Influence of different data-averaging methods on mean values of selected variables derived from preoperative cardiopulmonary exercise testing in patients scheduled for colorectal surgery

Abstract

Introduction: Patients with a low cardiorespiratory fitness (CRF) undergoing colorectal cancer surgery have a high risk for postoperative complications. Cardiopulmonary exercise testing (CPET) to assess CRF is the gold standard for preoperative risk assessment. To aid interpretation of raw breath-by-breath data, different methods of data-averaging can be applied. This study aimed to investigate the influence of different data-averaging intervals on CPET variables used for preoperative risk assessment, as well as to evaluate whether different data-averaging intervals influence preoperative risk assessment.

Methods: A total of 21 preoperative CPETs were interpreted by two exercise physiologists using stationary time-based data-averaging intervals of 10, 20, and 30 seconds and rolling average intervals of 3 and 7 breaths. Mean values of CPET variables between different data averaging intervals were compared using repeated measures ANOVA. The variables of interest were oxygen uptake at peak exercise (VO2peak), oxygen uptake at the ventilatory anaerobic threshold (VO2VAT), oxygen uptake efficiency slope (OUES), the ventilatory equivalent for carbon dioxide at the ventilatory anaerobic threshold (VE/VCO2VAT), and the slope of the relationship between the minute ventilation and carbon dioxide production (VE/VCO2-slope).

Results: Between data-averaging intervals, no statistically significant differences were found in the mean values of CPET variables except for the ventilatory equivalent for carbon dioxide at the ventilatory anaerobic threshold (P = 0.001). No statistically significant differences were found in the proportion of patients classified as high or low risk regardless of the used data-averaging interval.

Conclusion: There appears to be no significant or clinically relevant influence of the evaluated data-averaging intervals on the mean values of CPET outcomes used for preoperative risk assessment. Clinicians may choose a data-averaging interval that is appropriate for optimal interpretation and data visualization of the preoperative CPET. Nevertheless, caution should be taken as the chosen data-averaging interval might lead to substantial within-patient variation for individual patients.

Clinical trial registration: Prospectively registered at ClinicalTrials.gov (NCT05353127).

Fig 1

Visualization of the plot with oxygen uptake (VO₂) and carbon dioxide production (VCO₂) over time without data-averaging (graph A) and using the five different data-averaging intervals: a stationary time-based average of 10 seconds (graph B), 20 seconds (graph C), and 30 seconds (graph D), a rolling average interval of 3 breaths (graph E) and 7 breaths (graph F) in patient 21. See S1 File for a graphical display of the Wasserman plots of patient 21 with the different data-averaging intervals. Note that the number of data points is lower when stationary time-based averaging is used (and decreasing with longer data-averaging intervals) compared to when a rolling average is used. In addition, a lower number of data points leads to smoothing of the VO₂ and VCO₂ curves. Abbreviations: VAT = ventilatory anearobic threshold; VCO₂ = carbon dioxide production; VO₂ = oxygen uptake; VO_2peak = oxygen uptake at peak exercise. Vertical grey dotted lines represent start of the warm-up phase (W), test phase (T), and recovery phase (R).

Fig 2

Variation in the observed values of VO_2peak (graph A), VO_2VAT (graph B), OUES (graph C), VE/VCO_2VAT (graph D), and the VE/VCO₂-slope (graph E) within individual patients. Dots represent individual numerical value with a unique color for each data-averaging interval throughout the graphs (red = 10 seconds; yellow = 20 seconds; green = 30 seconds; blue = 3 breaths; purple = 7 breaths). Error bars represent the mean values and 95% confidence intervals. Horizontal dotted lines represent known risk assessment thresholds defined as 18.2 mL/kg/min for VO_2peak (graph A), 11.1 mL/kg/min for VO_2VAT (graph B), <20.6 for OUES (graph C), and >30.9 for VE/VCO_2VAT (graph D). Note that individual values of patients often cross the risk threshold (dotted horizontal line). These patients might have a different risk estimation depending on the data-averaging interval. Abbreviations: OUES = oxygen uptake efficiency slope; VE/VCO₂-slope = the slope of the relationship between the minute ventilation and carbon dioxide production; VE/VCO_2VAT = ventilatory equivalent for carbon dioxide at the ventilatory anaerobic threshold; VO_2peak = oxygen uptake at peak exercise; VO_2VAT = oxygen uptake at the ventilatory anaerobic threshold.