A new method for computer-assisted determination of airways resistance

Conventional methods for determining airways resistance, based on the recording of pressure and flow as X-Y displays, may yield inconsistent results because airways resistance is only one of a number of factors determining the shape of such displays. The temporal behavior of alveolar pressure and flow during panting suggests that the relationship between pressure and flow should be formulated in terms of differential equations. An equation is postulated to include terms characterizing resistance, gas inertance, and the behavior of the lungs as a number of parallel compartments with time constants that may be different. A simple algorithm allows these terms to be deduced from measured pressure and flow signals. Measurements obtained using the new method correlate well with those obtained using conventional methods. Variation of specific airways conductance is significantly reduced when compared with values obtained by conventional methods. Measured values for inertance agree well with theoretically predicted values.