A novel method for assessing cerebral autoregulation in preterm infants using transfer function analysis

Abstract

Background: Autoregulatory dysfunction is an important contributor to brain injury in premature infants, particularly intraventricular hemorrhage (IVH). The autoregulatory system acts as a filter that dampens the systemic blood flow to follow a normal cerebral perfusion profile.

Methods: Simultaneous arterial blood pressure and cerebral near-infrared spectroscopy (NIRS) data were collected from infants born before 28 wk estimated gestational age. The resulting data were preprocessed and then divided into nonoverlapping 20-min epochs. The transfer function estimate was calculated to determine dampening ability.

Results: Sixty-two infants were prospectively recruited with a mean estimated gestational age of 25.4 ± 1.3 wk and birth weight of 832 ± 199 g. 67% were male, 24/62 had IVH, 17/62 received dopamine, 47/62 had antenatal steroid exposure, and 22/62 received fentanyl.Advancing estimated gestational age and birth weight z-score predicted stronger dampening while African-American race and IVH of any grade predicted weaker dampening.

Conclusion: This preliminary report suggests an impairment in dampening ability associated with immaturity, decreased birth weight z-score, and African-American race. Decreased dampening is also associated with IVH, although these results cannot distinguish between decreased dampening as an antecedent or sequela of IVH. These observations should be studied in a larger sample.

Figure 1

Data quality example. The dampening curve for a single subject is shown after ensemble averaging of (A) 50, (B) 150, and (C) 300 data epochs respectively. The estimate of the dampening ability as the number of samples in the ensemble average is increased is shown in (D).

Figure 2

Dampening ability by gestational age. Broadband frequency response of the autoregulatory system by gestational age at birth. The response (dampening) of the autoregulatory system is indicated on the Y-axis for discrete frequencies between 0 and 0.25 Hz. Note the increased dampening at approximately 0.1 Hz (Mayer frequency band). Infants are grouped by gestational and color coded (red-24 weeks (n=17), yellow-25 weeks (n=15), purple-26 weeks (n=19), green-27 weeks (n=5), blue-28 weeks (n=6)).

Figure 3

Magnitude of dampening vs. frequency for infants with IVH (solid line) and without IVH (dashed line).