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Biomedical subjects

A C Volkers

Publications and source records attributed to A C Volkers.

15 recordsLinked to original sources
PubMed2004

Effects of imipramine, fluvoxamine and depressive mood on autonomic cardiac functioning in major depressive disorder.

OBJECTIVE: Diminished HR variability is considered to be associated with depression and the increased risk of cardiovascular disease. The pharmacological effects of antidepressants and depressive mood itself may contribute to alterations in autonomic cardiac functioning, but a limited amount of data is available. We studied the effects of two different types of antidepressant treatments (imipramine and fluvoxamine), in addition to the effect of depressive mood, on the cardiovascular system in depressed patients. METHODS: Depressed inpatients were studied during a drug-free period and after 4 weeks of adequate treatment with imipramine (n = 17) or fluvoxamine (n = 24). Heart rate variability, blood pressure variability, and a baroreflex sensitivity index during supine rest and orthostatic challenge were analyzed by means of spectral techniques to obtain noninvasive parameters of sympathetic and parasympathetic activity. RESULTS: Both imipramine and fluvoxamine reduced sympathetic and parasympathetic activity, although the effects of imipramine were much more pronounced. Severity of depression was positively related to mean levels of heart rate and blood pressure in the total patient group. There was no convincing evidence that these relationships differed between depressed patients treated with imipramine and those treated with fluvoxamine. CONCLUSION: Our findings suggest that alterations in mean heart rate and blood pressure in depressed patients after antidepressant treatment are the result of a combined effect of pharmacological actions of antidepressants and improvement of depressive mood state. The present study did not confirm the relationship between clinical state and cardiovascular variability or baroreflex sensitivity.

Adult↗
PubMed1995

Multiple usage of the CD PLUS/UNIX system: performance in practice.

In August 1994, the CD PLUS/Ovid literature retrieval system based on UNIX was activated for the Faculty of Medicine and Health Sciences of Erasmus University in Rotterdam, the Netherlands. There were up to 1,200 potential users. Tests were carried out to determine the extent to which searching for literature was affected by other end users of the system. In the tests, search times and download times were measured in relation to a varying number of continuously active workstations. Results indicated a linear relationship between search times and the number of active workstations. In the "worst case" situation with sixteen active workstations, the time required for record retrieval increased by a factor of sixteen and downloading time by a factor of sixteen over the "best case" of no other active stations. However, because the worst case seldom, if ever, happens in real life, these results are considered acceptable.

CD-ROM↗
PubMed1990

Relation between form and function in the sacroiliac joint. Part I: Clinical anatomical aspects.

Observations on sectioned and opened preparations of human sacroiliac joints (SI joints) show the presence of cartilage-covered ridges and depressions, which are complementary on the auricular surfaces. These macroscopically visible features of the joints, which become visible relatively early in life, are more pronounced in men than in women. This type of roughening, as well as that by increased coarseness of the auricular surface, is viewed as a nonpathologic adaptation to the forces exerted at the SI joints, leading to increased stability. Differences between men and women may be attributed to childbearing and to a difference in the center of gravity. It is emphasized that intra-articular ridges and depressions can be misinterpreted roentgenologically as osteophytes.

Adult↗
PubMed1990

Relation between form and function in the sacroiliac joint. Part II: Biomechanical aspects.

The amount of friction between the articular surfaces of sacroiliac (SI) joints was determined and related to the degree of macroscopic roughening. Results show that articular surfaces with both coarse texture and ridges and depressions have high friction coefficients. The influence of ridges and depressions appears to be greater than that of coarse texture. The data are compatible with the view that roughening of the SI joint concerns a physiologic process.

Adult↗
PubMed1990

Analysis of external and internal interlibrary loan requests: aid in collection management.

The analysis of 60,779 external interlibrary loan requests for copies of periodical articles from the collection of Erasmus University Medical Library in 1988 is described. The study was used for planning the length of backruns to be retained due to space limitations that forced the disposal of older volumes. More than 50% of requests were for the most recent two-year period, and 90% of requests could be filled with a twenty-year run of periodicals. In 1989, 4,157 internal requests were received for periodicals not owned; these were analyzed to determine those most commonly requested. Prior to subscribing, new titles were reviewed as to price, bibliometric indicators, number of requests, length of backfile, and the number of requesting departments. The Library Advisory Board decides on cancellation or purchase of periodicals; the elements considered are described.

Interlibrary Loans↗
PubMed1987

Spatial contrast sensitivity and the diagnosis of amblyopia.

The relationship was studied between spatial contrast sensitivity function and type of pathology of the visual system. Two characteristics were found to be typical for amblyopia: there is a discrepancy between the high-frequency cut-off ('grating acuity') and the Snellen acuity; the contrast sensitivity is strongly dependent on the width of the stimulus. In optic nerve degeneration a decrease in contrast sensitivity is found at low spatial frequencies. Decreased contrast sensitivity at high spatial frequencies is atypical but occurs in those disorders associated with decreased Snellen visual acuity. From these findings a relationship is defined which enables spatial contrast sensitivity tests to be used to differentiate between amblyopia and optic nerve degeneration.

