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Pial vessel caliber and cerebral blood flow become dissociated during ischemia-reperfusion in cats
E Tasdemiroglu1, R Macfarlane, E P Wei
1Neurology Service, Massachusetts General Hospital, Harvard Medical School, Boston 02114.
Insights
Following cerebral ischemia, pial arterioles dilated significantly, but this did not fully restore cerebral blood flow (CBF). Parenchymal vessels, not pial ones, likely regulate CBF during reperfusion.
Area of Science:
- Neuroscience
- Cerebrovascular Physiology
- Ischemia-Reperfusion Research
Background:
- Global cerebral ischemia can lead to significant alterations in cerebral blood flow (CBF) and cerebrovascular resistance.
- Understanding the role of pial arterioles in regulating CBF during reperfusion is crucial for developing effective treatments.
Purpose of the Study:
- To investigate the relationship between pial arteriolar caliber and cerebral blood flow (CBF) during reperfusion after global cerebral ischemia.
- To determine the contribution of pial arterioles to the restoration of CBF and cerebrovascular resistance post-ischemia.
Main Methods:
- Global cerebral ischemia was induced in cats via four-vessel occlusion and hypotension.
- Reperfusion was maintained for up to 120 minutes.
- Cerebral blood flow (CBF) was measured using radiolabeled microsphere injection.
- Pial arteriolar caliber was assessed using the closed cranial window technique.
Main Results:
- CBF increased dramatically (588%) 30 minutes post-reperfusion, with concurrent pial arteriolar dilation (172%).
- At 60 and 120 minutes, CBF returned to near baseline, while pial arterioles remained dilated (133% and 115%, respectively).
- Total cerebrovascular resistance normalized by 45 minutes, despite persistent pial arteriolar dilation.
Conclusions:
- Pial arteriolar dilation alone does not fully explain normal blood flow restoration after ischemia-induced hyperemia.
- Increased resistance within parenchymal vessels, rather than pial vessels, is likely responsible for regulating CBF during the post-hyperemic phase.
- Further research is needed to determine if obstruction or vasoconstriction causes increased resistance in intraparenchymal vessels.
Abstract:
The relationship between pial arteriolar caliber and cerebral blood flow (CBF) was examined in 11 cats subjected to reperfusion for up to 120 min after 10 min of global cerebral ischemia induced by four-vessel occlusion and systemic hypotension. Thirty minutes after reperfusion CBF, as assessed by radiolabeled microsphere injection, had increased to 588% of control in middle cerebral artery (MSEC) cortical gray matter territory. The caliber of MSEC pial arterioles measured using the closed cranial window technique (greater than 33 to less than 213 microns) increased to 172% of baseline. By 60 min of reperfusion, CBF was 76% of basal levels, but pial arterioles remained 133% of baseline. After 120 min, CBF approximated baseline values, but pial dilatation persisted (115% of control). Intracranial pressure measurements did not differ significantly from resting values. At 45 min and beyond, total cerebrovascular resistance did not differ from resting values. The coexistence of vasodilatation within pial arterioles and normal blood flow in cortical gray matter indicates that pial vessels (greater than 33 microns) cannot be responsible for normal blood flow restoration following postocclusive hyperemia. Resistance during the posthyperemic phase must be increased selectively within parenchymal vessels to account for normal total cerebrovascular resistance, pial vessel dilatation, and normal-low parenchymal blood flow. Whether obstruction rather than vasoconstriction explains the resistance changes within intraparenchymal vessels remains for further study.