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Biomedical subjects

P van Dijk

Publications and source records attributed to P van Dijk.

At least 19 recordsLinked to original sources
PubMed2006

Local health systems in 21st century: who cares?-An exploratory study on health system governance in Amsterdam.

BACKGROUND: There is a growing awareness that there should be a public health perspective to health system governance. Its intrinsic population health orientation provides the ultimate ground for determining the health needs and governing collaborative care arrangements within which these needs can be met. Notwithstanding differences across countries, population health concerns are not central to European health reforms. Governments currently withdraw leaving governance roles to care providers and/or financiers. Thereby, incentives that trigger the uptake of a public health perspective are often ignored. METHODS: In this study we addressed this issue in the city of Amsterdam. Using a qualitative study design, we explored whether there is a public health perspective to the governance practices of the municipality and the major sickness fund in Amsterdam. And if so, what the scope of this perspective is. And if not, why not. RESULTS: Findings indicate that the municipality has a public health perspective to local health system governance, but its scope is limited. The municipality facilitates rather than governs health care provision in Amsterdam. Furthermore, the sickness fund runs major financial risks when adapting a public health perspective. It covers an insured population that partly overlaps the Amsterdam population. Returns on investments in population health are therefore uncertain, as competitors would also profit from the sickness fund's investments. CONCLUSION: The local health system in Amsterdam is not consistently aligned to the health needs of the Amsterdam population. The Amsterdam case is not unique and general consequences for local health system governance are discussed.

Cities↗
PubMed2006

Pharmacodynamic effects and pharmacokinetic profile of a long-term continuous rate infusion of racemic ketamine in healthy conscious horses.

Ketamine (KET) possesses analgesic and anti-inflammatory activity at sub-anesthetic doses, suggesting a benefit of long-term KET treatment in horses suffering from pain, inflammatory tissue injury and/or endotoxemia. However, data describing the pharmacodynamic effects and safety of constant rate infusion (CRI) of KET and its pharmacokinetic profile in nonpremedicated horses are missing. Therefore, we administered to six healthy horses a CRI of 1.5 mg/kg/h KET over 320 min following initial drug loading. Cardiopulmonary parameters, arterial blood gases, glucose, lactate, cortisol, insulin, nonesterified fatty acids, and muscle enzyme levels were measured, as were plasma concentrations of KET and its metabolites using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Levels of sedation and muscle tension were scored. Respiration and heart rate significantly increased during the early infusion phase. Glucose and cortisol significantly varied both during and after infusion. During CRI all horses scored 0 on sedation. All but one horse scored 0 on muscle tension, with one mare scoring 1. All other parameters remained within or close to physiological limits without significant changes from pre-CRI values. The mean plasma concentration of KET during the 1.5 mg/kg/h KET CRI was 235 ng/mL. The decline of its plasma concentration-time curve of both KET and norketamine (NKET) following the CRI was described by a two-compartmental model. The metabolic cascade of KET was NKET, hydroxynorketamine (HNK), and 5,6-dehydronorketamine (DHNK). The KET median elimination half-lives (t1/2alpha and t1/2beta) were 2.3 and 67.4 min, respectively. The area under the KET plasma concentration-time curve (AUC), elimination was 76.0 microg.min/mL. Volumes of C1 and C2 were 0.24 and 0.79 L/kg, respectively. It was concluded that a KET CRI of 1.5 mg/kg/h can safely be administered to healthy conscious horses for at least 6 h, although a slight modification of the initial infusion rate regimen may be indicated. Furthermore, in the horse KET undergoes very rapid biotransformation to NKET and HNK and DHNK were the major terminal metabolites.

Analgesics↗
PubMed2005

[Immobilization of cattle and bison with a combination of xylazine, zolazepam-tiletamine and ketamine].

The aim of this study was to find a safe and reliable alternative to Immobilon for the immobilization of (feral) cattle. A combination of xylazine, zolazepam-tiletamine and ketamine was tested in Limousin cattle, Scottish Highland cattle, and American bison. Bodyweight, induction time, arterial O2 saturation and the total downtime were measured. Arterial blood was taken for pH and blood gas analysis. The animals were then injected with atipamezole and the recovery time was recorded. A combination of 500 mg zolazepam, 500 mg tiletamine, 500 mg xylazine, and 1000 mg (10 ml) ketamine, administered in a dosage of 1 ml per 100-150 kg bodyweight (depending on the species), proved to be most reliable and effective. The combination resulted in a fast immobilization. In all animals slight respiratory depression was seen, which indicates that oxygen suppletion may be needed for long-lasting immobilization. After reversal of the xylazine component, almost all animals recovered within 4 minutes. No long term adverse effects were reported by the owners.

