MRI detection of weak magnetic fields due to an extended current dipole in a conducting sphere: a model for direct detection of neuronal currents in the brain.

To investigate the feasibility of direct MR detection of neuronal activity in the brain, neuronal current flow was modeled as an extended current dipole located in a conducting sphere. The spatially varying magnetic field induced within the sphere by such a dipole was calculated, including its form close to and within the current source. The predicted field variation was experimentally verified by measurements of the variation in phase of the MR signal in a sphere containing a model dipole. The effects of the calculated magnetic field distributions on the phase and magnitude of the signal in MR images were explored. The minimum detectable dipole strength under normal experimental conditions was calculated to be about 4.5 nAm, which is similar in magnitude to dipole strengths from evoked neuronal activity, and is an order of magnitude smaller than dipole strengths expected from spontaneous activity. This minimum detectable dipole strength increases with increasing spatial extent of the primary current distribution. In the experimental work, the effects of a field of [1.1 +/- 0.5] x 10(-10) T strength were detected, corresponding to the maximum net field caused by a dipole of 6.3 nAm strength with a spatial extent of 3 x 3 x 2 mm(3).     

血管加压素受体Ⅰ在实验性糖尿病大鼠肾脏和肝脏的调节

本文利用链脲佐菌素诱导的实验性糖尿病大鼠,在糖尿病形成2周时分别测定血糖、肾小球滤过率(GFR)、血浆精氨酸血管加压素(AVP)、血钠及血浆渗透压,并用选择性AVP受体Ⅰ(V1)的放射配体~(125)I[d(CH_2)_5-Sarcosine~7]AVP对肾髓质膜和肝细胞膜V1受体进行结合分析。实验分三组:糖尿病组(D组)、胰岛素治疗组(T组)和对照组(C组)。结果表明,糖尿病形成2周时,各组血糖值为:D=37±7.5mmol/L;T=19±5.78mmol/L: C=7.63±0.59mmol/L。DT两组的GFR均增加,血浆AVP在D组明显高于对照组。膜受体结合试验显示:肾髓质膜V1受体最大结合容量(Bmax)在各组均无明显差异,解离常数(Kd值)D组大于T、C两组,肝细胞膜Bmax在T组增加,而Kd值在各组均未见改变。     

Magnetic resonance imaging of the behaviour of oil-in-water emulsions in the gastric lumen of man

Pre-processed foods often contain a high percentage of lipid, present as emulsions stabilised with various surface-active agents. The acidic gastric environment can affect the behaviour of such emulsions, modifying the lipid spatial distribution and, in turn, the rate of gastric emptying and nutrient delivery to the gut. The aim of the present study was to use echo-planar magnetic resonance imaging (EPI) to determine the behaviour of model olive oil emulsions during gastric processing. Six healthy male volunteers were intubated nasogastrically on two separate occasions and fed 500 ml 15 % (w/w) olive oil-in-water, surfactant-stabilised emulsions designed to have identical droplet size distribution and which were either stable or unstable under gastric acid conditions. EPI was used to assess the oil fraction of the intragastric emulsions, gastric emptying and to visualise the spatial distribution of the oil at 10, 30 and 50 min postprandially. The in vivo imaging measurements of the oil volume fraction of the emulsions correlated well (r 0.66, acid-stable; r 0.52, acid-unstable) with that assayed in the gastric aspirates. Compared with the acid-stable emulsion, the acid-unstable emulsion in the gastric lumen rapidly separated into lipid-depleted 'aqueous' and lipid layers. Phase separation in the acid-unstable meal allowed the oil-depleted component to empty first and more rapidly than the stable emulsion as determined by the gastric emptying curves. These pilot data suggest that gastric processing and emptying of high-fat foods could be manipulated by careful choice of emulsifier.     

