Statistical analyses
All data are expressed as mean ± standard deviation (SD) for continuous
variables. Categorical data are expressed as absolute values and
percentages. All data was tested for normality using the
Kolmogorov-Smirnov statistical test. Pearson’s correlation coefficients
(r) or Spearman’s coefficients (rho) were used to determine
relationships between haemodynamic and echocardiographic responses.
VO2 was averaged every 10 seconds and were linked with
corresponding S’ values every minute. E’, LVEF, GLS and circumferential
strain values were linked with corresponding S’ values at rest, 5
minutes and when the RER was over 1. Values at rest, at 5 minutes and
when RER was over 1 were compared using one-way ANOVA and Tukey post-hoc
analyses to determine differences between groups. A scatter plot with
95% confidence interval was plotted. The augmentation curve was
investigated in more detail (LVEF, systolic and diastolic volumes, LVOT
VTI and GLS) and correlated with corresponding VO2peak
values. Inter- and intraobserver measurement variability was performed
for 5 randomly selected participants for echocardiographic parameters
and for 15 randomly selected participants for CPET parameters. Two BSE
accredited operators (JVZ, SB) with extensive experience in performing
CPET simultaneously with echocardiography performed the inter- and
intra-observer measurements. The intraclass correlation coefficient
(ICC) and 95% confidence intervals was used to quantify
reproducibility. All statistical analyses were performed using the
Statistical Package for the Social Sciences (SPSS version 20.0; SPSS,
Inc). A P-value of < 0.05 was considered statistically
significant.