Background In contrast to the conventional parameters of airway dynamics mostly obtained by the two-point approximation method, the effective specific airway resistance (sReff), its reciprocal value the effective specific airway conductance (sGeff) resp., obtained by the integration of the entire tidal breathing loop, features promising target parameters for differentiating between individual functional disease patterns. sReff can be computed as the ratio between the integral of the area enclosed by the plethysmographic shift volume–tidal flow loop, featuring the specific aerodynamic work of breathing (sWOB), and the tidal flow–volume loop, sGeff by the ratio of the integral of the tidal flow–volume loop and the sWOB, respectively. However, normative values for sWOB, sReff and sGeff at resting level are not yet available.
Methods We aimed to define reference equations in healthy infants (n=28), children (n=47) and adults (n=273), which incorporates not only the standard anthropometric measures, but also lung volume and breathing pattern indices (including both volume and time indices). Retrospectively exported data were collected from databases of 5 Swiss lung function centres, in which plethysmography (Jaeger Würzburg, Germany) was performed using standard techniques (ATS-ERS criteria) for the assessment of airway dynamics, static lung volumes and forced breathing flow-volume loops.
Results Using multi-linear modelling, reference equations of sReff, sGeff, and sWOB could be defined taking as independent parameters apart from anthropometric parameters, also parameters given by the ratio between the tidal volume (VT) and functional residual capacity (FRCpleth), and the ratio between VT and inspiratory time (VT/TI).
In addition, we examined the effect of age on the breathing pattern, the relationship between breathing pattern (tidal volume) and timing (inspiratory time).
Conclusions An alternative statistical approach to define reference equations of airway dynamics reveals that apart from the subject’s anthropometric measurements, parameters of the magnitude of static lung volumes, the breathing pattern, and the timing of breathing are co-variants of reference equations of airway dynamics over a large age range.