We appreciate the interesting and important comments by Linden and Diehl. Interpretation of LF oscillations of HR is complex and remains a matter of discussion. Likewise, the validity of the LF/HF ratio as an index of "sympatho-vagal" balance is also a matter of heated debate. We agree that assuming that the LF/HF ratio is an indicator of sympathetic and parasympathetic tone, particularly in the supine position, may be overly simplistic. However, due to limitations during the performance of the Wada test and subsequent angiographic studies we were unable to evaluate the performance of the role of orthostatic changes in these subjects. As clearly stated in the "Comment" section of our article,1 we do not assume that LF oscillations are an indicator of sympathetic tone.
Yoon B, Morillo CA, Cechetto DF, Hachinski V. Spectral Analysis of Heart Rate: Interpretational Limitations—Reply. Arch Neurol. 1998;55(2):264-265. doi: