PubMed Health⌕ Search

Biomedical subjects

J M Boon

Publications and source records attributed to J M Boon.

At least 37 records · Page 2Linked to original sources
PubMed2001

Facilitated phosphatidylcholine flip-flop across erythrocyte membranes using low molecular weight synthetic translocases.

The transmembrane distribution of phospholipids plays an important regulatory role in human erythrocytes. Membrane-bound translocase enzymes maintain an asymmetric phospholipid distribution across the membrane monolayers by promoting transmembrane diffusion or flip-flop. Mechanistic understanding of the flip-flop process is weak at the molecular level. Recently, we discovered that amide and sulfonamide derivatives of tris(aminoethyl)amine facilitate phospholipid flip-flop across vesicle membranes; that is, they act as low molecular weight, synthetic translocases. In this report, NMR evidence is provided that suggests that the synthetic translocases work by forming a hydrogen-bonded complex with the phosphocholine headgroup which decreases headgroup polarity and promotes diffusion across the lipophilic interior of the membrane. Also cell morphology and fluorescence probe methods are used to show that these synthetic translocases facilitate phosphatidylcholine flip-flop across erythrocyte membranes. Addition of a small amount of dilauroylphosphatidylcholine to erythrocytes produces echinocyte morphology which takes days to revert back to the original discocyte shape. The rate of return is significantly accelerated by the presence of the synthetic translocases. The synthetic translocases facilitate inward-translocation (flip) of the fluorescent phosphatidylcholine probe, 1-palmitoyl-2-(N-[7-nitrobenz-2-oxa-1,3-diazol-4-yl]aminohexanoyl)-sn-glycero-3-phosphocholine (PC-NBD).

Biological Transport↗
PubMed2001

Evaluation of clinical relevance of problem-oriented teaching in undergraduate anatomy at the University of Pretoria.

Problem oriented medical curricula claim to be based on the fact that the clinical sciences facilitate and encourage the understanding of basic sciences. The question was asked whether the correlation of gross anatomy in the Abdomen Block in the new Pretoria medical curriculum, with clinically relevant content (i.e. relevant physical examination, imaging anatomy, clinical procedures, clinical presentations and clinical case studies) facilitates the understanding of human anatomy and enhances the development of the clinical thinking fundamental to clinical practice. The clinical anatomy component of the Abdomen Block (11 weeks duration) in the third year was developed by using standardized patients, cadaver material, skeletons, X-rays, CT scans, MRIs and multimedia programs. Student perceptions were assessed by a Likert scale questionnaire. Most students thought that integrating the physical examination enhanced their understanding of the relevant anatomy (mean: 3.55). A substantial number of students thought the clinical anatomy in the block laid a good foundation for imaging anatomy of the abdomen (mean: 3.41). The majority of students thought the clinical anatomy laid a good basis for the understanding of surgical procedures relevant to the abdomen (mean: 3.63). Students were mostly confident that clinical anatomy enhanced their understanding of clinical presentations (mean: 3.68). Although slightly fewer, the majority reckoned that the clinical case studies gave them a better understanding of the relevant anatomy (mean: 3.30). It seems evident that the integration of clinically relevant content facilitates and encourages the understanding of anatomy and thus aids in the development of clinical thinking.

Anatomy↗
PubMed2001

Variations of the position of the colon as applied to percutaneous nephrostomy.

The widespread and increasing usage of percutaneous nephrostomy procedures makes an awareness of the anatomical variations of the colon in relation to the kidney essential. Injury to the colon during this procedure is associated with significant morbidity. The aim of this study was to determine the relation of the colon to the insertion line used during a percutaneous nephrostomy and therefore determine whether the colon is at risk of injury. 333 CT-scans taken in a supine position were studied in order to determine the position of both the ascending and descending colon to the percutaneous nephrostomy insertion line on the level of the superior pole, hilum and inferior pole of the kidneys. In the majority of cases, the ascending and descending colon lie anterior to the line of insertion, and were therefore not at risk. However the descending colon was found to be at risk in 16.1% of cases and the ascending colon in 9.0% of cases on the level of the inferior pole of the kidney. The risk was significantly lower on the level of the hilum and superior pole of the kidneys on both sides. Age distribution analysis showed that the colon is rarely at risk under twenty years of age and the highest risk being in the age range above 40 years. Adequate radiographic evaluation is essential before performance of percutaneous nephrostomy procedures, especially to evaluate the position of the colon as related to the inferior poles of the kidneys.

Adolescent↗
PubMed1993

Congenital myotonic dystrophy; a report on thirteen cases and a review of the literature.

The congenital variant of myotonic dystrophy (CMD) is a severe disease with a high mortality. CMD is only seen in the offspring of mothers who themselves have myotonic dystrophy (MD). We present 13 patients with clinical symptoms of CMD and neuropathological findings of five of them. The most characteristic symptoms during pregnancy are reduced fetal movements and polyhydramnios. In the neonatal period generalized hypotonia, facial weakness, hyporeflexia, feeding and respiratory difficulties are present. Most of the children have a characteristic tented upper lip. The symptoms greatly diminish after a few weeks. All the children who survive the neonatal period are psychomotor retarded. On pathological examination no specific features were found in muscle tissue or in the brain. The pathogenesis and the cause of the maternal inheritance of CMD is not clear. A review of the literature is provided.

Brain↗
PubMed1992

Enzyme activities of the mitochondrial energy generating system in skeletal muscle tissue of preterm and fullterm neonates.

