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Biomedical subjects

S Rossitti

Publications and source records attributed to S Rossitti.

At least 19 recordsLinked to original sources
PubMed1998

Shear stress in cerebral arteries carrying saccular aneurysms. A preliminary study.

PURPOSE: To investigate whether the branching geometry determines an underlying increase of shear stress (SS) on the vessel wall in cerebral arteries of patients with aneurysms located distally to the circle of Willis. Increased SS is regarded as a major factor in the etiology of intracranial saccular aneurysm. Aneurysms occur commonly in the Willisian arteries, where the role of hemodynamic forces are evident, but they occur also in more peripheral arteries. MATERIAL AND METHODS: The ratio between SS in the branches and SS in the parent vessel at bifurcations was estimated using exponential relations of vessel caliber. The absolute difference of SS branch ratios in every bifurcation represents the SS gradient at the apex. Cerebral angiograms of 10 patients with aneurysm of the distal anterior cerebral artery were analyzed and compared with normal values from an earlier study. RESULTS: The branching geometry determines a relatively small but significant increase of SS in branches and of SS gradients at bifurcation apices in cerebral arteries of patients with aneurysm. CONCLUSION: The results may reflect increased cerebral vessel tone after subarachnoidal hemorrhage, or alternatively an underlying derangement of the regulation of cerebral arterial caliber and SS in these patients.

Adult↗
PubMed1996

Relative dispersion analysis enhances perimetric sensitivity.

Objective identification of minor visual field defects is problematic. A possible solution is to examine spatial correlations by means of relative dispersion analysis, a tool of fractal analysis. We studied patients with glaucoma, previous optic neuritis, chiasmal compression and lesions of the brain hemispheres, using high-pass resolution perimetry. One-hundred visual field records were drawn consecutively for each category and ranked according to severity of defects. Records with scores ranking below the 35th percentile, i.e. those with the smallest field defects, were analysed. Relative dispersion analysis recognized 1.3-2.4 times more abnormal subjects than did pattern standard deviation. A previously described form index was intermediate in sensitivity. Specificity was 96%. Relative dispersion analysis appears to capture a novel aspect of visual field abnormality, with good sensitivity and specificity. The analysis is easily performed.

Adolescent↗
PubMed1995

Shear stress in cerebral arteries supplying arteriovenous malformations.

Arteries supplying cerebral arteriovenous malformations (AVMs) are known to dilate with time. These changes are reversible, and the feeders have been shown to slowly decrease in calibre after removal of the AMV. There is evidence that arteries alter their internal diameters in response to sustained changes of blood flow so that shear stress is kept constant. This implies that blood flow-induced shear stress might be the driving force for remodelling of the cerebral vascular network in the presence of an AVM, and for reversion of these changes after radical operation. The objective of this study is to examine the hypothesis that the shear stress in cerebral arteries supplying AMVs is of the same magnitude as in arteries supplying normal brain tissue in spite of larger blood flow rate. Fifteen patients with supratentorial cerebral AVMs admitted for endovascular treatment were examined with transcranial Doppler ultrasound in the distal Willisian vessels. Vessel calibres were measured in angiograms with magnification correction. Shear stress was estimated assuming a constant value for blood viscosity. Corresponding arteries in the cerebral hemisphere with AVM and in the contralateral one were compared in pairs. Thirty-four pairs of homonymous arteries were studied. The arteries on the AVM side presented larger calibres, higher axial blood flow velocities, lower pulsatility index and larger blood flow rates than the contralateral side. There was a clear positive correlation between blood flow velocities and vessel calibres. The estimates of shear stress did not differ significantly in corresponding arteries of both hemispheres (p = 0.18). The results indicate a precise adjustment of cerebral arterial calibre and blood flow-induced shear stress that presumably induces the progressive dilation of AVM feeders, and the slow regression of the vessel calibres to average dimensions after removal of the lesion. Each vessel seems to remodel itself in response to long-term changes in blood flow rate so that the vessel calibre is reshaped to maintain a constant level of wall shear stress.

Adolescent↗
PubMed1995

[Changes in pulsatility of the middle cerebral artery during the hyperemic phase after carotid compression. Studies with simultaneous bilateral transcranial Doppler].

