This study seeks to evaluate indices of pulmonary artery (PA) stiffness in patients with COPD and compare with normal controls. We hypothesize that patients with COPD would have increased pulmonary artery stiffness. To test this we determine the pulmonary artery area change (distensibility in %) by cardiac MRI and relate the distensibility to a wide range of severity of COPD.
The MESA COPD Study recruited 290 patients (135 patients of various COPD severity and 155 controls) from four field centers in the US, age 50-79 years with ≥10 pack-years of smoking, all free of clinical cardiovascular disease. COPD was defined on post-bronchodilator spirometry by GOLD criteria (FEV1/FVC <70%, FEV1 % predicted >80% = mild, 50-80%=moderate, <50%=severe). All participants underwent full-lung CTs. Percent emphysema was defined as the percentage of total voxels within the lung field that fell below -910 Hounsfield units. MRI studies were performed using 1.5T scanners. To measure ventricular function, the entire heart was imaged in short-axis orientation using a retrospectively gated steady-state free precession sequence. Phase-contrast images of the pulmonary arteries were obtained using a segmented fast gradient echo sequence with free breathing and analyzed quantitatively using dedicated software (FLOW, Medis). Distensibility of the pulmonary vessels (in %) are measured by the following formula, 100×(maximum PA area-minimum PA area)/minimum PA area. The base model (model 1) was adjusted for age, gender, height, weight, race/ethnicity and cohort of selection, given relationships of COPD severity to the pulmonary distensibility. We then additionally adjusted for smoking status, pack-years, diabetes mellitus, hypertension, oxygen saturation, LDL, HDL and statin use (model 2).
Table 1 summarizes the clinical characteristics of 290 participants stratified by COPD severity. Distensibility of the main, right and left PA was reduced in COPD compared to controls in both models (Table 2). Main and right pulmonary distensibilities were inversely related to percent emphysema after minimal adjustment (model 1, P=0.21 and 0.07, respectively) and similar trends with statistical significance in the full model (model 2, P=0.049 and 0.01, respectively). Pulmonary distensibilities was positively associated with the percent predicted FEV1 but only left PA attain statistical significance after base adjustment (model 1, P=0.047).
We conclude that in COPD patients without overt cardiovascular disease, pulmonary artery distensibility is reduced. Higher pulmonary arterial stiffness also correlated with the percent emphysema on CT scan and FEV1.
National Institutes of Health R01-HL093081 R01-HL077612, R01-HL075476 and N01-HC95159-HC95169, UL1 RR024156.