Oxygen uptake efficiency slope measured by cardiopulmonary exercise testing: applicability analysis of the available prediction equations in a Brazilian healthy sample
Authors: Milani J G P O , Milani M , Cipriano G F B , Cipriano Junior G 
Published: May 2023

Abstract

Funding Acknowledgements
Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) and Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq).

Background
Oxygen uptake efficiency slope (OUES) measured by cardiopulmonary exercise testing (CPET) is a measure derived from submaximal oxygen uptake values and has prognostic significance in heart failure patients. Measured values are compared to reference standards for an adequate individual assessment. However, current reference values prediction equations have applicability limitations due to differences in ergometer and sample characteristics (age range and nationatilies), which may impact external validation, as international heterogeneities in peak oxygen uptake values have already been demonstrated by Milani et al. and Peterman et al.

Purpose
To analyze the applicability of the available prediction equations for OUES in a healthy Brazilian sample from the Midwest region.

Methods
Cross-sectional study of subjects assessed by treadmill CPET in the Brazilian Midwest region between January/2011 to March/2020. The inclusion criteria were CPET performed on a treadmill in healthy subjects aged 20 years or older, and with respiratory exchange ratio ≥ 1.0. The exclusion criteria were any history of cardiovascular or pulmonary disease, presence of cardiovascular risk factors (such as hypertension, diabetes mellitus, current smoking, and obesity) and abnormalities on CPET. The following available prediction equations were used for comparisons with the measured OUES: 1) Buys et al. from Belgium/Netherlands; 2) Hollemberg et al. from United States; 3) Sun et al. from United States; 4) Brazilian prediction equations calculated in our same sample using sex, age and anthropometric variables. Statistical comparisons between measured and predicted OUES were performed using Spearman correlation test and Bland-Altman agreement analysis.

Results
During the study period, 7,843 CPETs were performed and included for eligibility. After applying the inclusion and exclusion criteria, 3,544 assessments of healthy individuals were included (1,574 women; 1,970 men; age 20 to 80 years). All correlations between measured and predicted values were significant, with rho ranging from 0.325 to 0.396 in females and from 0.391 to 0.450 in males (Figure 1). The mean errors by the Bland-Altman agreement analysis were heterogeneous between the OUES predition equations, with better results in our Brazilian equation. Greater bias were observed in the equation by Sun et al. for both sexes, in the equation from Buys et al. for females and in the equation by Hollemberg et al. for males (Figure 2).

Conclusions
The applicability analysis of the international prediction equations for OUES revealed great heterogeneity, limiting the external validation of the available equations, and highlighting the importance of using country-specific reference values for OUES to ensure a correct individual evaluation.