Conference poster displayed at the Clinical Trials Symposium, RD&E Exeter, 5/11/15

Barker, A. R.

Chubbock, L. V.

Oades, Patrick

Saynor, Z.

Stevens, D

Tomlinson, Owen

Williams, Craig A.

RD&E Research Repository

Oxygen uptake efficiency slope is not a valid submaximal measure of aerobic capacity  in paediatric cystic fibrosis patients Introduction  • Patients with cystic fibrosis (CF) with higher maximal oxygen consumption   (VO2 peak) have significantly higher survival rates.1   • Aerobic fitness testing based on maximal effort - patients with CF may be unable or unwilling  to reach volitional exhaustion - submaximal measures could be more practical.2   • Oxygen uptake efficiency slope (OUES) is a submaximal parameter showing the relationship between oxygen uptake (VO2) and the common logarithm of minute ventilation (Log VE)3   • OUES at 80% duration is valid in adults with CF4 but not in a paediatric population as only moderately correlated with VO2 peak5   • Standardisation of OUES to %duration of the test is flawed as not  representative of each individual’s exercise intensity relative to their metabolic boundaries.   • Oxygen uptake efficiency (OUE) is the ratio of VO2 to VE6 other submaximal indicators include gaseous exchange  threshold (GET), respiratory compensation point (RCP) and the plateau of highest consecutive values (OUEP).    The aim of the study was to investigate the validity of   submaximal exercise measures in the paediatric CF patients.  Methods  • Cardiopulmonary exercise test (CPET) data collected from 79 patients with CF and 31 healthy controls (13.1 ± 2.9 y , 156.0 ± 14.7 cm, 50.6 ±16.2 kg) was retrospectively analysed.  • OUE was determined at GET and RCP using a 60 s average, and OUEP with a 90 s average. Six of the 79 patients with CF did not have a detectable GET so were not included in any further analyses.  • OUES was calculated at 50%, 75% and 100% of test duration and VO2 peak, GET and RCP. Values standardised for body surface area (BSA).   • Pearson’s correlation coefficient was calculated between OUES/BSA measures and VO2 peak relative to body mass (mL.kg-1.min-1), and independent t-tests were conducted between CF and healthy groups. Results   • Descriptive statistics for participants included in the study are shown in Table 1.   Table 1. Characteristics of 104 subjects (mean ± SD)                      BMI= body mass index; BSA= body surface area; FVC= Forced vital capacity; FEV1= Forced expiratory volume in 1 s  • VO2 peak (mL.kg-1.min-1) and OUE/BSA at GET, RCP and plateau were significantly lower in adolescents with CF than healthy adolescents (Table 2).  Table 2. CPET Exercise Variables (mean ± SD)                          WR=work rate, HR= heart rate, RER= respiratory exchange threshold;  * p< 0.05 Results  • Significant moderate correlations between OUES/BSA and peak VO2 adjusted to body mass for  adolescents with CF and healthy controls, at all intensities, durations and thresholds (p< 0.01), shown in Table 3. Correlations were moderate (0.332 - 0.601) in adolescents with CF, but moderate to strong in healthy adolescents (0.497 - 0.800).   Table 3. Correlations between OUES/BSA and Peak VO2 (mL.kg-1.min-1) at the different thresholds                                     ** p< 0.01   • No significant difference in OUES/BSA between healthy adolescents and adolescents with CF at any of the thresholds of the CPET (see Figure 1).                        Figure 1. Comparison of OUES/BSA values between adolescents with CF and healthy adolescents at different exercise thresholds. L.V. Chubbock1,  A.R. Barker1, O.W. Tomlinson1, Z. Saynor1, D. Stevens2, P. J. Oades3, C.A. Williams1,3 1Children’s Health & Exercise Research Centre, University of Exeter, UK; 2Faculty of Medicine, Dalhousie University, Halifax, Canada;  3Royal Devon and Exeter NHS Foundation Trust Hospital, Exeter, UK.  