Method and apparatus for selecting differential input leads

An physiological data acquisition apparatus includes three or more leads, at least one AC current source, a switching mechanism structured to selectively couple the current source to selected lead pairs to inject an AC current across the selected lead pairs which produces an AC voltage across the selected lead pair, and a processing device. The processing device is structured to (i) determine an impedance across the current selected lead pair based on the AC voltage, (ii) determine whether the impedance is less than a predetermined threshold, (iii) if the impedance is less than the predetermined impedance threshold cause the current selected lead pair to be used for generating physiological parameter data, and (iv) if the impedance is not less than the threshold cause the switching mechanism to couple the at least one AC current source to a new selected pair of the leads.