Analysis of oxygen uptake efficiency parameters in young people with cystic fibrosis

Abstract

Purpose: This study characterised oxygen uptake efficiency (OUE) in children with mild-to-moderate cystic fibrosis (CF). Specifically, it investigated (1) the utility of OUE parameters as potential submaximal surrogates of peak oxygen uptake ([Formula: see text]), and (2) the relationship between OUE and disease severity.

Methods: Cardiopulmonary exercise test (CPET) data were collated from 72 children [36 CF, 36 age- and sex-matched controls (CON)], with OUE assessed as its highest 90-s average (plateau; OUEP), the gas exchange threshold (OUE_GET) and respiratory compensation point (OUE_RCP). Pearson's correlation coefficients, independent t tests and factorial ANOVAs assessed differences between groups and the use of OUE measures as surrogates for [Formula: see text].

Results: A significant (p < 0.05) reduction in allometrically scaled [Formula: see text] and all OUE parameters was found in CF. Significant (p < 0.05) correlations between measurements of OUE and allometrically scaled [Formula: see text], were observed in CF (r = 0.49-0.52) and CON (r = 0.46-0.52). Furthermore, measures of OUE were significantly (p < 0.05) correlated with pulmonary function (FEV_1%predicted) in CF (r = 0.38-0.46), but not CON (r = -0.20-0.14). OUEP was able to differentiate between different aerobic fitness tertiles in CON but not CF.

Conclusions: OUE parameters were reduced in CF, but were not a suitable surrogate for [Formula: see text]. Clinical teams should, where possible, continue to utilise maximal CPET parameters to measure aerobic fitness in children and adolescents with CF. Future research should assess the prognostic utility of OUEP as it does appear sensitive to disease status and severity.

Keywords: Adolescence; Aerobic fitness; Exercise testing; Paediatrics; Respiratory disease.

Fig. 1

Profiles of OUEP, OUE_GET and OUE_RCP in a representative CPET from an individual child with CF (female, 12 years, homozygous ΔF508, FEV₁ 82.0%_predicted, $\dot{V}{\text{O}}_{2\text{peak}}$ 36.5 mL kg⁻¹.min⁻¹, 73.26 mL kg^−0.86.min⁻¹). Vertical line at 180 s indicates end of warm-up, and beginning of ramp phase. Vertical lines also indicate point of GET and RCP. Horizontal lines between 200–290 s = OUEP (31.9 mL L⁻¹), 240–300 s = OUE_GET (31.0 mL L⁻¹), 500–560 s = OUE_RCP (19.7 mL L⁻¹)

Fig. 2

Differences in OUE ($\dot{V}{\text{O}}_2$/${\dot{V}}_{\text{E}}$) between two representative children, CF (open square) and CON (open circle), throughout a ramp incremental CPET. Vertical line at 180 s indicates the end of the warm-up and beginning of ramp phase of the test. Vertical lines at 610 and 640 s indicate exhaustion for CF and CON participants, respectively. Solid horizontal lines at 31.9 mL L⁻¹ (CF) and 43.0 mL L⁻¹ (CON) indicate OUEP (highest 90 s average) for each group, respectively

Fig. 3

Individual differences between age- and sex-matched CON and CF pairs for CPET-derived variables. All plots are calculated as CON minus CF, i.e. bars underneath y = 0 on x-axis indicate participant with CF has a greater value than CON counterpart. a Differences in allometrically scaled $\dot{V}{\text{O}}_{2\text{peak}}$ between pairs. b Differences in OUEP between pairs, independent of differences in $\dot{V}{\text{O}}_{2\text{peak}}$. c Differences in $\dot{V}{\text{O}}_{2\text{peak}}$ (mL kg^−0.86.min⁻¹) between pairs, plotted alongside within-pair differences in OUEP (mL L⁻¹). Black bars represent $\dot{V}{\text{O}}_{2\text{peak}}$ and grey bars indicate OUEP

Fig. 4

Comparison of $\dot{V}{\text{O}}_{2\text{peak}}$ (a) and OUE parameters (b OUEP; c OUE_GET; d OUE_RCP) between CF (black) and CON (white), split by $\dot{V}{\text{O}}_{2\text{peak}}$ tertile. *Significant (p < 0.05) difference from highest tertile (within group). ^§Significant (p < 0.05) difference from middle tertile (within group). ^†Significant (p < 0.05) difference between groups (within tertile)