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B Hillen

Publications and source records attributed to B Hillen.

At least 37 records · Page 2Linked to original sources
PubMed1998

Early atherosclerotic lesions spiraling through the femoral artery.

Atherosclerosis is common in the adductor hiatus region. The aim of this study was to evaluate atherosclerosis in relation to themorphological structure of the femoropopliteal region. Two anatomic features are thought to play an important role in the origin of these lesions: (1) curvature of the vessel, which may lead to unfavorable local hemodynamic factors that change during leg flexion; and (2) abrupt changes in stiffness of surrounding tissues of the vessel. The distal part of 23 postmortem femoral arteries were investigated. Cross sections were obtained every 1 mm over a length of 100 mm. For each cross section, lesion thickness was measured at 12 points along the circumference of the vessel. No apparent relation was found between surrounding structures of the femoral artery and location of atherosclerotic lesions. Three-dimensional reconstructions showed that atherosclerotic lesions were spiraling through the artery in 18 of 23 cases. Spiraling atherosclerotic lesions may be consistent with expected flow patterns in this part of the femoral artery.

Aged↗
PubMed1998

Localizing role of hemodynamics in atherosclerosis in several human vertebrobasilar junction geometries.

Atherosclerosis is a common finding in the vertebrobasilar junction and in the basilar artery. Several theories try to link the process of atherogenesis with the forces exerted by the flowing blood. An attractive relation has been found between the locations in vessels at which atherosclerotic plaques are often present and the locations in models where complicated flow patterns exist. Most of the studies provided data on bifurcations. Finding a similar relation in an arterial confluence would certainly add to the credibility of the (causal) relationship between hemodynamics and atherosclerosis. Further support can be provided if variations of the geometry result in changes of the location of the atherosclerotic lesions, corresponding to the changes of the flow force distribution. In our previous numerical and experimental work, the influence of geometric and hemodynamic parameters, such as asymmetrical inflow, confluence angle, and blunting of the apex, on the flow in vertebrobasilar junction models has been investigated in detail. Recirculation areas and distribution of the wall shear stress have been computed. In this anatomic study, the effect of modulation of these geometric and hemodynamic parameters on the flow pattern is compared with the size and location of plaques in human vertebrobasilar junctions and basilar arteries. In addition, a comparison is made between the preferential areas of atherosclerotic plaques in junctions and bifurcations to demonstrate the localizing role of hemodynamics in atherogenesis. The apex of the vertebrobasilar junction and the lateral walls of the basilar artery appeared to be prone to atherosclerosis. In 43 of 85 vertebrobasilar junctions, a plaque was found at the apex. Furthermore, the summed plaque thickness at both lateral walls differs significantly (paired t test, P=.03) from that at the walls facing the pons and the skull base. In contrast, several authors found that the lateral walls of the mother vessel and the apex in bifurcations are often spared. Modulation of the various parameters in the models changed the size of the regions with low wall shear stress and/or recirculation areas dramatically. A comparable effect was found in the occurrence of plaques in the human vertebrobasilar junction; eg, for an atherosclerotic plaque at the apex, a predicted probability larger than 0.5 was computed for blunted apexes and for sharp-edged apexes with a confluence angle exceeding 90 degrees. Apparently, two geometric risk factors for an atherosclerotic plaque at the apex can be distinguished: a blunted apex and a large confluence angle.

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PubMed1998

The effect of rotational head and neck movements on the afferent cerebral blood flow.

OBJECTIVE: To determine the effect of lateral rotational head and neck movements on the afferent cerebral blood flow in healthy adult humans so as to increase our knowledge of the relationship between arterial resistance and blood flow in the afferent cerebral arteries and in the arterial segments of the circle of Willis. DESIGN: Prospective, experimental study. SETTING: Department of Radiology and Department of Functional Anatomy, Utrecht University, Utrecht, The Netherlands. SUBJECTS: Nine healthy adult male human volunteers aged between 24 and 52 years participated in this study with informed consent. MAIN OUTCOME MEASURES: The changes in the afferent cerebral blood flow between the neutral (face to the front) and the rotated head positions (turn to the right and turn to the left). The relationship between the changes in the afferent cerebral blood flow and the angle of the head rotation. RESULTS: There were no significant differences between the changes in the afferent cerebral blood flow of the neutral and of the rotated head positions (p = 0.930 and p = 0.508 for the right and left head turns respectively). The correlation coefficients between the changes in the afferent cerebral blood flow and the angle of head rotation which ranged between 44.5 degrees and 72 degrees for the right turn and between 45 degrees and 72 degrees for the left turn were also not statistically significant (p = 0.191 for the right turn and p = 0.570 for the left turn). CONCLUSION: The most likely explanation for these observations was that the changes in resistance in the afferent cerebral arteries of these healthy volunteers were too small to produce significant blood flow changes. Therefore, we conclude that normal physiological lateral rotational head and neck movements do not produce any significant blood flow changes in the afferent cerebral arteries of healthy adults.

