Ambulatory impedance pneumography device for quantitative monitoring of volumetric parameters in respiratory and cardiac applications

Aims: The estimation of respiratory flow and volume parameters is difficult to perform and uncomfortable for the patient during long-term monitoring outside the clinical environment. It is also hard to perform during sleep due to the usage of a facemask. The impedance pneumography (IP) device allows monitoring of breathing activity, estimates the respiratory rate and provides the quantitative measurements of the static and dynamic respiratory parameters, e.g. tidal volume (TV) or peak expiratory flow (PEF). A miniaturized, Holter-type impedance pneumography device, Pneumonitor, with analog output and intrinsic digital memory, was designed and constructed. The system allows long-term assessment of ventilation by measuring changes in thoracic impedance using the tetrapolar method. Methods: The Artificial Patient module was used to check the stability of the amplitude and frequency of the application current (sinusoidal, 100kHz, 250μA) and to calibrate the measurements obtained by the IP device by finding the transfer function between voltage and impedance. Impedance values obtained by the IP device from patients were compared those from another bioimpedance measuring device in different electrode placement configurations in patients (for cardiac and respiratory applications). The volume-related impedance signal was also compared with the volume signal calculated from pneumotachometry (PNT). These measurements were conducted in a group of 12 young, healthy volunteers (8 male). Results: The comparison of impedance values from the IP device with those from another one bioimpedance measuring showed high agreement in all tested electrode configurations. High values of determination coefficients (R²), describing the fit of the linear regression model relating corresponding IP and PNT signals, varied in the range of 0.934 to 0.997 (average: 0.985). However, the differences between average tidal volume parameters (calculated for each subject) derived from - P and PNT are statistically significant, although negligible (average relative error is 3.2%; 1.9% min., 7% max.). Conclusion: Preliminary results show that our portable IP device provides impedance values related to respiratory activity according to a formula obtained individually for each subject. An impedance pneumography signal describing volumetric parameters could be used in analysis of respiratory and cardiac activities, e.g. might be helpful in asthma monitoring or autonomous nervous system testing.