Previous studies have quantified changes in the proximal and distal pulmonary vascular tree in resting pulmonary arterial hypertension (PAH). Pulmonary arterial hypertension detected by response to exercise in patients with normal or borderline resting pressures may be an early form of PAH, but there remains ongoing debate about the pathophysiology of, and the clinical approach to this group. In this investigation we sought to determine if changes to pulmonary vascular morphology quantifiable on CT imaging were present in this subgroup of patients.
Subjects were retrospectively selected from patients presenting to the dyspnea clinic with available imaging, supine right heart catheterization and upright invasive exercise testing. Exercise pulmonary arterial hypertension was defined as normal resting supine cardiac catheterization (mPAP<25mmHg) but with elevated PVR(PVR>168 dyn*s*cm-5 for age>50, PVR>107 dyn*s*cm-5 for age<50) and mPAP(33 mmHg age>50, 30mmHg age<50) and normal wedge pressures with exercise. In all subjects measurements of the pulmonary artery, ascending aorta and both the right and left pulmonary artery diameters were made. In patients with CT angiograms, 3D reconstructions of the pulmonary vasculature using the Chest Imaging Platform (www.chestimagingplatform.org) were used to compute the small vessel fraction BV5/TBV (Volume of vessels less than 5mm2 in cross-section divided by total vessel volume).
Results & Conclusion
Data from 15 control subjects and 20 subjects with EPH (12 with 3D reconstructions) were analyzed. Patients with EPH had a larger pulmonary artery to aortic diameter ratio (0.90 vs. 0.81 p=0.015), right and left pulmonary artery to aortic diameter ratio (0.74 vs 0.67, p=0.042; 0.70 vs 0.65 p=0.047), combined diameters to aorta diameter ratio (2.3 versus 2.1, p=0.005) and decreased BV5/TBV as compared to controls (0.43 vs 0.54 p=0.04). This data supports the hypothesis that PAH detected by exercise is associated with significant changes in CT based vascular morphology.