Abstract
Developing near-infrared spectroscopy (NIRS) parameter recovery techniques to more specifically resolve brain physiology from that of the overlying tissue is an important part of improving the clinical utility of the technology. The Valsalva maneuver (VM) involves forced expiration against a closed glottis causing widespread venous congestion within the context of a fall in cardiac output. Due to the specific anatomical confines and metabolic demands of the brain we believe a properly executed VM has the ability to separate haemodynamic activity of brain tissue from that of the overlying scalp as observed by NIRS, and confirmed by functional magnetic resonance imaging (fMRI). Healthy individuals performed a series of standing maximum effort VMs under separate observation by frequency domain near-infrared spectroscopy (FD-NIRS) and fMRI. Nine individuals completed the clinical protocol (6 males, age 21-40). During the VMs, brain and extracranial tissue targeted signal were significantly different (opposite direction of change) in both fMRI and NIRS (p=0.00025 and 0.00115 respectively), with robust cross correlation of parameters between modalities. Four of these individuals performed further VMs after infiltrating 2% xylocaine/1:100,000 epinephrine (vasoconstrictor) into scalp tissue beneath the probes. No significant difference in the cerebrally derived parameters was observed. The maximum effort VM has the ability to separate NIRS observable physiology of the brain from the overlying extracranial tissue. Observations made by this FD cerebral NIRS device are comparable with fMRI in this context.
Highlights
Since its clinical introduction cerebral near-infrared spectroscopy (NIRS) has developed into an attractive method of monitoring brain tissue in a variety of clinical contexts
Healthy individuals performed a series of standing maximum effort Valsalva maneuver (VM) under separate observation by frequency domain near-infrared spectroscopy (FD-NIRS) and functional magnetic resonance imaging (fMRI)
During VM, both fMRI and NIRS output parameters showed a decrease in saturation for brain targeted approaches, while extracranial tissue (ECT) targeted approaches showed an increase
Summary
Since its clinical introduction cerebral near-infrared spectroscopy (NIRS) has developed into an attractive method of monitoring brain tissue in a variety of clinical contexts. The development of NIRS parameter recovery techniques and its related hardware is progressively evolving. This expands its potential utility into an ever wider range of clinical and scientific disciplines [1]. The influence of overlying ECT and its rich blood supply on brain targeted NIRS recovered parameters is one of the principle challenges of NIRS technology development. This is true within the clinical setting, when NIRS is being introduced as a cerebral monitoring modality. In such cases a simple and reproducible physiological manoeuvre that could clearly separate the morphology of haemodynamic activity of extracranial and intracranial tissues would be extremely useful
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