Adolescents with CF n=73 Healthy adolescents n=31 p-value Gender (m/f) 46/27 10/21 Age (y)  13.16 ± 2.88 12.94 ± 3.02        p= 0.169 Stature (cm) 156.0 ± 15.5     155.9 ± 13.1   p= 0.981 Body mass (kg) 52.31 ± 17.55      46.58 ± 11.96      p= 0.100 BMI (kg.m-2) 20.84 ± 3.72        18.83 ± 2.43 * p= 0.007 BSA (m2) 1.50 ± 0.33          1.41 ± 0.24          p=0.193 FVC 3.10 ± 1.17         n=72 FVC % predicted 97.74 ± 16.82     n=71 FEV1 2.80 ± 1.00         n=72 FEV1 % predicted 95.10 ± 14.45     n=71 OUES/BSA threshold CF Healthy 50%VO2 peak 0.398** 0.497** 75% VO2 peak 0.487** 0.710** 100% 0.601** 0.800** GET 0.332** 0.524** RCP 0.557** 0.800** Discussion  • Despite significant correlations between OUES/BSA and VO2 peak at all thresholds, OUES/BSA was not significantly different between healthy adolescents and those with CF at any threshold point, supporting Bongers et al.5 that OUES is not a valid submaximal measure in adolescents with CF.   • A novel finding was adolescents with CF had significantly lower values than healthy adolescents for OUE@GET/BSA, OUE@RCP/BSA and OUEP/BSA  • GET occurred at 53% of VO2 peak in this sample of 73, so OUE at this threshold could be more representative of the individual’s ability to cope with sub-threshold activity demands compared to exercise above the threshold point.  • OUE & OUEP could provide alternative measure for adolescents unable to reach volitional maximum.   Conclusion:  OUES is not a valid submaximal measure of aerobic capacity in adolescents with CF, however OUE & OUEP as alternative measures should be investigated.  Adolescents with CF n=73 Healthy adolescents n=31 p-value WRpeak (W) 162 ± 73               154 ± 60               p=0.522 VO2peak (L.min-1) 1.86 ± 0.68           1.91 ± 0.82           p=0.748 VO2peak (ml.kg-1.min-1) 37.03 ± 6.88         41.05 ± 10.55 * p=0.023 GET (L.min-1) 0.96 ± 0.34           1.06 ± 0.47           p=0.295 GET (%VO2peak) 53.27 ± 9.57         55.91 ± 7.37        p=0.133 VEpeak 78.26 ± 33.81       60.42 ± 30.03  *     p=0.010 OUE@GET/BSA 24.62 ± 6.73     n=72 31.60 ± 5.16 * p=0.000 OUE@RCP/BSA 20.58 ± 5.86     n=72 26.07 ± 4.92 * n=27  p=0.000 OUEP/BSA 25.25 ± 6.42         33.03 ± 6.16 * p=0.000 References 1. P. A. Nixon et al. (1992). The prognostic value of exercise testing in patients with cystic fibrosis. N Engl J Med 327:1785-1788 2. C.A. Williams et al. (2014). Cystic fibrosis and physiological responses to exercise. Expert Rev Respir Med 8(6):751-762 3. R. Baba et al. (1996). Oxygen uptake efficiency slope: A new index of cardiorespiratory functional reserve derived from the relation between oxygen uptake and minute ventilation during incremental exercise. J Am Coll Cardiol 28:1567-1572 4. M. Gruet et al. (2010).  Clinical utility of the oxygen uptake efficiency slope in cystic fibrosis patients. J Cyst Fibros 9:307-313 5. B.C. Bongers et al. (2012). Validity of the oxygen uptake efficiency slope in adolescents with cystic fibrosis and mild-to-moderate airflow obstruction. Pediatr Exerc Sci 24:129-141 6. X. Sun, J.E. Hansen and W.W. Stringer (2011). Oxygen uptake efficiency plateau: physiology and reference values. Eur J Appl Physiol 112:919-928  % VO2 peak 

Oxygen uptake efficiency slope is not a valid submaximal measure of aerobic capacity in paediatric cystic fibrosis patients

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Oxygen uptake efficiency slope is not a valid submaximal measure of aerobic capacity in paediatric cystic fibrosis patients

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