Adrenergic alpha-Antagonists↗
PubMed2005

A two-step scenario for hearing assessment with otoacoustic emissions at compensated middle ear pressure (in children 1-7 years old).

OBJECTIVE: Otoacoustic emissions (OAEs) are widely used for assessing congenital and early-acquired sensorineural hearing loss in young children. Middle ear pathology has a negative effect on the presence of OAEs. In this study we investigated whether measuring OAEs at compensated middle ear pressure (CMEP) resulted in a higher pass rate than at ambient pressure. Secondly, we analysed the influence of 12 different pass definitions on the pass rates. METHODS: One hundred and eleven children (age 1-7 years, mean 4 years and 5 months) were measured twice in one session: first at ambient pressure and then at CMEP. RESULTS: The study showed a higher pass rate of OAEs at CMEP than at ambient pressure. A two-step scenario reduced the number of fails by 18-26%, depending on the pass/fail definition used. CONCLUSION: Measuring OAEs at CMEP results in higher pass rates. Secondly, pass/fail definitions have a large influence on pass rates and this issue deserves further attention. Further studies must be done, before this method is readily applicable to universal neonatal screening.

Acoustic Impedance Tests↗
PubMed2005

Otoacoustic emissions at compensated middle ear pressure in children.

Middle ear pathology has a negative effect on the detectability of otoacoustic emissions. In this study, we investigated the effect of compensating a deviant static middle ear pressure while measuring transient evoked otoacoustic emissions (TEOAEs). In 59 children (mean age 4 years, 5 months) TEOAEs were measured twice in one session: first at ambient pressure and than at compensated middle ear pressure. On average, TEOAE amplitudes increased by 1.9 dB as a result of middle ear pressure compensation. The amplitude increase was largest in frequency bands centred at 1 and 2 kHz and a statistically significant correlation was found between the amount of compensated pressure and the TEOAE amplitude increase. In the higher frequency bands centred at 3 and 4 kHz, TEOAE amplitudes were almost insensitive to pressure compensation. These results show that measuring OAEs at compensated middle ear pressure enhances the amplitude of TEOAEs, and thus improves the detectability.

Acoustic Impedance Tests↗
PubMed2003

How does the cold stenothermal gadoid Lota lota survive high water temperatures during summer?

The cold-stenothermal freshwater gadid Lota lota inhabiting the potamic regions of lowland rivers in central Europe, is exposed to summer temperatures up to 25 degrees C, which is far above the thermal preferendum of this species. Oxygen consumption rates, determined in field catches sampled at different times of the year, revealed that the basal metabolic rate is depressed during summer when water temperatures are high (152+/-16 micromol O2 100 g(-1) h(-1)at 22 degrees C in July compared to 250+/-33 micromol O2 100 g(-1) h(-1) at 6 degrees C in November). This observation led us to investigate whether the observed depression of the metabolic rate is caused by oxygen limitation due to thermal impairment of the ventilatory system, as has been observed in other species. Determination of anaerobic end products (lactate and succinate) in the liver tissue of fish caught at different sampling dates did not show an accumulation of anaerobic end products during the summer, indicating no oxygen limitation. Measurements of enzyme activities in the white musculature and liver suggest that enzymes involved in aerobic metabolism were down-regulated during summer, which may have contributed to the observed reduction of metabolic rate.

Acclimatization↗
PubMed2003

Effects of intravenous lidocaine on isoflurane concentration, physiological parameters, metabolic parameters and stress-related hormones in horses undergoing surgery.

