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

Tomlinson OW, Barker AR, Oades PJ, Williams CA.

Med Sci Sports Exerc. 2017 May 9. doi: 10.1249/MSS.0000000000001314. [Epub ahead
of print]

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.