LOCAL BLOOD-FLOW VELOCITIES IN THE CAROTID-BODY OF FETAL SHEEP AND NEWBORN LAMBS

Elastically-suspended microelectrodes were used in the vascularly isolated blood-perfused carotid body of fetal and newborn lambs as well as of 6-7-day-old lambs to measure local blood flow velocities by means of hydrogen clearance. Fetal sheep (n = 9) carotid bodies elicited mean local blood velocity values between 0.008 and 0.11 cm.s-1, whereas newborn lamb carotid bodies (n = 7) showed values between 0.008 and 0.067 cm.s-1 at a perfusion pressure range between 30 and 150 mmHg. The 6-7-day-old lamb carotid bodies (n = 5) were characterized by values of 0.003 and 0.049 cm.s-1 over the same perfusion pressure range. Fetal carotid body values were statistically significantly higher than the values of the 6-7-day-old lamb carotid bodies, whereas the newborn carotid body values showed no significant difference to both other groups. The flow velocity/perfusion pressure relationship peaked at perfusion pressure values between 100 and 150 mmHg in all groups with a reduced steepness in the lamb carotid body. It is concluded that local blood flow velocities in the carotid body are similar to that in other organs, and that after birth local blood flow velocities in the carotid body decrease during the first week of life, probably induced by vasoconstriction, changed blood gas values, and/or increasing shunt flow.