Pulmonary arteries connect blood flow from the heart to the lungs in order to oxygenate blood before being pumped through the body. The main pulmonary artery (MPA) starts at the right ventricle of the heart and divides into the left (LPA) and right pulmonary arteries (RPA), which branch out into the lungs. The main pulmonary artery in healthy subjects has an average diameter of 2.72 cm. Anatomical differences in MPA diameter have also been documented between genders, with a mean MPA diameter of 2.77 cm for males and 2.64 cm for females.
Examples of complications seen in the pulmonary arteries include pulmonary hypertension and pulmonary embolisms. Pulmonary arterial hypertension (PAH) is a chronic disease that occurs when the blood vessels between the heart and lungs narrow and harden, increasing the pressure in the pulmonary arteries. The increased resistance makes it difficult for the heart to pump blood to the lungs, adding strain to and weakening the right ventricle. PAH is a serious condition, with a median survival of less than 3 years if left untreated,causing over 15,000 deaths and 260,000 hospital visits in the United States in 2002.
Significant vascular remodeling is observed in PAH patients, with larger proximal pulmonary arteries and more convoluted branches when compared to healthy patients. In a study examining three-dimensional hemodynamics of the pulmonary arteries, PAH patients were found to have an average main pulmonary diameter of 3.5 ± 0.5 cm, where healthy patients had an average of 2.7 ± 0.1 cm.
A pulmonary embolism is another condition seen the pulmonary arteries, involving one or more arteries being blocked by a blood clot. The blood clots typically originate elsewhere in the body and travel to the pulmonary arteries. The effects of a pulmonary embolism can be quiet severe, with the first sign being sudden death in 25% of pulmonary embolism cases. However, prompt application of anti-clogging medication can help avoid mortality and further complications.
Patient-specific volumetric image data was obtained to create physiological models and blood flow simulations. The RAS coordinate system was assumed for the image data orientation. Voxel Spacing, voxel dimensions, and physical dimensions are provided in the Right-Left (R ), Anterior-Posterior (A), and Superior-Inferior (S) direction. The patient was 67 years old and female. Details of the image data are listed as below:
Volumetric image data details (CT)
|Voxel Spacing (mm)||0.5859||0.5859||1.25|
|Physical Dimensions (mm)||300||300||247.5|
Coronal MIP image:
The models extend from the main pulmonary artery to various levels of branching in the left and right pulmonary arteries. Using Simvascular and the image data above, the geometrical models are generated by selecting centerline paths along the vessels, creating 2D segmentations along each of these paths, and then lofting the segmentations together to create a solid model. A separate solid model was created for each vessel and Boolean addition was used to generate a single model representing the complete aortofemoral model. The vessel junctions were then blended to create a smoothed model.
Geometric model details
|Number of inlets||Number of outlets||Volume(cm3)||Surface Area(cm2)||Number of Vessel Paths||Number of 2-D Segmentations|
|Blood Viscosity||Blood Density|
|0.04 g/cm•s2||1.06 g/cm3|
Vessel Geometric Model:
The inflow waveform was adapted to be an average resting pulmonary artery flow waveform for healthy subjects.
Period and Cardiac Output:
|Period (s)||Cardiac Output (L/min)||Profile Type|
Resistance values for exercise conditions were assigned at each outlet, calculated using the outlet area, LPA/RPA flow split, and pulmonary pressures.
Resistance Values and Presure Offset in cgs and mmHg:
|Face Name||Rp||Po||Face Name||Rp||Po|
Conservation of mass and Navier-Stokes equations were solved using 3D finite element methods assuming rigid and non-slip walls. The number of time steps per cycle is 1000 with fixed time step size. The simulation was run in cgs units for several cardiac cycles to allow the flow rate and pressure fields to stabilize. Simulation results were quantified for the last cardiac cycle. Paraview, an open-source scientific visualization application, was used to visualize the results. A volume rendering of velocity magnitude for three time points during the cardiac cycle can be seen.
Surface distribution of time-averaged blood pressure (TABP), time-averaged wall shear stress (TAWSS) and oscillatory shear index (OSI) were also visualized and can be seen.