A simplified approach to the measurement of specific airway resistance.

A simple algebraic manipulation of known formulas leads to a direct expression for the specific airway resistance (SRaw) which precludes separate measurements of the airway resistance (Raw) and the thoracic gas volume (TGV). The equation is: SRaw = tg beta (PBar - PH2O) e2, in which tg beta stands for the relation between the plethysmographic box volume and pneumotachograph flow fluctuations; PBar - PH2O is the barometric por graphical units. Thanks to this new formula SRaw can now be easily measured with great precision and quickly calculated, even in the case of those children (Table 1) with whom this was not previously possible. No further cooperation is needed than breathing at a normal rate through mouthpiece into a whole-body plethysmograph. The intraindividual coefficient of variation (CV) for SRaw is about 8% and never exceeds 15% (Table 1).