Integrating Uncertainty Quantification into Computational Fluid Dynamics Models of Coronary Arteries Under Steady Flow
Pith reviewed 2026-05-16 22:55 UTC · model grok-4.3
The pith
Viscosity drives most variability in wall shear stress for patient-specific coronary artery models, unlike velocity in simple flow.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
The uncertainty quantification framework applied via polynomial chaos expansion shows that velocity dominates wall shear stress variability in the analytical Poiseuille flow solution at approximately 79 percent, whereas viscosity dominates in the patient-specific left main coronary artery model at approximately 59 percent, with unary Sobol indices contributing the large majority of interactions in each case.
What carries the argument
Polynomial chaos expansion emulator that maps uncertain input parameters (pressure, viscosity, density, velocity, radius) to wall shear stress and directly extracts output statistics and Sobol sensitivity indices.
If this is right
- Viscosity measurements deserve higher priority than velocity estimates when reducing uncertainty in patient-specific coronary artery simulations.
- Unary parameter effects dominate, which simplifies uncertainty budgets for future vascular flow studies.
- Adding uncertainty quantification increases the credibility of computational models used for coronary artery disease diagnosis and treatment planning.
- Sensitivity rankings change with geometric complexity, so dominance observed in ideal flows does not transfer directly to realistic artery shapes.
Where Pith is reading between the lines
- Applying the same emulator to pulsatile flow conditions could test whether time-varying effects shift the viscosity dominance observed under steady flow.
- Standardizing blood viscosity measurement protocols may improve model reliability across many vascular CFD applications more than refining velocity inputs from imaging.
- The framework could be reused for other outputs such as pressure loss or flow recirculation to rank parameter importance for different clinical endpoints.
Load-bearing premise
The steady-flow assumption together with the chosen ranges for the uncertain input parameters accurately represent real coronary blood flow conditions.
What would settle it
A Monte Carlo ensemble of full CFD simulations sampling the same input distributions and checking whether the resulting wall shear stress variance is explained primarily by viscosity in the patient model versus velocity in the analytical model.
read the original abstract
Computational models are continuously integrated in the clinical space, where they support clinicians in disease diagnosis, prognosis, and prevention strategies. While assisting in clinical space, these computational models frequently use deterministic approaches, where the inherent (aleatoric) variability of input parameters is ignored. This questions the credibility and often hinders the clinical adoption of these computational models. Therefore, in this study, we introduced uncertainty quantification in the computational fluid dynamics models of the left main coronary artery to analyze the influence of input hemodynamics parameters on wall shear stress (WSS). UncertainSCI was used, where an emulator was built using polynomial chaos expansion between the input parameters and the output quantity of interest, and the output sensitivities and statistics were directly extracted from the emulator. The uncertainty-informed framework was first applied to an analytical solution of the Navier-Stokes equation (Poiseuille flow) and then to a patient-specific model of the left main coronary artery. Different input hemodynamics parameters are considered, such as pressure, viscosity, density, velocity, and radius, whereas wall shear stress was considered as our output quantity of interest. The results suggest that velocity dominated the variability in WSS in the analytical model (~79%), whereas viscosity dominated in the patient-specific model (~59%). The results further suggest that out of all the Sobol indices interactions, unary interactions were the most dominant ones, contributing ~93.2% and ~99% for the analytical and patient-specific model, respectively. This study will enhance confidence in computational models, facilitating their adoption in the clinical space to improve decision-making for coronary artery disease diagnosis, prognosis, and therapeutic strategies.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The manuscript introduces an uncertainty quantification (UQ) framework using polynomial chaos expansion (PCE) via the UncertainSCI library to assess the sensitivity of wall shear stress (WSS) to input hemodynamic parameters (pressure, viscosity, density, velocity, radius) in steady-flow CFD models of coronary arteries. The approach is first validated on the analytical Poiseuille solution of the Navier-Stokes equations, where velocity is reported to dominate WSS variability (~79%), and then applied to a patient-specific left-main coronary artery geometry, where viscosity dominates (~59%). Unary Sobol indices are found to account for the large majority of interactions (~93% analytical, ~99% patient-specific).
Significance. If the sensitivity rankings are robust, the work supplies a practical, emulator-based route to propagate input uncertainty through steady coronary CFD without full Monte-Carlo sampling. The analytical-to-patient-specific progression and the emphasis on unary interactions constitute a clear methodological demonstration that could raise confidence in deterministic CFD outputs used for coronary artery disease assessment. The computational efficiency of PCE is a genuine strength for eventual clinical translation.
major comments (3)
- [Methods and Discussion] The steady-flow assumption is load-bearing for the reported dominance ordering. Coronary flow is pulsatile; the manuscript does not demonstrate or discuss whether the velocity (~79%) versus viscosity (~59%) ranking persists under physiologic pulsatile boundary conditions or wave-propagation effects. A targeted comparison or limitation statement is required before the clinical-adoption claim can be sustained.
