Effects of 4-dimethylaminophenol on blood flow and blood gases in the brain.

The effects of i.v. injected 4-dimethylaminophenol HCl, a ferri-hemoglobin-forming substance, on cerebral blood flow, brain temperature, blood gases, and lactate concentration in the sinus sagittalis blood were measured on male beagle dogs anesthetized with chloralose. An increase in cerebral blood flow became measurable when 5% or more of the hemoglobin was oxidized to ferrihemoglobin. The local cerebral blood flow of the cingulum region and the flow in the sinus sagittalis increased, while the sinus pO2 decreased. An increase in the ferrihemoglobin content of some 20% of the total hemoglobin at a constant arterial pO2 and pCO2 was attended with a decrease in the sinus pO2 of about 10 mm Hg when less than 40% of the heme iron was oxidized. The sinus pO2 approached a threshold value of some 8 mm Hg when the ferrihemoglobin content was increased above 40%. The lactate concentration began to rise very rapidly when 40-50% of the hemoglobin was oxidized. At the same time pCO2 increased and pH decreased in the sinus blood. The brain temperature remained unchanged. The behavior of conscious dogs with a ferrihemoglobin content of 40% of the total hemoglobin showed no abnormalities.