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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Acta neurochirurgica 127 (1994), S. 21-26 
    ISSN: 0942-0940
    Keywords: Cerebral aneurysm ; nimodipine ; prognosis ; rebleed ; subarachnoid haemorrhage
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The management of aneurysmal subarachnoid haemorrhage has recently changed considerably. Emergency admission to specialized centres and early surgery have become common practice. In addition, the use of nimodipine has gained widespread acceptance. Little data are available concerning the frequency and temporal profile of reruptures under the current policies. The case histories of 387 patients treated for aneurysmal subarachnoid haemorrhage between January 1984 and March 1992 were reviewed with regard to the incidence of in-hospital reruptures. All patients were managed according to the same protocol including a policy of individually timed early surgery and intravenous nimodipine. A total of 44 first in-hospital rebleeds were observed during the waiting period. Two percent of the patients admitted on the day of haemorrhage had a rebleed on the same day after admission to the hospital. No rebleeds were observed on the day after subarachnoid haemorrhage. Rebleed rates on day 2 and 3 were also low with 0.6 and 0.8% of the population with an undipped aneurysm. For the following 10 days, the daily rate of rerupture increased. A further peak was observed during the 4th week. Using life-table methods, the cumulative rate of rebleeds was calculated as 23% within 2 weeks and 42% within 4 weeks. Although patients suffering rebleeds differed in several respects from patients without rebleeds, most of the differences could be identified to be a consequence of a selection bias resulting in a longer period of exposure to the risk of rerupture for certain subgroups. Only patients suffering a loss of consciousness after the initial subarachnoid haemorrhage were definitively exposed to a higher daily risk of rerupture. Comparison with other series suggests that nimodipine treatment may add to the protective effect of bedrest, control of blood pressure and stress deprivation during the first days after subarachnoid haemorrhage. However, it cannot be excluded that withdrawal of nimodipine together with the general precautions in patients with unclipped aneurysms is responsible for the late peak of rebleeds. With regard to the timing of surgery, the low rebleed rates between days 1 and 3 justify semi-elective timing within this interval. On the other hand, in patients in whom aneurysm elimination has been deferred because of bad neurological condition or concomittant medical problems, surgery should be performed prior to the 4th week, unless the prognosis is considered hopeless at this time.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Acta neurochirurgica 86 (1987), S. 98-105 
    ISSN: 0942-0940
    Keywords: Cerebral aneurysm ; fluid dynamics ; haemodynamic stress ; wall shear stress ; viscoelastic fluid ; experimental aneurysm
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The flow velocities in lateral glass and silastic aneurysm models were quantitatively measured with the non-invasive laser Doppler method. The influences of the elasticity of the wall, the pulse wave and the properties of the perfusion medium on the intra-aneurysmal circulation were investigated. As shown previously, the inflow into the aneurysm arose from the downstream lip and was directed toward the centre of the fundus. Backflow to the parent vessel took place along the walls of the fundus. With non-pulsatile perfusion, flow velocities in the centre of the standardized aneurysms varied between 0.4 and 2% of the maximum velocity in the parent vessel. With pulsatile perfusion, flow velocities in the centre of the fundus ranged between 8 and 13% of the flow velocity in the axis of the parent vessel. Flow velocities in the aneurysms were slower with a macromolecular perfusion medium with blood like properties compared to a glycerol/water solution. Flow velocity measurements near the aneurysmal wall allowed the estimation of the shear stresses at critical locations. The maximum shear stresses at the downstream lip of the aneurysm were in the range of the stresses measured at the flow divider of an arterial bifurcation. The present results suggest that in human saccular aneurysms intra-aneurysmal flow and shear stress on the wall are directly related to the pulsatility of perfusion,i.e. the systolic/diastolic pressure difference and that the tendency to spontaneous thrombosis depends on the viscoelastic properties of the blood, namely the haematocrit.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Acta neurochirurgica 93 (1988), S. 18-23 
