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Biomedical subjects

B Hillen

Publications and source records attributed to B Hillen.

At least 55 records · Page 3Linked to original sources
PubMed1996

Review of the functional anatomy of the cartilages and muscles of the nose.

This paper reviews the anatomy of the nasal cartilages and muscles. Accurate anatomical knowledge of these structures may facilitate the design of a model to study the mobility and support of the lateral nasal wall and ala and may thus provide information on the dynamics of valve area. It is concluded that a uniform description of nasal cartilages and muscles is still lacking. This is especially true for the attachments of the nasal cartilages to neighbouring structures, as well as the location and function of the muscles influencing the valve area. The use of uniform, preferably anatomical, terminology is encouraged.

Humans↗
PubMed1995

Effects of anterior communicating artery diameter on cerebral hemodynamics in internal carotid artery disease. A model study.

BACKGROUND: Collateral circulatory pathways are considered the primary determinant of cerebral hemodynamics in patients with obstructive lesions of the internal carotid arteries (ICaAs). However, the hemodynamic effects of the diameter of the anterior communicating artery (ACoA) have never been assessed quantitatively in humans. METHODS AND RESULTS: Two different mathematical models were used to simulate changes affecting blood pressures and flows in cerebral arteries as a function of ACoA diameter and ICaA stenoses or occlusions. Small changes in ACoA diameter were found to have marked hemodynamic effects when they occurred within the range of 0.4 to 1.6 mm, a situation observed in 80% of the cases. Outside this range, changes in ACoA diameter had no effect. Simulated pressure drops through a stenotic ICaA were consistent with those observed. They were found to depend on the degrees of the stenoses in both ICaAs and on ACoA diameter according to a simple equation. Pressure reserve in the middle and anterior cerebral arteries decreased to below the lower limit of autoregulation, despite a normal mean arterial blood pressure, when the arteries were distal to a unique 70% ICaA stenosis associated with a small-diameter ACoA or to a 50% ICaA stenosis associated with a contralateral ICaA occlusion and a large-diameter ACoA. Above these thresholds, the circle of Willis allowed for an almost complete global cerebral blood flow compensation that involved all the afferent and communicating vessels. CONCLUSIONS: ACoA diameter strongly modulates the effects of ICaA lesions on cerebral hemodynamics. Some proposals for endarterectomy indications can be derived from our study.

Blood Flow Velocity↗
PubMed1995

Paradoxical arterial wall shrinkage may contribute to luminal narrowing of human atherosclerotic femoral arteries.

BACKGROUND: This study was done to assess how local changes in vessel size, together with plaque load, determine luminal narrowing in atherosclerotic arteries. Fifty-one human femoral arteries were analyzed: 32 postmortem and 19 in vivo by 30-MHz intravascular ultrasound. METHODS AND RESULTS: Histological and intravascular ultrasound cross sections were examined every 0.5 cm over an arterial segment 10 to 15 cm long. In each cross section we measured the lumen area and the area circumscribed by the internal elastic lamina (the IEL area). In each arterial segment, the cross section that contained the least amount of plaque was the reference site. For each cross section, the lumen area stenosis was expressed as percent of the lumen area in the reference site. Similarly, the IEL area was expressed as percent of the IEL area in the reference site (the relative IEL area). There was a significant negative correlation between the relative IEL area and the lumen area stenosis percentage (r = -.62, P < .001 for histology and r = -.66, P < .001 for intravascular ultrasound). When lumen area stenosis was less than about 25%, mainly compensatory enlargement was observed. When lumen area stenosis exceeded about 25%, however, mainly a decrease of the IEL area was observed, which is consistent with arterial wall shrinkage. Furthermore, the increase in plaque area does not account for the total loss of luminal area. There was a moderate correlation between an increase in plaque area and reduction of the corresponding lumen area (r = .49 and r = .56 for histology and intravascular ultrasound, respectively). CONCLUSIONS: The decrease in luminal area cannot be attributed to plaque increase alone. Arterial wall shrinkage is a paradoxical mechanism that may contribute to severe luminal narrowing of the atherosclerotic human femoral artery.

