Abstract
Near-infrared spectroscopy (NiRS) is a relatively new technology of brain imaging with its potential in the assessment of cerebrovascular health only recently discovered. Encouraging early results suggest that NiRS can be used as an inexpensive and portable cerebrovascular health tracking device using a recently proposed pulse relaxation function (PReFx). In this paper, we propose a new NiRS timing index, text {TI}_{rm NiRS}, of cerebrovascular health. text {TI}_{rm NiRS} is a novel use of the NiRS technology. text {TI}_{rm NiRS} is motivated by the previously proved relationship of the timing of the reflected wave with vascular resistance and compliance in the context of pressure waveforms. We correlated both text {TI}_{rm NiRS} and PReFx against age, a non-exercise cardiorespiratory fitness (CRF) index, and two existing indices of cerebrovascular health, namely transcranial Doppler (TCD) augmentation index, text {AI}_{rm TCD}, and magnetic resonance imaging (MRI) blood flow pulsatility index, text {PI}_{rm MRI}. The text {TI}_{rm NiRS} correlations with Age, CRF, text {PI}_{rm MRI} and text {AI}_{rm TCD} all are significant, i.e., r=0.53 (p=0.002), r=-0.44 (p=0.011), r=0.45 (p=0.012) and r=0.46 (p=0.010), respectively. PReFx, however, did not have significant correlations with any of the vascular health factors. The proposed timing index is a reliable indicator of cerebrovascular aging factors in the NiRS waveform.
Highlights
Near-infrared spectroscopy (NiRS) is a relatively new technology of brain imaging with its potential in the assessment of cerebrovascular health only recently discovered
Note that PReFx is an index of vascular compliance whereas TINiRS is an index of vascular stiffness that is inversely proportional to compliance
The proposed systolic peak and reflected wave peak detection algorithm for TINiRS detected 228 channels with a systolic peak corresponding to an inflection point
Summary
Near-infrared spectroscopy (NiRS) is a relatively new technology of brain imaging with its potential in the assessment of cerebrovascular health only recently discovered. TINiRS is motivated by the previously proved relationship of the timing of the reflected wave with vascular resistance and compliance in the context of pressure waveforms We correlated both TINiRS and PReFx against age, a non-exercise cardiorespiratory fitness (CRF) index, and two existing indices of cerebrovascular health, namely transcranial Doppler (TCD) augmentation index, AITCD , and magnetic resonance imaging (MRI) blood flow pulsatility index, PIMRI. Due to the increased PWV in a stiff arterial system, the reflected waves travel faster, thereby reaching the incident wave earlier in systole and increasing the local pulse pressure even further Both forward and reflected waves leave a peak or an inflection point on the pressure waveform, we will refer to these peaks as the systolic and the reflected peaks, respectively. Based on a comprehensive review, cerebral SVD is believed to be one of the main causes of vascular cognitive impairments and accounts for a quarter of all acute ischaemic strokes[15]
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