ABSTRACT
In a 3-year period, 110 patients with central nervous system infections of various causes were examined serially by means of transcranial Doppler sonography. In viral-induced infections, no changes of flow velocity in basal cerebral arteries were seen, whereas in bacterial meningitis, a significant increase of blood flow velocity in the middle cerebral artery was recorded. Its extent was mainly associated with the type of the infectious agent, most frequently observed in pneumococcal meningitis (77%). The increase was up to 100% of the baseline values and was reversible in all cases. All patients were offered full-scale neurointensive care, and all subjects with bacterial meningitis were fully heparinized.
Subject(s)
Blood Flow Velocity , Brain/blood supply , Central Nervous System Diseases/diagnostic imaging , Adolescent , Adult , Aged , Bacterial Infections/diagnostic imaging , Bacterial Infections/physiopathology , Central Nervous System Diseases/physiopathology , Female , Humans , Male , Meningitis, Pneumococcal/diagnostic imaging , Meningitis, Pneumococcal/physiopathology , Middle Aged , Ultrasonography , Virus Diseases/diagnostic imaging , Virus Diseases/physiopathologyABSTRACT
Densitometry, Raman spectroscopy and small angle neutron scattering are employed to elucidate the miscibility behavior of lipid mixtures organized as liposomal dispersions. First, temperature-composition-phase diagrams for several binary alloys of dialkyl-lecithins differing in chain lengths by an increasing number of CH2-groups are derived. A mixture of dimyristoyllecithin and distearoyllecithin (delta CH2 = 4) shows a peritectic phase behavior with a miscibility gap in the gel state. In the fluid phase, at high enough temperatures, homogeneous mixtures of the two components are formed at all molar ratios. However, upon approaching a critical point by either lowering the temperature or increasing the hydrostatic pressure, critical concentration fluctuations are observed. If one component of a binary mixture is charged, electrostatic interactions can be used to induce phase separation at constant temperature. This is demonstrated for Ca2(+)-driven demixing in alloys of lecithin and negatively charged phosphatidylglycerol. The influence of the various concepts for the induction of lateral structure formation in lipid membranes on integral functional units like ionophores is demonstrated by analysing the single channel current fluctuations of gramicidin in bimolecular lipid membranes. Ca2+, as well as polyelectrolyte-induced phase separations are shown and discussed as examples for the important (lateral) order-function relationship in biomembranes.
Subject(s)
Membrane Lipids/chemistry , Electrochemistry , Liposomes/chemistry , Membrane Fluidity , Molecular Conformation , ThermodynamicsABSTRACT
The temperature-composition phase diagram of dimyristoylphosphatidylcholine and dipentadecylphosphatidylglycerol (DiC15PG) was determined by mass densitometry. For a mixture containing 30 mol% DiC15PG, the homogeneous distribution of the 2 components is demonstrated in the fluid state at T = 35 degrees C by small-angle neutron scattering in combination with the inverse contrast variation method. By the same technique, the coexistence of fluid and condensed phases at T = 23.3 degrees C could be shown in agreement with the densitometric data. Furthermore, it is demonstrated that Ca++ induces, even at T = 35 degrees C, separation into 2 fluid phases. A corresponding phase separation is found in bimolecular lipid membranes ("black films") by analysis of the single-channel conductance fluctuations of gramicidin A incorporated into an equimolarly mixed membrane of neutral lecithin and charged phosphatidic acid. The results are discussed as primary examples on the model-membrane level for the important structure-function relationship of biomembranes.