Aged↗
PubMed1995

Arterial tortuosity in the femoropopliteal region during knee flexion: a magnetic resonance angiographic study.

Dynamic changes in curvature are expected in the femoropopliteal region during knee flexion. The location of the artery dorsal to the axis of movement implicates a relative length excess that may influence local morphology. To study arterial morphology in vivo, magnetic resonance angiography was performed in 22 healthy volunteers (aged 23-68 y). The curvature of the femoral vessels was studied and quantified in stretched and flexed positions. During knee flexion the vessel followed the movement of the leg and in the sagittal plane one curve was visible distal to the adductor hiatus. Three or more small curves were seen proximal to the knee joint in all volunteers. In the group aged under 30 y these minor curves were located proximal to the adductor hiatus as if the artery curls up in Hunter's canal. In the group aged over 45 y one or more curves were located distal to the adductor hiatus in the popliteal fossa. In volunteers aged 60 y and older some of these curves did not disappear during knee extension. In older individuals, natural elongation and loss of arterial elasticity will contribute to the formation of these curves. Impairment of the free gliding mechanism of the femoral vessels in the adductor canal could explain the differences in location of these minor curves between younger and older subjects. It is concluded that morphological changes in the femoral artery occur during knee flexion and that this tortuosity is age dependent. This may influence local haemodynamics and therefore possibly contribute to atherogenesis.

Adult↗
PubMed1994

The arterial pattern at the base of arhinencephalic and holoprosencephalic brains.

The mechanisms by which the anatomical variations of the circle of Willis develop is considered to be related to haemodynamic factors, i.e. the differential growth of the various parts of the brain will continuously change the haemodynamic demands and consequently the flow patterns in the cerebral arteries. It is therefore to be expected that, if a selected part of the brain does not develop, the change in the haemodynamic demand will affect the development of some cerebral arteries. Consequently the arteries at the base of 2 arhinencephalic and 8 holoprosencephalic brains were studied in conjunction with the brain malformations. The defects of holoprosencephaly are believed to arise from a failure of the prosencephalon to separate fully into the telencephalon and diencephalon and become manifest at the time that the prosencephalon normally starts to separate into the hemispheres, i.e. 28-34 d p.c. Arhinencephalic brains are fully diverticulated. There is only a partial or complete agenesis of the olfactory tracts and bulbs. The defect causing arhinencephaly starts at 43 d p.c. In the arhinencephalic brains no particular vascular abnormalities were found. However, at the base of the holoprosencephalic brains no complete circle of Willis was present; the anterior part was lacking and was replaced by anterior branches which emerged unilaterally or bilaterally from the internal carotid artery. The choroidal arteries were of very large calibre and ran to the highly vascularised wall of the dorsal cyst which is usually present in holoprosencephalic brains. In contrast to the anterior part, the posterior arterial pattern was almost identical to the posterior part of the circle of Willis of normal brains. The basic vascular patterns found in the holoprosencephalic brains displayed the features of Padget's developmental stages 2 and 3 of the cerebral vasculature, i.e. the pattern that has normally developed within 28-40 d p.c. The further modification of this pattern could largely be understood from the functional demand imposed on the circulation by the enlarged anterior choroidal arteries. Because the development of the anterior part of the circle of Willis precedes the developmental derangement causing arhinencephaly, a complete circle was found in these brains.

Brain↗
PubMed1993

A quantitative investigation of the variability of the major cerebral arterial territories.

BACKGROUND AND PURPOSE: We have previously reported that the topographic variability of the territories of the anterior, middle, and posterior cerebral arteries is much larger than is generally considered in the literature. In the current study, we quantitatively investigated the variability of the territorial distribution of the major cerebral arteries and analyzed its relation to the variability of the circle of Willis. METHODS: In 23 human brains, the volumes of the major cerebral territories were calculated and the diameters of the contributing arteries were measured and standardized for size. RESULTS: The variability of the standardized territorial volumes proved to be considerably large and strongly correlated with the variability of the diameters of the arteries emanating from the circle of Willis. Furthermore, the relative vascular densities in the gray and white matter were determined. Taking these densities into account, an estimation of the relative peripheral resistance of the contributing arteries was made. CONCLUSIONS: We hypothesize that the morphological variability of the cerebral vascular system is related to the peripheral resistance of the major cerebral arteries and, consequently, to flow patterns, both of which are hemodynamic factors. We suggest that hemodynamic factors predominantly determine the form and size of the cerebral vascular system.

