Whole-body and Thoracic Bioimpedance Measurement: Hypertension and hyperhydration in Hemodialyisis patients

Mono-frequency (50 kHz) and multi-frequency (3 kHz - 1 MHz) whole-body and thoracic segment bioimpedance measurement were doing before and after hemodialysis session in 20 patients. The patients were classified in hypertensive or non-hypertensive according to the mean blood pressure, BPmean. The relation between hyperhydration in thorax segment through real part of impedance and mean blood pressure was analyzed. Also the bioelectrical impedance vector analysis method was used to analyze the displacement of Z/H vector in order to establish the relation with hyper-hydration (edema). Finally we made multi- frequency measurements with the objective to find a significative change in high and low frequency. We obtained a significant difference (P<0.05) in impedance parameters before and after HD session. Some patients are located in hyper-hydration zone, below the inferior pole of the 75% tolerance ellipse, whereas others patients were within the tolerance ellipses. The real part of the impedance in thorax region can identify over-hydrated patients with an increased risk for cardiovascular disease associate to hypertension. Multi-frequency bioimpedance measurement show an important change at low and high frequency and indicate that is possible to obtain more information about extra-cellular or intra-cellular fluid status, to find the relation between fluid loads, bioimpedance parameters, extra-cellular water, and blood pressure.