Search PubMed⌕ Search

Biomedical subjects

B Hillen

Publications and source records attributed to B Hillen.

At least 73 records · Page 4Linked to original sources
PubMed1989

Mathematical models of the flow in the basilar artery.

The flow in the basilar artery arises from the merging of the flows from the two vertebral arteries. This study deals with the question whether a parabolic (Poiseuille) profile will have been established before the basilar artery divides into both posterior cerebral arteries. The inlet length (that is, the downstream distance needed for the flow to become approximately equal to the limiting Poiseuille flow) and velocity profiles have been computed from two- and three-dimensional mathematical models in which flow pulsatility and vessel wall distensibility have been neglected and the complex geometry of the junction has been taken into account in a simplified form. The results show that the flow at the end of the basilar artery is far from being parabolic and that an asymmetry in the entrance flow will be carried along towards the end of the basilar artery, thus affecting flows in the circle of Willis.

Basilar Artery↗
PubMed1989

Functional anatomy of the vagina fibrosa of the flexors of the fingers.

The flexor tendon sheaths of 40 fingers were investigated to determine which classification of the annular and cruciform pulleys seems to be justified. The classification of Kleinert et al. (1981) into five annular and four cruciform pulleys was the most consistent with our results. The constant presence of the mid-phalangeal annular pulleys in zones III and VII shows their major role in preventing the tendons from bow-stringing. The cruciform pulleys seem to allow the tendon sheath to deform during flexion.

Fingers↗
PubMed1989

US location of the adductor canal hiatus: morphologic study.

In the lower extremities, the adductor canal hiatus is a site of predilection for arterial stenoses and occlusions. The high incidence of vascular disease in this region is thought to be due to a local factor. To gain more insight into the mechanisms leading to such disease, the authors used ultrasound to locate the adductor canal hiatus in dissecting room preparations and in healthy volunteers.

Femoral Artery↗
PubMed1988

Ultrasonography of the peroneal nerve muscle group in normal subjects and patients with peroneal paresis.

A method for measuring the cross-sectional area (CS area) of the peroneal nerve muscle groups (PNMG) by ultrasonography is presented. The method has a good reliability and can be performed easily. The mean value of the ratio (x 100) of the right-sided PNMG CS area to the left-sided PNMG CS area in right-handed normal subjects was 98%, with a standard deviation of 8.5%. The normal range for this value was 81%-115% (mean +/- 2 SD). Examples of these measurements in patients with peroneal pareses during denervation and reinnervation are given.

Adult↗
PubMed1988

Analysis of flow and vascular resistance in a model of the circle of Willis.

A very simple model of the flow in the circle of Willis is described in this paper. Disregarding pulsatility and vessel wall elasticity, fluxes in all segments of the circle of Willis and its afferent and efferent vessels are calculated by applying the Poiseuille-Hagen formula. Comparison with the fluxes calculated numerically from a more sophisticated mathematical model, including pulsatility, vessel wall elasticity and nonlinear effects, revealed only very slight differences. In short, fluxes in the afferent vessels and the segments of the circle of Willis are influenced by any change of resistance within the network, whereas the fluxes in the efferent segments are dominated by the efferent resistance distribution. However, a great advantage of the present simple model is that it offers the possibility of an analytical approach which yields both an easy sensitivity analysis of parameters and an insight into the mechanisms that govern the flow in a network like the circle of Willis. It can be concluded that these mechanisms are similar to the principles of the Wheatstone bridge, known from electrical circuit theory.

Circle of Willis↗
PubMed1988

Carpal tunnel release; postoperative care.

By demonstrating slight bowstringing of the flexor tendons, computer tomography can explain any weakness of grip. A strong plea for adequate immobilization (three to six weeks) after carpal tunnel release is made.

Bandages↗
PubMed1987

Anatomical relations in the carpal tunnel: a computed tomographic study.

Computed tomography of the carpal tunnel was performed in the hands of both patients and controls in a neutral position, in flexion and in extension. The median nerve was not compressed between the long flexors and the flexor retinaculum in either flexion or extension of the wrist. In flexion, the nerve usually moved dorsally, away from the flexor retinaculum. No difference could be found between the cross-sectional area of the carpal tunnel between patients and controls.

