Patient-specific computational modeling of blood flow in the pulmonary arterial circulation.

Computational fluid dynamics (CFD) modeling of the pulmonary vasculature has the potential to reveal continuum metrics associated with the hemodynamic stress acting on the vascular endothelium. It is widely accepted that the endothelium responds to flow-induced stress by releasing vasoactive substances that can dilate and constrict blood vessels locally. The objectives of this study are to examine the extent of patient specificity required to obtain a significant association of CFD output metrics and clinical measures in models of the pulmonary arterial circulation, and to evaluate the potential correlation of wall shear stress (WSS) with established metrics indicative of right ventricular (RV) afterload in pulmonary hypertension (PH). Right Heart Catheterization (RHC) hemodynamic data and contrast-enhanced computed tomography (CT) imaging were retrospectively acquired for 10 PH patients and processed to simulate blood flow in the pulmonary arteries. While conducting CFD modeling of the reconstructed patient-specific vasculatures, we experimented with three different outflow boundary conditions to investigate the potential for using computationally derived spatially averaged wall shear stress (SAWSS) as a metric of RV afterload. SAWSS was correlated with both pulmonary vascular resistance (PVR) (R(2)=0.77, P<0.05) and arterial compliance (C) (R(2)=0.63, P<0.05), but the extent of the correlation was affected by the degree of patient specificity incorporated in the fluid flow boundary conditions. We found that decreasing the distal PVR alters the flow distribution and changes the local velocity profile in the distal vessels, thereby increasing the local WSS. Nevertheless, implementing generic outflow boundary conditions still resulted in statistically significant SAWSS correlations with respect to both metrics of RV afterload, suggesting that the CFD model could be executed without the need for complex outflow boundary conditions that require invasively obtained patient-specific data. A preliminary study investigating the relationship between outlet diameter and flow distribution in the pulmonary tree offers a potential computationally inexpensive alternative to pressure based outflow boundary conditions.

The role of wall shear stress in the assessment of right ventricle hydraulic workload.

Pulmonary hypertension (PH) is a devastating disease affecting approximately 15-50 people per million, with a higher incidence in women. PH mortality is mostly attributed to right ventricle (RV) failure, which results from RV hypotrophy due to an overburdened hydraulic workload. The objective of this study is to correlate wall shear stress (WSS) with hemodynamic metrics that are generally accepted as clinical indicators of RV workload and are well correlated with disease outcome. Retrospective right heart catheterization data for 20 PH patients were analyzed to derive pulmonary vascular resistance (PVR), arterial compliance (C), and an index of wave reflections (Γ). Patient-specific contrast-enhanced computed tomography chest images were used to reconstruct the individual pulmonary arterial trees up to the seventh generation. Computational fluid dynamics analyses simulating blood flow at peak systole were conducted for each vascular model to calculate WSS distributions on the endothelial surface of the pulmonary arteries. WSS was found to be decreased proportionally with elevated PVR and reduced C. Spatially averaged WSS (SAWSS) was positively correlated with PVR (R (2) = 0.66), C (R (2) = 0.73), and Γ (R (2) = 0.5) and also showed promising preliminary correlations with RV geometric characteristics. Evaluating WSS at random cross sections in the proximal vasculature (main, right, and left pulmonary arteries), the type of data that can be acquired from phase-contrast magnetic resonance imaging, did not reveal the same correlations. In conclusion, we found that WSS has the potential to be a viable and clinically useful noninvasive metric of PH disease progression and RV health. Future work should be focused on evaluating whether SAWSS has prognostic value in the management of PH and whether it can be used as a rapid reactivity assessment tool, which would aid in selection of appropriate therapies.

A case of primary intrahepatic gastrinoma.

Gastrinoma is an uncommon but important cause of peptic ulcer disease. These tumors are most commonly located in the duodenum or pancreas. We present a case of a primary intrahepatic gastrinoma. Only 20 such cases have been previously reported in the literature. Metastatic hepatic gastrinomas are much more common, but it is important to differentiate between a primary and metastatic lesion because of the worse prognosis associated with a metastatic lesion.

A validation study of 3 grading systems to evaluate small-bowel cleansing for wireless capsule endoscopy: a quantitative index, a qualitative evaluation, and an overall adequacy assessment.

BACKGROUND: Capsule endoscopy (CE) is a powerful tool for evaluating the small bowel. Assessment of small-bowel cleansing for CE is an essential quality measure. OBJECTIVE: Our purpose was to validate 3 new scales that grade small-bowel cleansing for CE. DESIGN: Prospective, randomized, single-center study. SETTING: Tertiary university hospital. INTERVENTION: Five experienced capsule endoscopists read 40 CEs twice, separated by 1 month, to grade small-bowel cleansing on 3 scales-quantitative index (QI; 0-10), qualitative evaluation (QE; poor, fair, good, excellent), and overall adequacy assessment (OAA; inadequate, adequate). The QI and QE evaluated both the entire and distal small bowel. Investigators received no prior training in these scales. MAIN OUTCOME MEASUREMENTS: Intraclass correlation coefficients to assess intraobserver (test-retest) and interobserver reliability. PATIENTS: Forty patients who underwent 1 CE between June 2005 and May 2006 and who satisfied entry criteria. RESULTS: Intraobserver reliability was moderate to substantial for the QI (0.60-0.66), moderate for the OAA (0.56), and fair to moderate for the QE (0.37-0.47). Interobserver scores were lower: QI and OAA moderate (0.47-0.52, 0.41, respectively) and slight to fair for the QE (0.20-0.24). QI scores for the entire and distal small bowel were highly correlated for each reader (0.57-0.87), and distal small-bowel scores were lower by 1.3 points, indicating poorer cleansing (P = .001). A dichotomized QE of excellent/good versus fair/poor had moderate to substantial intraobserver and interobserver reliability (0.58-0.66, 0.41-0.49, respectively). There was a strong and highly significant association among all 3 scales (P < .001 between QI and both QE and OAA). CONCLUSION: We have described and validated 3 scales for grading small-bowel cleansing for CE. An evaluation of small-bowel cleansing should be routinely incorporated into the CE report.