PubMed · 14008598
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D G WYATT. 1961. Some notes on flow generators.. https://doi.org/10.1088/0031-9155%2F6%2F2%2F309
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BACKGROUND: Flow quantification in real time by phase-contrast MRI (PC-MRI) may provide unique hemodynamic information in congenital heart disease, but available techniques have important limitations. We sought to validate a novel real-time magnetic resonance flow sequence in children. METHODS AND RESULTS: In 14 pediatric patients (mean age 5.2+/-2.0 years) with cardiac left-to-right shunt, pulmonary (Q(p)) and aortic (Q(s)) flow rates were determined by nontriggered free-breathing real-time PC-MRI with single-shot echo-planar imaging combined with sensitivity encoding, which yielded 25 phase images per second at 2.7x2.7-mm in-plane resolution (field of view 30x34 cm2). Over a 9.5-second period that included 2 to 5 respiratory cycles, 16.6+/-2.6 subsequent stroke volumes (range 13 to 22) were acquired in each vessel. Results were compared with conventional retrospectively ECG-gated PC-MRI. Mean Q(p)/Q(s) by conventional PC-MRI was 1.91+/-0.64, and it was 1.94+/-0.68 (mean+/-SD) by real-time PC-MRI. For blood flow rate through pulmonary artery and aorta, we found differences of 2% to 3% (Bland-Altman analysis), with lower limits of agreement of -11% to -13% (mean-2 SD) and upper limits of 18% to 19% (mean+2 SD), which demonstrated good agreement between both methods. Mean difference for Q(p)/Q(s) was 1%, with limits of agreement ranging between -18% and 22% (mean+/-2 SD). High repeatability but some flow overestimation was observed in vitro (pulsatile flow phantom) with real-time PC-MRI, whereas conventional PC-MRI was accurate. Beat-to-beat stroke-volume variation was 6.1+/-2.3% in vivo and 3.7+/-0.3% in vitro. CONCLUSIONS: Beat-to-beat quantification of pulmonary and aortic flows and hence left-to-right shunt within a few seconds is reliable by nontriggered real-time PC-MRI with echo-planar imaging and sensitivity encoding. Good spatial/temporal resolution and a large field of view may render the sequence valuable for multiple applications in congenital heart disease.
The identification of chemokines has profoundly changed the way we interpret the immune response, elucidating the mechanism by which inflammatory cells are recruited to the site of infection by local secretion of chemoattractants such as CXC chemokine ligand 8 (CXCL8)/interleukin-8, chemokine ligand 2 (CCL2)/monocyte chemoattractant protein 1. This novel view of the immune response has been remodeled further following observations that lymphoid tissue development derives from the coordinated secretion of homeostatic chemokines such as CCL19, CCL21, and CXCL13, which mediate recruitment and clustering of the cells involved in lymphoid organogenesis. The study of primary immunodeficiencies has demonstrated that the number of circulating leukocytes is dependent on migration amongst bone marrow, blood circulation, and inflamed tissues. Defects of leukocyte adhesion and chemotaxis as a result of mutations of beta2-integrins lead to abnormal leukocytosis and susceptibility to skin infections, as observed in leukocyte adhesion deficiency. Conversely, neutropenia in children with myelokathexis is a result of leukocyte retention in the bone marrow because of the mutations of CXC chemokine receptor 4, which affect the capacity of cells to recirculate between blood and bone marrow. Moreover, the identification of the genetic basis of primary immunodeficiencies has shown that many primary immunodeficiencies such as Wiskott-Aldrich syndrome and common variable immunodeficiencies are characterized by altered migration of leukocytes and/or disregulation of cellular response to chemokines. This paper will be focused on the interpretation of primary immunodeficiencies as defects in leukocyte circulation between blood and primary and secondary organs.
Transthoracic Doppler echocardiography provides noninvasive measurements of coronary blood flow in the left anterior descending coronary artery (LAD). This method has the potential to show the effects of acute changes in loading conditions on blood flow. Coil closure of patent ductus arteriosus (PDA) is a model of acute changes in blood pressure and left ventricular (LV) preload that influences coronary blood flow. We applied this technique to assess the coronary blood flow changes for patients with PDA before and immediately after PDA coil closure. We examined 9 patients (1.8 +/- 1.1 years) with simple PDA and 8 age-matched healthy children. LV dimensions and LV mass were measured. Maximum peak flow velocity and flow volume in the LAD were measured. Pulmonary to systemic flow ratios (Qp/Qs) were obtained by cardiac catheterization. After PDA coil closure, LV end-diastolic dimension decreased, and systolic and diastolic blood pressures increased significantly. The maximum peak flow velocity, LAD flow volume, and the ratio of LAD flow volume to LV mass increased significantly. The changes in maximum peak flow velocity and the ratio of LAD flow volume to LV mass (F/M) correlated positively with the changes in diastolic pressure and Qp/Qs. In 5 patients who had Qp/Qs > 1.5, the mean F/M was significantly lower compared with control subjects, but they increased to normal values after coil closure of PDA. PDA coil closure increases diastolic pressure and decreases Qp/Qs, resulting in improvement of myocardial perfusion. These findings provide new insights into the relationship between cardiac function and coronary circulation in pediatric patients with heart diseases associated with PDA.