1. Chronic low blood pressure has been associated with fatigue and low mood. However, in the chronic fatigue syndrome (CFS) the blood pressure (BP) and heart rate profile and their variabilities have not been characterized as yet.

2. We performed office and 24 h ambulatory BP recordings in 38 subjects (age, 34.8 ± 8.0 years) who fulfilled the Holmes criteria for CFS and in 38 healthy control subjects (age 35.6 ± 10.5 years), as well as short-term beat-to-beat BP and RR-interval recordings for 10 min in supine and standing position, and calculated spectral indices.

3. In CFS office (123 ± 19/70 ± 12 mmHg) as well as 24-h, day- and night-time blood pressure values (116 ± 11.1/71 ± 11.1, 121 ± 9.2/77 ± 8.0 and 110 ± 10.5/65 ± 9.2 mmHg respectively) were within reference limits.

4. Heart rate was consistently higher (P < 0.01) in CFS patients, based on both office (77 ± 12 compared with 68 ± 12 beats min−-1) and 24 h ambulatory recordings (77 ± 12 compared with 67 ± 15 beats min−-1).

5. In supine position, spectral indices of BP variability (total, low-frequency and high-frequency variances) were all significantly (P < 0.01) lower in CFS. In standing position the differences disappeared. Analysis of RR-interval variability could not detect major alterations in autonomic function in CFS.

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