Proceedings of the Physiological Society, 30 June‐ 1 July 1989, Oxford Meeting: Communications

Abstract

Impaired autoregulation of cerebral blood flow has been implicated as a major aetiological factor for intraventricular haemorrhage and cerebral ischaemia in preterm infants (Lou & Lassen, 1979). The purpose of this study was to determine the degree of cerebral autoregulation in high-risk preterm infants.Simultaneous beat to beat measurements of cerebral blood flow velocity from the middle cerebral artery and mean intra-arterial blood pressure were made in 83 preterm infants (gestational age 24-36 weeks, birth weight 565-2750 g, age 1-2 days). The velocity measurements were obtained using the Vingmed CFM700 ultrasound unit interfaced to a computer. These data were stored using BVA (Andiamo A/S, Oslo, Norway) data acquisition system which also stored mean arterial pressure and heart rate. The recordings were 1-3 min long, and made when the infants were in a stable clinical condition, with normal blood gases. Records where spontaneous alterations in blood pressure of more than 10% of the resting level occurred without significant alteration in heart rate were used for the analysis. The percentage change in blood velocity per mmHg blood pressure was determined for each baby. In 23 babies the percentage change was less than 2 %/mmHg (not significant), in 33 babies between 2 and 8 %/mmHg and in 10 babies greater than 8 %/mmHg. In 17 babies insufficient alteration in blood pressure made analysis unsatisfactory. All babies over 32 weeks gestation were in the first group and all babies under 28 weeks were in the last two groups. Between 28 and 32 weeks gestation there was a fairly even distribution between the groups. All babies with severe intracranial lesions on early serial ultrasound scan had changes greater than 2 %/mmHg. However, half the babies with normal scans also had changes greater than 2 %/mmHg.These findings indicate that cerebral autoregulation is gestational age dependent and poorly developed below 28 weeks gestation. However, many babies over this age also do not regulate well but this does not necessarily lead to the development of severe intracranial pathology.