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Biomedical subjects

J van Mourik

Publications and source records attributed to J van Mourik.

6 recordsLinked to original sources
PubMed2002

Random graph coloring: statistical physics approach.

The problem of vertex coloring in random graphs is studied using methods of statistical physics and probability. Our analytical results are compared to those obtained by exact enumeration and Monte Carlo simulations. We critically discuss the merits and shortcomings of the various methods, and interpret the results obtained. We present an exact analytical expression for the two-coloring problem as well as general replica symmetric approximated solutions for the thermodynamics of the graph coloring problem with p colors and K-body edges.

Journal Article↗
PubMed2000

Platelets release thrombopoietin (Tpo) upon activation: another regulatory loop in thrombocytopoiesis?

Thrombopoietin is produced at a constant rate by the liver and kidney and is removed from the circulation upon binding and subsequent uptake via the Tpo receptor, c-Mpl, expressed by platelets and mega-karyocytes. Apart from uptake, this study shows that platelets can also function as a storage pool for Tpo. Upon stimulation with various platelet agonists, full-length biologically active Tpo was released by platelets. Platelet fractionation experiments indicated that this Tpo most likely is contained in the granules. When platelets were preincubated with Tpo-peptide mimetic or truncated Tpo prior to maximal activation, a three- to fivefold increment in Tpo release was seen. whereas, the release of other granule proteins such as vWF-propeptide or serotonin remained unchanged. Therefore, the Mpl agonists might compete with Mpl-bound Tpo, thereby releasing Tpo into the platelet supernatant. Intravascular release of Tpo by platelets might occur in patients with massive platelet activation, as occurs in patients with disseminated intravascular coagulation. The Tpo concentration in these patients is elevated (p <0.01) and correlates with markers for thrombin generation, TAT complexes and F1+2(r(p)= 0.8 and 0.9; p <0.01). This suggests that the increment in Tpo concentration was attributed to Tpo release by activated platelets in vivo, which might be instrumental in subsequent stimulation of thrombocytopoiesis.

Adult↗
PubMed1997

Radiographic anthropometry in patients with multiple epiphyseal dysplasia.

OBJECTIVE: This study investigated the diagnostic value of radiographic anthropometry in patients with multiple epiphyseal dysplasia (MED). SUBJECTS AND METHODS: In 15 children of one family with MED (12 affected, three unaffected), all of whom were less than 16 years old, measurements were made of the distal femoral metaphysis and epiphysis on standard anteroposterior radiographs of the knee. In each individual, the height of the epiphysis was plotted against the width of both the epiphysis and the metaphysis. Sensitivity, specificity, and positive and negative predictive values were calculated. RESULTS: In 11 of 12 children with MED, the plotted values were more than 2 SDs below the mean. Sensitivity was 92%, specificity was 100%, and positive predictive value was 100%. CONCLUSION: Anthropometry is useful to detect involvement of a child in a family with MED. For this particular family, anthropometry had a high positive predictive value.

Adolescent↗
PubMed1994

Treatment of patients with spontaneous pneumothorax during videothoracoscopy.

Thoracoscopy for spontaneous pneumothorax has been performed over the years by many pulmonologists. The aim of the procedure was merely diagnostic: the detection of blebs and bullae. Therapeutic modalities were restricted to chemical pleurodesis. The development of videothoracoscopy has made more complex interventions, such as bullectomy possible. A protocol for videothoracoscopic treatment of spontaneous pneumothorax, with all treatment modalities in one session, has been developed. All patients with spontaneous pneumothorax underwent videothoracoscopy under general anaesthesia with double lumen tube intubation. If no abnormalities were found on the visceral pleura, talc pleurodesis was performed. Small lesions, blebs or bullae < 2 cm, were coagulated prior to pleurodesis. In case of blebs or bullae > 2 cm, thoracoscopic resection with an EndoGIA stapling device was performed, followed by scarification, i.e. electrocoagulation, of the parietal pleura. In 43 patients, 44 procedures were performed. In 15 cases (34%) no blebs or bullae were found. In 6 cases (14%) only blebs < 2 cm were found. In 23 cases (52%) blebs and bullae > 2 cm were found. In 21 out of 44 cases (48%), talc pleurodesis was performed, and in 23 cases (52%) bullectomy was performed. No major complication occurred. The average hospital stay was 5.7 days after talc pleurodesis and 6.0 days after bullectomy. There were 2 recurrences (5%) after a follow-up of at least 18 months. In conclusion, the use of videothoracoscopy in spontaneous pneumothorax makes it possible to continue a diagnostic procedure as a therapeutic session.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1989

Platelet aggregation induced by type IIb platelet von Willebrand factor.

Platelet lysates from five patients with a form of type IIb von Willebrand's disease (vWd), associated with spontaneous platelet aggregation and thrombocytopenia, induced platelet aggregation of normal and other vWd's platelet-rich plasma (PRP). Platelet lysate from normals, type I or type IIa vWd did not cause platelet aggregation of normal PRP. When polyclonal monospecific antibodies directed against plasma von Willebrand factor (vWf) were incubated with the type IIb platelet lysate, they inhibited the platelet aggregation. Monoclonal antibodies directed against the glycoprotein (GP) Ib binding domain of plasma vWf incubated with the type IIb platelet lysate did not inhibit the platelet aggregation. Normal platelets suspended in afibrinogenaemic plasma did not aggregate when type IIb vWd platelet lysate was added. Normal platelets incubated with monoclonal antibodies directed against the fibrinogen and vWf binding site(s) on the GPIIb/IIIa were not aggregated by the type IIb platelet lysate. Bernard-Soulier PRP aggregated when type IIb vWd platelet lysate was added, while Glanzmann's thrombasthenic platelets did not. Peptides containing the RGDS sequence or the sequence of the carboxy terminal 15 amino acids of the gamma chain of fibrinogen inhibited the type IIb vWd platelet lysate-induced platelet aggregation. These data suggest that type IIb platelet vWf can cause platelet aggregation of PRP without the addition of any agonist. This interaction is different from that observed with the plasma vWf from these patients.

Antibodies, Monoclonal↗