Figures
- FIGURE 1
Patient flow chart. 6MWD: 6-min walk distance; PH: pulmonary hypertension; V′O2max: maximal oxygen uptake.
- FIGURE 2
Correlation between 6-min walk distance (6MWD) and maximal oxygen uptake (VO2max). The three panels show the correlation for all observations, the training dataset and the testing dataset. Correlation coefficients (r) and p-values are given for all three datasets separately.
- FIGURE 3
Comparison of predictive models. The panels show the predicted values for maximal oxygen uptake (VO2max) against 6-min walk distance (6MWD) for each model separately. In each panel, the original data from the testing dataset is depicted for comparison; standard error of the estimate (SEE) for each model is shown below the panel headers. Mean oxygen uptake (V′O2) as determined by the generalised equation by Ross et al. [14] is shown in the corresponding panel.
- FIGURE 4
Bland–Altman graphs for the comparison of maximal oxygen uptake (V′O2max) determined by cardiopulmonary exercise testing versus using a predictive model based on 6-min walk test. The x-axis shows the calculated mean between the observed and the predicted values for V′O2max while the y-axis shows the difference between the two methods. The line corresponds to the mean difference in V′O2max and the two dashed lines show the 95% confidence interval. Each panel shows a different model as indicated by the panel's headers.
Tables
- TABLE 1
Characteristics of the training and testing datasets
Training dataset Testing dataset Observations n 194 82 Female 118 (61) 58 (71) Diagnosis PAH 117 (60) 50 (61) PH due to left heart disease 1 (1) PH due to lung disease 4 (2) 1 (1) CTEPH 64 (33) 28 (34) Miscellaneous 8 (4) 3 (4) Haemodynamics at baseline mPAP, mmHg 42±4.1 39±13.0 PVR, mmHg 12±63 6±4 PAWP, mmHg 11±4 11±4 CI, mL/min/kg 2.8±0.8 2.9±0.7 Characteristics Age, years 59±14 58±15 Height, cm 169±11 169±10 Weight, cm 76±19 73±17 BMI, kg/m2 27±5 25±5 NYHA functional class 2.2±0.7 2.2±0.6 6-min walk test 6-min walk distance, m 504±85 503±90 At rest Systolic BP, mmHg 125±18 120±14 Diastolic BP, mmHg 79±12 78±12 Heart rate, bpm 84±14 84±12 Peripheral oxygen saturation, % 96±3 96±3 At peak exercise Systolic BP, mmHg 145±25 142±26 Diastolic BP, mmHg 83±14 82±13 Heart rate, bpm 121±21 121±22 Heart rate response, bpm 37±19 37±20 Peripheral oxygen saturation, % 89±9.0 90±7.8 BORG CR10, score 4.7±2 4.6±2 Cardiopulmonary exercise test V′O2max, mL/min/kg 15.3±3.8 16.1±3.7 Maximal workload, Watts 93±33 96±36 Data are presented as n (%) or mean±sd, unless otherwise stated. BMI: body mass index; BP: blood pressure; CI: cardiac index; CTEPH: chronic thromboembolic pulmonary hypertension; mPAP: mean pulmonary arterial pressure; NYHA: New York Heart Association; PAH: pulmonary arterial hypertension; PAWP: pulmonary arterial wedge pressure; PH: pulmonary hypertension; PVR: pulmonary vascular resistance; V′O2max: maximal oxygen uptake.
- TABLE 2
Coefficients of different linear regression models and application to testing data
Ross et al. [14] mean (r=0.82) p-value Ross et al. [14] (r=0.59) p-value Miyamoto et al. [16] (r=0.68) p-value Zapico et al. [17] (R2=0.48) p-value New model (R2=0.48) p-value Observations n 1038 1083 27 82 194 Intercept 4.948 4.682 4.213 −21.626 1.83 0.248 6MWD, m 0.023 0.025 0.026 0.026 <0.001 0.031 <0.001 Sex 4.103 0.002 Height, cm 0.174 0.043 Weight, kg −0.071 0.02 −0.023 0.22 HRR, bpm −0.015 0.047 Applied to testing dataset SEE, mL/min/kg 3.03 3.22 4.36 3.08 SEE% mean 19% 20% 27% 19% Ability to classify to low risk (V′O2max >15 mL/min/kg) Sensitivity 0.96 0.96 0.91 0.69 Specificity 0.23 0.23 0.22 0.78 PPV 0.63 0.63 0.63 0.82 NPV 0.80 0.80 0.64 0.64 r from correlation between maxima oxygen uptake (V′O2max) and 6-min walk distance (6MWD); R2 from linear regression of V′O2max against 6MWD. HRR: heart rate response in 6-min walk test (heart rate at maximal exercise – heart rate at rest); NPV: negative predictive value; PPV: positive predictive value; SEE: standard error of the estimate; SEE% mean: SEE as percentage of mean peak oxygen uptake. All coefficients, p-values and R2 for Ross et al. [14], Miyamoto et al. [16] and Zapico et al. [17] are copied from the original publications.
