Biplane angiography for experimental validation of computational fluid dynamic models of blood flow in artificial lungs.

This article presents an investigation into the validation of velocity fields obtained from computational fluid dynamic (CFD) models of flow through the membrane oxygenators using x-ray digital subtraction angiography (DSA). Computational fluid dynamic is a useful tool in characterizing artificial lung devices, but numerical results must be experimentally validated. We used DSA to visualize flow through a membrane oxygenator at 2 L/min using 37% glycerin at 22°C. A Siemens Artis Zee system acquired biplane x-ray images at 7.5 frames per second, after infusion of an iodinated contrast agent at a rate of 33 ml/s. A maximum cross-correlation (MCC) method was used to track the contrast perfusion through the fiber bundle. For the CFD simulations, the fiber bundle was treated as a single momentum sink according to the Ergun equation. Blood was modeled as a Newtonian fluid, with constant viscosity (3.3 cP) and density (1050 kg/m3). Although CFD results and experimental pressure measurements were in general agreement, the simulated 2 L/min perfusion did not reproduce the flow behavior seen in vitro. Simulated velocities in the fiber bundle were on average 42% lower than experimental values. These results indicate that it is insufficient to use only pressure measurements for validation of the flow field because pressure-validated CFD results can still significantly miscalculate the physical velocity field. We have shown that a clinical x-ray modality, together with a MCC tracking algorithm, can provide a nondestructive technique for acquiring experimental data useful for validation of the velocity field inside membrane oxygenators.

Improved computational fluid dynamic simulations of blood flow in membrane oxygenators from X-ray imaging.

Computational fluid dynamics (CFD) is a useful tool in characterizing artificial lung designs by providing predictions of device performance through analyses of pressure distribution, perfusion dynamics, and gas transport properties. Validation of numerical results in membrane oxygenators has been predominantly based on experimental pressure measurements with little emphasis placed on confirmation of the velocity fields due to opacity of the fiber membrane and limitations of optical velocimetric methods. Biplane X-ray digital subtraction angiography was used to visualize flow of a blood analogue through a commercial membrane oxygenator at 1-4.5 L/min. Permeability and inertial coefficients of the Ergun equation were experimentally determined to be 180 and 2.4, respectively. Numerical simulations treating the fiber bundle as a single momentum sink according to the Ergun equation accurately predicted pressure losses across the fiber membrane, but significantly underestimated velocity magnitudes in the fiber bundle. A scaling constant was incorporated into the numerical porosity and reduced the average difference between experimental and numerical values in the porous media regions from 44 ± 4% to 6 ± 5%.

Preprocedural planning with prospectively triggered multidetector row CT angiography prior to bronchial artery embolization in cystic fibrosis patients with massive hemoptysis.

STUDY OBJECTIVES: The aim of this study was to determine if electrocardiographically synchronized, prospectively triggered multidetector row computed tomography (ECG-MDR-CT) angiography of the aorta can accurately predict the location of ectopic bronchial arteries in patients with cystic fibrosis (CF) with massive hemoptysis prior to bronchial artery embolization (BAE). DESIGN AND SETTING: The study was a prospective, observational study from September 1, 2009 to June 30, 2011, conducted at a university hospital with an adult CF center. PATIENTS: The study included adult CF patients with massive hemoptysis. RESULTS: A total of four adult patients (mean [± SD] age = 31.5 ± 7.9 years) with CF and massive hemoptysis underwent ECG-MDR-CT angiography. The location of the bleeding source was predicted in each case based on lung pathology observed on ECG-MDR-CT angiography. All four patients eventually required BAE without the need for conventional aortograms since the locations of the bronchial arteries were determined prior to the procedure. Review of lung pathology and arterial networks from the ECG-MDR-CT angiography data limited the number of selective catheterizations necessary to complete the procedures. BAE resulted in complete resolution of hemoptysis in three patients and successful mitigation of the bleeding in the fourth patient until lung transplantation was performed 1 week later. CONCLUSIONS: ECG-MDR-CT angiography accurately depicted bronchial artery anatomy in CF patients with massive hemoptysis and provided excellent preprocedural planning for BAE. The information provided by ECG-MDR-CT angiography of the aorta prior to conventional angiography decreased the BAE radiation dose and contrast volume and likely reduced table time.

Patient discomfort associated with the use of intra-arterial iodinated contrast media: a meta-analysis of comparative randomized controlled trials.

BACKGROUND: Discomfort characterized by pain and warmth are common adverse effects associated with the use of intra-arterial iodinated contrast media (CM). The objective of this review was to pool patient-reported outcomes available from head-to-head randomized controlled trials (RCTs) and to compare the discomfort rates associated with iso-osmolar contrast media (IOCM; i.e., iodixanol) to those reported with various low-osmolar contrast media (LOCM). METHODS: A review of the literature published between 1990 and 2009 available through Medline, Medline Preprints, Embase, Biological Abstracts, BioBase, Cab Abstracts, International Pharmaceutical Abstracts, Life Sciences Collection, Inside Conferences, Energy Database, Engineering Index and Technology Collection was performed to compare rates of discomfort associated with the use of the IOCM (iodixanol) vs. various LOCM agents in head-to-head RCTs. All trials with a Jadad score ≥2 that reported patient discomfort data following intra-arterial administration of CM were reviewed, coded, and extracted. RESULTS: A total of 22 RCTs (n = 8087) were included. Overall discomfort (regardless of severity) was significantly different between patients receiving IOCM and various LOCMs (risk difference [RD] -0.049; 95% confidence interval [CI]: -0.076, -0.021; p = 0.001). IOCM was favored over all LOCMs combined with a summary RD value of -0.188 (95% CI: -0.265, -0.112; p < 0.001) for incidence of pain, regardless of severity. A greater reduction in the magnitude of pain was observed with IOCM (iodixanol), particularly with selective limb and carotid/intracerebral procedures. Similarly, the meta-analysis of warmth sensation, regardless of severity, favored IOCM over LOCMs with an RD of -0.043 (95% CI: -0.074, -0.011; p = 0.008). A positive linear relationship was observed between the discomfort effect size and age and a negative relationship with increasing proportion of women. The opposite trends were observed with warmth sensation. CONCLUSIONS: IOCM was associated with less frequent and severe patient discomfort during intra-arterial administration. These data support differences in osmolality as a possible determinant of CM discomfort.