Determination of respiratory resistance by an oscillation method. Studies of long-term and short-term variability and dependence upon lung volume and compliance.

The respiratory resistance (Ros) as measured by an oscillation method, and the airway resistance (Raw) as measured by body plethysmography were determined in 10 healthy volunteers thrice daily every week over a period of 22 weeks. Ros in 9 of this group was measured at different breathing levels at constant respiratory rate and volume. Additionally, the phase angle between oscillatory pressure and flow (phi), the thoracic gas volume, the end-tidal volume, the functional residual capacity, Raw and the lung compliance were determined. Furthermore Ros of 116 patients was measured together with the lung and thorax compliance. Compared to Raw, the variability of Ros is smaller and the sensitivity is higher. There is a reciprocal relationship between Ros and lung volume, lung compliance, and compliance of the lung and thorax system. Therefore, measurements of Ros should be performed at a normal, stabilized mean breathing level.