Adult↗
PubMed1987

The variability of the circulus arteriosus (Willisii): order or anarchy?

The variation of the circulus arteriosus is studied using multivariate methods. The data which form the basis of this study are 19 measurements of half the circumference of the arteries that form the circle of Willis and its afferent and efferent branches; 100 circles of Willis were measured for this purpose. Since the number of variables per individual is large, multivariate statistical techniques are the most appropriate method to gain insight in the relations of vessel sizes that exist within the circle of Willis. So a principal component analysis was performed on the data. The results clearly show a number of relations between vessel sizes. In general, inverse relationships were found of vessels that have (at least partially) an identical irrigation area: both internal carotid arteries and the ipsilateral posterior communicating artery show an intimate relationship and are together inversely related to the basilar artery and the precommunicating part of the posterior cerebral artery. Inverse relationships are also found for both vertebral arteries and both precommunicating parts of the anterior cerebral arteries. The homonymous efferent arteries appear to be closely related and show an independent variation. Together the first six principal components explain 69% of the variance. These results support a haemodynamical hypothesis on the explanation of the variability of the circle of Willis. Moreover, the differential growth in the head-neck region during the first two decades of life is postulated to be the origin of a part of the variation.

Cerebral Arteries↗
PubMed1986

Correlations between the cross-sectional area of the jaw muscles and craniofacial size and shape.

In adult human subjects, the correlations were determined between the cross-sectional areas of the jaw muscles (measured in CT scans) and a number of facial angles and dimensions (measured from lateral radiographs). Multivariate statistical analysis of the skeletal variables in a group of 50 subjects led to the recognition of six independent factors determining facial shape, i.e., cranial base length, lower facial height, cranial base flexure and prognathism, facial width, mandibular length, and upper facial height. In 29 of these subjects, the cross-sectional areas of the jaw muscles were determined, and correlations between these areas and the scores on the above-mentioned factors were calculated. It appeared that the cross-sectional areas of temporalis and masseter muscles correlated positively with facial width, whereas the areas of masseter and both pterygoid muscles did so with mandibular length. It has been shown experimentally that a decrease in jaw muscle size in various animals likewise has an effect on facial width and mandibular length. Our results therefore support the hypothesis that in man too the jaw muscles affect facial growth and partly determine the final facial dimensions. They also hint that the role of each muscle is different.

Adult↗
PubMed1986

A mathematical model of the flow in the circle of Willis.

A mathematical model of the flow in the circle of Willis has been designed and the effects of (a) the large anatomical variation of the communicating arteries and (b) physiological changes of the resistances of the vertebral arteries have been studied. The influence of the posterior perforating arteries on the flow in the posterior communicating arteries has been investigated as well, with special attention being paid to the possible occurrence of a 'dead point'. In the model, the influence of diameters of the communicating arteries on the flow in the afferent vessels and the segments of the circle turns out to be considerable, especially in the range of the anatomical variation of the diameters. Within this range flow reductions due to an increased resistance of the vertebral artery will be compensated for by the system. Assuming that the values and ratios of the peripheral resistances are within the physiological range, a dead point is not to be expected in the flow in the posterior communicating arteries.

Cerebrovascular Circulation↗
PubMed1986

The variability of the circle of Willis: univariate and bivariate analysis.

The results are presented of a statistical analysis of the variability of the circle of Willis using univariate and bivariate methods. For this purpose 100 circles of Willis were available. From each circle 19 indexes of arterial size were determined, the basilar artery was measured in two places. Half the circumference was measured. This data yielded no evidence of differences between left- and right-sided vessels in the sample. An important source of variation is the general size of all vessels considered. When the data are cleared from this general size variation, correlation coefficients reveal interesting relations between the vessels. The posterior communicating arteries are strongly related to the ipsilateral carotid artery, whereas a strong inverse relationship exists with the basilar artery and the precommunicating part of the ipsilateral posterior cerebral artery. These relationships can be understood from the expected patterns of the blood flow in these vessels. Similar relationships can be found in the anterior part of the circle of Willis and in the vertebro-basilar junction. In a different manner, based on previous haemodynamic studies, the relation between blood flow and vessel size within the circle of Willis can be demonstrated by relating the ratios of the sizes of afferent and efferent arteries to the sizes of the posterior communicating arteries, an "intuitive" model. The supposed correlations of the outcome of this "intuitive" model with the size of the communicating arteries appeared to by highly significant. It is concluded that the variations of the circle of Willis are related to the individual variations of the blood flow in this arterial network.

