Comparative measurements of airway resistance.

Three different ways to calculate airway resistance with the whole body plethysmograph during spontaneous breathing and the MBC maneuver were tested on normal subjects and patients with obstructive airway disease. The 'effective resistance values' calculated by applying periodic electric current theory correlate well with a linear interpolation of the various alveolar pressure-flow loops. These apparent linear airway resistance values are as good as the procedure described by Jaeger and Otis, based on the main assumption of sinusoidal flow, to calculate airway resistance. The difficulties in assessing the ventilated lung volume, e.g. in patients with obstructive airway disease, justifies use of the 'apparent resistance values' which are easy to calculate for clinical testing.