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Biomedical subjects

P Kok

Publications and source records attributed to P Kok.

At least 19 recordsLinked to original sources
PubMed2004

[The value and limitations of the body mass index (BMI) in the assessment of the health risks of overweight and obesity].

--The Body Mass Index (BMI) is used as a measure of overweight and obesity. In epidemiological studies age, sex and ethnic background all have to be taken into consideration, particularly when determining the health risk caused by the amount of body fat. --Caution should be observed when using the BMI as a measure for interpreting overweight and obesity as body composition can be highly variable yet have the same BMI. Therefore, BMI is not a reliable measurement of body composition in individuals particularly in older and younger people. --Excess body fat in the visceral depot poses a separate health risk. The BMI does not give any insight into regional body fat distribution. Waist circumference is a valid index of visceral fat accumulation and can therefore be used as an indicator of health risks associated with visceral obesity.

Adipose Tissue↗
PubMed2004

A real-life prospective health economic study of elective single embryo transfer versus two-embryo transfer in first IVF/ICSI cycles.

BACKGROUND: We analysed the difference in maternal, neonatal and total costs after single (SET) versus double day 3 embryo transfer (DET). METHODS: We performed a two-centre prospective study of women in their first IVF/ICSI cycle choosing between SET or DET. Infertility treatment data were gathered from a database; maternal and neonatal outcome data from a case report form (CRF); health economic data from medical acts registered in the CRF for the outpatient part and from hospital bills. SET was performed in 206/367 (56.1%) and DET in 161/367 (43.9%) women. RESULTS: In all, 367 transfers yielded 186 positive pregnancy tests, 148 ongoing pregnancies and 136 live deliveries (50.7, 40.3 and 37.1% per embryo transfer) of which 15 (11.0%) were twins. Live birth rate was 37.4% for SET, 36.6% for DET. Intention-to-treat analysis showed differences for: duration of pregnancy (SET: 39.0 +/- 1.4 versus DET: 38.3 +/- 2.2 weeks; P = 0.055), percentage prematurity (8.5 versus 23.8%; P = 0.033), percentage of neonates hospitalized (5.7 versus 17.9%; P = 0.121) and duration of neonatal hospitalization (6.3 +/- 2.2 versus 10.3 +/- 10.1 days; P = 0.01). Total cost after DET was higher (SET: 4700 +/- 3239 versus DET: 8613 +/- 10 105; P = 0.105), due to significantly higher neonatal costs (451 +/- 957 versus 3453 +/- 8154; P < 0.001) and not to differences in maternal costs (4250 +/- 2882 versus 5160 +/- 4106; P = 0.152). CONCLUSIONS: This prospective health economic study shows that transfer of a single top quality embryo is equally effective as, but substantially cheaper than, double embryo transfer in women <38 years of age in their first IVF/ICSI cycle.

Birth Rate↗
PubMed2001

A randomized trial comparing two laryngeal mask airway insertion techniques.

This study was undertaken to compare laryngoscopic-guided LMA insertion with a standard insertion technique. A total of 149 patients undergoing elective general surgical and orthopaedic procedures were randomly divided into two groups. Study endpoints included ease of insertion, haemodynamic changes, local trauma bleeding, and postoperative sore throat. There were no statistically significant differences found. The laryngoscope may aid laryngeal mask airway insertion in some circumstances.

Adult↗
PubMed2000

Quantum interferometric optical lithography: exploiting entanglement to beat the diffraction limit

Classical optical lithography is diffraction limited to writing features of a size lambda/2 or greater, where lambda is the optical wavelength. Using nonclassical photon-number states, entangled N at a time, we show that it is possible to write features of minimum size lambda/(2N) in an N-photon absorbing substrate. This result allows one to write a factor of N2 more elements on a semiconductor chip. A factor of N = 2 can be achieved easily with entangled photon pairs generated from optical parametric down-conversion. It is shown how to write arbitrary 2D patterns by using this method.

Journal Article↗
PubMed1998

Epilepsy in practice.

Epilepsy is a common and often neglected illness in developing countries requiring a conscious effort by health workers, especially at community level, to enhance access to regular treatment and to motivate patients to continue treatment. Effective new drugs have recently come on to the market. However, their high cost means that they often cannot be afforded by poor countries. Strengthening local and national level organizations may help to motivate health workers and the public, improving health services for those with epilepsy and preventing serious complications.

