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Abstract

A method and device for impedance plethysmography, with relative immunity to skin-electrode contact resistance drift are provided. The method comprises: (a) placing: (i) first and second measurement electrodes on a biological object; (ii) first and second reference electrodes on opposite sides of the first measurement electrode; and (iii) third and fourth reference electrodes on opposite sides of the second measurement electrode, so as to define a measurement electrical circuit and six reference electrical circuits; (b) measuring: (i) a first electrical impedance of the measurement circuit; (ii) a second, third and fourth electrical impedances of three reference circuits which include the first measurement electrode, the first reference electrode and the second reference electrode; (iii) a fifth, sixth and seventh electrical impedances of three reference circuits which include the second measurement electrode, the third reference electrode and the fourth reference electrode; (c) calculating: (i) the skin-electrode resistance drift of the first measurement electrode based on the second, third and fourth electrical impedances; (ii) the skin-electrode resistance drift of the second measurement electrode based on the fifth, sixth and seventh electrical impedances; and (d) calculating the internal impedance of the biological object by subtracting the skin-electrode resistance drifts of the first and second measurement electrodes from the first electrical impedance.

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