## 3 Results
### Lung PBV Score and Pulmonary Vascular Resistance  
Of the 113 patients with CTEPH included in the analysis, 58 (51%) with PSP on DE-CT were assigned to the poorly perfused group, and 55 (49%) without PSP were assigned to the normally perfused group. Figure 4 shows the relationship between the lung PBV score and pulmonary vascular resistance (PVR) of (a) patients with PAH, (b) patients with CTEPH in the poorly perfused group, and (c) patients with CTEPH in the normally perfused group. In the patients with PAH and those with CTEPH in the poorly  
Figure 2: Study flow chart. perfused group, there was no significant correlation between the lung PBV score and PVR (PVR = 986.5 \(\times\) lung PBV score\({}^{-0.11}\), R\({}^{2}\) = 0.005, \(p\) = 0.99, and PVR = 4199 \(\times\) lung PBV score\({}^{-0.55}\), R\({}^{2}\) = 0.072, \(p\) = 0.059, respectively); however, a strong nonlinear and inverse correlation between the lung PBV scores and PVR was observed in patients with CTEPH in the normally perfused group (PVR = 12,112 \(\times\) lung PBV score\({}^{-0.98}\), R\({}^{2}\) = 0.324, \(p\) < 0.01). \begin{table}
\begin{tabular}{l c c c} \hline \multicolumn{1}{c}{**Variable**} & **PAH (\(\mathbf{u}\) = 23)** & **CTEPH (\(\mathbf{u}\) = 113)** & \(\mathbf{p}\) **Value** \\ \hline \multicolumn{4}{l}{_Baseline characteristics_} \\ \multicolumn{4}{l}{Age (years)} & 68 \(\pm\) 14 & 70 \(\pm\) 13 & 0.450 \\ \multicolumn{4}{l}{Male (\(n\), \(\%\))} & 10 (43) & 27 (24) & 0.054 \\ \multicolumn{4}{l}{NYHA FC (I/II/III/IV) (\(\%\))} & 4/39 /53/4 & 1/20/72/7 & 0.128 \\ \multicolumn{4}{l}{BNP (pg/mL)} & 170 [210] & 263 [204] & 0.208 \\ \multicolumn{4}{l}{DE-CT parameters} \\ \multicolumn{4}{l}{Poor subpleural perfusion (\(n\), \(\%\))} & 1 (4\%) & 58 (51\%) & \textless{}0.001 \\ \multicolumn{4}{l}{Lung PBV score (Hounsfield Unit)} & 21.5 \(\pm\) 6.51 & 24.0 \(\pm\) 6.5 & 0.188 \\ \multicolumn{4}{l}{_Baseline hemodynamics_} \\ \multicolumn{4}{l}{Mean RAP (mmHg)} & 4.0 \(\pm\) 3.3 & 5.0 \(\pm\) 3.6 & 0.963 \\ \multicolumn{4}{l}{Systolic PAP (mmHg)} & 59 \(\pm\) 13.2 & 63 \(\pm\) 18.7 & 0.071 \\ \multicolumn{4}{l}{Diastolic PAP (mmHg)} & 25 \(\pm\) 7.5 & 22 \(\pm\) 7.8 & 0.138 \\ \multicolumn{4}{l}{Mean PAP (mmHg)} & 38 \(\pm\) 8.3 & 37 \(\pm\) 10.9 & 0.826 \\ \multicolumn{4}{l}{PAWP (mmHg)} & 8.0 \(\pm\) 3.8 & 8.0 \(\pm\) 3.8 & 0.826 \\ \multicolumn{4}{l}{Cardiac output (L/min)} & 3.16 \(\pm\) 0.76 & 3.54 \(\pm\) 2.22 & \textless{}0.001 \\ \multicolumn{4}{l}{Cardiac index (L/min/m2)} & 2.12 \(\pm\) 0.43 & 2.06 \(\pm\) 0.78 & 0.216 \\ \multicolumn{4}{l}{PVR (dynes-sec/cm5)} & 703 \(\pm\) 413 & 564 \(\pm\) 395 & 0.207 \\ \multicolumn{4}{l}{_Exercise capacity_} \\ \multicolumn{4}{l}{6 MWD (m)} & 300 \(\pm\) 116 & 318 \(\pm\) 97 & 0.416 \\ \multicolumn{4}{l}{Peak VO\({}_{2}\) in CPET (mL/min/kg)} & 13 \(\pm\) 5.2 & 12.4 \(\pm\) 4.1 & 0.526 \\ \multicolumn{4}{l}{_VE/VCO\({}_{2}\) slope in CPET_} & 37.3 \(\pm\) 14.2 & 39.1 \(\pm\) 11.5 & 0.697 \\ \multicolumn{4}{l}{_Lung function test_} \\ \multicolumn{4}{l}{\%VC (\%)} & 89.6 \(\pm\) 20.0 & 90.35 \(\pm\) 17.3 & 0.691 \\ \multicolumn{4}{l}{FEV 1.0\% (\%)} & 84.9 \(\pm\) 17.3 & 85.4 \(\pm\) 18.7 & 0.325 \\ \multicolumn{4}{l}{\%DLCO/VA (\%)} & 39.8 \(\pm\) 22.0 & 70.1 \(\pm\) 17.5 & \textless{}0.001 \\ \hline \end{tabular}
\begin{tabular}{l c c} \hline \multicolumn{4}{l}{_List of abbreviations_: NYHA FC: New York Heart Association functional class; BNP: brain natriuretic peptide; PBV: pulmonary blood volume; RAP: right atrial pressure; PAP: pulmonary artery wedge pressure; PVR: pulmonary vascular resistance; 6 MWD: 6 min walk distance; VO\({}_{2}\): oxygen consumption; CPET: cardio-pulmonary exercise test; VE/VCO\({}_{2}\): ventilatory equivalent for carbon dioxide; VC: vital capacity; FEV: forced vital capacity; DL\({}_{\text{CO}}\)/VA: diffusing capacity for carbon monoxide divided by the alveolar volume. Data are given as mean \(\pm\) standard deviation or median [interquartile range].  
\end{table} 
Table 1: Hemodynamics and characteristics of patients with PAH and CTEPH at diagnosis.