Adult↗
PubMed1997

Impact of local atherosclerotic remodeling on the calculation of percent luminal narrowing.

The choice of the reference site in order to calculate percent luminal narrowing mainly depends on which diagnostic tool is used for examination. In intravascular ultrasound or histology, the local area encompassed by the internal elastic lamina (IEL) area is used as a reference. However, the local IEL area, and thereby the reference value, may have been altered by atherosclerotic remodeling. In the present study we examined the impact of local arterial remodeling on the calculation of luminal narrowing. Forty-five human femoral arteries were analyzed, 32 postmortem and 20 in vivo, by intravascular ultrasound. Cross sections were examined every 0.5 cm over an arterial segment length of 10 to 15 cm. In each cross section we measured the lumen area and the IEL area. Two reference areas were used to calculate percent luminal narrowing: (1) the lumen area in the cross section that contained the least amount of plaque (distant reference); and (2) the local IEL area (local reference). In each cross section, the IEL area was expressed as percent of the IEL area in the cross section that contained the least amount of plaque (relative IEL area). Using the distant reference, we found that less luminal narrowing was observed for cross sections with a relative IEL area > 100% (indicating compensatory enlargement) than for those with a relative IEL area < 100% (indicating shrinkage), whereas percent luminal narrowing calculated using the local reference hardly differed between cross section with a relative IEL area > 100% and < 100%. Thus, arterial wall remodeling makes the local IEL area an unreliable reference for calculation of percent luminal narrowing. The calculated percent luminal narrowing using a distant, nondiseased reference site reflects the actual change of the luminal area more accurately.

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PubMed1997

The influence of the blunting of the apex on the flow in a vertebro-basilar junction model.

The apex of human vertebro-basilar junctions can be sharp-edged or blunted. In the present study, the effect of blunted apex on the flow in vertebro-basilar junction models is investigated. We compared the flow phenomena in a series of junction models with blunted apices and confluence angles 45, 85, and 125 deg with the flow phenomena in a series of junction models with sharp-edged apices and the same range of confluence angles, studied in a previous paper (Ravensbergen et al., 1996b). The blunting of the apex appears to have an effect on the size of the local recirculation area near the apex and the prevailing low velocities. Large recirculation areas are found in the models with blunted apices, especially in those with small confluence angles. In addition, the blunting of the apex has no influence on the flow further downstream, nor on the structure and strength of the secondary flow field. Furthermore, a blunted apex appears to be a geometric risk factor for atherosclerosis. This supports the hypotheses that recirculation areas and low wall shear stress influence the development of atherosclerotic plaques.

Arteriosclerosis↗
PubMed1997

Compensatory enlargement in coronary and femoral arteries is related to neither the extent of plaque-free vessel wall nor lesion eccentricity. A postmortem study.

Arteries may demonstrate compensatory enlargement in response to plaque accumulation. It has been proposed that enlargement is achieved by the expansion of the nondiseased (plaque-free) vessel wall. In this study, we assessed this hypothesis. Post mortem, 32 atherosclerotic coronary arteries (left anterior descending, n = 10; left circumflex, n = 11; and right coronary, n = 11) and 54 atherosclerotic femoral arteries were pressure fixed. Cross sections (coronary arteries, n = 537; femoral arteries, n = 1602) were obtained for analysis every 2.5 mm for the coronary arteries and every 5.0 mm for the femoral arteries. From these cross sections, we determined the degree of remodeling and an eccentricity index. Finally, we measured the extent of plaque-free vessel wall. The plaque-free vessel wall was defined as (1) no plaque present or (2) plaque thickness < 0.5 mm. A very weak, negative correlation was observed between the degree of remodeling and the extent of the plaque-free vessel wall (coronary arteries: no plaque r2 = .13, P < .01; < 0.5 mm plaque r2 = .15, P < .05; femoral arteries: no plaque r2 = .02, P < .01; < 0.5 mm plaque r2 = 0.04, P < .01). The degree of remodeling did not correlate with the eccentricity index (coronary arteries r2 = .002, P > .05 and femoral arteries r2 = .001, P > .05). Thus, compensatory enlarged segments did not reveal a larger circumference of plaque-free vessel wall compared with segments that failed to enlarge. This study provides no support for the hypothesis that nondiseased vessel-wall expansion is responsible for compensatory enlargement in atherosclerotic arteries.

