Computation of the equivalent airway resistance: a comparison with routine evaluations of plethysmographic...

Equivalent (effective) values of airway resistance were determined for total breaths, inspiration and expiration in spontaneously breathing patients by means of an off-line processing system. An improvement in the alveolar pressure determination was achieved by subtracting thermal pressure drifts of the pressure plethysmograph and by taking into account instantaneous values of the intrathoracic gas volume. Equivalent resistance values were compared with the results of several simulated routine evaluations. It was found that the equivalent resistance is best approximated by the graphical procedure using average pressure points at +/- 0.5 liter/sec flow levels.