Quadriceps muscle specimens from autopsy of 28 neonates (gestational age 25-42 weeks) were investigated to determine pyruvate and malate oxidation rates and several enzymes of the mitochondrial oxidative process. In general, the levels of all mitochondrial parameters measured, including carnitine levels, were lower in the neonates who died within the first week of life than those in the control group (age > 5 years). Pyruvate and malate oxidation rates (P < 0.05), activities of pyruvate dehydrogenase complex (P < 0.10) and succinate: cytochrome c oxidoreductase (P < 0.05) increased significantly with gestational age. Pyruvate oxidation rates (P < 0.05) as well as activities of citrate synthase (P < 0.05) and NADH:Q1 oxidoreductase (P < 0.05) were significantly lower in the group of very preterm infants at an age of 1-7 days compared with very preterm infants at an age between 3-8 weeks. We conclude from our study that special reference values are necessary for a correct biochemical diagnosis of mitochondrial encephalomyopathies in the neonatal period. Differences between preterm and fullterm children of the same age (1 week) indicate a maturational process in human muscle tissue during gestation. Comparison of two different age groups within the very preterm neonates point to a postnatal maturation of the mitochondrial energy metabolism, at least in preterm neonates.

Carnitine↗
PubMed1989

Comparison of ketoconazole suspension and nystatin in the treatment of newborns and infants with oral candidosis.

Ketoconazole suspension (20 mg per ml) was compared with nystatin (100,000 units per ml) in the treatment of oral candidosis in newborns and infants. In all patients Candida infection was proven by culture. Twenty patients were treated with ketoconazole and 15 patients with nystatin. Treatment was discontinued 2 days after clinical cure, or after 3 weeks. The investigator assessed the severity of the thrush and accompanying symptoms at the start of the study and at weekly controls. After one week all 20 patients on ketoconazole (100%) and 8 (53%) patients on nystatin were cured clinically. At the end of the treatment 12 patients on nystatin (80%) were cured. Clinical cure was confirmed by negative culture in 94% of the patients on ketoconazole and in 73% of the patients on nystatin. No side-effects were observed in the patients on ketoconazole. Only in the case of one patient on nystatin, was vomiting observed. This study shows that ketoconazole cures thrush faster and more effectively than nystatin.

Candidiasis, Oral↗
PubMed1985

Survival probabilities of infants delivered prior to the 34th week of pregnancy as estimated by means of a logistic model.

Survival of 188 infants born alive before the 34th wk of pregnancy is assessed in relation both to birthweight and duration of pregnancy. A logistic model is used which describes, based on these parameters, probabilities of 1-yr survival of relatively small populations in a continuous way. Although there may be differences between measured and estimated birthweight, this method might enable the perinatologist to estimate before birth the survival probabilities if he knows the duration of pregnancy and estimated birthweight.

Birth Weight↗
PubMed1985

One-year morbidity in very premature infants: prognostic value of duration of pregnancy, birthweight and neonatal morbidity.

Morbidity in the first year of life of 120 infants, born before the 34th wk of pregnancy, was studied in relationship to both duration of pregnancy and birthweight. Moreover, the interrelationships of morbidity in three time-periods (first-hour, first 28 days and first year after delivery) were studied. The major handicap rate at one year was 5%, without major handicaps in infants born before 29 wk or weighing less than 1250 g. This finding seems to justify intensive treatment of even the youngest and smallest infants. Significantly more morbidity in the first 28 days of life was found when intervention within the first hour after delivery was necessary, indicating that morbidity in the first hour after delivery may be a prognostic bad sign for morbidity in the first 28 days of life. However, no significant differences in handicap rates at one year of age were found in infants with and without morbidity in the first hour or in the first 28 days. This indicates that early morbidity will not necessarily be followed by morbidity in later life, but, on the other hand, absence of early morbidity does not preclude handicaps later on.

Cerebral Palsy↗
PubMed1984

[Noninvasive blood pressure determination in newborn infants].

In 69 newborns (birth weight 900-3820 grams; gestational age 27-41 weeks) the Dinamap device was used to establish normative values for systolic and diastolic blood pressure, mean arterial pressure and pulse pressure for this indirect, non-invasive blood pressure monitoring system. Reference values for the first day after delivery in different birth weight groups are given and the changes during the first three days of life are shown. Blood pressure variability as a possible additional parameter in neonatal monitoring was found to be independent of birth weight and gestational age.

Birth Weight↗
PubMed1983

Rickets in a preterm infant during intravenous alimentation.

A preterm baby given intravenous feeding developed severe rickets. Laboratory investigation revealed hypophosphatemia as the main cause of this picture. Recovery was achieved by giving extra phosphorus supplementation. This case demonstrates that conventional infusates do not meet the phosphorus requirement of rapidly growing infants.

Female↗
PubMed1980

Serum-free amino acid concentrations in low birth weight infants during the first 4 weeks of life.

To obtain more information about the correct protein intake in low birth weight children, serum amino acid concentrations were determined. In 59 formula-fed, low birth weight children, serum amino acid concentrations were determined at 3, 24 and 72 h after birth and at the age of 1, 2, 3 and 4 weeks. Mean serum concentrations of all amino acids decreased during the first 24 h of life, except of aspartate and tyrosine. This decrease was followed by an increase during the first weeks of life and a variable pattern afterwards. A hypertyrosinemia (serum-tyrosine concentration > 250 mumol/l) was not found in any case. Taurine concentrations decreased gradually, as was expected because of the low taurine concentrations in cow's milk. Mean concentrations of alanine, glycine, proline and valine were higher in small for date children. Concluding, parenteral supplementation of amino acids is advisable during the first days of life to low birth weight children.

Amino Acids↗