Child-specific thoracic gas volume prediction equations for air-displacement plethysmography

Objective: To develop child-specific thoracic gas volume (TGV) prediction equations for use in air-displacement plethysmography in 6- to 17-year-old children. Research Methods and Procedures: Study 1 developed TGV prediction equations using anthropometric variables after completing a measured TGV and air-displacement plethysmography test in 224 healthy boys and girls (11.2 +/- 3.2 years, 45.3 +/- 18.7 kg, 149.9 +/- 18.5 cm). Study 2 cross-validated the prediction equations in a separate cohort of 62 healthy boys and girls (11.2 +/- 3.4 years, 44.2 +/- 15.3 kg, 149.4 +/- 19.3 cm). Results: In Study 1 (development of TGV prediction equations), the quadratic relationship using height as the independent Variable and the measured TGV as the dependent variable yielded the highest adjusted R-2 and the lowest SE of estimate in both genders, thus producing the following prediction equations: TGV = 0.00056 x H-2 - 0.12422 x H + 8.15194 (boys) and TGV = 0.00044 x H-2 - 0.09220 x H + 6.00305 (girls). In Study 2 (cross-validation), no significant difference between the predicted and measured TGVs (-0.018 +/- 0.377 liters) was observed. The regression between the measured TGV and the predicted TGV yielded a slope and intercept that did not significantly differ from the line of identity. Prediction accuracy was good as indicated by a high R-2 (0.862) and low SE of estimate (0.369 liters). Discussion: The new child-specific TGV prediction equations accurately, precisely, and without bias estimated the actual TGV of 6- to 17-year-old children.