Broadband NIRS Cerebral Evaluation of the Hemodynamic and Oxidative State of Cytochrome-c-Oxidase Responses to +Gz Acceleration in Healthy Volunteers.

F Lange,I Tachtsidis,P Kaynezhad,R D Pollock,A Stevenson,G Bale

doi:10.1007/978-3-030-34461-0_43

F Lange, I Tachtsidis + Show 4 more

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https://doi.org/10.1007/978-3-030-34461-0_43

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Abstract

We used a miniature broadband NIRS system to monitor concentration changes in brain oxygenation (oxy- and deoxy- haemoglobin [HbO2], [HHb]) and oxidised cytochrome-c-oxidase ([oxCCO]) during a high +Gz acceleration, induced by a human centrifuge, on two healthy experienced volunteers (2 male, 34 and 37 years). We performed a sequence of several +Gz exposures that were terminated at the onset of visual symptoms (loss of peripheral vision). Systemic parameters were recorded (i.e. heart rate, blood pressure and arterial saturation), and brain tissue blood volume changes ([HbT] = [HbO2] + [HHb]) and oxygen delivery ([HbDiff] = [HbO2] - [HHb]) were calculated. Volunteer 1 demonstrated a decrease in [HbT] of −3.49 ± 0.02 μMol and [HbDiff] of −3.23 ± 0.44 μMol, and an increase of [oxCCO] of 0.42 ± 0.01μMol. Volunteer 2 demonstrated a decrease in [HbDiff] of −4.37 ± 0.23 μMol, and no significant change in [HbT] (0.53 ± 0.06 μMol) and [oxCCO] (0.09 ± 0.06 μMol). The variability of the brain metabolic response was related to the level of ischaemia, suggesting that suppression of metabolism was due to lack of glucose substrate delivery rather than oxygen availability.

Highlights

IntroductionMost Near-infrared spectroscopy (NIRS) systems use simple instrumentation and only measure the change in attenuation of 2 or 3 wavelengths, which is enough to calculate the changes in [HbO2] and [HHb]
Near-infrared spectroscopy (NIRS) is a common tool for monitoring non- invasively the tissue in-vivo changes in oxy- and deoxy haemoglobin ([HbO2] [HHb]) [1], and has been extensively used to monitor the function and physiology of the brain [2, 3].Most NIRS systems use simple instrumentation and only measure the change in attenuation of 2 or 3 wavelengths, which is enough to calculate the changes in [HbO2] and [HHb]
Broadband NIRS monitors the changes in the redox state of CCO using the difference between the oxidised and reduced CCO spectra ([oxCCO]), for further information on this topic see the review by Bale et al [6]

Summary

Introduction

Most NIRS systems use simple instrumentation and only measure the change in attenuation of 2 or 3 wavelengths, which is enough to calculate the changes in [HbO2] and [HHb]. Recent developments in NIRS instrumentation enables measurement of the change in attenuation of more than a hundred wavelengths [4, 5]. This technique is called broadband NIRS and can be used to retrieve information of a third chromophore, cytochrome-c-oxidase (CCO). It has been demonstrated that broadband NIRS has the potential to provide a realtime assessment of brain metabolism during neonatal hypoxic-ischaemic encephalopathy (HIE), and that oxCCO could be a clinically relevant metabolic marker [7]

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