    ISSN: 0942-0940
    Keywords: Cerebral aneurysm ; experimental aneurysm ; haemodynamic stress ; laser-Doppler-anemometer ; wall shear stress
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The flow velocities in glass and silastic aneurysm models located at bifurcations were quantitatively determined using the non-invasive laser-Doppler method. The geometrical relation between aneurysm and parent vessels was found to be the primary factor governing the intra-aneurysmal flow pattern. Flow was stagnant in straight terminal models, with the aneurysm forming an extension of the afferent vessel, as long as the outflow through the branches of the bifurcation was balanced. Average flow velocities in the fundus were small but turbulent flow fluctuations of high amplitudes were observed. Asymmetric outflow through the branches of the bifurcation induced a rotatory intra-aneurysmal circulation from the dominant to the subordinate branch. The circulation in angled terminal aneurysms with the aneurysmal axis at a 45 degree angle to the plane of the bifurcation was a vortex, which was a natural consequence of the excentric inflow from the afferent vessel. Maximum flow velocities measured in the centre plane of the angled terminal aneurysms were in the range of 50 to 80% of the axial velocity in the afferent vessel. The elasticity of the models did not affect the global turnover rates but it damped the intra-aneurysmal pulse wave. On the basis of the measured velocity gradients near the walls maximum shear stresses on the wall of human terminal aneurysms were estimated to be in the order of 50 dynes/cm2 (5 Pascal), a value that is similar to the maximum wall shear stresses estimated for lateral aneurysms.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Acta neurochirurgica 83 (1986), S. 131-137 
    ISSN: 0942-0940
    Keywords: Cerebral aneurysm ; aneurysm growth ; rupture ; turbulence
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Intra-operative Doppler recordings were carried out on cerebral saccular aneurysms in 12 patients. Distinct fluctuations of flow superimposed on the pulse wave were seen in 6 patients. The fluctuations appeared to be periodic with measured period lengths of 60 to 150 msec. In 3 other patients flow irregularities could be discerned acoustically but a definite periodicity could not be visualized on screen. In 3 patients flow appeared smooth during the entire pulse cycle, acoustically as well as visually. Concomitant flow observations in glass model aneurysms also revealed flow instabilities in certain aneurysm types at a Reynold's number of 300. All observed irregularities of flow were observed in zones of deceleration of flow in the models. Signs of fully developed turbulence were not found, neither in human aneurysms nor in the glass models. It appears likely that the fluctuations of flow induce vibrations of the aneurysmal wall and contibute to aneurysm progression and eventual rupture.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Acta neurochirurgica 100 (1989), S. 74-78 
    ISSN: 0942-0940
    Keywords: Cerebral aneurysm ; pathogenesis ; growth ; rupture ; yield stress ; stress relaxation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The strength of aneurysm walls obtained intraoperatively or at autopsy immediately after death was evaluated by measurements of the force response to one-directional stretch and compared to the walls of intracranial arteries. The maximum stress that aneurysm tissue could tolerate was found slightly lower than in arteries, which is most probably due to the amount of immature forms of collagen. The stress resistance of aneurysms and arterial tissue decayed over a period of several hours. The relaxation curve could be approximated by the sum of 2 exponential terms. The half decay times of these terms were found identical in aneurysms and arteries, they appear to be collagen characteristics. The strength measured in vitro was compared to the stress in vivo, which was calculated on the basis of blood pressure and aneurysm radius. The stress tolerated by aneurysm walls over a period of 24 hours was found to be in the range of the stress that is imposed in vivo by the mean blood pressure. Arteries resisted stresses corresponding to pressures 10 to 20 times higher than physiological values. The thickness of the aneurysm walls correlated with the aneurysm radius in a linear fashion. It is suggested that aneurysm growth can be understood as passive yield to blood pressure, and reactive healing and thickening of the wall with increasing aneurysm diameter.
    Type of Medium: Electronic Resource
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