AIM: The aim of the present study was to investigate the hypothesis that the transient hyperaemic response (THR), i.e. the TCD measured increase in MCA blood flow velocity, indicate an intact cerebral autoregulation. METHOD: THR tests were performed repeatedly in 6 healthy volunteers during simultaneous bilateral TCD recording of the MCA Doppler spectrum. The changes in the pulsatility index (PI) and the pulsatility transmission index (PTI) during the THR were compared with their baseline values. RESULTS: THR was observed in all subjects on each side. PTI of the MCA decreased during the THR. PI did not change on the side of carotid compression, but increased in the contralateral MCA. CONCLUSION: The results suggest that the cerebrovascular resistance is decreased during the THR and that the THR indicates a functioning cerebral autoregulation. While PI is strongly influenced by upstream haemodynamic forces, PTI seems to be an indicator of cerebrovascular resistance downstream to the sample volume.

Adult↗
PubMed1995

Regulation of vascular tone.

The intimal surface of the blood vessel in vivo is subject to shear stress resulting from blood flow, which in most of the circulation, at least at rest, is laminar. Turbulence can occur at bifurcations, especially those of the large arteries, and where vessels curve significantly. Shear stress is a frictional tangential force exerted at the fluid-intimal interface in the long axis of the vessel. It is now known that hemodynamic shear stress can influence a large variety of biological processes in endothelial cells, which vary from those with a short response time, just a few milliseconds, such as the opening of ion channels, to those that change over a period of minutes to several hours, for example, endocytosis and cytoskeleton rearrangement, and those features that alter much more slowly, such as cell shape and stiffness. In addition to these types of changes, there are suggestions that flow acting through shear stress may be responsible for several basic attributes of the vasculature, including the relative size and diameter of the components of a branching vascular system. In this symposium on the flow regulation of the blood vessel, the first presentation dealt with optimality principles that appear to govern the dimensions of the vasculature, in particular the geometry of the arterial branching and the role of shear stress. An optimally designed system is one that requires the least metabolic work to perform its function.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

Energetic and spatial constraints of arterial networks.

The principle of minimum work (PMW) is a parametric optimization model for the growth and adaptation of arterial trees. A balance between energy dissipation due to frictional resistance of laminar flow (shear stress) and the minimum volume of the blood and vessel wall tissue is achieved when the vessel radii are adjusted to the cube root of the volumetric flow. The PMW is known to apply over several magnitudes of vessel calibers, and in many different organs, including the brain, in humans and in animals. Animal studies suggest that blood flow in arteries is approximately proportional to the cube of the vessel radius, and that arteries alter their caliber in response to sustained changes of blood flow according to PMW. Remodelling of the retinal arteriolar network to long-term changes in blood flow was observed in humans. Remodelling of whole arterial networks occurs in the form of increase or diminishing of vessel calibers. Shear stress induced endothelial mediation seems to be the regulating mechanism for the maintenance of this optimum blood flow/vessel diameter relation. Arterial trees are also expected to be nearly space filing. The vascular system is constructed in such a way that, while blood vessels occupy only a small percentage of the body volume leaving the bulk to tissue, they also crisscross organs so tightly that every point in the tissue lies on the boundary between an artery and a vein. This review describes how the energetic optimum principle for least energy cost for blood flow is also compatible with the spatial constraints of arterial networks according to concepts derived from fractal geometry.

Animals↗
PubMed1994

Temporal heterogeneity of the blood flow velocity at the middle cerebral artery in the normal human characterized by fractal analysis.

The objective of this study is to characterize the temporal fluctuation of the axial blood flow velocity (BFV) at the middle cerebral artery (MCA). Biological observables such as BFV present complex oscillations. The irregularity of physiological systems may be assessed by fractal analysis by computing the fractal dimension (D gamma) and the corresponding temporal correlation (r gamma). The BFV at the MCA was registered with transcranial Doppler ultrasonography (TCD) in four adult volunteers. As fractal processes are assumed to have no absolute time scale, two time scales were compared. The digitized signal was averaged respectively at 1-s intervals and for each heart beat. D gamma and r gamma were determined using relative dispersion analysis. The results were D gamma = 1.24 +/- 0.09 and r gamma = 0.45 +/- 0.19 (mean +/- SD) for the 1-s based time scale and D(r) = 1.17 +/- 0.09 and r gamma = 0.57 +/- 0.20 for the heart-beat scale. We conclude that the temporal heterogeneity of the BFV at the MCA in the normal human has fractal properties. Fractal analysis of TCD data may become useful in clinical diagnosis because loss of complexity in physiological systems has been linked to senescence or disease conditions. Wide variations of the so called normal values of BFV measured by TCD have been reported. The physiological BFV fluctuations may explain, in part, the variability of values recorded during routine TCD diagnostic examinations. Our observations may also be of value for understanding the interaction of the vascular endothelium and the blood flow stream (shear stress).

