Cardiopulmonary and metabolic responses during a 2-day CPET in myalgic encephalomyelitis/chronic fatigue syndrome: translating reduced oxygen consumption to impairment status to treatment considerations.

Observed Findings

• ME/CFS participants failed to reproduce CPET-1 performance on CPET-2, with significant declines in peak VO₂, ventilation, exercise time, heart rate, and work output
• Declines persisted at ventilatory threshold for ventilation/CO₂ exchange, end-tidal CO₂, and oxygen pulse
• Healthy controls maintained stable CPET measures across both test days, indicating normal post-exertional recovery
• Matched-pair analysis controlling for baseline aerobic capacity, age, and sex confirmed ME/CFS-specific exertional impairment was not simply due to lower baseline fitness
• Second CPET signaled worse impairment status in ME/CFS compared to first CPET, indicating objective worsening with exertional stress

Inferred Conclusions

• ME/CFS involves abnormal post-exertional cardiopulmonary and metabolic responses that are distinct from deconditioning or fitness level
• Disrupted autonomic nervous system regulation of blood flow and oxygen delivery likely contributes to exertional intolerance
• Observable post-exertional declines in physiological function translate to measurable worsening of impairment status
• Sequential CPET protocols provide validated, objective evidence of exertional intolerance suitable for clinical assessment and research

Remaining Questions