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The hemodynamic effects of internal carotid artery stenosis and occlusion
Insights
Cerebral ischemia occurs with carotid artery occlusion due to impaired hemodynamic regulation. However, even severe carotid artery stenosis (90%) did not lead to hemodynamic cerebral ischemia in primates.
Area of Science:
- Neurology
- Vascular Surgery
- Cerebrovascular Research
Background:
- Cerebral ischemia can result from embolic or hemodynamic factors.
- Understanding the mechanisms of ischemia following carotid artery compromise is crucial for clinical management.
Purpose of the Study:
- To investigate whether hemodynamic mechanisms contribute to cerebral ischemia after carotid artery occlusion or stenosis in non-human primates.
- To compare hemodynamic versus embolic mechanisms in the context of carotid artery pathologies.
Main Methods:
- Utilized xenon-133 technique to measure cerebral blood flow (CBF) and mean arterial blood pressure (MABP).
- Employed carbon-14-labeled iodoantipyrine autoradiography for regional CBF assessment in normotensive and hypotensive baboons.
- Indicated carotid artery occlusion or stenosis models were used.
Main Results:
- Carotid artery occlusion led to a loss of cerebral autoregulation, making CBF dependent on MABP.
- Significant reductions in regional CBF were observed in boundary zones with carotid artery occlusion and hypotension.
- Cerebral autoregulation was preserved in animals with 90% carotid artery stenosis and in normal controls.
Conclusions:
- Hemodynamic ischemia develops with carotid artery occlusion.
- Hemodynamic cerebral ischemia was not observed with 90% carotid artery stenosis.
- Cerebral autoregulation remains intact in cases of severe carotid stenosis without occlusion.
Abstract:
The purpose of this study was to determine in subhuman primates whether hemodynamic mechanisms (as compared with embolic mechanisms) contribute to cerebral ischemia following carotid artery occlusion or stenosis. Following carotid artery occlusion there was loss of cerebral autoregulation: cerebral blood flow (CBF) measured with the xenon-133 technique became passively dependent upon the mean arterial blood pressure (MABP) over an MABP range of 30 to 110 mm Hg. By contrast, autoregulation was preserved in normal animals and in animals with a 90% carotid artery stenosis. Regional CBF was measured with carbon-14-labeled iodoantipyrine autoradiography in normotensive baboons, in hypotensive animals, and in hypotensive animals with carotid artery occlusion or stenosis. With carotid artery occlusion and hypotension, reduced levels of local CBF were seen ipsilaterally in the boundary zones between the anterior and middle cerebral arteries with 35% of the area of an anterior section through the hemisphere displaying a CBF value of less than 20 ml/100 gm/min. Comparable values with hypotension were 21% with carotid artery stenosis, 20% with no proximal vascular lesion, and 1% in normotensive animals. These areas of reduced CBF corresponded with areas of boundary-zone ischemia seen with light microscopy. The study suggests that while hemodynamic ischemia develops with carotid artery occlusion, it does not occur with even a 90% carotid artery stenosis or in normal animals.