CEREBRAL WAVE-FORM INDEXES OF THE OVINE FETUS WITH CHANGES IN BEHAVIORAL ACTIVITY

Objective: We have used a transit time flow probe on the carotid vascu lature of the ovine fetus as a continuous measure of cerebral blood fl ow to further investigate the functional link between cerebral wavefor m indices and vascular resistance with spontaneous changes in behavior al activity. Methods: Ten animals were studied near term during period s of low-voltage electrocortical (ECOG) activity and/or breathing move ments (LV/FBM) and high-voltage ECOG activity and/or apnea (HV/apnea). The transit time flow probe was used for the assessment of mean and p ulsatile blood flow to the brain with the resistance index (RI) calcul ated for the pulsatile measurements, Additionally, perfusion pressure was monitored, and cerebral vascular resistance, impedance, and the pr essure pulsatility index (PI) were calculated. Results: Mean cerebral blood flow was significantly increased during periods of LV/FBM when c ompared with periods of HV/apnea, with an associated decrease in cereb ral vascular resistance, but with little change in flow RI. This was t he result of a corresponding increase in the ratio pressure PI/impedan ce, with the percent change in the flow RI for each animal strongly re lated to the overall percent change in the pressure PI/impedance x cer ebral vascular resistance. Conclusions: The utility of the Doppler tec hnique in monitoring dynamic events of the fetal cerebral circulation by the use of flow velocity waveform indices may well depend on the co nditions of study and the extent to which impedance and pressure pulsa tility are also affected,