Reduced contralateral cerebrovascular reserve in patients with unilateral steno-occlusive disease
Kevin Sam1, Elizabeth Small, Julien Poublanc
1Department of Physiology, Toronto Western Hospital, Toronto, Ont., Canada.
Insights
Unilateral carotid stenosis impairs cerebrovascular reactivity (CVR) in both brain hemispheres. This reduced CVR in the unaffected hemisphere suggests a trade-off in blood flow regulation, impacting overall brain vascular reserve.
Area of Science:
- Neurology
- Vascular Medicine
- Medical Imaging
Background:
- Unilateral internal carotid artery (ICA) steno-occlusive disease presents a unique challenge to cerebral blood flow regulation.
- Assessing cerebrovascular reactivity (CVR) is crucial for understanding the brain's response to hemodynamic changes.
Purpose of the Study:
- To evaluate CVR in major arterial territories of both hemispheres in patients with unilateral ICA steno-occlusive disease.
- To compare CVR between the affected and unaffected hemispheres and with healthy control subjects.
Main Methods:
- Retrospective observational study including 27 patients with right ICA and 21 patients with left ICA steno-occlusive disease, plus 41 controls.
- Cerebrovascular reactivity (CVR) quantified using blood oxygen level dependent (BOLD) MRI signal changes in response to altered partial pressure of carbon dioxide (PaCO2).
- CVR assessed in ipsilateral and contralateral hemispheres, comparing territories.
Main Results:
- Significant reduction in CVR in the ipsilateral anterior circulation of patients compared to their contralateral side and controls.
- The contralateral anterior circulation also showed a significant 50% reduction in CVR compared to controls.
- These findings highlight widespread CVR impairment in unilateral ICA steno-occlusive disease.
Conclusions:
- Unilateral carotid stenosis affects vascular reserve in both brain hemispheres, not just the affected side.
- Collateral blood flow to the affected hemisphere comes at the expense of reduced reserve capacity in the contralateral hemisphere.
- This suggests potential reductions in functional hyperemia and raises questions about long-term clinical consequences.
Unlabelled:
The purpose of this study was to evaluate cerebrovascular reactivity (CVR) of major arterial vascular territories, particularly in the contralateral hemodynamically unaffected hemisphere, in patients with unilateral internal carotid artery (ICA) steno-occlusive disease compared to control subjects with risk factors for cerebrovascular disease.
Methods:
In this retrospective observational study, twenty-seven patients with right-sided unilateral ICA steno-occlusive disease (age range, 25 to 91 years; 17 males) and twenty-one patients with left-sided unilateral ICA steno-occlusive disease (age range, 24 to 83 years; 14 males) and 41 control subjects were studied. CVR was quantitated as the change in blood oxygen level dependent (BOLD) MRI signal (as a surrogate of cerebral blood flow), in response to a consistently applied step change in the arterial partial pressure of carbon dioxide (PaCO2). The CVR of each major arterial vascular territory was assessed in the ipsilateral hemodynamically affected hemisphere and compared to the corresponding territory in the contralateral hemisphere.
Results:
In patients, a significant reduction in CVR was observed in the ipsilateral anterior circulation compared to that of the corresponding territory on the contralateral side (0.027 ± 0.083 vs. 0.109 ± 0.066% BOLD change/mm Hg, p < 0.0001) and to controls (0.195 ± 0.054% BOLD change/mm Hg, p < 0.0001). The CVR of the contralateral anterior circulation was reduced on average by 50% compared to controls (p < 0.0001).
Conclusions:
The implication of these findings is that unilateral carotid stenosis affects the vascular reserve of both sides of the brain compared to control subjects. This indicates that the collateral blood flow support from the contralateral to the ipsilateral hemisphere comes at a cost of reduced reserve capacity in the contralateral hemisphere. The findings suggest that there may be a reduction in functional hyperemia associated with neuronal activation, not only affecting the hemisphere ipsilateral to an occlusion, but also the hemisphere contralateral to an occlusion. It remains to be determined if 'stealing' from the 'rich' to support the 'poor' has clinical consequences over the long term.
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