Brain↗
PubMed1992

Computation of steady three-dimensional flow in a model of the basilar artery.

The flow in the basilar artery arises from the merging of the flows from the two vertebral arteries. To study the flow phenomena in the basilar artery, computations have been performed using a finite element (FE) method. We consider steady flow in a geometrically symmetric confluence. For simplicity, channels with a rectangular cross-section have been used. Both symmetric and asymmetric flow cases have been considered. The results show that for the Reynolds number of interest the flow downstream of the junction is highly three-dimensional, and that the flow at the end of the basilar artery, where it splits again, will not be fully developed. The computed phenomena have been confirmed by laser Doppler velocity measurements.

Basilar Artery↗
PubMed1992

Variability of the territories of the major cerebral arteries.

Recent morphological and functional studies on the circle of Willis suggest that the areas of supply of the six major cerebral arteries show a considerable variation in distribution, in contrast to the relatively consistent pattern generally accepted; therefore, the cortical and intracerebral distribution of the territories of these arteries was investigated in 25 unfixed human brains obtained at routine autopsy. The six major cerebral arteries were simultaneously injected under the same pressure with different-colored Araldite F mixtures under standardized conditions to obtain the most realistic territorial distribution. The cortical boundaries were examined and recorded in relation to the cerebral gyri and sulci, and the territories of the anterior, middle, and posterior cerebral arteries were analyzed and compared. The intracerebral distribution of these territories was investigated after the injected brains were cut in parallel slices. The variability of the territories of these arteries was much larger than generally described in the literature. Twenty-six variations in the territory of the anterior cerebral artery, 17 variations in the area of the middle cerebral artery, and 22 variations in the area of the posterior cerebral artery were found in the cortex of 50 hemispheres. Intracerebrally, the anterior, middle, and posterior cerebral arteries contributed in varying degrees to the blood supply of the lobar white matter, the internal capsule, the caudate nucleus, and the lentiform nucleus. The large variation in the area in which the cortical and intracerebral boundaries between these territories was located was demonstrated by illustrating the minimum and maximum extent of each. The results are compared with prior findings, and their implications for both experimental model studies and clinical practice are discussed.

Adolescent↗
PubMed1992

The microvascular architecture of the scalp in the human fetus at term. Implications for measuring blood gases and flow rate.

A microscopic study is presented on the depth distribution of the microvessels in the scalp of two human fetuses at term. The basal membrane showed a smooth line without papillary structures resulting in a thin epidermal layer of 25 microns. The distance from the scalp surface to the periosteum appeared to be almost 1.8 mm. The capillary density showed a peak of approximately 1.2 capillary cross-sections per 10(4) microns 2 in the first 200 microns of the dermis. In the middle of the dermis the capillary density fell to 0.2 cross-sections per 10(4) microns 2 to rise again in the lower part of the dermis to 1.6 cross-sections per 10(4) microns 2, which remained the approximate count in the subcutaneous tissue. The arterioles and venules showed significant numbers in the lower part of the dermis and were virtually absent in the subcutis. Of all 4570 microvessel cross-sections that were studied in a tissue volume of 0.6 mm3, not a single one showed the features of an arteriovenous anastomosis. The possible implications for laser Doppler flowmetry and continuous blood gas measurement of the fetal scalp are discussed.

Blood Flow Velocity↗
PubMed1991

Review of the variability of the territories of the major cerebral arteries.

