Sympathetic overactivity in subjects complaining of unexplained fatigue

1. Theoretical and practical considerations suggest that in subjects complaining of fatigue, in the absence of evident organ dysfunction, an alteration in the autonomic nervous system might be present as a functional correlate. 2. Autoregressive spectral analysis of R-R interval variability from a surface EGG, was used in healthy control subjects (n=24, age 45 \ub1 4 years) and in subjects complaining of unexplained fatigue (n=53, age 46 \ub1 9 years) to obtain quantitative indices of the state of the sympathovagal balance, both at rest and during a mental stimulus (mental arithmetic), capable of enhancing sympathetic drive. Sympathetic and vagal modulations were inferred from the normalized powers of the low frequency and high frequency spectral components respectively. 3. We observed in patients, at rest, a prevailing low frequency component of R-R variability (patients low frequencys 73 \ub1 11, control subjects 51 \ub1 10 normalized units, P