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PubMed1997

The impact of atherosclerotic arterial remodeling on percentage of luminal stenosis varies widely within the arterial system. A postmortem study.

Luminal stenosis can be based on large atherosclerotic plaques in compensatory enlarged segments or on relatively little plaques in shrunken segments. In the present study, the contribution of plaque formation and remodeling to luminal narrowing was compared among six types of arteries prone to symptomatic atherosclerosis. Cross-sections (n = 5195) were obtained at regular intervals from 329 arteries. For each artery, the cross-section that contained the least amount of plaque was considered to be the reference. For each cross-section, the percentage of lumen area decrease was expressed as a percentage of the lumen area at the reference site (luminal stenosis). Similarly, the area encompassed by the internal elastic lamina (IEL area) was expressed as a percentage of the IEL area at the reference site (relative IEL area). All cross-sections were categorized in three groups: relative IEL area > 105% (enlargement), 95% to 105% (no remodeling), and < 95% (shrinkage). The prevalence of enlargement (50% to 75%) was significantly higher compared with shrinkage (8% to 25%). Shrinkage was observed most frequently in the femoral arteries (25%) and infrequently in the renal arteries (8%). For all types of arteries, the relative IEL area correlated negatively with luminal stenosis (P < .001). Regression analysis of relative IEL area on luminal stenosis, however, showed significant differences in the first-order regression coefficients among artery types. On average, plaque increase was more compensated for by enlargement in the coronary, common carotid, and renal arteries compared with the arteries obtained from the lower extremities. Anatomic regional differences were observed in the impact of arterial wall remodeling on percent luminal stenosis in de novo atherosclerotic lesions.

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PubMed1997

Arterial remodelling by atherosclerosis.

Until recently, plaque formation was considered to be the only determinant of atherosclerotic luminal narrowing. Recent post-mortem and intravascular ultrasound studies, however, revealed that arterial remodelling is another important determinant of luminal narrowing in de novo atherosclerosis. The change in total arterial circumference relative to a reference cross-section ranges from excessive enlargement with an actual increase in lumen to arterial shrinkage contributing to lumen narrowing. The mechanisms responsible for this spectrum of remodelling are unknown, but their identification will be important for the potential development of therapeutic strategies to promote favourable remodelling.

Adaptation, Physiological↗
PubMed1996

Atherosclerotic arterial remodeling in the superficial femoral artery. Individual variation in local compensatory enlargement response.

BACKGROUND: In previous studies on atherosclerotic arterial remodeling, compensatory enlargement of the artery in response to plaque accumulation was inferred from pooled data based on one cross section per artery. We assessed local arterial remodeling individually by analyzing 45 artery segments at 0.5-cm intervals over a length of 10 to 15 cm. METHODS AND RESULTS: Twenty patients were studied by 30-MHz intravascular ultrasound (IVUS) before balloon angioplasty of the superficial femoral artery (370 cross sections), and 25 femoral artery segments were studied postmortem (551 cross sections). In each cross section, the area surrounded by the internal elastic lamina (IEL area) and the plaque area were measured. The IEL area was larger in the cross section with the largest plaque area than in the cross section with the smallest plaque area (32.5+/-13.0 and 32.0+/-11.5 mm2 versus 28.9+/-9.7 [P=NS] and 26.7+/-10.1 [P<.05] mm2 for IVUS and histology, respectively [mean+/-SD]). A significant positive correlation was found between plaque area and IEL area for the pooled data (r=.61 and r=.47 and slope=1.07 and 0.90 for IVUS and histology, respectively; both P<.001). In 12 of 20 and 16 of 25 individual arterial segments, however, no significant correlation was observed between plaque area and IEL area for IVUS and histology, respectively. A large variation was found in the correlation of the regression of plaque to IEL area (IVUS, r=-.40 to .89; histology, r=-.13 to .91) and slope (IVUS, -0.28 to 1.29; histology, -0.18 to 1.32). CONCLUSIONS: In the majority of atherosclerotic femoral arteries, significant compensatory enlargement could not be determined. It is inferred that arterial remodeling in response to plaque formation may vary among individuals.

