NEONATAL CEREBRAL BLOOD-FLOW VELOCITY RESPONSES TO CHANGES IN POSTURE

Maintaining a constant cerebral blood flow during a change in cerebral perfusion pressure is known as autoregulation. The integrity of this phenomenon is considered to be important in preventing cerebral lesions in preterm infants. A study was carried out using Doppler ultrasound measurements of cerebral blood flow velocities (CBFV) as an indicator of alterations in cerebral haemodynamics. CBFV were recorded on a beat to beat basis over 60 second epochs, during which time the cerebral perfusion pressure was changed by rapidly altering the infants' posture from horizontal to either 20-degrees head up or head down. An informative response in CBFV was considered to be either (a) a uniphasic, immediate, passive alteration in velocity occurring with t he change in posture and without a subsequent change or (b) a biphasic response of an initial change in CBFV followed within 20 seconds by a second response. This latter response is considered to be consistent with autoregulatory activity. A total of 501 epochs in 60 neonates of gestational age 24-41 weeks was analysed. It was shown that any one infant can make either response, but the reliability of making an active, biphasic response increases with increasing gestational age.