The premature brain embodies an underdeveloped vascular system, which can lead to poor cerebral blood flow (CBF), impaired metabolism, and subsequent brain injury. NNeMo (Neonatal NeuroMonitor) is an in-house built brain monitor that provides continuous and simultaneous measurements of CBF, tissue saturation (StO2), and metabolism. Nine premature infants were monitored for 6 h on day 1 and 3 of life. An oscillatory signal was observed in CBF and StO2 which diminished by day 3; metabolic response was not impacted by minor fluctuations in perfusion. Hemodynamic neuromonitoring could aid in predicting the onset of cerebral hemorrhaging or gauging brain injury severity.
KEYWORDS: Near infrared spectroscopy, Positron emission tomography, Tissue optics, Injuries, Magnetic resonance imaging, Tissues, Oxygen, Brain, Medical research
This is the first multimodal study of cerebral tissue metabolism and perfusion post-hypoxic-ischaemic (HI) brain injury with broadband near-infrared spectroscopy (bNIRS), diffuse correlation spectroscopy (DCS), positron emission tomography (PET) and magnetic resonance spectroscopy (MRS). In 5 piglet models of HI, we measured cerebral tissue saturation (StO2), cerebral blood flow (CBF), cerebral oxygen metabolism (CMRO2), changes in the mitochondrial oxidation state of cytochrome-c-oxidase (oxCCO), cerebral glucose metabolism (CMRglc), and tissue biochemistry (Lac+Thr/tNAA). At baseline, the parameters measured were: 64±6 % StO2, 35±11 ml/100g/min CBF, and 2.0±0.4 μmol/100g/min CMRO2. After HI the parameters measured were: 68±6% StO2, 35±6 ml/100g/min CBF, 1.3±0.1 μmol/100g/min CMRO2, 0.4±0.2 Lac+Thr/tNAA, and 9.5±2.0 CMRglc. This study demonstrates the capacity of a multimodal set up to interrogate the pathophysiology of HIE using a combination of optical methods, MRS, and PET.
Optical methods are attractive tools for neuromonitoring given their safety and sensitivity to key markers of brain health: tissue oxygenation can be assessed by near-infrared spectroscopy (NIRS) and cerebral blood flow by diffuse correlation spectroscopy (DCS). Although the application of these tools to neonatal patients is fairly straightforward, since it is reasonable to model the head as an optically homogeneous medium, their use with adult patients is more complicated due to substantial signal contamination caused by hemodynamic fluctuations in the extracerebral (EC) tissue. The purpose of this study was to assess the magnitude of this contamination by acquiring NIRS and DCS data in response to a hypercapnic challenge with and without scalp contributions. Scalp blood flow was impeded by a pneumatic tourniquet, which was confirmed by dynamic contrast-enhanced (DCE) NIRS. The results showed that EC contamination for intensity measurements could be as high as 75%; however, using time-resolved detection can reduce this value to 30%.
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