A system and method for measuring the impedance and impedance changes in a body segment are disclosed. By utilizing an ECG buffer, at least one plethysmograph buffer, and concurrently performing at least extraction of an ECG waveform stored in the ECG buffer and extraction of impedance waveforms stored in the at least one plethysmograph buffer, enhanced signal-to-noise ratios of output signals of impedance plethysmographs are achieved. In an embodiment, improved waveform selection using template matching is also achieved. With template matching, a new candidate waveform is compared in shape to the previous average waveform and may be accepted for current averaging based on the comparison.