Design: Cross-sectional analysis of a prospective multicentre cohort (PVDOMICS)
Population: 252 adults with chronic lung disease with CT and right heart catheterisation
Primary outcome: Association and diagnostic accuracy of PA size for pulmonary hypertension
Effect: PA diameter AUC 0.79 overall; PA:aorta AUC 0.70 interstitial v 0.87 obstructive

An analysis of the PVDOMICS cohort in Chest (24 September) measured pulmonary artery diameter and pulmonary artery-to-aorta ratio on CT in 252 people with chronic lung disease — 81 obstructive, 125 interstitial, 46 without parenchymal disease — and compared them with mean pulmonary artery pressure on right heart catheterisation.

Overall, a larger artery was associated with pulmonary hypertension (top v bottom third: OR 4.30 for diameter, 5.66 for ratio) and detected it moderately well (AUC 0.79 for diameter, 0.77 for ratio). But the relationship varied by disease. The ratio tracked pressure closely without parenchymal disease (correlation 0.75) and discriminated well in obstructive disease (AUC 0.87), but only weakly in interstitial disease (correlation 0.37, AUC 0.70). For the same rise in pressure, the artery widened less in fibrosis.

In practice, a normal-calibre pulmonary artery on CT is less reassuring in a patient with interstitial lung disease than in one with COPD. When breathlessness is out of proportion to the lung disease, or DLCO has fallen disproportionately, echocardiography and referral for assessment are warranted even if the artery looks unremarkable.

A normal pulmonary artery calibre on CT does not exclude pulmonary hypertension in interstitial lung disease.
In COPD, a dilated artery or raised PA:aorta ratio is a reasonably reliable prompt to investigate.
Look for pulmonary hypertension when breathlessness or DLCO is out of proportion to the lung disease.
Confirm suspected pulmonary hypertension with echocardiography and right heart catheterisation where indicated.

Why it matters

A familiar CT sign is least reliable in the patients where pulmonary hypertension is common and prognostically important.

The statistics, in plain English

An AUC of 0.70 is modest discrimination, against 0.87 in obstructive disease. A correlation of 0.37 means artery size explains only a small part of the variation in pressure in interstitial disease. With 125 interstitial patients, these estimates carry some uncertainty.