Physiological parameters, metabolic parameters and stress-related hormones are evaluated in horses anaesthetized with isoflurane in oxygen combined with lidocaine intravenously. Two groups of horses anaesthetized with isoflurane (six horses in each group) were studied: a lidocaine group (IL), which received intravenous lidocaine and a control group (C), which received intravenous saline. Horses in both groups were premedicated with detomidine (i.v.), and anaesthesia was induced with midazolam-ketamine (i.v.). The lidocaine group received intravenous lidocaine as a loading dose of 2.5 mg kg(-1) at 15 min after induction of anaesthesia directly followed by a maintenance dosage of 50 microg kg(-1) min(-1), while the control group received saline (i.v.) following the same regime. End-tidal isoflurane and standard physiological parameters were measured. Blood was sampled for measurement of lidocaine, stress hormones and metabolic parameters. The end-tidal isoflurane concentration in the lidocaine group was 0.96 +/- 0.06% versus 1.28 +/- 0.06% (mean +/- SD) in the control group, a significant (P < 0.05) reduction of 25%. No significant differences were found regarding stress-related hormones, metabolic and physiological parameters. This study suggests that the use of lidocaine to decrease the concentration of isoflurane to obtain a sufficient surgical anaesthesia has no subsequent effects on physiological and metabolic parameters or stress-related hormones.

Anesthesia↗
PubMed2003

Hormonal, metabolic and physiological effects of laparoscopic surgery using a detomidine-buprenorphine combination in standing horses.

OBJECTIVE: To assess the hormonal, metabolic and physiological effects of laparascopic surgery performed under a sedative analgesic combination of detomidine and buprenorphine in standing horses. STUDY DESIGN: Prospective study. ANIMALS: Eight healthy adult Dutch Warmblood horses and five healthy adult ponies undergoing laparoscopy were studied. Five healthy adult horses not undergoing laparoscopy were used as a control group. METHODS: The sedative effect of an initial detomidine and buprenorphine injection was maintained using a continuous infusion of detomidine alone. The heart and respiratory rate, arterial blood pH and arterial oxygen and carbon dioxide tensions were monitored, while blood samples were taken for the measurement of glucose, lactate, cortisol, insulin and nonesterified fatty acids (NEFA). The same variables were monitored in a control group of horses which were sedated, but which did not undergo surgery. At the end of the sedation period the effects of detomidine were antagonized using atipamezole. RESULTS: The protocol provided suitable conditions for standing laparoscopy in horses. Laparoscopy induced obvious metabolic and endocrine responses which, with the exception of NEFA values, were not significantly different from changes found in the control group. While atipamezole did not produce detectable adverse effects, it is possible that anatagonism may not be essential. CONCLUSIONS: The technique described reliably produces adequate sedation and analgesia for laparoscopic procedures. The level of sedation/analgesia was controlled by decreasing or increasing the infusion rate. Antagonism of the effects of detomidine may not be necessary in all cases.

Analgesics, Opioid↗
PubMed2002

Simultaneous sampling of event-related BOLD responses in auditory cortex and brainstem.

Event-related functional magnetic resonance imaging (fMRI) was applied to investigate blood oxygen level dependent (BOLD) responses in the human auditory system. Auditory fMRI is hindered by the disturbing acoustical noise of echo planar imaging (EPI). A sparse acquisition technique was used in which the delayed hemodynamic response was imaged at discrete sampling time-points after a brief auditory stimulus. Long repetition times (10 heartbeats (HBs)) were used to avoid interactions between the activation due to the sound stimulation and scanner noise. In addition, only a single slice was acquired, to ensure that the scanner noise was minimal in duration and intensity. The image acquisition was triggered by the HB to prevent artifacts from cardiac-related brainstem motion. An image was acquired every 10th HB. Significant hemodynamic BOLD time-course responses were measured from the primary and secondary auditory cortices, as well as the inferior colliculi in the brainstem. No systematic differences were found between the cerebral cortex and the brainstem in terms of activation amplitude or in onset time of the hemodynamic response. Apparently, the slow dynamic nature of the BOLD response signal is similar across spatially separated auditory brain regions, suggesting a corresponding design of vessels and capillaries.

Acoustic Stimulation↗
PubMed2001

Distortion product otoacoustic emissions in the tree frog Hyla cinerea.

The frog inner ear contains two hearing organs: the amphibian and the basilar papilla. The amphibian papilla is sensitive to low- and mid-frequency stimuli (0.1--0.5 and 0.5--1.3 kHz, respectively, in Hyla cinerea), while the basilar papilla is sensitive to high-frequency stimuli (2.8--3.9 kHz in H. cinerea). Distortion product otoacoustic emissions (DPOAE) were recorded from the ear of the tree frog H. cinerea. In each of six ears investigated, a cubic distortion product (DP) at 2f(1)--f(2) was present when the primary frequencies f(1) and f(2) and the DP frequency were close to either the mid- or the high-frequency range. At frequencies between the sensitive ranges of both papillae, no emissions were observed. For the basilar papilla, the dependence of DP level on the primary tone frequency ratio f(2)/f(1) showed a pattern characteristic of the response of a single nonlinear resonator. Thus, in agreement with neural data, DPOAE from the basilar papilla reflect the contribution of a single auditory filter to emission generation.

