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Transfer function analysis of dynamic cerebral autoregulation in preterm infants

Presented at the Neonatal Society 2016 Spring Meeting.

Ng I1, Yiallourou S2, Sands S2,3, Wong F2,4

1 School of Clinical Medicine, University of Cambridge, UK
2 The Ritchie Centre, Hudson Institute of Medical Research, Monash University, Australia
3 Brigham and Women’s Hospital, Harvard Medical School, USA
4 Monash Newborn, Monash Medical Centre, Australia

Background: Impaired cerebral autoregulation has been demonstrated in preterm infants and has been associated with adverse clinical outcomes. We hypothesise that maturation of cerebral autoregulation may be observed in preterm infants as they progress towards term corrected age, using transfer function analysis.

Methods: Infants less than 30 weeks gestation at birth were studied weekly for 2 hours during sleep, from 7 days of age. At each study, multiple 2-minute epochs of continuous non-invasive mean arterial blood pressure (MAP, FinometerTM, Finometer Medical Systems, The Netherlands) and tissue oxygenation index (TOI, NIRO 200, Hamamatsu Photonics, Japan) measurements were obtained. Transfer function analysis was applied to assess the concordance between MAP and TOI in the frequency domain as a measure of cerebral autoregulation, using the parameters of coherence and gain. At a given frequency, coherence >0.5 indicates a significant correlation between the waveforms of MAP and TOI, and therefore suggests impaired autoregulation. Gain indicates the magnitude of impaired autoregulation when the coherence value is >0.5. Coh and Gain were analysed for frequencies of 0.02 – 0.1 Hz, corresponding to changes taking place across 10 – 50 seconds.

Results: Four infants, of median gestational age 28 (range 28-29) weeks and median birth weight 1069.5 (range 975 – 1107) grams, were studied for a median of 7 (range 5-7) weeks after birth. Decreasing mean maximum coherence is seen in 3 out of the 4 infants studied as they reach term gestational age. Of the three infants who continued to have high coherence of >0.5 towards term corrected age, decreasing mean gain at maximum coherence with increasing gestational age was observed in two infants.

Conclusion: Cerebral autoregulatory impairment is frequent in preterm infants. Improvement and maturation of cerebral autoregulation occurs postnatally as preterm infants approach term corrected age. A larger number of infants to be studied will enable characterisation of the postnatal change in cerebral autoregulation in preterm infants. This may be useful in identifying preterm infants prone to impaired or delayed maturation of cerebral autoregulation, and may guide clinical practice.

Corresponding author: ihxn2@cam.ac.uk

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