title: Reduced contralateral cerebrovascular reserve in patients with unilateral steno-occlusive disease.
abstract: 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.
authors.affiliation: Department of Physiology, Toronto Western Hospital, Toronto, Ont., Canada.
authors.forename: Kevin
authors.initials: K
authors.lastname: Sam
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Small
authors.forename: Julien
authors.initials: J
authors.lastname: Poublanc
authors.forename: Jay S
authors.initials: JS
authors.lastname: Han
authors.forename: Daniel M
authors.initials: DM
authors.lastname: Mandell
authors.forename: Joseph A
authors.initials: JA
authors.lastname: Fisher
authors.forename: Adrian P
authors.initials: AP
authors.lastname: Crawley
authors.forename: David John
authors.initials: DJ
authors.lastname: Mikulis
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001921:Brain / Q000098:blood supply*; D002343:Carotid Artery, Internal / Q000473:pathology / Q000601:surgery*; D016893:Carotid Stenosis / Q000175:diagnosis / Q000601:surgery*; D002560:Cerebrovascular Circulation / Q000502:physiology*; D003097:Collateral Circulation / Q000502:physiology*; D005260:Female; D006801:Humans; D018810:Magnetic Resonance Angiography / Q000379:methods; D008279:Magnetic Resonance Imaging / Q000379:methods; D008297:Male; D008875:Middle Aged; D012189:Retrospective Studies; D016896:Treatment Outcome