both groups similarly, but CO2 changes only partially explain why ME/CFS patients often have reduced blood flow to the brain during position changes.
Why It Matters
ME/CFS patients commonly experience inadequate blood flow to the brain during position changes, which contributes to symptoms like dizziness and cognitive difficulties. Understanding whether CO2-related mechanisms explain this problem helps researchers identify the true cause and could guide targeted treatments. This study clarifies that CO2 regulation is not the primary culprit, pointing investigators toward other mechanisms.
Observed Findings
Both ME/CFS patients and healthy controls showed significant correlations between blood CO2 levels and brain blood flow during tilt testing (p<0.0001 in patients).
CO2 changes predicted brain blood flow changes in both groups, but this relationship was weak, explaining only a small portion of the variation (low R² values).
ME/CFS patients with normal heart rate/blood pressure responses and those with POTS showed similar CO2-brain blood flow relationships, suggesting a common mechanism.
Patient status (having ME/CFS vs. being healthy) was an independent predictor of brain blood flow changes, separate from CO2 effects.
Inferred Conclusions
CO2 reactivity (the brain's sensitivity to CO2 changes) is preserved and similar in ME/CFS patients compared to healthy controls.
CO2-related mechanisms play only a minor role in the abnormal brain blood flow observed during orthostatic stress in ME/CFS.
Other factors beyond CO2 regulation are primarily responsible for the reduced brain blood flow seen in ME/CFS patients during position changes.
Remaining Questions
What other physiological mechanisms (autonomic dysfunction, vascular stiffness, etc.) are responsible for the abnormal brain blood flow in ME/CFS?
Do these findings hold true in male ME/CFS patients, or are there sex-specific differences in CO2 reactivity?
What This Study Does Not Prove
This study does not prove what actually causes the abnormal brain blood flow in ME/CFS—only that CO2 changes are not the main explanation. It is a cross-sectional snapshot and cannot establish causation or long-term outcomes. The findings apply primarily to women and may not generalize to men with ME/CFS.