Abstract: A device to measure tissue impedance comprises drive circuitry coupled to calibration circuitry, such that a calibration signal from the calibration circuitry corresponds to the current delivered through the tissue. Measurement circuitry can be coupled to measurement electrodes and the calibration circuitry, such that the tissue impedance can be determined in response to the measured calibration signal from the calibration circuitry and the measured tissue impedance signal from the measurement electrodes. Processor circuitry comprising a tangible medium can be configured to determine a complex tissue impedance in response to the calibration signal and the tissue impedance signal. The processor can be configured to select a frequency for the drive current, and the amount of drive current at increased frequencies may exceed a safety threshold for the drive current at lower frequencies.

Abstract: An adherent device to monitor a tissue hydration of a patient comprises an adhesive patch to adhere to a skin of the patient. At least four electrodes are connected to the patch and capable of electrically coupling to the patient. Impedance circuitry is coupled to the at least four electrodes to measure a tissue resistance of the patient, where the circuitry is configured to determine the tissue hydration in response to tissue resistance. The circuitry may comprise a processor system and the tissue resistance may correspond to a change in patient body fluid. The impedance circuitry is configured to measure the hydration signal using at least one low measurement frequency, which may be in the range of 0 to 10 kHz. Multiple measurement frequencies may be used and the hydration signal may include a tissue reactance measurement.