Analysis of Variance↗
PubMed1985

Physiological cross-section of the human jaw muscles.

The cross-sectional areas of the masseter, temporalis, medial pterygoid and lateral pterygoid muscles were determined by means of computer tomography in 16 male subjects with healthy dentitions. The physiological cross-section (PCS) of these muscles was predicted from the previously determined relationship between PCS and scan cross-sections. In our subjects, mean total PCS of the jaw muscles was twice as high as in cadavers with few natural teeth. The average distribution of total PCS over the four muscles was the same in the two groups. There was considerable individual variation. Strong correlations in cross-sectional area were only found between the masseter and medial pterygoid muscles. Variation in PCS of these two muscles determines 80% of the variation in combined cross-sectional area.

Adult↗
PubMed1984

Arthrography and the medial compartment of the patello-femoral joint.

In four groups of patients with normal patellar cartilage, synovitis, patellar chondropathy , and degenerative changes of the patellar surface of the femur, the anatomical relationships within the medial compartment of the patello-femoral joint were examined. Clear differences were observed between these groups in the incidence of visualization of the medial alar plica and the mediopatellar synovial plica. As a consequence, an explanation has been sought for the occurrence of patellar chondropathy and degenerative changes of the patellar surface of the femur. It seems probable that a long-standing traumatic synovitis with effusion, attenuation of the synovial membrane, and the composition of the synovial fluid can lead to patellar chondropathy . The degenerative changes of the patellar surface of the femur are usually secondary to those of the load-bearing patellar facet. Insufficient covering of the cartilage by soft tissue may play a role in chondropathy of the nonload -bearing portion of the patella and the femoral condyle.

Cartilage Diseases↗
PubMed1984

Relationship between the physiological cross-section of the human jaw muscles and their cross-sectional area in computer tomograms.

Physiological cross-section (PCS) and cross-sectional area in computer tomograms made at right angles to the mean fibre direction were compared in the masseter, temporalis and pterygoid muscles of six human cadavers. PCS was determined as (1) total cross-section of teased fibre bundles (2) total fibre weight divided by mean fibre length. The two measures correlated strongly, but the first was always 25% lower than the second, irrespective of the muscle concerned. The cross-sections in the tomograms (SCS) were smaller than the PCS, except in the lateral pterygoid. In all muscles, a statistically significant correlation was found between SCS and PCS. The SCS can be used to predict PCS, with an error of 0.3-1.0 cm2. In our material, cross-sections were about 20% higher than reported in the literature. It is suggested, that this discrepancy is caused by the loss of natural teeth.

Adult↗
PubMed1984

Relationships between masticatory muscle cross-section and skull shape.

Cross-sectional areas of the masseter, temporalis and medial, and lateral pterygoid muscles were determined in 16 subjects by means of computer tomography. In each subject three scans were made, intersecting the thickest part of the muscles at right angles to the fiber direction. The masseter and medial pterygoid muscles are large in persons with brachycephalic skulls, short faces, and a small jaw angle. The cross-sectional areas of the temporalis and lateral pterygoid muscles showed no correlation with facial dimensions.

Adult↗
PubMed1984

Intra-articular reconstruction of the anterior cruciate ligament. An experimental study of length changes in different ligament reconstructions.

An anatomic model was developed to test different types of intra-articular anterior cruciate ligament reconstructions. Four cadaver knees were tested in an identical fashion. In each knee 12 different positions were tested. The results indicate that over-the-top repair is not suitable for anterior cruciate ligament reconstruction from a mechanical standpoint. It is likely that this type of repair in human knees will lead to excessive stretching and insufficiency of the reconstructed tissue. A posterior approach through the lateral femoral condyle is more desirable. The position of the tibial tunnel is less crucial, but a more anterior tunnel is preferable. When the tunnels are properly drilled, fixation of the reconstructed ligament is advocated with the knee in 45 degrees-90 degrees of flexion. Postoperative immobilization in 45 degrees of flexion is suggested.

Adult↗