Africa↗
PubMed1997

Resonance Raman spectroscopy of 2H-labelled spheroidenes in petroleum ether and in the Rhodobacter sphaeroides reaction centre.

As a step towards the structural analysis of the carotenoid spheroidene in the Rhodobacter sphaeroides reaction centre, we present the resonance Raman spectra of 14-2H, 15-2H, 15'-2H, 14'-2H, 14,15'-2H2 and 15-15'-2H2 spheroidenes in petroleum ether and, except for 14,15'-2H2 spheroidene, in the Rb. sphaeroides R26 reaction center (RC). Analysis of the spectral changes upon isotopic substitution allows a qualitative assignment of most of the vibrational bands to be made. For the all-trans spheroidenes in solution the resonance enhancement of the Raman bands is determined by the participation of carbon carbon stretching modes in the centre of the conjugated chain, the C9 to C15' region. For the RC-bound 15,15'-cis spheroidenes, enhancement is determined by the participation of carbon-carbon stretching modes in the centre of the molecule, the C13 to C13' region. Comparison of the spectra in solution and in the RC reveals evidence for an out-of-plane distortion of the RC-bound spheroidene in the central C14 to C14' region of the carotenoid. The characteristic 1240 cm-1 band in the spectrum of the RC-bound spheroidene has been assigned to a normal mode that contains the coupled C12-C13 and C13'-C12' stretch vibrations.

Alkanes↗
PubMed1994

Towards a vibrational analysis of spheroidene. Resonance Raman spectroscopy of 13C-labelled spheroidenes in petroleum ether and in the Rhodobacter sphaeroides reaction centre.

We report resonance Raman spectra of the carotenoid spheroidene and its 14'-13C and 15'-13C substituted analogues in petroleum ether and bound to the reaction centre of Rhodobacter sphaeroides R26. The spectra in petroleum ether correspond to planar all-trans spheroidene while those of the reaction centres are consistent with a nonplanar 15,15'-cis spheroidene. The effect of 13C labelling is largest in the carbon-carbon double-bond stretching region. The 15'-13C substitution of the reaction centre bound spheroidene, however, hardly changes the C=C band as compared to that for the natural abundance spheroidene apart from a new weak band at 1508 cm(-1). This observation has been interpreted as a decoupling of the C15=C15' stretch from the other double-bond stretches in combination with a small intrinsic Raman intensity of this local mode for 15,15'-cis spheroidene.

Alkanes↗
PubMed1994

Preservation of myelinated fibers for electron microscopy: a qualitative comparison of aldehyde fixation, microwave stabilisation and other procedures all completed by osmication.

A qualitative comparison was made of a variety of electron microscopic preservation methods for nervous tissue, especially with respect to myelinated fiber areas. The methods studied were aldehyde perfusion/immersion fixation, aldehyde-tannic acid immersion fixation (stimulated by either microwave or conventional heating), microwave stabilisation, saline treatment with conventional heating (all with secondary osmication), and primary osmication. For all methods three morphological aspects, the ultrastructural quality of myelin sheath and axon and the coherence between the two were judged separately. It appears that the best version of each method studied is capable of providing a good overall ultrastructural result but always shows a preference for one or two of the three separate morphological aspects. When aiming at good axon quality together with good axon/myelin coherence, aldehyde perfusion/immersion, saline treatment or primary osmication are almost equivalent. Microwave stabilisation, on the other hand, can be chosen when good myelin quality has to be combined with good axon quality. For more specific purposes the following examples can be given. When excellent myelin quality is needed both microwave-stimulated aldehyde-tannic acid fixation or microwave stabilisation can be considered. When the preservation of the axon quality has priority the aldehyde-perfused tissue should be further immersed in a heated aldehyde-tannic acid solution. Primary osmication guarantees excellent axon/myelin coherence. Despite the differences in detail, a remarkable correspondence is stressed between the overall results of sometimes extremely different methods of tissue preservation. Probably they all guarantee a reliable reflection of the in vivo situation. With respect to the use of microwave irradiation for tissue preservation, it appeared that stabilisation procedures are rather capricious. However, if successful, the results are not inferior to those of aldehyde fixation.