Adhesion of platelets to human artery subendothelium: effect of factor VIII-von Willebrand factor of various multimeric composition

The relationship between the multimeric size of factor VIII-von Willebrand factor (FVIII-vWF) and the support of platelet adhesion to subendothelium was studied in an annular perfusion chamber, employing human renal and umbilical arteries. Commercial factor VIII concentrates containing multimers of low molecular weight that had been shown not to correct the bleeding time upon infusion into patients with von Willebrand's disease did not support platelet adhesion in the perfusion chamber. Cryoprecipitate and two experimental FVIII-vWF concentrates containing multimers of high molecular weight supported platelet adhesion. Factor VIII-vWF purified from cryoprecipitate was subdivided into three fractions of different molecular weights (6.0-14.0, 4.0-9.0, and 3.0-7.5 X 10(6) dalton). These fractions appeared to bind equally well and to be equally effective in supporting platelet adhesion. Factor VIII-vWF with multimers of low molecular weight (0.5-1.5 X 10(6) dalton) were prepared by partial reduction. Binding of FVIII-vWF to subendothelium was not impaired, and the support of platelet adhesion appeared to be more resistant to the effect of reduction than the ristocetin cofactor activity. At high shear rate (2,500 sec-1), increased platelet adhesion was observed with partially reduced FVIII- vWF. These data indicate that the ability of FVIII-vWF preparations to correct the bleeding time is reflected in enhanced platelet adhesion to subendothelium in a perfusion chamber. These data also emphasize that multimeric size is not the only factor determining whether FVIII-vWF will support platelet adhesion.     

Static morphometric bases for CT identification and evaluation of the outflow chamber of the left ventricle. Preliminary study in formalin-fixed heart

Summary A static morphometric study of the outflow chamber of the left venticle (OCLV) was investigated in a series of 10 formalin-fixed hearts. A spatial reconstruction of the shape and the volume of the OCLV was carried out by means of a Somaton Plus TR4 Tomodensitometer (Siemens). The technic allows evaluation of the surface of the aortic and the mitral orifices and visualization of the three-dimensional OCLV and LV morphology, as well as calculation of their volumes. The limits of the technic in the dynamic study of the OCLV are presented.

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Bases morphométriques statiques d'identification et d'évaluation de la chambre de chasse du ventricule gauche par tomodensitométrie. Etude préliminaire sur le coeur formolé

Résumé Les auteurs présentent sur une série de 10 coeurs formolés une étude statique morphométrique de la chambre de chasse du ventricule gauche (CCVG). La reconstruction spatiale de la forme et du volume de la CCVG est réalisée grâce au Scanner Somaton Plus (Siemens). La technique permet d'évaluer la surface des orifices aortique et mitral, de visualiser la morphologie tridimensionnelle du VG et de la CCVG et de calculer leur volume. Les auteurs souligenent les limites de la technique présentée dans l'étude dynamique de la CCVG.

     

Polymerase chain reaction-based detection of MN blood group-specific sequences in the human genome

The MN blood group antigens have traditionally been detected by serotyping; however, development of a DNA-based method offers flexibility in the determination of this highly polymorphic system. Genotyping the MN blood group antigens was performed by polymerase chain reaction amplification of the specific alleles (PASA) in the human genome. In separate paired reactions, M or N allele-specific oligonucleotide primers were amplified with a common distal primer. Only in the presence of the homologous template was a 781-base pair polymerase chain reaction amplification product visible after agarose gel electrophoresis and ethidium bromide staining. This method of genotyping could be performed using either 1 microgram of extracted DNA or 0.5 microL of whole blood, and the results showed 100-percent correlation with those obtained by serotyping. PASA-based genotyping of MN blood group antigens, which requires a small amount of starting material, has application in linkage and population studies and in forensic medicine.     

A Study of Danazol's Safety

In a review of medical records of 530 recipients of danazol at Group Health Cooperative of Puget Sound, we identified 154 (29%) people who reported at least one adverse event that occurred within 45 days after receiving the drug. In no patient did the event require hospitalization, and there were no known long-term sequelae.     

Cerebral Doppler and misrepresentation of flow changes

To determine whether cerebral blood flow velocity (CBFV) measurements were representative of cerebral blood flow (CBF) changes in pathological flow situations five newborn piglets were investigated. They underwent measurements of CBF by electromagnetic flowmetry on a modified common carotid artery where extracerbral branches were tied off simultaneously with Doppler recording either from the same precerebral or an intracerebral artery. The two methods agreed well within moderate carbon dioxide and blood pressure changes. During severe hypotension and hypertension Doppler overestimated CBF by 25-100%. During transfusion of infected or incompatible blood the two methods differed in opposite directions with Doppler reading from 30-200% of CBF. Transfusion of chilled blood caused CBFV to overestimate 15% and heated blood caused 20% underestimation. These results could be explained by diameter changes in response to variation in myogenic tone or vasoactive substances. CBFV measurements could be seriously misleading in severe clinical derangements where neonatal brain damage might occur.