Microvasculopathy in chronic thromboembolic pulmonary hypertension involving pulmonary arterioles, venules and capillaries. Schematic representation of anastomosis between systemic and pulmonary circulation through hypertrophic bronchial arteries and vasa vasorum. PA: pulmonary artery; PVOD: pulmonary veno-occlusive disease; PAH: pulmonary arterial hypertension. Reproduced and modified from  with permission.
Patient with inoperable chronic thromboembolic pulmonary hypertension showing a typical aspect of subpleural hypoperfusion at the capillary phase of pulmonary angiography. Image kindly provided by P. Dartevelle, French National Reference Centre of Pulmonary Hypertension, Hôpital Bicêtre, Le Kremlin-Bicêtre, France.
Relationship between pulmonary vascular obstruction (PVO) and pulmonary vascular resistance in chronic thromboembolic pulmonary hypertension (CTEPH) and acute pulmonary embolism (PE). a) Patient AL: 24-year-old female with CTEPH. Percentage of PVO estimated on perfusion lung scan at 75%. Total occlusion of left lung and occlusion of right middle and lower lobes. Haemodynamics: mean pulmonary arterial pressure (PAP) 32 mmHg; cardiac index 1.7 L·min-1·m-2; total pulmonary vascular resistance (TPR) 18.8 mmHg·L-1·min·m2. Despite 75% PVO, the TPR was only 18.8. b) Patient BJ: 54-year-old female with CTEPH. Percentage of PVO estimated on perfusion lung scan at 35%; multiple bilateral segmental and subsegmental perfusion defects. Haemodynamics: mean PAP 45 mmHg; cardiac index 1.4 L·min-1·m-2; TPR 32.1 mmHg·L-1·min·m2. c) Relationship between percentage of PVO assessed by perfusion lung scan and TPR in patients with acute PE (n=31). A strong hyperbolic correlation was found. d) For a given degree of PVO, most patients with CTEPH (n=45) have higher TPR values than patients with acute PE (n=31), suggesting that, in addition to mechanical obstruction by organised clots, they have small-vessel disease. Patient AL is located on the hyperbolic correlation (no microvasculopathy), whereas patient BJ has a disproportionate and very high level of TPR compared to mild PVO (severe microvasculopathy). Reproduced and modified from  with permission.