Physical and computer modelling of blood flow in a systemic-to-pulmonary shunt.

UNLABELLED: The aim of this work was the application of computer and physical in vitro simulation methods for estimating surgery procedure hemodynamics. The modified Blalock-Taussig (mB-T) palliative surgical procedure is performed to increase the pulmonary blood flow in children with congenital heart defects. Such a systemic-to-pulmonary shunt yields substantial modification in the blood flow within the large blood vessels. The objective of the present study was to investigate basic characteristics of the flow, flow pattern and pressure-flow efficiency, before and after opening of the mB-T graft. METHODS: The model was based on the vessel geometry obtained from the Visible Human Project and included the arch of aorta, the three arteries branching from the arch, the pulmonary trunck, and the left and right pulmonary arteries. The graft was added between the left subclavian artery and the left pulmonary artery. The glass model of the vessels was produced and investigated in a physical model of the cardiovascular system with an artificial ventricular device as the blood pump. Flow rate and hydrostatic pressure were measured at the inlet to and outlets from the glass model and in a few points within the system. Laser flow visualization was also performed. Computer simulations were done using the boundary conditions from the physical model. RESULTS: The opening of the mB-T graft changed flow distribution in all branches (including inflow). A complex flow pattern with large eddies and channelling of the flow in the vicinity of the graft and within it was observed in flow visualization and in computer simulations. Because of that complexity the local measurements of hydrostatic pressure at the vessel wall could not predict the average flow rate. The reversed flow in the graft was observed during the systole. CONCLUSIONS: The complex flow pattern developed in the physical model of the mB-T graft. The channelling of the flow and the formation of large eddies may yield high shear stress and modify blood properties. The rigid wall model can describe only some flow characteristics observed in vivo. Computer simulation is a very fast and accurate method which permits earlier qualification of cardiac surgeons on how to change cardiac vascular blood flow after operations.

[Hepatitis B virus infection in children]. / Wirusowe zapalenie watroby typu B u dzieci.

Retrospective analysis of 256 medical records of children with confirmed diagnosis of hepatitis B virus infection was done. The study focused on significance of patient's age and sex in the course of the disease, on circumstance accompanying the HBV infection and on course of infection, especially a chronic HBV infection. It has been found that factors increasing the risk of infection include: former hospitalizations, surgical procedures, malfunctions of an immune system and familial contacts. Hepatitis occurred more frequently in infants and young children and in this age it more often converted into a chronic form. The course of hepatitis infection depended on dynamics of the disease process. Seroconversion occurred more often after acute phase of the disease and asymptomatic course of infection most often resulted in chronic form. Treatment with immuno-potent (TFX, isoprinosine) had no effect on the course of hepatitis B infection. It should be recommended to extend prophylaxis to children of the risk group and to introduce routine test for HBs antigen in each inpatient child.

Con A-induced suppressor cells in man. I. Introduction and characterization of suppressor cells.

Con A-induced suppressor cells were studied in autologous co-cultures of normal human lymphocytes. Lymphocytes pretreated with 5 microgram/ml, 20 microgram/ml, or 50 microgram/ml of Con A were cultured for 24, 48, 72 hours. Subsequently, the whole mononuclear (MN) cell subpopulation or T-enriched, B-enriched, and monocyte-enriched fractions were added to freshly obtained lymphocytes, stimulated with 5 microgram/ml of Con A and cultured for a further 96 hours. MN cells pretreated with 5 microgram/ml of Con A did not significantly affect the DNA synthesis in co-cultures with unfractionated MN cells, while cells pretreated with 20 microgram/ml or 50 microgram/ml for 48 and 72, but not for 24 hours, possessed the suppressive activity. The suppressor cells were found in T-, but not B-enriched subpopulations. Moreover, suppression was induced by T-enriched fraction from MN cells pretreated with 5 microgram/ml of Con A, while unfractionated cells failed to exhibit inhibitory activity. The degree of T-cell-induced suppression was dose-dependent. Irradiation with 3000 R diminished the suppressive activity of cells derived from 48-hour cultures and abrogated the activity of cells from 72-hour cultures. The present data indirectly prove that Con A-induced suppressor cells are radiosensitive T lymphocytes. The observation that induction of suppressor cells by Con A is dose-and time-dependent provides the further insight into regulatory immunological mechanism in humans.

Con A-induced suppressor cells in man. II. Role of monocytes and their interaction with soluble inhibitory factors.

Monocyte dependence of Con A-induced suppression was studied in co-cultures of normal human lymphocytes. Con-A-pretreated (25 microgram/ml for 48 hours) peripheral blood mononuclear (MN) cells inhibited the 3H-thymidine uptake by fresh autologous or allogeneic lymphocytes stimulated with Con A. Monocyte-depleted lymphocytes pretreated with 25 microgram/ml of Con A failed to exhibit the suppressor properties. Supernatants of MN cell activated with 25 microgram/ml Con A for 72 hours inhibited the mitogenic response of fresh allogeneic cells when added in proportion 1:1 to the culture medium. No inhibition was observed when supernatants of monocyte-depleted, Con A activated cultures were tested. The short preincubation with suppressive supernatants rendered blood adherent mononuclear cells suppressive for 3H-thymidine incorporation by autologous MN cells stimulated with Con A. These studies indicate that monocytes are essential for induction of suppressor cells in Con A stimulated cultures. The suppressor cells produce a soluble inhibitory factor(s) which has the property of binding to the surface of fresh monocytes. Such monocytes become responsible for suppression of mitogenic response of autologous lymphocytes.

Suppression of anti-hapten (TNP) antibody response by suppressor T cells and their product. The role of macrophages.

The effect of the lymphocytes from picryl sulfonic acid treatment animals on primary and secondary humoral immune response to TNP hapten was investigated. These cells known to inhibit contract sensitivity reactions were also able to depress primary IgM response. When peritoneal exudate cells from normal mice incubated in suppressor supernatant were transferred into primed mice the suppression of IgM but no IgM secondary response was observed. In contrast peritoneal exudate cells incubated in control supernatant augmented IgM but didn't affect IgG response. It is postulated that normal peritoneal exudate cells (presumably macrophages) can stimulate IgM response. This enhancing activity could be partially blocked by soluble suppressor factor.

Feedback inhibition of IgM memory cells by high antigen dose.

The ability of high and low antigen doses (SRBC) to recruit IgM memory cells has been compared in several strains of mice. In intact animals priming with low doses was more efficient than priming with high doses. If, however, mice of different strains were X-irradiated two days after priming and repopulated, regardless of whether syngeneic or allogeneic splenocytes were used, they fell into two categories--those in which more memory cells were found after low antigen priming and those in which the reverse was true (Swiss mice). Two possible explanations are offered to explain these interstrain differences--antibody mediated suppression, and generation of suppressor T cells. Our data favor the latter, and we assume that suppressor T cells appear at different intervals after priming in different strains of mice, and that these cells are radioresistant.