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Biomedical subjects

A Ring

Publications and source records attributed to A Ring.

At least 73 records · Page 4Linked to original sources

Linear network representation of multistate models of transport.

By introducing external driving forces in rate-theory models of transport we show how the Eyring rate equations can be transformed into Ohm's law with potentials that obey Kirchhoff's second law. From such a formalism the state diagram of a multioccupancy multicomponent system can be directly converted into linear network with resistors connecting nodal (branch) points and with capacitances connecting each nodal point with a reference point. The external forces appear as emf or current generators in the network. This theory allows the algebraic methods of linear network theory to be used in solving the flux equations for multistate models and is particularly useful for making proper simplifying approximation in models of complex membrane structure. Some general properties of linear network representation are also deduced. It is shown, for instance, that Maxwell's reciprocity relationships of linear networks lead directly to Onsager's relationships in the near equilibrium region. Finally, as an example of the procedure, the equivalent circuit method is used to solve the equations for a few transport models.

Biological Transport↗

Impedance of the frog gastric mucosa, the Teorell-Wersäll effect.

The small signal impedance of frog gastric mucosa has been measured from 1 Hz to 500 kHz. The results obtained in Ringer's solution have been compared with the effect of replacing sodium with potassium on the nutrient side of the mucosa. The substitution to potassium reduces the membrane resistance and changes the impedance locus from a flat to a semicircular shape. We have examined this effect, the Teorell-Wersäll effect, in relation to changes in membrane permeabilities. The experimental data are consistent with a model based on the electrical behaviour of transmission cables (the geometric requirement for this may be found in the gastric duct) and the observed electrical properties can be predicted from an increase in conductance of the secretory membrane when replacing sodium with potassium.

Animals↗

[A course of pregnancy with herpes gestationis (author's transl)].

A 24-years old III.-para and III.-gravida was hospitalized in the 36th week of gravidity, with premature labour and distinct symptoms of herpes gestationis. It is reported in literature that the clinical picture of herpes gestationis is combined with a high rate of abortion and fetal anomalies. Therefore an intensive prenatal super vision was carried through with daily cardiotocographic controls and checkings of total estrogens in 24-hours-urine, also measurements of Alpha-Fetoproteins, human placenta lactogen and serumoxytocinase. After inducting labour because of maternal indication the patient gave birth to a healthy female infant (3720 g, 50 cm) with Apgar 10 in the 39th week of gravidity. The investigation of the placenta and all biochemical parameters did not point to an interference of gravidity. The present literature is discussed. Some authors doubt that herpes gestationis is met with a high rate of abortion, stillbirth and fetal anomalies as is assumed till now.

Adult↗

Haematopoietic transplant potential of unrelated and related cord blood: the first six years of the EUROCORD/NETCORD Bank Germany.

To date, human umbilical cord blood (CB) has been employed successfully in well over 1000 allogeneic (unrelated and sibling) stem cell transplantations. Because of primary limitations in volume and cell numbers, over 90% of these transplantations were performed in children. Therefore requests for well standardised cord blood units of high quality are now increasing constantly. Examination and standardisation of unrelated and related cord blood stem cell preparations and banking as well as their biological characterisation was already initiated in Düsseldorf in 1992. Hitherto a total of 3236 CB samples with a mean volume of 89 +/- 25 ml, a mean total number of nucleated cells (NC) of 10 +/- 5 x 10(8) and a mean number of CFU-GM of 6 +/- 5 x 10(5) have also been validated by haematological, immunological and microbiological criteria. In addition to that, 97 directed CB donations of siblings with a clinical indication have been characterised and banked along the same lines. All CB units were collected from the umbilical cord vein immediately after vaginal full term delivery or caesarean section, then frozen and stored in liquid nitrogen. 1940 CB units were stored unseparated, the other 1296 were volume reduced using Hetastarch (HES) with a mean recovery of 85 +/- 13% of the nucleated cells, 86 +/- 12% and 84 +/- 13% for CFC and CD34+ cells, respectively. Only 5.0 ml of a CB sample is required for routine laboratory testing as there are HLA-class I typing, HLA-class II typing by sequence specific oligonucleotide probes (PCR-SOP), ABO typing, sterility control, assessment of progenitor and stem cells by colony forming assays, and CD34+ status as well as certain viral infections such as CMV, Hepatitis B, C, HIV, Parvo B19 by PCR technology before releasing the CB unit for transplantation. For apparent viral infections, maternal sera obtained at birth were tested for HBsAg, anti-HBc, anti-HCV, -HAV-(IgG, IgM), -HIV-1-2, -EBV- (IgG, IgM), -HTLVI-II, -CMV (IgM, IgG), toxoplasmosis and syphilis. Within the last three years a total of 4860 preliminary searches and 680 extended unit reports were submitted to the CB bank Düsseldorf by fax or World Wide Web. So far 68 unrelated and 3 related CB units were delivered. From these 70 have been transplanted in 30 different transplant centres world-wide. Until now the evaluation of the first 53 unrelated CB-transplantations was performed together with the EUROCORD transplant registry. Three patients were excluded from the analysis, since they received an unrelated CB-transplant for non-engraftment after previous allotransplants. The median patient age of these 50 patients was 5.0 years (range 0.3-44), the median weight 18 kg (range 4-70 kg). The majority of the patients transplanted for malignancies (66%) suffered from ALL (n = 19), AML (n = 7), CML (n = 4) and lymphoma (n = 2) with two third (75%) in an intermediate (2nd CR) or advanced stage of disease (> 2nd CR); 13 patients had metabolic diseases and immunodeficiencies and three had aplastic anaemia. All CB samples as well as the patients' blood samples were typed in Düsseldorf for HLA-class I by serology confirmed by PCR-SSP and by high resolution DNA typing for HLA-DRB1 and HLA-DQB1 alleles. 96% of the 50 patients receiving unrelated CB were mismatched at one or more HLA-antigens. 41 of the 50 patients transplanted with unrelated CB from Düsseldorf were evaluable for engraftment with an overall engraftment rate of 83%. According to the defined criteria of EUROCORD, 9 of the 50 patients were not evaluable for engraftment, since they died before day 60. The present median follow-up time is 14 months (1.4-38). The Kaplan-Meier estimate of survival at one year is 42 percent. The three paediatric patients after sibling CB transplantations (ALL, amegakaryocytic thrombocytopenia and CML) are alive with a follow-up time of 350, 379 days and 531 days. (ABSTRACT TRUNCATED)

Adolescent↗

Sleep disturbances in children with attention-deficit/hyperactivity disorder: a comparative study with healthy siblings.

The sleep profiles of 13 children with attention-deficit/hyperactivity disorder (ADHD) who were treated with a fixed dose of methylphenidate for at least 1 month were compared with those of 16 healthy siblings. Sleep disturbances were assessed according to a structured sleep questionnaire, and the severity of ADHD was evaluated via the Conners Parents Teachers Rating Scale. The results indicated that significantly more children with ADHD demonstrated single or multiple sleep disturbances as well as higher rates of specific sleep disorders, such as initial and middle insomnia, compared with their siblings. No correlation was found between the severity of ADHD and disturbed sleep. Sleep duration and satisfaction with sleep were similar in the two groups. These findings raise important questions regarding the association between ADHD and disturbed sleep.

Attention Deficit Disorder with Hyperactivity↗