Adult↗
PubMed1994

Remodelling of the retinal arterioles in descending optic atrophy follows the principle of minimum work.

Mathematical modelling indicates that the minimum energy cost for blood flow is achieved when the arteries are arranged in a branching hierarchy such that the radii of the vessels are adjusted to the cube root of the volumetric flow (principle of minimum work). This is known to apply over several magnitudes of vessel calibres, and in many different organs, including the brain, in humans and in animals. This paper addresses the issue of remodelling of one and the same arterial network to long-term changes in blood flow. This has not been studied previously in humans. We measured the radius of parent (r0) and branch segments (r1 and r2) of the retinal arteriolar network in fundus photographs of six patients with blinding, non-vascular retrobulbar optic nerve lesions, mostly traumatic in origin, before and after the development of descending optic atrophy. Attenuation of retinal arterioles is a well-known phenomenon in descending optic atrophy, and is attributable to decreased metabolic demand secondary to loss of the retinal ganglion cells and their axons. On average, arteriolar diameters decreased by 15.2 +/- 17.7% (SD), with 95% confidence intervals of 18.7% and 11.7%; the radii decreased significantly (P = 0.0001) (n = 99). The area ratio of the bifurcations, defined as (r2(1) + r2(2))r-2(0), was 1.23 +/- 0.2 before, and 1.18 +/- 0.2 after optic atrophy (n = 36); the change of area ratio was not significant. The branching geometry of the retinal arteriolar network obeyed strictly the optimum branching rule of the principle of minimum work, or r3(0) = r3(1) + r3(2).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1994

[Modified lateral approach for surgery of thoracic disk herniation. Technical note].

The thoracic spine may be approached by different ways: posterior, posterolateral, anterolateral and anteriorly, with associated removal of diverse osseous structures as facet joints, costal processes, pedicles and ribs, subsequently imposing the use of diverse fusion procedures in some cases. The extreme lateral approach to the thoracic disc space produces minimum disruption of the normal spinal musculoskeletal anatomy, avoids retraction of the spinal cord and preserves the intercostal neurovascular bundle and the segmental radicular arteries. The operation is carried out with the patient in the prone position, and the patient is rotated away from the surgeon as necessary when the deeper levels are accessed. Radioscopy is used to identify the correct level after positioning of the patient. A straight transversal paravertebral incision is recommended in single-level operations. Alternatively an elliptical incision, concave medially and centered at the marked rib, is done and the skin flap is refleted medially. The muscles are partially divided at right angles over the rib to be excised and refleted cranial and caudally, exposing the rib and transverse process. The target disc is approached by removal of about 5 cm of the rib which has its insertion at the disc level, if necessary associated with partial removal of the transverse process, followed by partial pediculotomy (exclusively at the base of the pedicle) and a little lateral rachotomy (vertebral body ressection), which permits opening of the spinal canal exclusively ventral to the intervertebral foramen. In this way any kind of hemilaminectomy or facectomy is avoided. The discectomy is then carried out. This is a minimally invasive approach in comparison to the current ones.(ABSTRACT TRUNCATED AT 250 WORDS)

Humans↗
PubMed1993

Lumbar radiculopathy caused by a lost silverclip.

The case of an adult patient with lumbar radiculopathy (L:4) caused by a migrated silverclip, which was probably lost during the successful extirpation of a cerebellar tumor many years before is presented. The clip was removed surgically and the nerve root was submitted to a partial neurolysis. Increased tension in the root due to corrosion of the clip and scar formation is the proposed pathophysiological mechanism in this case.

Astrocytoma↗
PubMed1993

The transoccipital approach for transcranial Doppler ultrasonography of the vertebrobasilar circulation.

With the transoccipital paramedian approach for transcranial Doppler examination of the vertebrobasilar circulation, a complete examination of the intracranial vertebral arteries and basilar artery is possible without moving the patient from the supine position; this may be of value in intensive care conditions. Blood flow velocity and flow direction in these vessels are registered through the occipital bone at relatively more superficial levels, and identification of right and left vertebral arteries usually represents no problem.

Adult↗
PubMed1993

The extreme lateral approach to thoracic disc herniations: technique and preliminary results.

