Abstract
Near infrared spectroscopy (NIRS) has potential to offer a fast and non-invasive method of assessing cerebral
saturation in a clinical setting, however, there are concerns that NIRS brain measures suffer contamination
from superficial tissues. This study used the Valsalva manoeuver (VM) to determine whether NIRS could
differentiate between superficial (from somatic tissue) and neurological changes in the context of traumatic
brain injury. A potent vasopressor was used to assess the effect of reducing total haemoglobin concentration
in the superficial regions of the forehead. Frequency domain NIRS measurements during the VM pre and post
vasoconstrictor injection, combined with simulation data, conclusively show that NIRS can detect
neurological changes, in both haemoglobin content and saturation, when positioned on the forehead. The
effect of superficial contamination in this instance appeared to be insignificant, with no statistically significant
change in saturation over 8 patients, even with a drop in superficial haemoglobin concentration due to the
vasoconstrictor, confirmed by laser Doppler. Nevertheless, simulations indicated that the absolute values of
the recovered NIRS parameters are not quantitatively accurate; however a direct comparison with invasive
measures is needed to confirm this.
