Aortic stiffness and distensibility

Aortic stiffness and distensibility phenotypes summarize cyclic aortic area change from the dedicated aortic distensibility cine acquisition. This page is source-audited for the current aortic_dist.csv output names and explicitly separates current CardiacNexus outputs from literature-only pulse wave velocity context.

Modality

Aortic distensibility cine CMR plus central pulse pressure table

UKB source

Data Field 20210; pressure table configured through runtime pressure_file and pressure_col_name

Pipeline step

Ascending/descending aortic segmentation QC, area tracking, equivalent-diameter calculation, pressure-normalized distensibility

Outputs

aortic_dist.csv, visualization/aorta/aortic_area.png, timeseries/aortic_area.png

Maturity

Source-audited phenotype page

Clinical question

Aortic distensibility asks whether the aortic lumen expands normally during the cardiac cycle after accounting for pulse pressure. This is related to vascular stiffness and cardiovascular risk, but CardiacNexus reports local area-change phenotypes; it does not currently emit pulse wave velocity or diagnose atherosclerosis, hypertension, Marfan syndrome, bicuspid valve disease, or heart failure from these rows.

Anatomical and physiological definition

The current implementation labels two regions in the aortic distensibility cine segmentation: ascending aorta (AAo) and descending aorta (DAo). For each frame, it counts segmented pixels, converts them to cross-sectional area using in-plane image spacing, and derives an equivalent circular diameter from that area.

Distensibility is calculated as:

\mathrm{Distensibility} =
\frac{A_\mathrm{max} - A_\mathrm{min}}{A_\mathrm{min} \times \mathrm{central\ pulse\ pressure}} \times 10^3

The output unit is 10^-3/mmHg. The pressure denominator is the configured central pulse pressure value, not an image-derived measurement [1] [2].

Source acquisition and UKB field

The image input is the UK Biobank aortic distensibility cine series, represented in the pipeline as aortic_dist.nii.gz and seg_aortic_dist.nii.gz. The segmentation label convention is 1 for ascending aorta and 2 for descending aorta. Pressure input comes from the configured pressure CSV and column, and the implementation treats central pulse pressure below 10 mmHg as invalid.

What exactly CardiacNexus measures

Ascending and descending area phenotypes

For both ascending and descending aorta, eval_aortic_dist.py emits maximum, mean, and minimum cross-sectional area in mm^2. It also emits maximum, mean, and minimum equivalent circular diameter in mm, calculated as 2 * sqrt(area / pi).

Pressure-normalized distensibility

When central pulse pressure is available and at least 10 mmHg, the implementation computes ascending and descending aortic distensibility. If either calculated distensibility exceeds the current QC threshold of 20 10^-3/mmHg, the subject is skipped for those output rows.

Pulse wave velocity boundary

PWV is an important vascular-stiffness phenotype in the literature, but this page does not list a PWV output because the current aortic_dist.csv extraction route does not emit one. PWV remains background context only [3].

Output columns and units

CardiacNexus writes the current aortic distensibility phenotype family into aortic_dist.csv.

Output reconciliation

Required upstream inputs

• aortic_dist.nii.gz;
• seg_aortic_dist.nii.gz, with labels 1 for ascending aorta and 2 for descending aorta;
• pixel spacing from the NIfTI header;
• pressure CSV and configured central pulse-pressure column;
• aortic segmentation QC pass from aorta_pass_quality_control.

Reference ranges with cohort and method context

Source-located registry status: reference_range_sources.yml maps diameter context to Turkbey/MESA sources, automated distensibility context to UKB distensibility literature, stiffness/PWV boundary context to Cavalcante/Westenberg-style sources, and outcome context to Redheuil/MESA. Public numeric rows remain deferred because pressure source, automated area-derived diameter, and local distensibility conventions must be matched before threshold display.

Disease interpretation

Lower aortic distensibility and higher stiffness have been reported with aging, hypertension, atherosclerosis, coronary disease, heart failure, Marfan syndrome, congenital heart disease, bicuspid aortic valve physiology, and other aortopathy contexts [2] [3] [4]. These disease badges are interpretation aids only. CardiacNexus does not classify vascular disease, valve disease, or heart failure from aortic_dist.csv.

QC caveats and maturity boundary

Distensibility is pressure-dependent and segmentation-sensitive. Motion, through-plane prescription, partial volume, arrhythmia, incorrect label assignment, or a missing/invalid central pulse-pressure row can change or suppress outputs. Area-derived diameter assumes circular equivalence and should not be merged with scout-derived 3D aortic geometry without method labels.

Legacy column names contain Maxium; those labels are current compatibility debt and should not be silently renamed outside a versioned schema migration.

Implementation provenance

Source audit

• Current output labels, pressure conditionals, and QC thresholds were checked against src/feature_extraction/Aortic_Distensibility_20210/eval_aortic_dist.py.
• docs/data/reference_sources.yml is present and used as the curated reference-source registry for this page.
• Textbook context boundary: page-specific implementation, CMR aortic-diameter, UKB aortic-distensibility, and aortic-stiffness literature are sufficient for draft rollout; Braunwald/Hurst background was not needed for the phenotype-specific output contract.
• One PWV methods schematic is displayed from a page-local public path and registered in docs/data/figure_provenance.yml; it is literature-boundary context only because PWV is not a current CardiacNexus output on this page.

Related pages

• Aortic distensibility imaging
• Aortic structure
• Valvular and flow phenotypes
• Quality control

References

1. Turkbey EB, Jain A, Johnson C, Redheuil A, Arai AE, Gomes AS, Carr J, Hundley WG, Teixido-Tura G, Eng J, Lima JAC, Bluemke DA. Determinants and normal values of ascending aortic diameter by age, gender, and race/ethnicity in the Multi-Ethnic Study of Atherosclerosis. Journal of Magnetic Resonance Imaging. 2014;39(2):360-368.
2. Cecelja M, Ruijsink B, Puyol-Anton E, Li Y, Godwin H, King AP, Razavi R, Chowienczyk P. Aortic distensibility measured by automated analysis of magnetic resonance imaging predicts adverse cardiovascular events in UK Biobank. Journal of the American Heart Association. 2022;11(23):e026361.
3. Cavalcante JL, Lima JAC, Redheuil A, Al-Mallah MH. Aortic stiffness. Journal of the American College of Cardiology. 2011;57(14):1511-1522.
4. Redheuil A, Wu CO, Kachenoura N, Ohyama Y, Yan RT, Bertoni AG, Hundley GW, Duprez DA, Jacobs DR, Daniels LB, Darwin C, Sibley C, Bluemke DA, Lima JAC. Proximal aortic distensibility is an independent predictor of all-cause mortality and incident cardiovascular events in MESA. Journal of the American College of Cardiology. 2014;64(24):2619-2629. PMID:25524341; PMCID:PMC4273646.