The results of recent model studies indicate that the variability in territorial distribution of the major cerebral arteries may be much greater than has been previously recognized. We review the literature on the cortical and intracerebral territories of the anterior, middle, and posterior cerebral arteries. Although most authors claim that these territories are relatively consistent, the results of their studies show many and considerable discrepancies. The variability described by Beevor has been neither excluded nor completely confirmed, yet somehow the concept of a relatively unchanging pattern of the peripheral cerebral vascularization has gradually settled into the literature. We discuss the considerable variability of the cerebral territories, as well as the discrepancies in investigation techniques, injection materials, and specimen conditions that could be factors producing these dissimilar results. Our study shows that there are no arguments in the literature to negate the variability of the cerebral territories.

Caudate Nucleus↗
PubMed1991

Three-dimensional computer reconstruction of the eustachian tube and paratubal muscles.

A new method of anatomic dissection and image reconstruction using computer techniques for better understanding of eustachian tube (ET) functioning is presented. Coronal sections of two noncleft fetal skulls were photographed and projected on a graphic tablet. Contours of the pertinent structures were digitized using a mouse. Coordinates of all digitized points were entered into a special computer program. The data were transformed into three-dimensional representations of anatomic structures. The levator veli palatini muscle (M-LVP) was found to have a close relationship with the ET running underneath it and passing at the inside of the pharyngeal edge of the medial cartilage before entering the soft palate. On M-LVP contraction, this part of the medial ET cartilage appears to be the sole point of impact for ET opening. The tensor veli palatini muscle (M-TVP) is connected with the lateral cartilage of the ET and leaves the ET, rounding the pterygoid hamulus before entering the palatal aponeurosis. On this anatomic basis, action of the muscle by isotonic contraction appears to be more likely than isometric contraction.

Cartilage↗
PubMed1991

Functional anatomy of the circulus arteriosus cerebri (WillisII).

The requirements for understanding the role played by the circle of Willis in the cerebral circulation are two-fold: 1. The basic patterns of blood flow in the circle of Willis should be studied in relation to the interindividual variation of the circle itself and 2. The interindividual variation should be investigated in a quantitative way and possible hemodynamically induced relations should be clarified. With regard to the first question an extensive study on mathematical models of the cerebral circulation was performed, revealing that flow patterns can be understood by applying the principles of the Wheatstone bridge, known from electric circuit theory. With this knowledge the question of the variability was investigated. For this purpose 19 measurements of 100 circles of Willis were obtained from human cadavers. This data set was analysed using both bivariate and multivariate statistical techniques. The result of this analysis indicated that several sources of variation are involved. The first one is the size: some people have larger vessels than others, probably depending on age sex and genetic factors. Other sources of variation appeared to be of hemodynamic origin. The clear hemodynamic relation between vessel sizes in the circle of Willis indicate that they are adapted to the amount of flow, just like vessels elsewhere in the body. For instance, the size of the posterior communicating artery reflects the relative contribution of the anterior (carotid) and posterior (vertebral) vessels to the cerebral circulation. Furthermore, a relation could be established between the variations of the major cerebral vascular territories and the circle of Willis, both during development and in adults.(ABSTRACT TRUNCATED AT 250 WORDS)

Circle of Willis↗
PubMed1991

A comparative study of the circle of Willis in fetal and adult life. The configuration of the posterior bifurcation of the posterior communicating artery.

The configuration of the posterior bifurcation of the posterior communicating artery is commonly described as the 'adult configuration' if the diameter of the precommunicating part of the posterior cerebral artery (P1) is larger than the diameter of the posterior communicating artery itself (PCA). In these cases the blood supply to the occipital lobes is mainly from the vertebro-basilar system. Only in a minority of cases is the fetal or embryonic configuration found. Here the diameter of the PCA is larger than the diameter of the P1 and the blood supply to the occipital lobes is mainly from the internal carotid artery via the posterior communicating artery. In order to track the origin of these different configurations, 53 complete circles of Willis (106 sides) in brains of fetuses and infants aged from 12 weeks to 60 weeks after conception were examined with the aid of an operating microscope, and measurements were made of the diameters of the PCA, P1 and P2. It is concluded that the variations of this part of the circle of Willis are the result of developmental modifications. This is confirmed by a statistical analysis that shows a relation between the stage of development of the brain and the occurrence of the different configurations. The frequencies of the adult and fetal configurations gradually increase at the expense of the transitional configurations. This configuration is found early in development and is characterised by the equality of the diameters of the PCA and P1. These findings contradict the views, found in the literature, that the variations either exist early in development as a consequence of genetic factors or arise after birth as a consequence of mechanical genetic factors.

