Pathogenesis of brain edema and hemorrhage: Role of the brain capillary

It has recently been suggested that the massive periventricular brain hemorrhages that occur in many sick premature infants have their origins in the capillaries. This proposal is supported by an apparent breakdown in the autoregulation of cerebral blood flow in sick premature infants. This system normally maintains a constant flow of blood through the capillary bed of the brain despite wide variations in systemic blood pressure. I propose that a hemorrhage would occur in this circumstance only if the basement membrane had been weakened prior to the increase in blood flow. We have recently found that brain capillaries isolated from immature animals have fourfold less basement membrane material than capillaries isolated from adults. Therefore, it may take less damage in the immature to weaken the basement membrane and allow for rupture and hemorrhage. Investigations of the mechanisms by which basement membrane is synthesized, degraded, and injured, could give us new insights into the pathogenesis and possible prevention of intraventricular hemorrhages.