Aged↗
PubMed1996

Electromyography of the human nasal muscles.

Electromyographic (EMG) activity of six nasal muscles was monitored in 17 male volunteers without nasal complaints. Surface electrodes were placed on the nasal skin in such a way that they selectively recorded the activity of these muscles. Recordings were made under different breathing conditions and during voluntary nasal movements. Inspiratory EMG activity was observed during nasal and oral breathing in one or more of the following muscles: dilator naris, nasalis muscle (alar and transverse parts) and apicis nasi. EMG activity increased markedly in response to physical exercise and was more often present in subjects with decreased nasal patency. During voluntary nasal movements a combined activity of the six nasal muscles was consistently found. We conclude that the function of the dilator naris, the nasalis muscle and the apicis nasi strongly relates to respiration. These muscles probably contribute to the prevention of collapse of the nasal valve. The role of the procerus and levator labii superioris alaeque nasi seems to be primarily concerned with facial expression.

Adult↗
PubMed1996

New ways of performing in vivo flow velocity measurements in the basilar artery.

The basilar artery is the only large artery in which two flows merge, and this is reflected in the flow downstream. We report quantitative flow-velocity measurements with a phase-based MR technique, i.e. the Fourier velocity encoding method, in the basilar artery of a volunteer. To our knowledge, this has not previously been performed successfully. A comparison is made with the results of flow velocity measurements in the basilar artery with transcranial Doppler ultrasonography; the techniques agreed very well. Although Doppler ultrasonography is still most widely used, no information on the flow rate and the flow velocity distribution in the basilar artery can be provided. MR flow measurement techniques appear promising when detailed information on the flow velocity distribution and flow rate is needed.

Adult↗
PubMed1996

The influence of the angle of confluence on the flow in a vertebro-basilar junction model.

In earlier work, it was demonstrated that the flow in models of the vertebro-basilar junction is highly three-dimensional and the geometry exerts a strong influence on the hemodynamics. The morphology of the vertebro-basilar junction is very variable amongst individuals. In a study of 85 human vertebro-basilar junctions, the angle between the vertebral arteries varied between 10 and 160 degrees. To determine how the flow is influenced by this geometrical parameter, the flow is studied both experimentally, with laser Doppler velocimetry, and numerically, with a finite element package. A series of junction models is used with a range of confluence angles (45, 85 and 125 degrees). It appears that the angle of confluence has a strong influence on the structure and strength of the secondary flow field. The secondary velocities persist far downstream. Furthermore, near the apex, a region with low velocities is present. The larger the confluence angle is, the larger this region is, and even backflow may occur. In addition, the occurrence of atherosclerotic plaques in 85 human vertebro-basilar junctions is studied. Only one preferential location was found: the apex, the other plaques seem to be randomly distributed. The magnitude of the confluence angle of junctions with sharp-edged apices has a significant influence (p = 0.006) on the occurrence of a plaque at the apex. Apparently, a large confluence angle is a geometrical risk factor for atherosclerosis.

Arteriosclerosis↗
PubMed1996

Numerical simulation of blood flow in an artery with two successive bends.

Blood flow in an artery with two successive bends is simulated by a finite-element computation of steady flow of a Newtonian viscous fluid through a rigid tube having the same shape as a specific part of the femoral artery. Notwithstanding the fact that the bends in the model geometry are rather gentle, the axial and secondary flow patterns, computed for a range of values of the Reynolds number Re, show strong and complicated three-dimensional flow effects. In particular, the flow pattern in the second bend for relatively small values of Re (Re < 240) turns out to be drastically different from that for larger Re-values.

Arteries↗
PubMed1996

A two-dimensional kinematic analysis of the distal radioulnar joint.

The triangular fibrocartilage and its function in the kinematics of pronation and supination in the distal radioulnar joint was studied. Measurements of the constituent parts of this joint in 11 cadavers showed that the palmar radioulnar ligament is at least 2 mm longer than the dorsal radioulnar ligament. Based on these measurements the movements of the joint were modelled in a two-dimensional kinematic chain. Predictions based on this chain could be confirmed by direct observation and videotaping dissections of joints of unfixed specimens and three-dimensional reconstructions of a CT scan of a healthy volunteer. It could be concluded that (a) the dorsal part is tight during pronation and the palmar part during supination and (b) considerable asymmetrical translations, (dorsal translation being the largest) occur because of the length differences of the ligaments.

