SIMULTANEOUS MEASUREMENTS OF CEREBRAL-CIRCULATION WITH ELECTROMAGNETIC FLOWMETRY AND DOPPLER ULTRASOUND VELOCITY IN THE NEWBORN PIG

Cerebral blood flow measurement has been an important investigative to ol in newborns at risk for perinatal brain damage. The validity of Dop pler cerebral blood flow velocity measurements depends on a constant v essel diameter. We have validated Doppler against the electromagnetic flowmeter (EM) using a modified common carotid artery model in the 1-d -old piglet. Two sets of continuous and simultaneous recordings were p erformed: 1) the Doppler and EM probe on the same common carotid arter y (extracerebral branches were ligated), and 2) the EM probe on the co mmon carotid artery and the Doppler probe recording from an intracereb ral artery through an artificial fontanel. Arterial partial pressure o f carbon dioxide (Paco(2)) was manipulated (2.8-7.4 kPa), as was arter ial blood pressure (3.7-9.3 kPa). Simultaneous EM flow and estimated D oppler flow were compared. Ninety-three recordings were obtained with bath transducers on the modified carotid artery, and 49 were obtained with the Doppler insonicating an intracerebral artery. A multiple regr ession model was used for statistical analysis. The correlation betwee n EM and both sets of Doppler measurements for individual animals was >0.95 and was unaffected by changes in arterial blood pressure or Paco (2). Thus, the common carotid and the intracerebral artery investigate d did not change their diameter significantly in response to Pace, or arterial blood pressure. The relationships between EM and Doppler in t he individual animal were all linear but revealed great variability in the slopes due to the unknown vessel diameter and angle of insonicati on. We conclude that relative changes of cerebral blood flow velocity in the modified common carotid artery and intracerebral arteries show the same changes as common carotid artery blood flow (determined by an EM) in the healthy 1-d-old piglet.