Normal lung volume as measured with computer-aided 3D quantitative analysis of chest CT correlates with mean pulmonary artery pressure as measured by right heart catheterization in pneumonia patients, making CT an attractive, noninvasive alternative for predicting pulmonary hypertension, according to a study published in the August issue of American Journal of Roentgenology.

“Although early diagnosis of pulmonary hypertension is important, the overlapping main symptoms—shortness of breath and exercise limitation—make it difficult to detect pulmonary hypertension in patients with [idiopathic interstitial pneumonia],” wrote authors Tae Iwasawa, MD, PhD, of the department of radiology at the Kanagawa Cardiovascular and Respiratory Center in Japan, and colleagues. “Right heart catheterization is the most accurate diagnostic tool for pulmonary hypertension. However, because [right heart catheterization] is invasive and expensive, a reliable and noninvasive surrogate marker is desirable.”

The authors investigated the correlation between CT lung volume and pulmonary artery pressure in 40 patients with idiopathic interstitial pneumonia who underwent both chest CT and right heart catheterization. Thirty-three patients were smokers or former smokers.

Lungs in the 3D CT images were automatically categorized pixel-by-pixel with gaussian histogram normalized correlations using a computer-aided system.

Results showed that normal lung volume on the 3D CT images correlated negatively and significantly with pulmonary hypertension. Regression analysis showed decreased lung volume accurately predicted hypertension.

The authors did note that there was a weak correlation between mean pulmonary artery pressure and fibrosis. Total lung volume on CT did not correlate with mean pulmonary artery pressure, though this is explainable by the coexistence of emphysema, the authors added.

“The pathobiology of pulmonary hypertension in pulmonary fibrosis is not completely understood,” wrote Iwasawa and colleagues. “However, our results suggest that quantitative measurement of normal lung volume can be useful for predicting pulmonary hypertension in patients with chronic fibrosing interstitial pneumonia, especially those with coexisting emphysema.”