Indexing Cerebrovascular Health Using Transcranial Doppler Ultrasound

Afkhami, Rashid Ghorbani; Wong, Rachel H. X.; Ramadan, Saadallah; Walker, Frederick R.; Johnson, Sarah J.

doi:10.1016/j.ultrasmedbio.2020.12.022

Cited by 5 publications

(5 citation statements)

References 43 publications

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“…While no previous NiRS studies have reported a timing index, the correlations of with age and CRF match those of the TCD reported by our group 20 . That is, correlations of and between TCD TI and age in two different datasets and a correlation of between TCD TI and CRF.…”

Section: Discussionsupporting

confidence: 87%

“…All experiments were performed in accordance with relevant guidelines and regulations. TCD recordings from these participants were previously reported in 20 . Each participant attended the Hunter Medical Research Institute and the University of Newcastle Callaghan campus over two consecutive days and participated in three scanning sessions.…”

Section: Methodsmentioning

confidence: 99%

“…Based on this model, we have introduced a new timing index (TI) as the inverse of the reflection time, similar to PPG SI but without the height parameter. In a previous experimental study we have shown that TI calculated using TCD blood flow velocity waveforms correlates significantly with vascular health factors such as age and CRF 20 . Here, we propose NiRS timing index ( ) as a measure of cerebrovascular health.…”

Section: Introductionmentioning

confidence: 94%

“…Of these two, is the most commonly used TCD index due to its ease of calculation. However, has been shown to have a stronger correlation with cerebrovascular health indicators such as age and cardiorespiratory fitness (CRF) 20 . The MRI pulsatility index ( ) is the commonly adopted MRI-based cerebrovascular health measure 14 .…”

Section: Introductionmentioning

confidence: 99%

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Indexing cerebrovascular health using near-infrared spectroscopy

Afkhami

Walker

Ramadan

et al. 2021

Sci Rep

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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, $$\text {TI}_{\rm NiRS}$$ TI NiRS , of cerebrovascular health. $$\text {TI}_{\rm NiRS}$$ TI NiRS is a novel use of the NiRS technology. $$\text {TI}_{\rm NiRS}$$ TI 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 $$\text {TI}_{\rm NiRS}$$ TI 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, $$\text {AI}_{\rm TCD}$$ AI TCD , and magnetic resonance imaging (MRI) blood flow pulsatility index, $$\text {PI}_{\rm MRI}$$ PI MRI . The $$\text {TI}_{\rm NiRS}$$ TI NiRS correlations with Age, CRF, $$\text {PI}_{\rm MRI}$$ PI MRI and $$\text {AI}_{\rm TCD}$$ AI TCD all are significant, i.e., $$r=0.53$$ r = 0.53 ($$p=0.002$$ p = 0.002 ), $$r=-0.44$$ r = - 0.44 ($$p=0.011$$ p = 0.011 ), $$r=0.45$$ r = 0.45 ($$p=0.012$$ p = 0.012 ) and $$r=0.46$$ r = 0.46 ($$p=0.010$$ 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.

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Section: Discussionsupporting

confidence: 87%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 94%

Section: Introductionmentioning

confidence: 99%

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Indexing cerebrovascular health using near-infrared spectroscopy

Afkhami

Walker

Ramadan

et al. 2021

Sci Rep

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“…The proposed model for T refl and AI can facilitate studies of vascular ageing by providing means to understand how changes is vascular properties such as R and C are reflected in these indices [40].…”

Section: Discussionmentioning

confidence: 99%

Wave reflection: More than a round trip

Afkhami

Johnson

2021

Medical Engineering & Physics

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Wave Reflection: More Than A Round Trip

Afkhami

Johnson

2020

Preprint

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Reflected pressure waves are key to the understanding of vascular aging, a prominent factor in major cardiovascular events. Several different metrics have been proposed to index the effect of wave reflection on the pressure waveform and thereby serve as an indicator of vascular aging. The extent to which these indices are influenced by factors other than vascular health remains a matter of concern. In this paper, we will first derive a mathematical model for the reflection time (Trefl), and the augmentation index (AI), assuming a general extended model of the arterial system. Then, we test our model against values reported in the literature. Finally, we discuss insights from the model to common observations in the literature such as age-related "shift" in the reflection site, the variation of AI with heart rate, and the flattening of Trefl in older participants. Our results indicate that although both Trefl and AI are affected by aging, the load properties are important factors to consider. Especially for Trefl, the delay caused at the load site can account for more than 50% of its value. The comparison between model outputs and reported values confirms the validity of the model. The proposed model describes how vascular parameters affect the reflection time and the augmentation index.

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Indexing Cerebrovascular Health Using Transcranial Doppler Ultrasound

Cited by 5 publications

References 43 publications

Indexing cerebrovascular health using near-infrared spectroscopy

Indexing cerebrovascular health using near-infrared spectroscopy

Wave reflection: More than a round trip

Wave Reflection: More Than A Round Trip

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