Pulmonary Artery Diameter Enlargement Ratio (CT-based) Calculator
- Ascending Aorta (AA) diameter — same slice/level (mm)
- Sex (for sex-specific mPA normal limits)
- 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.
References:
Truong QA, et al. Reference values for normal pulmonary artery dimensions by noncontrast cardiac CT: The Framingham Heart Study. Circ Cardiovasc Imaging. 2012;5:147–154. (Sex-specific mPA ≤29 mm men, ≤27 mm women; PA/Ao healthy-reference ≈<0.90).
Wells JM, et al. Pulmonary arterial enlargement and acute exacerbations of COPD. N Engl J Med. 2012;367:913–921. (COPD cohorts: PA/Ao >1 associated with severe exacerbations).
Iyer AS, et al. CT scan–measured PA:A ratio and echocardiography for diagnosing PH in severe COPD. Chest. 2014;145:824–832. (PA/Ao >1 linked to PH in selected populations).
Ussavarungsi K, et al. The significance of pulmonary artery size in imaging. Diseases. 2014;2:243–259. (Synthesis of cutoffs and correlations with PH).
Truong QA, et al. A four-tier classification system of pulmonary artery metrics by CT. J Cardiovasc Comput Tomogr. 2018;12:129–137. (Granular categorization around Framingham limits).
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