To assess the sympathetic-parasympathetic balance in individuals with fibromyalgia (FM), and its response to orthostatic stress, by power spectral analysis of heart rate variability.
We studied 19 women with FM and 19 age matched controls. A high resolution electrocardiogram was obtained in supine and standing postures after achieving a stable heart rate. Spectral analysis of R-R intervals was done by the fast Fourier transform algorithm.
Analyses of the different frequency components revealed significant difference between the 2 groups in the low frequency (0.050-0.150 Hz) band, which reflects modulation of the sympathetic nervous system. Controls displayed an increased power spectral density upon standing (+0.081 +/- 0.217 Hz); individuals with FM had a discordant response (-0.057 +/- 0.097 Hz) (p = 0.018).
In FM, there is a deranged sympathetic response to orthostatic stress. This abnormality may have implications regarding the pathogenesis of FM.