Developmental Medicine and Child Neurology vol:30 issue:3 pages:334-41
Stable infants with anaemia needing a transfusion with adult red blood-cells were studied to elucidate changes in brain blood-flow velocity. Within 24 hours and at five to six days following transfusion a substantial mean flow velocity reduction was observed. Haemodynamic factors contributing to the reduction were an increase in cerebrovascular resistance and an increase in whole blood viscosity, as reflected by a raised pulsatility index. Transfusion with adult red blood-cells causes an elevation in haemoglobin concentration, thereby increasing the total oxygen-carrying capacity of arterial blood; however, this lowers the concentration of fetal haemoglobin which possesses a higher affinity for oxygen. Since cerebral oxygen transport is equal to the product of cerebral blood-flow and arterial oxygen content, this finding suggests the existence of a homeostatic mechanism for cerebral oxygen transport. The actual amount of cerebral oxygen transport was found to increase progressively as the percentage of fetal haemoglobin rose above 30 per cent. At higher fetal haemoglobin levels, appropriate elevations in cerebral blood-flow occurred, causing an increase in the supply of oxygen to the brain.