Does asthma-like increased breathing load influence impedance pneumography signal?

Asthma is a chronic disease characterized by recurrent attacks of breathlessness and wheezing. During an asthma attack, a bronchospasm occurs. In order to overcome increased resistance of airways forced breathing is necessary. It affects the intrapleural pressure, blood volume within the thoracic cavity and therefore it may affect also impedance pneumography signal. We tried to imitate asthma-like conditions by increasing breathing load in to find out, whether it influences impedance pneumography signal. Forced breathing was performed as a respiration through adjustable respiratory loads. The study subjects breathed through 4, 7 and 10 cmH2O*s/liter breathing loads, at 6 and 12 breathes per minute rates. A calibration coefficient between tidal volume and impedance pneumography and the effect of breathing load on cardiac component of impedance pneumography signal were determined. We found that forced respiration did not significantly affect the impedance pneumography signal, thus it seems unlikely that asthma-like bronchospasms will disturb calibration of the impedance pneumography signal. Thus it is likely, that this technique can reliably measure respiratory parameters during long-term ambulatory monitoring of patients with asthma.