Acoustic Stimulation↗
PubMed2001

Factors influencing the occurrence of thrombophlebitis after post-surgical long-term intravenous catheterization of colic horses: a study of 38 cases.

Thrombophlebitis is a well-known complication of the use of long-term in-dwelling catheters. In humans, catheter material has been shown to strongly influence the occurrence of thrombophlebitis. In the horse, the influence of catheter material has been studied in healthy experimental animals, but information on the relative importance of this factor is lacking. To investigate which factors have most impact on the frequency of jugular vein thrombosis in post-surgical colic horses, a clinical study was performed on 38 animals. Horses were randomly divided into two groups. In one group a polytetrafluoroethylene catheter was used, in the other a polyurethane catheter. Both groups were clinically monitored and screened for signs of thrombophlebitis. Seven out of 38 horses developed thrombophlebitis. The type of catheter material used had no influence on thrombophlebitis development. Dwell time was significantly longer in horses that developed thrombophlebitis compared with those that did not. There was no relationship between the occurrence of thrombophlebitis and underlying disease or surgical treatment, suggesting that the general state of debilitation these horses experienced was the most important determinant for the development of thrombophlebiris. This was further stressed by the fact that seven horses developed thrombophlebitis of the contralateral vein that had been used for the induction of anaesthesia (this incidence is much higher than in horses anaesthetized for elective surgery). It is concluded that the state of debilitation is the most important determining factor for the occurrence of thrombophlebitis after the use of long-term in-dwelling intravenous catheters. This makes a substantial reduction of the incidence of thrombophlebitis difficult, but some progress can be made by consequently restricting dwell time.

Animals↗
PubMed2001

The behavior of evoked otoacoustic emissions during and after postural changes.

Click-evoked and stimulus frequency otoacoustic emissions (CEOAEs and SFOAEs, respectively) were studied in humans during and after postural changes. The subjects were tilted from upright to a recumbent position (head down 30 deg) and upright again. Due to the downward posture change, CEOAEs showed a phase increase (80 deg at 1 kHz) and a level decrease (0.5 at 1 kHz), especially for frequency components below 2 kHz. For SFOAEs, the typical ripple pattern showed a positive shift along the frequency axis, which can be interpreted as a phase shift of the inner-ear component of the microphone signal (90 deg at 1 kHz). This also occurred mainly for frequencies below 2 kHz. The altered posture is thought to cause an increase of the intracranial pressure, and consequently of the intracochlear fluid pressure, which results in an increased stiffness of the stapes system. The observed emission changes are in agreement with predictions from a model in which the stiffness of the cochlear windows was altered. For CEOAEs, the time to regain stability after a downward turn was of the order of 30 s, while this took about 20 s after an upward turn. For SFOAEs, this asymmetry was not found to be present (about 11 s, both for up- and downward turns).

Adult↗
PubMed2000

Stapedius muscle fibre composition in the rat.

The stapedius muscle (SM) is supposed to prevent cochlear damage by noise. Consequently functional demands are the ability of fast contraction with long endurance. This implies the presence of a large fraction of myosin type II fibres with an appreciable oxidative capacity. We determined the myosin composition of SM fibres using consecutive complete SM cross-sections (6 week old rats) which were processed by enzyme histochemistry (EHC) to determine acid/alkali lability of myofibrillar adenosine triphosphatase (mATPase) or by immunohistochemistry (IHC) using myosin heavy chain (MyHC) antibodies. Method accuracy was determined in co-processed extensor digitorum longus (EDL). Four hundred SM and 200 EDL fibres were assigned to mATPase type I, IIA, IIB, IIX or 'miscellaneous' ('Misc') categories. Per mATPase category the fibres were attributed to groups with specific MyHC composition. In the EDL, mATPase type I and IIB fibres expressed only MyHC I and IIB respectively, whereas about 10% of the type IIA and 40% of the type IIX fibres expressed more than one MyHC. Thus IHC detects amounts of myosin isoforms which are not detected by EHC. The mATPase IIX category criterion leaves the possibility that this category contains fibres with myosin type IIA and/or IIB in larger amounts. The criteria of the mATPase categories type I, IIA or IIB preclude assignment to these categories of fibres which also contain other myosin isoforms in larger amounts. Such fibres were classified in one of the mATPase 'Misc' categories. Thus in the EDL the capability of the EHC criteria to select 'pure' fibres in terms of myosin differs per mATPase category. None of the SM fibres were assigned to the mATPase type I or IIB categories, about 25% to the type IIA, 60% to type IIX and 15% (including most fibres which expressed MyHC I) to a 'Misc' category. All SM fibres expressed two or more MyHC isoforms, MyHC IIB occurring in all fibres and substantial amounts of MyHC IIA and/or IIX in most. These findings confirm the hypothesis that such fibres have the capacity to contract fast and have the better fatigue resistance.

