PURPOSE: Pulmonary arterial hypertension (PAH) is often associated with a restrictive lung pattern on pulmonary function testing. The etiology of this restriction is unknown. We hypothesized that one of the potential causes for this restriction is an enlarged right ventricle competing for volume in the thoracic cavity.
METHODS: Forty-nine patients with World Health Organization Category I PAH were included in a cross-sectional retrospective analysis. FVC, TLC, anthropometric data, echocardiographic dimensions, pulmonary artery catheter data, chest CT, and cardiothoracic index (CTI) from PA chest radiographs were collected at the time of initial referral to the Pulmonary Hypertension and Transplant Clinic.
RESULTS: A complete data set was available for 41 patients. FVC averaged 74.7% predicted +/−18.8 and CTI was 0.58+/−0.06. Both FVC and TLC were inversely related to CTI (r=−0.39,P=0.017 and r=−0.36,P=0.04)) but were not related to the presence of RV enlargement on echocardiography. The relationship between FVC and CTI was independent of BMI on regression analysis (P=0.02) as well as when controlling for ground glass opacity or possible interstitial lung disease on CT (r=−0.32, P=0.05). There was also an inverse relationship between pulmonary artery systolic pressure and FVC (r=−0.38, P=0.02) but not between FVC and pulmonary vascular resistance (r=0.19,P=0.2.
CONCLUSION: Right heart enlargement appears to be related to the restrictive lung defect in PAH. Measurement of CTI is predictive of this restriction whereas echocardiographic data are not. This association is independent of the presence of apparent lung disease identified by chest CT scan.
CLINICAL IMPLICATIONS: The CTI represents an easily obtainable parameter that correlates with pulmonary restriction in selected patients with PAH.
DISCLOSURE: Franz Rischard, None.