Heather M. O'Leary

Cerebral Hemodynamic Changes During Intensive Care of Preterm Infants

OBJECTIVES. The objectives of this study were to examine the circulatory changes experienced by the immature systemic and cerebral circulations during routine events in the critical care of preterm infants and to identify clinical factors that are associated with greater hemodynamic-oxygenation changes during these events. METHODS. We studied 82 infants who weighed <1500 g at birth and required intensive care management and continuous blood pressure monitoring from an umbilical arterial catheter. Continuous recording of cerebral and systemic hemodynamic and oxygenation changes was performed. We studied 6 distinct types of caregiving events during 10-minute epochs: (1) quiet baseline periods; (2) minor manipulation; (3) diaper changes; (4) endotracheal tube suctioning; (5) endotracheal tube repositioning; and (6) complex events. Each event was matched with a preceding baseline. We examined the effect of specific clinical factors and cranial ultrasound abnormalities on the systemic and cerebral hemodynamic oxygenation changes that were associated with the various event types. RESULTS. There were highly significant differences in hemodynamics and oxygenation between events overall and baseline epochs. The magnitude of these circulatory changes was greatest during endotracheal tube repositioning and complex caregiving events. Lower gestational age, higher illness severity, chorioamnionitis, low Apgar scores, and need for pressor-inotropes all were associated with circulatory changes of significantly lower magnitude. Cerebral hemodynamic changes were associated with early parenchymal ultrasound abnormalities. CONCLUSIONS. Routine caregiving procedures in critically ill preterm infants are associated with major circulatory fluctuations that are clinically underappreciated and underdetected by current bedside monitoring. Our data underscore the importance of continuous cerebral hemodynamic monitoring in critically ill preterm infants.

REPRODUCIBILITY OF TRIAL-BASED FUNCTIONAL MRI ON MOTOR IMAGERY

The investigation of the reproducibility in functional MRI (fMRI) is an important step in the quantification and analysis of paradigm-related brain activation. This article reports on reproducibility of cortical activation characterized by repeated fMRI runs (10 times) during the performance of a motor imagery and a passive auditory stimulation as a control task. Two parameters, the size of activation and BOLD signal contrast, were measured from regions-of-interest for 10 subjects across different threshold conditions. The variability of these parameters was normalized with respect to the mean obtained from 10 runs, and represented as the intrasession variability. It was found that the variability was significantly lower in the measurement of BOLD signal contrast as compared to the measurement of the size of activation. The variability of the activation volume measurement was greater in the motor imagery task than in the auditory tasks across all thresholds. This task-dependent difference was not apparent from the measurement of the BOLD signal contrast. The presence of threshold dependence in the variability measurement was also examined, but no such dependency was found. The results suggest that a measurement of BOLD signal itself is a more reliable indicator of paradigm-related brain activation during repeated fMRI scans.

Functional asymmetry in human primary auditory cortex: identified from longitudinal fMRI study.

The leftward hemispheric dominance in language processing may be associated with fundamental functional asymmetry in the primary auditory cortex (PAC). Based on repeated functional MRI (fMRI) measurements, we investigated the presence of functional asymmetry in the human PAC using binaural presentation of linguistic sounds (two-syllable nouns) and simple tonal stimulation. Eight right-handed volunteers underwent nine fMRI sessions, approximately eight weeks apart, spanning the duration of more than a year. The PAC from each hemisphere was manually segmented and the volume of activation, detected within the segmented region-of-interest, was measured across the subjects and sessions to generate functional laterality indices. Although variations existed in activation volume between sessions and subjects, we found predominant and consistent leftward functional asymmetry in PAC during both linguistic and non-linguistic sound stimulations.

Atlas-based multichannel monitoring of functional MRI signals in real-time: Automated approach

We report an automated method to simultaneously monitor blood‐oxygenation‐level‐dependent (BOLD) MR signals from multiple cortical areas in real‐time. Individual brain anatomy was normalized and registered to a pre‐segmented atlas in standardized anatomical space. Subsequently, using real‐time fMRI (rtfMRI) data acquisition, localized BOLD signals were measured and displayed from user‐selected areas labeled with anatomical and Brodmanns Area (BA) nomenclature. The method was tested on healthy volunteers during the performance of hand motor and internal speech generation tasks employing a trial‐based design. Our data normalization and registration algorithm, along with image reconstruction, movement correction and a data display routine were executed with enough processing and communication bandwidth necessary for real‐time operation. Task‐specific BOLD signals were observed from the hand motor and language areas. One of the study participants was allowed to freely engage in hand clenching tasks, and associated brain activities were detected from the motor‐related neural substrates without prior knowledge of the task onset time. The proposed method may be applied to various applications such as neurofeedback, brain‐computer‐interface, and functional mapping for surgical planning where real‐time monitoring of region‐specific brain activity is needed. Hum Brain Mapp 2008.

Placebo-controlled crossover assessment of mecasermin for the treatment of Rett syndrome

To measure the efficacy of mecasermin (recombinant human insulin‐like growth factor 1, rhIGF‐1), for treating symptoms of Rett syndrome (RTT) in a pediatric population using a double‐blind crossover study design.