Validity of new 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.