Impedance measurement during air and helium-oxygen breathing before and after salbutamol in COPD patients.

Abstract

1. The forced oscillation technique is an effort-independent method used to characterize the mechanical impedance of the respiratory system. To support the hypothesis that non-invasive partitioning of total pulmonary resistance is possible by this technique, impedance was measured during air breathing and after equilibration with a mixture of 80% helium (He) and 20% oxygen (O2) in 21 chronic obstructive pulmonary disease (COPD) patients by means of a forced pseudo-random noise pressure signal over a frequency spectrum from 4 to 52 Hz. Furthermore, during inhalation of both gas mixtures impedance was determined before and after inhalation of 0.400 mg Salbutamol. 2. He + O2 breathing caused less negative frequency dependence of resistance and a significant decrease in reactance over the range 16-52 Hz. Inhalation of Salbutamol caused a marked increase in reactance values over the range 8-40 Hz. However after equilibration with the He + O2 mixture, Salbutamol caused a significant decrease in resistance and a significant increase in reactance at all frequencies. 3. The results during He + O2 breathing are in accordance with a partitioning of airways resistance into central and peripheral components. The decrease in reactance during He + O2 can be explained by a density dependent decrease in inductive reactance. By comparing the impedance data during air and He + O2 breathing, it can be concluded that a distribution of pulmonary resistance with minimal losses in the larger airways is more sensitive for detecting changes in the peripheral airways in COPD patients.