Cerebral pressure passivity in newborns with encephalopathy undergoing therapeutic hypothermia

Abstract

We extended our recent modification of the power spectral estimation approach to quantify spectral coherence. We tested both the standard and the modified approaches on simulated data, which showed that the modified approach was highly specific and sensitive to the coupling introduced in the simulation while the standard approach lacked these features. We also applied the modified and standard approaches to quantify the pressure passivity in 4 infants receiving therapeutic hypothermia. This was done by measuring the coupling between continuous cerebral hemoglobin differences and mean arterial blood pressure. Our results showed that the modified approach identified a lower pressure passivity index (PPI, percent time the coherence was above a predefined threshold) than the standard approach (P = 0.0027).

Keywords: NIRS; cerebral oximetry; cerebral oxygen extraction; cerebral pressure autoregulation; neonatal encephalopathy; spectral analysis; therapeutic hypothermia.

Figures

Figure 1

Results of the coherence analysis of simulated data. Maximum coherence obtained in 0.05–0.25 Hz for scenario 1 using (A) standard approach and (B) the modified approach. Coherence obtained in 0.05–0.25 Hz for scenario 2 using (C) standard approach and (D) the modified approach. The horizontal line at the coherence value of 0.384 is the confidence limit for coherence estimate.

Figure 2

Results of the coherence analysis of MAP and HbD from two newborns from favorable outcome group receiving hypothermia therapy for neonatal encephalopathy. The maximum coherence in 0.05–0.25 Hz was shown in all the plots from time since birth. Results from the modified approach were shown in the left side (A,C) and the results from the standard approach were shown in the right side (B,D). Results from subject 1 were shown in (A,B) and the results from subject 2 were shown in (C,D). In all the plots, the results from the left hemisphere (LH) were shown in red and the results from the right hemisphere (RH) were shown in green. Also the pressure passivity index (PPI) calculated for LH and RH was given in the inset. The horizontal line at the coherence value of 0.384 is the confidence limit for the coherence estimate. We displayed the insets in (C,D) for the portion of the results from the period where the study was stopped at 45.5 h and restarted at 49 h. At the onset of the break, the modified approach showed no significant coherence while the standard approach showed a significant coherence in both hemispheres. Similarly at 49 h after the study was restarted, the modified approach showed coherence only in the left hemisphere while at this point the standard approach showed no significant coherence.

Figure 3

Results of the coherence analysis of MAP and HbD from two newborns from adverse outcome group receiving hypothermia therapy for neonatal encephalopathy. The maximum coherence in 0.05–0.25 Hz was shown in all the plots from time since birth. Results from the modified approach were shown in the left side (A,C) and the results from the standard approach were shown in the right side (B,D). Results from subject 3 were shown in (A,B) and the results from subject 4 were shown in (C,D). In all the plots, the results from the left hemisphere (LH) were shown in red and the results from the right hemisphere (RH) were shown in green. Also the pressure passivity index (PPI) calculated for LH and RH was given in the inset. The horizontal line at the coherence value of 0.384 is the confidence limit for the coherence estimate.