Scaling the Oxygen Uptake Efficiency Slope for Body Size in Cystic Fibrosis

Abstract

PURPOSE: The aim of this study was to describe the relationship between body size and the oxygen uptake efficiency slope (OUES) in paediatric patients with cystic fibrosis (CF) and healthy controls (CON), in order to identify appropriate scaling procedures to adjust the influence of body size upon OUES. METHODS: The OUES was derived using maximal and submaximal points from cardiopulmonary exercise testing in 72 children (36 CF and 36 CON). OUES was subsequently scaled for stature, body mass (BM) and body surface area (BSA) using ratio-standard (Y/X) and allometric (Y/X) methods. Pearson's correlation coefficients were utilised to determine the relationship between body size and the OUES. RESULTS: When scaled using the ratio-standard method, OUES had a significant positive relationship with stature (r = 0.54, P < 0.001) and BSA (r = 0.25, P = 0.031) and significant negative relationship with BM (r = -0.38, P = 0.016) in the CF group. Combined allometric exponents (b) for CF and CON were: stature 3.00, BM 0.86, BSA 1.40. A significant negative correlation was found between OUES and stature in the CF group when scaled allometrically (r = -0.37, P = 0.027). Non-significant (P > 0.05) correlations for the whole group were found between OUES and allometrically scaled BM (CF: r = -0.25, CON: r = 0.15) and BSA (CF r = -0.27, CON r = 0.13). CONCLUSIONS: Only allometric scaling of either BM or BSA, and not ratio-standard scaling, successfully eliminates the influence of body size upon OUES. Therefore this enables a more direct comparison of the oxygen uptake slope between patients with CF and healthy controls.