Assessment of Pulmonary Flow Using Impedance Pneumography

There is a lack of noninvasive pulmonary function measurement techniques suitable for continuous long-term measurement of tidal breathing in mobile subjects, although tidal breathing analysis has been shown to contain information that relates to the level airway obstruction. This paper is the first to assess the suitability of impedance pneumography (IP) for measurement of continuous pulmonary flow and volume signals instead of only the respiration rate (RR) or tidal volume (
VT
). We measured pneumotachograph (PNT) and IP signals simultaneously from 20 healthy male subjects in erect, dorsal supine, and lateral supine positions while voluntarily varying
VT
. IP was measured using five different impedance lead configurations with electrodes integrated into a textile chest belt. The IP signals were compared with PNT signals to assess agreement of IP with a more well-established measurement method. The pulmonary flow signal waveform agreement was assessed with standard error of measurement (SEM) between the time-differentiated IP signal and the PNT signal as ρ = 1-SEM. Additionally, we assessed the agreement of IP and PNT in
VT
estimation and the magnitude of the cardiogenic oscillation present in the impedance signal. The agreement in the pulmonary flow signal waveform shapes was found excellent at all tidal volumes and postures (mean ρ > 0.90). The agreement between the PNT-derived and the IP-derived
VT
estimates was very high when IP values were calibrated per subject and posture (mean difference <;3%). The main source of error in visual inspection of the IP signal was the cardiogenic distortion. From the five novel electrode configurations tested, the lateral ones were found clearly better than the anteroposterior ones. IP potentially enables the development of a noninvasive ambulatory measurement device for long-term studies of certain tidal breathing parameters in mobile subjects.