Biomechanical Phenomena↗
PubMed1996

Middle cerebral artery occlusion in Wistar and Fischer-344 rats: functional and morphological assessment of the model.

Cerebral infarction volume after occlusion of a short proximal segment of the middle cerebral artery (MCA) is reported to be different in Wistar compared to Fischer-344 (F344) rats, in both size and variability. Knowledge about the cause of these differences might enable us to explain and perhaps reduce the variation in infarct volume and create a reproducible model of focal cerebral ischemia in the rat. We investigated in Wistar and F344 rats both the effect of occlusion of a long proximal MCA segment on cerebral infarction volume, visualized by magnetic resonance imaging and histology, and the morphology of the major cerebral arteries. Occlusion of a long proximal MCA segment resulted in a striatal and a small cortical infarction in Wistar and a striatal and sizable cortical infarction in F344 rats (as is the case after occlusion of a short proximal MCA segment). In Wistar rats, however, occlusion of a long proximal MCA segment strongly reduced the variability in infarction volume in comparison to occlusion of a small proximal MCA segment. Analysis of the morphology of the major cerebral arteries showed a significantly higher number of proximal side branches of the long proximal MCA segment in Wistar rates than in F344 rats. We conclude that after short-segment proximal MCA occlusion, extreme variability in cerebral infarction volume in Wistar rats compared to F344 rats may be attributable to a significantly greater number of proximal MCA side branches in Wistar rats than in F344 rats.

Animals↗
PubMed1996

Perivascular nerves of the human basal cerebral arteries: I. Topographical distribution.

In the present study the topographical distribution of the intrinsic nerve plexuses of the basal cerebral arteries in humans was quantified and the relation between vessel diameter and nerve density was investigated. Whole-mount preparations of various segments of the basal cerebral arteries from middle-aged patients were stained for protein gene product (PGP) 9.5. The deep nerve plexuses, located at the adventitial-medial border, were quantified by image analysis. Confocal scanning laser microscopy was used to study nerve plexuses throughout the adventitia. Transverse cryostat sections were stained for PGP 9.5, tyrosine hydroxylase and neurofilament, and quantified. The results showed a three-layered configuration of the adventitial nerves. Measurements on whole-mounts demonstrated that nerve densities were highest in the posterior communicating artery (PCom), and next highest in the proximal parts of the posterior cerebral artery (PCA) and anterior choroidal artery. There appeared to be no clear relation between nerve density and vessel diameter. The measurements on sections confirmed the high nerve densities in the PCom and PCA. Tyrosine hydroxylase- and neurofilament-immunoreactivities appeared to demonstrate separate subpopulations of the overall nerve plexuses, representing sympathetic and, possibly, sensory fibers, respectively. Densities of both subgroups generally followed those of PGP 9.5-immunoreactive nerves. Transmission electron microscopy suggested motor function of the deep nerve plexuses. The results indicate a stronger neuronal influence on this part of the cerebral circulation than hitherto reported. It is concluded that human basal cerebral arteries display a topographical distribution of deep perivascular nerves, and that nerve density is determined by locality rather than by vascular diameter.

Adult↗
PubMed1996

Perivascular nerves of the human basal cerebral arteries: II. Changes in aging and Alzheimer's disease.

In the present study the intrinsic nerve plexuses of the basal cerebral arteries, derived from aged non-Alzheimer's and aged Alzheimer's disease patients were quantified and compared. A previous study described and quantified nerve density on similar arteries from healthy middle-aged patients. Whole-mount preparations of various segments of the basal cerebral arteries were stained for protein gene product 9.5. The deep nerve plexuses, located at the adventitial-medial border, were quantified by image analysis. Transverse cryostat sections were stained for various markers and quantified. Measurements on whole mounts demonstrated that nerve densities were highest in the posterior communicating artery and in the postcommunicating part of the posterior cerebral artery (PCA) for both aged and Alzheimer's groups. Statistical comparison showed a tendency toward decreased nerve density with aging, which was significant for the internal carotid artery, precommunicating part of the PCA, and the anterior choroidal artery in both non-Alzheimer's and Alzheimer's aged groups. In addition, in Alzheimer's patients nerve density was significantly lower in the precommunicating part of the anterior cerebral artery compared with the healthy aged group. Measurements on sections confirmed the tendency to decreased innervation with aging. It is concluded that densities of deep perivascular nerves of human basal cerebral arteries are subject to localized changes caused by aging and Alzheimer's disease.

Aged↗