The measurement of the complex respiratory impedance at a high temporal resolution is described. The measurement of impedance is correlated with the breathing cycle using electrical transthoracic impedance. This allows the determination of the complex impedance at any fixed point in the respiratory cycle, which results in lower variability in the measured data when compared to the original device. The respiratory impedance in normal subjects fluctuates during the breathing cycle and has two maxima during a single breath, which occur at peak inspiratory and expiratory flow. In addition, the measurement of impedance at a high temporal resolution enables the observation of novel features in the impedance which appear to be associated with certain respiratory disorders.