Aldehydes↗
PubMed1993

Valproate and sodium currents in cultured hippocampal neurons.

Cultured rat hippocampal neurons with short processes were investigated using the whole cell voltage clamp under conditions appropriate for isolating Na+ currents. After incubation of the neuron culture for a period of 15-30 min in 1 mM sodium valproate, several parameters of the Na+ current were changed. The peak Na+ conductance gp, measured using hyperpolarizing prepulses, was reduced by valproate in a voltage-dependent manner. In the membrane voltage range from -30 to +20 mV, this reduction showed a linear dependence on voltage, increasing from about zero to approximately 30% of gp, the maximum peak Na+ conductance of the neuron. At the holding voltage of -70 mV, the inactivation parameter h infinity decreased from 0.88 in the control to 0.64 in the valproate solution. This reduction originated mainly from a 10 mV shift in the sigmoid relation between h infinity and membrane voltage along the voltage axis to hyperpolarizing potentials. The decay of the maximum peak Na+ current (inactivation) could be fitted by a biexponential function. Time constants of the fast and slow component at -20 mV decreased in valproate by about 50%. Valproate also retarded the recovery from inactivation, as determined at the holding voltage. The sigmoid recovery from inactivation could reasonably be described by an exponential function with time constant tau r and delay time delta t. Both tau r and delta t increased more than 200% in valproate. Our results indicate that valproate affected the Na+ current in hippocampal neurons in a way that contributed to a considerable depression of Na+ reactivation.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗
PubMed1992

Does microwave irradiation have other than thermal effects on histological staining of the mammalian CNS? A light microscopical study of microwave stimulated staining under isothermal conditions in man and rat.

The question whether or not microwave irradiation exerts other than thermal effects on histological staining is still a matter of controversy. The present study was undertaken to reveal or reject such a so far hypothetical non-thermal irradiation effect. A device was developed, which enables exposure of histological sections or tissue pieces to microwave irradiation under isothermal conditions, i.e. with synchronous removal of the internal heat produced. Three classical neuroanatomical staining methods were tested on human and rat CNS. As control, identical procedures were performed without simultaneous microwave irradiation. The experiments were performed at three different temperature levels ranging from 5 to 50 degrees C. In none of the cases studied was a light microscopically appreciable difference observed between the microwave and non-microwave versions of a stain at the same temperature. The hypothesis of a separate non-thermal effect of microwave irradiation on histological staining is therefore rejected.

Animals↗
PubMed1986

Porcine tissue plasminogen activator. Immunoaffinity purification, structural properties and glycosylation pattern.

Tissue plasminogen activator was purified in high yield from pig heart by immunoaffinity chromatography and characterized by analysis of the glycosylation pattern and the N-terminal amino acid sequence. Comparisons with the human enzyme reveals residue exchanges in the A-chain at positions 3 (porcine Arg/human Gln) and 5 (Thr/Ile), and in the B-chain at positions 6 (Tyr/Phe), 10 (Thr/Ala) and 20 (Val/Ala). The glycosylation pattern for the porcine activator was determined by endoglycosidase treatment followed by gel electrophoresis. The A-chain contains a single high-mannose type of N-linked glycan structure and the B-chain contains a complex type of oligosaccharide. A similar but not identical pattern has been observed for the human activator, purified from melanoma cells.

Amino Acid Sequence↗
PubMed1986

Assay characteristics and fibrin affinity of plasminogen activators of the intrinsic fibrinolytic system.

Plasminogen activators (PA) in the euglobulin fraction of dextran sulfate activated plasma (DS-EF) were assayed on fibrin plates. Activity related to tissue plasminogen activator (t-PA) or urokinase (u-PA) was quantified by antiserum inhibition. The DS-EF contained 30% t-PA, 30% u-PA and 40-50% activity unrelated to t-PA or u-PA. The latter was completely inhibited by 1.7 mumol/1 C1-inhibitor (C1INH), the two former were less sensitive. Addition of flufenamate to the DS-EF (DS-EF/Fluf) from normal and two factor XII (F XII)-deficient plasmas increased their activities to the same high level. More than 50% of the activity was unrelated to t-PA or u-PA, 30-40% was u-PA and 5-10% t-PA related. After addition of fibrinogen to DS-EF/Fluf and clotting with thrombin, the remaining solution contained only about 30% of the total activity, including less than 10% u-PA. The epsilon-aminocaproic acid inhibition pattern obtained with the DS-EF was uniform, and thus different from the biphasic pattern obtained with the low fibrin affinity PA, two-chain urokinase. Thus, both the plasma u-PA and the major unidentified PA in plasma have affinity for fibrin.

