Fig. 2From: Non-invasive venous waveform analysis (NIVA) for volume assessment in patients undergoing hemodialysis: an observational studyRepresentative waveforms in the time and frequency domains. Raw waveform (top) and fast Fourier transform (bottom) of signals taken (a) prior to and (b) post-dialysis. (c) Description of technique for calculation of a NIVA value. c1–3 are weighted constants, pf0-f2 represent the powers of f0-f2Back to article page