Adult↗
PubMed1990

Araldite F as injection material for quantitative morphology of cerebral vascularization.

This study deals with the applicability of Araldite F as injection medium for quantitative morphology of the cerebral vascularization. The physical properties of the plastic that are essential for obtaining optimal results have been determined and tested by injection into the cerebral vessels of ten dog brains and five human brains. The dynamic viscosity (at 20 degrees C) of the plastic is 1.5 times that of blood. The polymerization time (+/- 45 min) is long enough to fill the whole vascular tree in a large organ such as the human brain. The plastic shows minimal volume shrinkage (3.90% +/- 0.05%), and the final cast is suitable for scanning electron microscopy (SEM) investigation after corrosion and histological morphometrical examination after embedding in 2-hydroxyethyl-methacrylate (GMA). Special attention has been paid to the conditions under which injection of Araldite F into the cerebral arteries must take place to obtain the most accurate quantitative data on cerebral vascularization and vascular area distribution. Simultaneous injection of the major cerebral arteries of fresh autopsy material, after having removed blood clots by perfusing Kabikinase, is recommended.

Animals↗
PubMed1990

A modified mallory-cason staining procedure for large cryosections.

The classic Mallory-Cason staining procedure has been modified for application to sections "on tape" obtained from large deep frozen tissue specimens. These 20 microns cryosections are collected on tape from a large heavy duty cryomicrotome. The stained sections provide anatomical details that are not revealed by other techniques. The merit of this procedure is found in the support of modern medical modalities, both for research and educational purposes.

Blood Cells↗
PubMed1990

Cross-sectional anatomy of the nose and paranasal sinuses. A correlative study of computer tomographic images and cryosections.

Anatomic relations in the nose and paranasal sinuses have been studied in computer tomographic images and cryosections, to highlight some details that are of importance for the functional nasal surgeon. From three heads the sections were obtained in three perpendicular planes (coronal, axial and sagittal). The most interesting sections are depicted in three ways: a computer tomographic image, the surface photography of the tissue block in the microtome and a stained section of 20 microns. A number of interesting relations that are clearly depicted are discussed.

Humans↗
PubMed1989

Linear and nonlinear one-dimensional models of pulse wave transmission at high Womersley numbers.

The accuracy of nonlinear and linear one-dimensional models in describing pulse wave propagation in a uniform cylindrical viscoelastic tube, with Womersley's parameter alpha equal to 7.6 at 1 Hz, was evaluated. To this end calculations of wave propagation using these models were compared with the experimentally determined propagation of the pressure wave in the tube. The experimentally generated pressure pulse had an amplitude of 9.0 kPa and caused a relative radius change of about 17%. The static pressure vs cross-sectional area relation was found to be nonlinear for these pressure changes. Maximum fluid velocity was about 2.9 ms-1, while the phase velocity was about 5.4 ms-1. The radius change and the ratio of fluid and phase velocities violated the linear model assumptions. The nonlinear model with viscous fluid friction modelled on the basis of Poiseuille's law and treating the tube wall as purely elastic, underestimated the damping of the pulse wave and predicted the formation of shock waves, which were not found experimentally. In the linear models, the viscous friction of the blood was modelled according to either Poiseuille's law or Womersley's theory and the tube wall was treated as either linearly elastic or linearly viscoelastic. A description of the viscous friction of the blood based on Poiseuille's law underestimated damping. Disregarding the viscoelasticity of the tube wall resulted in an underestimation of both phase velocity and damping. In spite of the nonlinearity of the system, the linear viscoelastic Womersley model described the pulse wave propagation satisfactorily.

Animals↗