Adult↗
PubMed1984

Sequence of formation of molecular forms of plasminogen and plasmin-inhibitor complexes in plasma activated by urokinase or tissue-type plasminogen activator.

The pathway of plasminogen transformation was studied in plasma, particularly in relation to fibrin formation and the subsequent stimulation of plasminogen activation. Plasminogen was activated by urokinase (low fibrin-affinity) or tissue-type plasminogen activator (high fibrin-affinity). Formation of 125I-labelled free and inhibitor-bound plasminogen derivatives was quantified after their separation by acetic acid/urea/polyacrylamide-gel electrophoresis. In plasma activator converted Glu-plasminogen (residues 1-790) into Glu-plasmin, which was complexed to alpha 2-plasmin inhibitor. When this inhibitor was saturated, Glu-plasmin was autocatalytically converted into Lys-plasmin (residues 77-790). No plasmin-catalysed Lys-plasminogen formation was observed. Upon fibrin formation, activation initially followed the same Glu-plasminogen-into-Glu-plasmin conversion pathway, and stimulation of plasminogen activation was only observed with tissue-type plasminogen activator. In agreement with the emergence of novel effector function, on early plasmin cleavage of fibrin [Suenson, Lützen & Thorsen (1984) Eur. J. Biochem. 140, 513-522] the fibrin-binding of Glu-plasminogen increased when solid-phase fibrin showed evident signs of degradation. This was associated with the formation of considerable amounts of the more easily activatable Lys-plasminogen, most of which was fibrin-bound. At the same time the rate of plasmin formation with urokinase increased over that in unclotted plasma and the rate of plasmin formation with tissue-type plasminogen activator accelerated. Altogether these processes favoured enhanced fibrin degradation. The rates of Lys-plasminogen and plasmin formation abruptly decreased after lysis of fibrin, probably owing to a compromised effector function on further fibrin degradation.

Antifibrinolytic Agents↗
PubMed1981

Fibrinolytic activity of cerebral tissue after experimental subarachnoid haemorrhage: inhibitory effect of tranexamic acid (AMCA).

The influence of tranexamic acid (AMCA) on the fibrinolytic activity induced by plasminogen activators (PA) of the cerebral leptomeninges, arteries and choroid plexus after artificial subarachnoid haemorrhage (SAH) was studied in 90 rabbits. SAH was induced by injection of 1-2 ml autologous blood into the suboccipital cistern. Half of the rabbits were given AMCA, 200 mg per kg body weight, in daily single i.v. injections. The rabbits were sacrificed after 3-5, 8-10 and 14-15 days respectively. Part of the leptomeninges, basilar artery and choroid plexus were removed for assaying PA by the histochemical fibrin slide and fibrin plate methods, using thiocyanate for extraction of plasminogen activator from the tissues. Quantitative assays for the fibrin plate method showed high PA in the arterial and meningeal tissues from the untreated animals 3-5 days after SAH. The PA had decreased to normal levels 8-10 days after SAH but increased again 14-15 days after SAH. A lower PA in the choroid plexus followed the same pattern. The concentration of the primary plasmin inhibitor in plasma had decreased to half of the normal value 8 days after SAH when compared to the concentration in pooled plasma from normal rabbits. In AMCA treated animals the meningeal PA, assayed by both methods, was decreased 3-5 days after SAH while no or an insignificant decrease in PA was seen 8-10 and 14-15 days after SAH. The PA of the arterial vessel wall and choroid plexus in the AMCA treated animals, assayed by the histochemical method, was moderately decreased 3-5 days after SAH, while no significant differences between untreated and AMCA treated animals were seen after 8-10 or 14-15 days when the tissues were assayed by either method. These findings indicate that AMCA suppresses PA primarily in the leptomeninges during the first few days after SAH and presumably before the meningeal fibrosis has developed.

Animals↗