Pulmonary Artery Diameter Enlargement Ratio (CT-based) Calculator

Ascending Aorta (AA) diameter — same slice/level (mm) Sex (for sex-specific mPA normal limits) -- choose -- Male Female Pulmonary Artery Diameter Enlargement Ratio (CT-based): Explanation and Clinical Context The pulmonary artery–to–ascending aorta diameter ratio (PA/Ao) is obtained from axial chest CT at the level of the main pulmonary artery bifurcation, measuring the short-axis diameters of the main PA and ascending aorta on the same slice. Population-based reference data from the Framingham Heart Study support sex-specific normal limits for main PA diameter—approximately ≤27 mm for women and ≤29 mm for men—and a healthy-reference PA/Ao ratio around <0.90 in asymptomatic individuals without cardiopulmonary disease. In clinical cohorts, a PA/Ao ratio ≥1.00 is widely used as an imaging marker of pulmonary artery enlargement and has shown association with pulmonary hypertension and adverse outcomes across conditions.

In patients with COPD, a PA/Ao >1 was associated with increased risk of severe exacerbations; in interstitial lung disease, ratios ≥1 have correlated with worse outcomes. Importantly, PA size and PA/Ao are surrogate markers and do not replace right heart catheterization for definitive hemodynamic diagnosis. Measurements should be made carefully (same axial level, inner-edge to inner-edge), considering technical factors (cardiac phase, inspiratory level) and body size; interpretation should be integrated with symptoms, echocardiography, biomarkers, and hemodynamics. “Original publication” thresholds incorporated here This calculator implements the Framingham sex-specific main PA normal limits (≤27 mm women, ≤29 mm men) and the healthy-reference PA/Ao <0.90, while also showing the commonly cited clinical enlargement threshold of PA/Ao ≥1.00 used in multiple outcome studies.

These values reflect the original population reference and subsequent validation literature to improve interpretive precision. No risk percentage is calculated because published works associate PA/Ao with outcomes but do not provide a universally validated multivariable risk equation suitable for broad clinical prediction.