Animals↗
PubMed2000

Apomixis technology and the paradox of sex.

Most plant species produce genetically variable seeds by the fusion of meiotically reduced egg cells and pollen grains. However, a small proportion of seed plants produces clonal, asexual seeds by the process of apomixis. The fixation of heterosis by apomixis is of great interest for plant breeding. The prospect of changing sexual crop species into apomictic crop species by genetic engineering--apomixis technology--has recently caused a boom in apomixis research. According to evolutionary biological theories, a dominant apomixis gene will rapidly become fixed in an outcrossing sexual population. Therefore, in theory, apomixis transgenes could have unconditional advantages that could result in the uncontrollable spread of the transgenes. By contrast, 'classic' transgenes might only have conditional advantages. Paradoxically, sexual reproduction and not apomixis is common in nature. However, this is no guarantee that apomixis transgenes will be ecologically safe because there could be essential differences between natural and transgenic apomicts.

Plant Physiological Phenomena↗
PubMed2000

Noise-evoked otoacoustic emissions in humans.

Click-evoked otoacoustic emissions (CEOAEs) and acoustical responses evoked by bandlimited Gaussian noise (noise-evoked otoacoustic emissions; NEOAEs) were measured in three normal-hearing subjects. For the NEOAEs the first- and second-order Wiener kernel and polynomial correlation functions up to the sixth order were calculated by cross correlating the noise stimulus and the emission response. Emission components were only found in the first-order Wiener kernel. These kernels were dependent on the stimulus level, indicative of the nonlinear response of the cochlea. For each subject the frequency contents of the CEOAE and the first-order Wiener kernel were nearly identical. In the second-order Wiener kernels and higher-order polynomial correlation functions no significant contributions were identified. Apparently, odd and even order nonlinearities cannot be detected by Wiener kernel analysis.

Acoustic Stimulation↗
PubMed2000

The behavior of spontaneous otoacoustic emissions during and after postural changes.

Spontaneous otoacoustic emissions (SOAEs) were studied in humans during and after postural changes. The subjects were tilted from upright to a recumbent position (head down 30 degrees) and upright again in a 6-min period. The SOAEs were recorded continuously and analyzed off-line. The tilting caused a change in the SOAE spectrum for all subjects. Frequency shifts of 10 Hz, together with changes of amplitude (5 dB) and width (5 Hz), were typically observed. However, these changes were observed in both directions (including the appearance and disappearance of emission peaks). The most substantial changes occurred in the frequency region below 2 kHz. An increase of the intracranial pressure, and consequently of the intracochlear fluid pressure, is thought to result in an increased stiffness of the cochlear windows, which is probably mainly responsible for the SOAE changes observed after the downward turn. The time for the spectrum to regain stability after a postural change differed between the two maneuvers: 1 min for the downward and less than 10 s for the upward turn.

Cochlea↗
PubMed1998

Understanding the discrepancies between 31P MR spectroscopy assessed liver metabolite concentrations from different institutions.

The high divergence between the liver metabolite concentrations and pH values reported in previous quantitative 31P magnetic resonance studies, for instance phosphomonoester (0.7-3.8 mM) and phosphodiester (3.5-9.7 mM), has not been addressed in the literature. To assess what level of discrepancy can be caused by processing and metabolite integration, in this study chemical shift imaging localized 31P magnetic resonance spectra of human liver were quantitated by three methods currently applied in clinical practice: peak areas defined manually by placement of two cursors vs. frequency domain curve fitting with the assumption of either Gaussian or Lorentzian line shapes. Large reproducible differences were found in liver metabolite peak areas but not in pH, indicating that processing and peak integration methods can only explain part of the discrepancies between the results from different institutions.

Adenosine Triphosphate↗