Thoracic impedance is modulated by events within
the respiratory cycle, which represents a source of “noise”
in impedance cardiography. Respiration itself, however,
is a physiological rhythm of interest to psychophysiologists.
We report here methods and validation for deriving impedance
pneumographic measures of respiration from impedance cardiography
signals, based on standard tetrapolar band electrodes.
We recorded the change in impedance (ΔZ),
the first derivative of the change in impedance (dZ/dt),
output from a strain-gauge respirometer, and criterion
spirometry from eight healthy adults during rest, paced
breathing, abdominal breathing, thoracic breathing, and
a mental arithmetic task. Transfer function analyses revealed
that a ΔZd signal (derived by integration
of the dZ/dt signal) provided the best estimate
of the criterion spirometric measure for all parameters
(coherence, phase, and gain), accounting for almost 90%
of the variance in respiratory waveform morphology. The
results document the potential utility of impedance pneumography,
as derived from standard impedance cardiography signals.