Impedance pneumography: Noise as signal in impedance cardiography

Thoracic impedance is modulated by events within the respiratory cycle, whi ch represents a source of "noise" in impedance cardiography. Respiration it self, however, is a physiological rhythm of interest to psychophysiologists . We report here methods and validation for deriving impedance pneumographi c measures of respiration from impedance cardiography signals, based on sta ndard tetrapolar band electrodes. We recorded the change in impedance (Delt a Z), the first derivative of the change in impedance (dZ/dt), output from a strain-gauge respirometer, and criterion spirometry from eight healthy ad ults during rest, paced breathing, abdominal breathing, thoracic breathing, and a mental arithmetic task. Transfer function analyses revealed that a D elta Z(d) Signal (derived by integration of the dZ/dt signal) provided the best estimate of the criterion spirometric measure for all parameters (cohe rence, phase, and gain), accounting for almost 90% of the variance in respi ratory waveform morphology. The results document thr potential utility of i mpedance pneumography, as derived from standard impedance cardiography sign als.