Hemodynamic changes during neural deactivation in human brain: A positron emission tomography study of crossed cerebellar diaschisis

Abstract

The mechanism of crossed cerebellar diaschisis (CCD) is considered to be secondary hypoperfusion due to neural deactivation. To elucidate the hemodynamics during neural deactivation, the hemodynamics of CCD was investigated. The cerebral blood flow (CBF), cerebral blood volume (CBV), cerebral oxygen extraction fraction (OEF), cerebral metabolic rate of oxygen (CMRO2), and vascular responses to hypercapnia and acetazolamide stress for CCD were measured in 20 patients with cerebrovascular disease by positron emission tomography with H2(15O), C15O, and 15O2. Vascular responses to hypercapnia and acetazolamide stress were almost the same between CCD side and unaffected side of the cerebellum, a finding that supports the idea that the mechanism of CCD is secondary hypoperfusion due to neural deactivation. The degree of decrease in CBF on the CCD side was almost the same as that in CBV, indicating that vascular blood velocity does not change during neural deactivation. The relation between CBF and CBV of the CCD and unaffected sides was CBV = 0.29 CBF0.56. On the CCD side, the degree of deerease in CMRO2 was less than that in CBF, resulting in a significantly increased OEF. The increased OEF along with the decreased CBV on the CCD side might indicate that neural deactivation primarily causes vasoconstriction rather than a reduction of oxygen metabolism.

Changes in Human Cerebral Blood Flow and Cerebral Blood Volume during Hypercapnia and Hypocapnia Measured by Positron Emission Tomography

“…According to Poiseuille's law, the flow of blood through a vessel is proportional to the fourth power of the vessel diameter; blood volume is proportional to the square of the diameter. Thus, CBV ‫ס‬ cCBF 0.5 (c: constant) (Ito et al, 2001;Ito et al, 2002), which corresponds to the relation between CBF and CBV we observed.…”

“…This suggests that augmentation for CBF and CBV might be governed by a common microcirculatory mechanism during both neural activation and hypercapnia. We also used PET to investigate changes in both regional CBF and CBV in crossed cerebellar diaschisis (Ito et al, 2002), which can be considered neural deactivation (Gold and Lauritzen, 2002). The degree of decrease in CBF and CBV during neural deactivation was almost identical (approximately 20% decrease in both CBF and CBV), indicating no change in vascular blood velocity during neural deactivation Cerebral cortex CBF (%/mm Hg) 6.0 ± 2.6 −3.5 ± 0.6 CBV (%/mm Hg)…”

“…However, the degree of decrease in CBF during hypocapnia was greater than that in CBV (approximately 40% decrease in CBF and 10% decrease in CBV), indicating a decrease in vascular blood velocity during hypocapnia. The relation between CBF and CBV during neural deactivation was CBV ‫ס‬ 0.29CBF 0.56 (Ito et al, 2002). This suggests that diminution for CBF and CBV might be governed by different microcirculatory mechanisms between neural deactivation and hypocapnia.…”

“…Scale maximum and minimum values are 70 and 0 mL·100 mL −1 min −1 for CBF, and 8 and 0 mL/100 mL for CBV, respectively. (Yamauchi et al, 1992;Ito et al, 2002). However, the degree of decrease in CBF during hypocapnia was greater than that in CBV (approximately 40% decrease in CBF and 10% decrease in CBV), indicating a decrease in vascular blood velocity during hypocapnia.…”

Brain Function and Neurophysiological Correlates of Signals Used in Functional Neuroimaging

“…This phenomenon, commonly known as diaschisis, has gained renewed interest from functional neuroimaging studies that revealed decreased metabolism and CBF in anatomically intact brain regions that were remote from a cerebral lesion (Baron et al, 1981;Martin and Raichle, 1983;Meneghetti et al, 1984;Price et al, 2001;Ito et al, 2002). We used decreased activity in the cortico-pontine-cerebellar projections to study the relationship between Purkinje cell spiking activity and CBF in the cerebellar cortex under conditions of deactivation (Fig.…”