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; VO2peak = oxygen uptake at peak exercise. Vertical grey dotted lines represent start of the warm-up phase (W), test phase (T), and recovery phase (R).
Table 1.
Baseline characteristics of subjects.
Table 2.
Numerical values of CPET variables using different data-averaging intervals.
Fig 2.
Variation in the observed values of VO2peak (graph A), VO2VAT (graph B), OUES (graph C), VE/VCO2VAT (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 VO2peak (graph A), 11.1 mL/kg/min for VO2VAT (graph B), <20.6 for OUES (graph C), and >30.9 for VE/VCO2VAT (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/VCO2VAT = ventilatory equivalent for carbon dioxide at the ventilatory anaerobic threshold; VO2peak = oxygen uptake at peak exercise; VO2VAT = oxygen uptake at the ventilatory anaerobic threshold.
Table 3.
Effect of different data-averaging intervals on classifying patients as having a high-risk for postoperative complications.