On the Advantages of Specific Airway Resistance

Abstract

Summary: The specific airway resistance (SR_aw) is a relatively precise parameter of bronchial quality and in normal children its relation with body length, although very significant (P < 0.001), is so poor that it can safely be disregarded (Fig. 4). Also the dispersion around the mean value remains stable at any body size (Fig. 4). Contrasting with the inverse relation between airway resistance (Raw) and lung volume, SR_aw does not show any systematic variation with lung filling (Fig. 5). These data are consistent with the new formulas: SR_aw = tg β; (P_B – P_H2O) and R_aw = SR_aw/TGV in which tg β; stands for the relation between the plethysmographic box volume and breathing flow fluctuations (Fig. 2); P_B – P_H2O represents the ambient pressure corrected for water vapor pressure at body temperature; TGV is the thoracic gas volume at mean expiratory level. In disease SR_aw varies more rapidly and markedly with any alteration of the airways than does R_aw (Fig. 6). Consequently, a normal value for SR_aw would indicate that both Raw and TGV must be in a normal range.

Speculation: For those who operate with a whole body plethysmograph the authors purpose to use specific airway resistance more frequently for the study of lung mechanics in children. It is a reliable parameter which can be measured very quickly and this should enhance knowledge about the mechanism of many lung diseases in pediatrics.

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