Estimation of Extracellular Volume by a Two‐Frequency Measurement

Abstract: An approach to determine intra‐ and extracellular conduction on the basis of Bode analysis is presented. Estimation of the ratio between intra‐ and extracellular conduction could be performed by phase measurement only, midrange in the bandwidth of interest. An important feature is that the relation between intra‐ and extracellular conduction can be continuously monitored by phase measurement and no curve fitting whatsoever is required. Based on a two‐frequency measurement determining Re at 4 kHz and ϕmax at 64 kHz, it proved possible to estimate extracellular volume (ECV) in 23 patients. Reference values on ECV were determined by sodium bromide. The results show a good correlation (r= 0.90) with the reference method. The average error of ECV estimation was −3.6% (SD 8.4).