Reduction of Functional Capillary Density in Human Brain after Stroke

Abstract

Summary:The blood flow of brain tissue often returns to normal after an ischemic episode. As "luxury" rather than "reactive" reperfusion, this hyperemia is associated with low metabolism. It is not known to what extent the high blood flow accompanies a high, normal, or low den sity of capillaries. The resolution of this question may indicate whether the functional capillary density is vari able and, if so, whether it is coupled to blood flow or metabolism. To answer these questions, we defined func tional capillaries as capillaries that transport glucose. We then calculated the density of functional capillaries (D cap) and the mean time of transit of blood through the capil laries (tca p) from hemodynamic variables obtained in vivo by positron tomography of five patients afflicted by cere bral ischemic stroke. Each patient was studied twice, within 36 h of the insult and 1 week later. We identified nominally "ischemic" regions in the first study as cortical gray matter regions, contiguous with the ischemic focus,The density of capillaries varies between the re gions of the brain (Craigie, 1945). The variation ap pears to have a cytoarchitectural basis, suggesting that the total number of capillaries in any region is a reflection of the normal average energy require ment of that region. However, evidence from other organs in animal experiments suggests that not all capillaries in a brain region function equally well as

Clinical impact of hemodynamic parameter measurement for cerebrovascular disease using positron emission tomography and 15O-labeled tracers

“…The continuous decrease in CPP in the chronic phase of CVD seems to reduce the diameter of resistance arteries to recover CPP and keep CBF at a lower level, as shown in a previous report suggesting that functional capillary density was decreased even in the subacute phase of ischemia [89].…”

“…The capillary hydrostatic pressure is assumed to remain constant by increasing capillary resistance in coronary arterial disease [96]. A decrease in functional capillary density in cerebral ischemic changes also indicates a similar mechanism in cerebral microvessels [89].…”

Functional Magnetic Resonance Imaging of the Spinal Cord: Current Status and Future Developments

“…9 The second theory suggests that the low diffusion rate of oxygen through the blood-brain barrier imposes a disproportionate increase of blood flow compared with the amount of consumed oxygen. 10 Following the first theory, one should observe a saturation of the metabolic rate of oxygen (MRO 2 ) when gradually increasing blood flow. In the second theory, one should observe a proportional relationship between the 2 parameters.…”

Coupling between neuronal activity and microcirculation: Implications for functional brain imaging

“…In humans, for example, CMRO 2 / CBF ratios as small as ϳ1 : 2 were found during sensory stimulation (Seitz and Roland, 1992) and only ϳ1:1 during cognitive stimulation (Roland et al, 1987). Other PET studies (Gjedde et al, 1990;Raichle et al, 1976;Roland et al, 1987) also showed that at rest, human cortical gray matter values of CBF, CMRO 2 , and CMRGlc (cerebral metabolic rate for glucose) are regionally coupled. A CMRO 2 / CBF ratio that varies with time upon continuous stimulation has also been reported (Mintun et al, 2002).…”