Adult↗
PubMed1987

Visual function and pattern visual evoked response in optic neuritis.

The disparity between clinical visual function and pattern visual evoked response (VER) was studied in 53 patients who had suffered an attack of optic neuritis (ON) more than six months before. The visual functions tested included Snellen visual acuity, colour vision, visual field, and contrast sensitivity. The effect of pattern presentation, check size, and luminance was tested by recording VERs with several stimulus configurations. VER amplitudes were found to be associated with the outcome of all four clinical tests, independently of check size, luminance, or the presentation method used. On the other hand VER latencies were hardly ever related to the results of any of the four clinical visual tests. These findings support the idea that VER amplitude provides information about visual spatial perception, while VER latency is more related to the extent of demyelination.

Adolescent↗
PubMed1987

Provocation of epicondylalgia lateralis (tennis elbow) by power grip or pinching.

The etiology of epicondylalgia lateralis humeri (tennis elbow) is not fully understood. A biomechanical model is introduced for those types of epicondylalgia where damage at the origin of the wrist and finger extensor muscles is caused by overloading. It shows that grasping and pinching always cause a flexing moment at the wrist joint. To avoid flexion of the joint, there must be equilibrium of moments, which is attained by activity of the extensor muscles. Simultaneous measurements of force and electromyograms support the biomechanical model.

Adult↗
PubMed1986

Estimation of visual function after optic neuritis: a comparison of clinical tests.

A group of 53 patients who had suffered an attack of unilateral (n = 45) or bilateral (n = 8) optic neuritis more than six months before were subjected to a battery of tests to determine their spatial contrast sensitivity, visual field, and colour vision. The 106 eyes investigated were classified according to their clinical status and visual acuity at the time of the study into unaffected (n = 45), recovered (n = 33), and non-recovered (n = 28). At least one of the three tests gave an abnormal result in 67%, 88%, 100% of the three groups respectively. The results obtained with these three tests showed a significant statistical association.

Adolescent↗
PubMed1981

Measurements of cerebral blood flow in the pig by the 133Xe clearance technique. Interpretation of the initial part of clearance curves.

The 133Xe clearance technique is used to measure cerebral blood flow in the pig. Previous publications have shown that the two-compartmental model is inadequate for interpreting the experimental data. The present study deals with certain phenomena seen during the initial part of the clearance curves, which can lead to correct estimation of the blood flow rate. Two types of initial peaks can be distinguished: one is a very fast type, which is interpreted as being due to transit of the tracer via large vessels and is referred to in the literature as the 'arterial peak'; the second is a slower 'tissue peak,' seen in animal experiments at high CO2 levels and in clinical patients with cerebrovascular instability. In animal preparations discrepancies were found between flow measurements according to the 133Xe clearance technique and those made with the aid of an electromagnetic flow probe situated around the carotid artery. A hysteresis effect was also found in the relation between respired CO2 level and cerebral blood flow. All these findings can be interpreted in terms of arteriovenous shunting, i.e., non-nutrient flow of blood, which is not necessarily due to anatomical anastomosis but can also be explained by the assumption that the clearance is partly limited by diffusion. The possibility of diffusion-limited clearance can have important clinical implications. Further research may provide a better basis for analysis of clearance curves to detect cerebral perfusion deficiencies that give rise to false flow calculations in present techniques.

Animals↗
PubMed1980

Measurement of cerebral blood flow in the pig by the Xe-133 clearance technique. Failure of the two-compartmental clearance model.

The Xe-133 clearance technique is used to measure cerebral blood flow in the pig, which often serves as an experimental animal for cardiovascular research. The clearance curves are fitted by a two-exponential model. However, the fitted parameters are incompatible with a two-compartmental model: the values found for the parameters depend on the length of the clearance curve analysed. The discrepancies are thought to be consequences of the heterogeneity of cerebral blood flow and of mathematical problems of parameter identification. The non-validity of the relative weight of the fast clearance component as an anatomical or functional parameter is demonstrated. The use of the mean time constant, mean transit time, mean decay constant and initial slope for determination of cerebral blood flow rates is discussed. The mean cerebral blood flow of the anaesthetized pig measured by the clearance technique is found to be lower than the blood flow measured by means of a flow probe around the common carotid artery (with the external carotid artery tied off). The existence of a significant arteriovenous shunt flow is postulated.

Animals↗
PubMed1976

Compartmental models of cerebral blood flow. Analysis using the 81-keV and 31-keV photons of 133Xe.

The clearance of 133Xe from the cerebrum after intra-arterial injection was studied in the pig. A mathematical model, consisting of two exponential terms and a constant, was fitted to decay curves obtained for both the 81-keV and the 31-keV radiation of 133Xe. The corresponding exponential terms for the 31-keV and 81-keV curves were found to differ significantly, implying that the two-compartmental model, based on the paritition of the white and gray matter of the brain, is not adequate to describe the clearance process. Other studies have shown that cerebral blood flow is more heterogeneous than the two-compartment model suggests. The discrepancies found here are interpreted as due to the simplification of representing a multiexponential clearance process by means of a two-exponential model.

Animals↗