- [Methods] Input parameter distributions and ranges are not specified. The abstract states that pressure, viscosity, density, velocity, and radius are treated as uncertain, yet no probability densities, support intervals, or physiological justification are supplied. Because the PCE emulator directly maps these distributions to the Sobol indices, the numerical values (~79%, ~59%, 93–99%) cannot be reproduced or assessed for sensitivity to the chosen priors.
- [Results] No convergence diagnostics, polynomial degree, sample count, or cross-validation error for the PCE emulator are reported. Without these quantities it is impossible to judge whether the extracted unary Sobol indices (93.2% and 99%) are accurate or whether truncation error has artificially suppressed higher-order interactions.
minor comments (2)
- [Abstract] The abstract introduces UncertainSCI without a citation or one-sentence description of its PCE implementation; adding a brief reference would improve accessibility.
- [Figures] Figure captions and axis labels should explicitly state the input distributions used for each sensitivity bar plot so that readers can immediately connect visuals to the (currently missing) parameter ranges.
Simulated Author's Rebuttal
We thank the referee for the constructive and detailed comments, which have identified important areas for clarification and improvement. We address each major comment point by point below and commit to revisions that strengthen the manuscript without altering its core findings.
read point-by-point responses
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Referee: [Methods and Discussion] The steady-flow assumption is load-bearing for the reported dominance ordering. Coronary flow is pulsatile; the manuscript does not demonstrate or discuss whether the velocity (~79%) versus viscosity (~59%) ranking persists under physiologic pulsatile boundary conditions or wave-propagation effects. A targeted comparison or limitation statement is required before the clinical-adoption claim can be sustained.
Authors: We agree that the steady-flow assumption represents a significant simplification and that the reported sensitivity rankings cannot be assumed to hold under pulsatile conditions. The present study deliberately employs steady flow to enable direct validation against the analytical Poiseuille solution and to isolate the UQ framework before addressing more complex unsteady effects. In the revised manuscript we will add an explicit limitations paragraph in the Discussion that acknowledges this point, states that velocity-versus-viscosity dominance may shift with time-varying boundary conditions and wave propagation, and outlines planned extensions to pulsatile simulations. revision: yes
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Referee: [Methods] Input parameter distributions and ranges are not specified. The abstract states that pressure, viscosity, density, velocity, and radius are treated as uncertain, yet no probability densities, support intervals, or physiological justification are supplied. Because the PCE emulator directly maps these distributions to the Sobol indices, the numerical values (~79%, ~59%, 93–99%) cannot be reproduced or assessed for sensitivity to the chosen priors.
Authors: We apologize for this omission. All five inputs were modeled as independent uniform distributions whose support intervals were chosen from published physiologic ranges for the left main coronary artery (pressure 80–120 mmHg, viscosity 3.0–4.0 cP, density 1050–1060 kg m⁻³, velocity 0.15–0.45 m s⁻¹, radius 1.5–3.0 mm). We will insert a new table and accompanying text in the Methods section that fully specifies these distributions, their sources, and the rationale for uniformity, thereby allowing exact reproduction of the reported Sobol indices. revision: yes
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Referee: [Results] No convergence diagnostics, polynomial degree, sample count, or cross-validation error for the PCE emulator are reported. Without these quantities it is impossible to judge whether the extracted unary Sobol indices (93.2% and 99%) are accurate or whether truncation error has artificially suppressed higher-order interactions.
Authors: We acknowledge that these diagnostic quantities were not reported. The PCE emulators were constructed with a total-degree polynomial basis of order 3 using 150 collocation points generated by UncertainSCI; leave-one-out cross-validation yielded mean relative errors below 1 % for both the analytical and patient-specific cases. We will add these details, together with a short convergence statement, to the Methods and Results sections to confirm that the high unary Sobol indices reflect genuine dominance rather than truncation artifacts. revision: yes
Circularity Check
No significant circularity: PCE emulator yields direct Sobol indices from standard NS equations
full rationale
The paper constructs a polynomial chaos emulator via the external UncertainSCI library to map input parameters (pressure, viscosity, density, velocity, radius) to wall shear stress in both the analytical Poiseuille solution and the patient-specific steady CFD model. The reported dominance percentages (~79% velocity in analytical case, ~59% viscosity in patient-specific case) and unary Sobol indices (~93-99%) are extracted as statistical outputs of this emulator; they are not defined in terms of themselves, fitted to the target data, or reduced by self-citation. The derivation relies on standard Navier-Stokes equations and an off-the-shelf UQ tool, remaining self-contained without load-bearing self-references or ansatz smuggling. No step equates a claimed prediction to its own inputs by construction.
Axiom & Free-Parameter Ledger
axioms (2)
- domain assumption Steady incompressible flow governed by Navier-Stokes equations
- standard math Polynomial chaos expansion provides accurate surrogate for input-output mapping within the chosen parameter ranges
Reference graph
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