Computed cardiopulmonography: Effects of physical characteristics on lung parameter estimates

Computed cardiopulmonography (CCP) is a technique that measures lung volumes (functional residual capacity and deadspace) together with novel parameters reflecting lung inhomogeneities (non-uniformities in lung inflation and deadspace path length). First, highly precise measurements of gas exchange are made during a nitrogen washout with a purpose-built molecular flow sensor. Second, an individual's lung physiology is then described by personalising the parameters of a bespoke cardio-respiratory model obtained by fitting the model to the data. The present study examines the effects of participants' physical characteristics on these parameter values, and from this also provides preliminary estimates for normal ranges. Data from 92 healthy individuals (27% female, age 40 ± 19 (mean ± SD) years, height 1.75 ± 0.09 m, mass 74 ± 14 kg) were used. A prediction equation for each CCP parameter was written as: y = α + βln(age) + γln(height) + δln(BMI) + ε(is_Female) + error, where BMI is body mass index. Non-significant terms (P > 0.1) were removed sequentially to identify just the significant characteristics. Physical characteristics exerted a large influence on volume-related CCP parameters. In contrast, only age had a significant influence on inhomogeneity-related CCP parameters. The prediction equations, together with their mean squared errors, were used to calculate z-scores for CCP data from three previously published studies in asthma, chronic obstructive pulmonary disease, and early cystic fibrosis. Values for these z-scores often lay beyond those commonly used to define a normal range (±1.65). In conclusion, reference values for inhomogeneity-based CCP parameters may only need correcting for age, and often appear as abnormal in airways disease.