The extreme lateral approach to the thoracic disc spaces produces minimum disruption of the normal spinal anatomy, avoids retraction of the spinal cord, and preserves the intercostal neurovascular bundle. It is achieved by removal of about 5 cm of the rib which has its insertion at the disc level, if necessary associated with partial removal of the transverse process, followed by partial pediculotomy and a limited lateral rachitomy (vertebral body resection), which permits the opening of the spinal canal exclusively ventral to the intervertebral foramen. The initial results of 6 patients, operated in up to four discs at the same occasion, are promising.

Adult↗
PubMed1993

Vascular dimensions of the cerebral arteries follow the principle of minimum work.

BACKGROUND AND PURPOSE: The principle of minimum work is a parametric optimization model for the growth and adaptation of arterial trees. It establishes a balance between energy dissipation due to frictional resistance of laminar flow (shear stress) and the minimum volume of the vascular system, implying that the radius of the vessel is adjusted to the cube root of the volumetric flow. The purpose of this study is to verify whether the internal carotid artery system obeys the principle of minimum work. METHODS: Measurements of the radius of parent and branch segments of the internal carotid, anterior, and middle cerebral arteries were performed on analog angiographs chosen at random from a set classified as normal. The branch angles were measured from lateral projections in bifurcations of the anterior cerebral artery. The relation of the calibers of parent and branch vessels was analyzed. RESULTS: The area ratio of the bifurcations (N = 174) was 1.2 +/- 0.4 (mean +/- SD). The equation (r0)n = (r1)n + (r2)n was solved for n, resulting in n = 2.9 +/- 0.7 (mean +/- SD, N = 157). Optimum proportions between the radii of parent (r0) and branch (r1 and r2) vessels in the internal carotid artery system were verified in normal carotid angiographs up to four branch generations, according to the theoretical equation r0(3) = r1(3) + r2(3) (r = 0.989, N = 174). No clear correlation was found between the measured branch angles, the relative branch cross-sectional area, and the theoretical optimum angles. CONCLUSIONS: This study demonstrates that the process of branching of the internal carotid artery system obeys the principle of minimum work, as the diameter exponent approximates 3. The principle of minimum work establishes strict functional relations between volumetric flow, flow velocity, and vessel radius. This model was extended to parametric optimization of branch angles, which has proved irrelevant in terms of functional optimization. Our results corroborate this finding. Shear stress-induced endothelial mediation seems to be the regulating mechanism for the maintenance of this optimum vessel design. The magnitude of wall shear stress is the same at every point in a vascular network obeying the principle of minimum work, because the flow rate influences the shear stress proportionally to the third power of the vessel radius. This observation has implications for understanding the remodeling of the cerebral vascular network in the presence of arteriovenous malformations and for the pathogenesis of saccular aneurysms.

Blood Flow Velocity↗
PubMed1993

Optimality principles and flow orderliness at the branching points of cerebral arteries.

BACKGROUND AND PURPOSE: The cerebral arteries present an optimum blood flow/vessel radius relation. However, branch angles may vary widely in the cerebral arteries because the parametric optimization of branch angles is irrelevant in terms of energy cost. The position of the flow divider in extracranial arteries has been suggested to be optimum in flow orderliness. No data exist on the flow divider of cerebral arteries. Thus, we hypothesized that in the cerebral arteries the apex of the bifurcations, which is known to be the site of maximum hemodynamic stress in a vascular network, may normally lie in a non-optimum position relative to the dividing flow streamline in the parent vessel, leading to disturbed laminar flow and increased vessel wall shear stress at the apical region despite the optimum blood flow/vessel radius relation. The objective of this study was to test our hypothesis. METHODS: We measured the branch angles and diameters of parent and branch segments of the anterior cerebral artery system from lateral projections to minimize the measurement error on angiographs chosen at random from normal sets. The position of the apex of the bifurcations in relation to the ostium of the parent artery (gamma) and the ratio of the branch diameters (d2/d1) were compared. Optimum curves for these parameters were calculated by a mathematical model. In addition, the separation of flow streamlines according to gamma was calculated for each bifurcation and related to the division of flow required by each branch according to the optimum blood flow/vessel radius relation. RESULTS: The data points on gamma and d2/d1 and the separation of flow according to gamma and the division of flow required by the branches were found to scatter around the optimum curves. However, a trend toward the theoretical optimum is discernible. The data points are suggested to be a random sample from a normal distribution around the optimum (.40 < P < .50). CONCLUSIONS: The bifurcations of the cerebral arteries appear to be optimized to avoid increased hemodynamic stresses both globally and locally in the same manner as extracranial arteries.

Aneurysm↗