Numerical solutions of differential equations of an ionization chamber: plane-parallel and spherical geometry

Despite the widespread availability of MR imaging, CT remains a vital modality for the evaluation of disorders of the spine, offering superior assessment of bone abnormalities, as well as calcification. Advances in technology have enhanced the capabilities of CT, providing exciting new options for data rendering and display. Depending on the clinical indication, either CT or MR may be the modality of choice in the evaluation of spinal disease.     

Position and velocity coupling of postural sway to somatosensory drive

Light touch contact of a fingertip to a stationary surface provides orientation information that enhances control of upright stance. Slight changes in contact force at the fingertip lead to sensory cues about the direction of body sway, allowing attenuation of sway. In the present study, the coupling of postural sway to a moving contact surface was investigated in detail. Head, center of mass, and center of pressure displacement were measured as the contact surface moved rhythmically at 0.1, 0.2, 0.4, 0.6, and 0.8 Hz. Stimulus amplitude decreased with frequency to maintain peak velocity constant across frequency. Head and body sway were highly coherent with contact surface motion at all frequencies except 0.8 Hz, where a drop-off in coherence was observed. Mean frequency of head and body sway matched the driving frequency 相似文献   

The effect of endothelin and its antagonist Bosentan on hemodynamics and microvascular exchange in cirrhotic rat liver

BACKGROUND/AIMS: To characterize the effects of endothelin-1 and of Bosentan, a mixed endothelin antagonist, on hepatic hemodynamics in cirrhotic animals in vivo and on hepatic microvascular exchange in the perfused rat liver. METHODS: Biliary cirrhosis was induced by bile duct ligation, and micronodular cirrhosis by chronic exposure to phenobarbital/CCl4 in male rats. Hepatic hemodynamics were studied under basal conditions and after administration of Bosentan (3-30 mg/kg) by the microsphere technique. Microvascular exchange was assessed in the in situ perfused rat liver by the multiple indicator dilution technique. RESULTS: Bosentan lowered portal pressure in a dose-dependent fashion; at the highest dose tested, this decrease averaged -29+/-11 and -26+/-8% in biliary and micronodular cirrhosis, respectively (p<0.01). This was achieved mainly via a marked decrease in hepatic arterial flow. In the perfused liver, endothelin-1 induced a dose-dependent vasoconstriction; up to 10(-9) mol/l; this was not associated with any effect on viability. At this dose, endothelin-1 markedly decreased extravascular albumin space in both controls and micronodular cirrhosis; this could be antagonized by Bosentan 10(-5) mol/l. CONCLUSIONS: Endothelin-1 affects hepatic microvascular exchange, presumably by a direct effect on hepatic sinusoidal endothelial cells. A mixed endothelin antagonist lowers portal pressure in vivo, presumably by acting on hepatic stellate cells, and counteracts the microvascular effects of endothelin-1 in vitro. These properties could prove useful in treatment of portal hypertension.     

Asking for the indicator function of bioassays evaluating soil contamination: are bioassay results reasonable surrogates of effects on soil microflora?

In evaluating the biological effect of solid materials like soil a bacterial contact assay often shows higher sensitivity than elutriate testing. Results of the Bacillus cereus contact assay for some environmental important toxicants are presented in this article. A comparison with another heterotrophic soil bacterium, Arthrobacter globiformis, shows comparable sensitivity. In a bioassay approach organisms at the level of individuals or populations are exposed to soil material to determine the significance of contaminants. An investigation that incorporates community level processes in comparison with toxicity test results provides a better understanding of the indicator function of bioassays. Comparison of soil bioassays (aqueous and solid phase) with ecological parameters demonstrates the problems in predicting ecological effects of soil contamination.     

In search of a reliable marker of tissue injury during heart surgery

We report on a new patient with d-transposition of the great arteries who was found to have deletion of 22q11.2. He had minor facial anomalies, normal T- and B-cell subsets, and transient hypocalcemia. Similar to rare previous reports, our patient's extracardiac manifestations were relatively mild.