Spirometry Reference Equations Including Existing and Novel Parameters

Spirometry is an essential component of pulmonary function testing, with interpretation dependent upon comparing results to normal. Reference equations for mean and lower limit of normal (LLN) are available for usual parameters, including forced vital capacity (FVC), forced expiratory volume in the first second of an FVC maneuver (FEV1), and FEV1/FVC. However, standard parameters do not fully characterize the flow-volume loop and equations are unavailable for the upper limit of normal (ULN). The aim of this study was to develop reference equations for existing and novel spirometry parameters, which more fully describe the flow-volume loop, and to compare these to previously reported equations.

Data from healthy participants in NHANES III was used to derive reference equations for existing and novel spirometry parameters accounting for birth sex, age, height, and ethnicity (Caucasian, Mexican American, Black) for ages 8 to 90 years. An iterative process determined %predicted LLN and ULN. Equations were compared to published reported equations.

Reference equations were developed for mean, LLN and ULN for existing and novel spirometry parameters for ages 8 to 90. The derived equations closely match mean values of previously published equations, but more closely fit the LLN. Mexican-American and Caucasian values were similar (within 2%) so they were combined, while Black relative to Caucasian/Mexican-American values were lower for some parameters.

These reference equations, which account for birth sex, age, height, and ethnicity for existing and novel spirometry parameters, provide a more comprehensive and quantitative evaluation of spirometry and the flow-volume curve.