Heart rate variability after complete autonomic blockade in man.

In a number of studies, using the autoregressive model for frequency domain analysis of R-R interval fluctuations, the low frequency (LF) component (centered at about 0.1 Hz) is claimed to index sympathetic activity level. The aim of this study was to investigate the mediation mechanism of the LF component by pharmacological blockade. Our results support earlier findings, obtained with the use of fast Fourier transformation, that in supine subjects spectral components of R-R interval variability at around 0.1 Hz are mediated mainly by cholinergic mechanisms. Therefore, the use of the LF component as sympathetic index appears questionable.