Hemodynamic response to burst-suppressed and discontinuous electroencephalography activity in infants with hypoxic ischemic encephalopathy

Abstract

Burst suppression (BS) is an electroencephalographic state associated with a profound inactivation of the brain. BS and pathological discontinuous electroencephalography (EEG) are often observed in term-age infants with neurological injury and can be indicative of a poor outcome and lifelong disability. Little is known about the neurophysiological mechanisms of BS or how the condition relates to the functional state of the neonatal brain. We used simultaneous EEG and diffuse optical tomography (DOT) to investigate whether bursts of EEG activity in infants with hypoxic ischemic encephalopathy are associated with an observable cerebral hemodynamic response. We were able to identify significant changes in concentration of both oxy and deoxyhemoglobin that are temporally correlated with EEG bursts and present a relatively consistent morphology across six infants. Furthermore, DOT reveals patient-specific spatial distributions of this hemodynamic response that may be indicative of a complex pattern of cortical activation underlying discontinuous EEG activity that is not readily apparent in scalp EEG.

Keywords: burst suppression; diffuse optical imaging; diffuse optical tomography; discontinuous; electroencephalography; hemodynamic response function; hypoxic ischemic encephalopathy.

Fig. 1

EEG electrodes on infant scalp and in elastic cap. (a) The arrangement of optical sources and detectors and EEG electrodes over the infant scalp. (b) The array of optical fibers and EEG electrodes in the elastic cap and in use during a study of a term infant.

Fig. 2

A representative example of EEG burst activity (gray, highlighted area) in patient 5. Note the very low-amplitude interburst activity.

Fig. 3

A histogram showing the distribution of the number of identified EEG bursts by duration for each infant.

Fig. 4

A schematic representation of the deconvolved HRFs to bursts lasting from 4 to 6 s in infant 2. The arrangement of the channels is based on the DOT channel layout [see Fig. 1(a)]. Note some channels are not displayed either due to rejection or for visualization purposes.

Fig. 5

This figure depicts the PCA-extracted representative hemodynamic response to bursts lasting between 4 and 6 s in each infant. The gray-shaded area indicates the period of the average duration burst. The value of “$N$” in each case indicates the number of bursts between 4 and 6 s identified in each infant.

Fig. 6

The reconstructed HbT image associated with the initial dip in the response to 4- to 6-s duration EEG bursts for infant 3. These images represent the change in HbT at the time point indicated by the black vertical line in the lower panel, which shows the PCA-extracted representative response for this infant. Note that the most significant decrease in HbT is localized to the bilateral temporal–parietal boundary. See Video 1 (MOV, 7.49 MB) [URL: http://dx.doi.org/10.1117/1.NPH.3.3.031408.1].

Fig. 7

The reconstructed HbT image associated with the peak increase in the response to 4- to 6-s duration EEG bursts for infant 3. These images represent the change in HbT at the time point indicated by the black vertical line in the lower panel, which shows the PCA-extracted representative response for this infant. Note the marked increase in HbT in the prefrontal cortex (see also Video 1).

Fig. 8

The reconstructed HbT image associated with the peak increase in the response to 4- to 6-s duration EEG bursts for infant 5. These images represent the change in HbT at the time point indicated by the black vertical line in the lower panel, which shows the PCA-extracted representative response for this infant. Note the marked increases in HbT in the bilateral temporal regions and the absence over the right superior parietal area. See Video 2 (MOV, 8.19 MB) [URL: http://dx.doi.org/10.1117/1.NPH.3.3.031408.2].

Fig. 9

The reconstructed HbT image associated with an undershoot in the response to 4- to 6-s duration EEG bursts for infant 5. These images represent the change in HbT at the time point indicated by the black vertical line in the lower panel, which shows the PCA-extracted representative response for this infant. Note that the undershoot is most apparent in the frontal cortices (see also Video 2).