Arterial bends: the development and decay of helical flows.

The macrocirculation is modelled by incompressible Newtonian flow through a rigid network of pipes for which possible simplifications are discussed. The common assumptions of two-dimensionality or axisymmetry can be generalised to helical symmetry, and in the first part of the paper, the three-dimensionality of arterial bends is considered by varying the curvature and torsion of a section of a helical pipe. The torsion is found to impart a preferential twist to the cross-sectional flow. This loss of symmetry ensures that flow separation is less severe for a helical bend than for a toroidal bend. The effects of variations in body size are examined using allometric scaling laws. In the second part of the paper, the approach to "fully developed" Dean or Womersley flow is considered in an attempt to quantify the regions of validity of idealised models. A perturbation approach, akin to hydrodynamic stability theory, is used. It is argued that often potential flows are more suitable for describing the rapid interactions between geometry and pulsatility rather than the eventual fully developed state so that, for example, the first 100 degrees of the aortic arch may be considered irrotational. Helical potential flows are found to develop faster than the corresponding toroidal flows, but slower than those in a straight pipe. The presence of vorticity in the core also retards the development of symmetric flows. It is concluded that while idealised flows can occur at some points in the body, in general experimental observation is needed to justify their use. Particular caution is recommended when interpreting calculations with Poiseuille input.

[The effect of specific immunotherapy on serum eotaxin level in patients with pollinosis: preliminary studies]. / Wplyw swoistej immunoterapii na zachowanie sie stezen eotaksyny w surowicy u chorych na pylkowice--doniesienie wstepne.

Eotaxin belongs to CC chemokines with selective activity for eosinophils and basophils. Specific immunotherapy (SIT) represents the only curative approach for allergic inflammation. The aim of this study was an evaluation of the effect of SIT on serum eotaxin level in patients with seasonal allergy. 40 patients (mean age 26 +/- 8.15 with seasonal allergy to birch, 25 with seasonal allergy to grasses) and 35 persons (mean age 27 +/- 8) of the control group took part in this study. Preseasonal immunotherapy (Allergovit, Germany) was performed in conventional schedule in patients with pollinosis. Clinical assessment of symptoms in season (score) was done by all of the patients studied. ELISA test was used to measure serum eotaxin level (pg/ml, kits from R&D) before, after immunotherapy, in pollen season and after season in patients with disease. There was observed increased eotaxin concentration in patients with allergy to birch (140.6 +/- 53.7) as compared to the eotaxin level in the control group (102.1 +/- 53.7) (p < 0.05). There was observed decreased eotaxin level after immunotherapy (115.9 +/- 49.9) (p < 0.05) in patients with allergy to birch, but no with allergy to grasses. When patients with clinical improvement were taken into account, the significant difference (p < 0.05) in eotaxin concentration was showed before (126.7 +/- 52.4) and after immunotherapy (102.5 +/- 44.8). The eotaxin level in pollen season of patients with clinical improvement was significantly (p < 0.05) decreased (116.5 +/- 54.3) as compared to the eotaxin level in patients without clinical improvement (139.8 +/- 46.3). The results suggest an involvement of eotaxin in pathomechanism of SIT. The effect depends on kind of allergen evaluated. Further longitudinal controlled investigations should establish the role measuring serum eotaxin level in the clinical evaluation of SIT.

Helical flow around arterial bends for varying body mass.

The three dimensionally curved aortic arch is modeled as a portion of a helical pipe. Pulsatile blood flow therein is calculated assuming helical symmetry and an experimentally measured pressure pulse. Appropriate values for the Womersley and Reynolds numbers are taken from allometric scaling relations for a variety of body masses. The flow structure is discussed with particular reference to the wall shear, which is believed to be important in the inhibition of atheroma. It is found that nonplanar curvature limits the severity of flow separation at the inner bend, and reduces spatial variation of wall shear.