Bioimpedance profiling of limb lymphoedema

Abstract

Bioelectrical impedance spectroscopy (BIS) has found a place in the quantitative assessment of lymphoedema of the whole limb. However, lymphoedema may be highly localised. Impedance, measured at a low frequency, reflects extracellular fluid including lymph, not simply total volume unlike other methods of lymphoedema assessment. It may also provide information about tissue composition (Cornish and Ward, this conference) and thus it would be of great value to develop localised tissue impedance assessment. We report here proof of concept data for localised BIS. Impedance was measured (ImpediMed SFB7) for 2.5 cm segments along each arm, commencing at the ulnar styloid processes, in female subjects. Segmental limb volume data were also obtained using perometry as a reference method. The apparent resistivity of arm tissue was calculated and used to estimate the volume of each 2.5 cm segment for comparison with the corresponding perometry values. Segmental impedances were highly correlated (r > 0.85) with perometric volumes. Although impedance-derived segmental volumes and those by perometry were similarly highly correlated, the absolute magnitudes of the differences varied between segments, reflecting differences in apparent resistivity due to differing tissue composition, e.g. bony (elbow) versus lean regions (midforearm). The method was further refined using specially designed electrodes and software to allow measurement resolution to < 1 cm. This study demonstrates that impedance profiling of the arm, to at least 10 mm resolution, is practical. Such measurements not only relate directly to tissue volume but can also provide information of tissue composition in lymphoedema. © Springer-Verlag 2007.