van de Luit, L, van der Meulen, J, Cleophas, T J et al. · Angiology · 1998 · DOI
This study found that people with ME/CFS have unusually large swings in heart rate and blood pressure throughout the day and night, even though the overall pattern matches healthy controls. Importantly, their nighttime blood pressure drops too low (below 100 mm Hg systolic), which may contribute to fatigue and other symptoms. When treated with a heart-strengthening medication called inopamil, nighttime blood pressure improved, but melatonin actually made it worse.
This is one of the first quantitative characterizations of circadian rhythm abnormalities in ME/CFS, providing objective physiological evidence linking disturbed autonomic function to fatigue. The finding that nighttime hypotension may be correctable with specific medications offers a potential therapeutic target and suggests ME/CFS involves treatable cardiovascular regulation dysfunction.
This study does not prove that amplified circadian rhythms cause ME/CFS fatigue, only that the association exists. The small 4-week pilot treatment trial cannot establish efficacy or optimal dosing of inopamil or definitively rule out melatonin, and open-label design means results are vulnerable to placebo effects. Causality between nighttime hypotension and symptoms remains unestablished.
About the PEM badge: “PEM required” means post-exertional malaise was an explicit required diagnostic criterion for participant inclusion in this study — not that PEM was studied, observed, or discussed. Studies using criteria that do not require PEM (e.g. Fukuda, Oxford) are tagged “PEM not required”. How the atlas works →
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