Cerebral Blood Flow Pulsatility Research Articles

Enhancing diffuse correlation spectroscopy pulsatile cerebral blood flow signal with near-infrared spectroscopy photoplethysmography.

Combining near-infrared spectroscopy (NIRS) and diffuse correlation spectroscopy (DCS) allows for quantifying cerebral blood volume, flow, and oxygenation changes continuously and non-invasively. As recently shown, the DCS pulsatile cerebral blood flow index () can be used to quantify critical closing pressure (CrCP) and cerebrovascular resistance (). Although current DCS technology allows for reliable monitoring of the slow hemodynamic changes, resolving pulsatile blood flow at large source-detector separations, which is needed to ensure cerebral sensitivity, is challenging because of its low signal-to-noise ratio (SNR). Cardiac-gated averaging of several arterial pulse cycles is required to obtain a meaningful waveform. Taking advantage of the high SNR of NIRS, we demonstrate a method that uses the NIRS photoplethysmography (NIRS-PPG) pulsatile signal to model DCS , reducing the coefficient of variation of the recovered pulsatile waveform () and allowing for an unprecedented temporal resolution (266Hz) at a large source-detector separation (). In 10 healthy subjects, we verified the quality of the NIRS-PPG during common tasks, showing high fidelity against ( ). We recovered CrCP and at 0.25Hz, times faster than previously achieved with DCS. NIRS-PPG improves DCS SNR, reducing the number of gate-averaged heartbeats required to recover CrCP and .

Sex differences in the relationship between physical activity levels and cerebral pulsatility

BACKGROUND: Greater cerebral blood flow pulsatility, measured as pulsatility index (PI), has recently been under investigation as a risk factor for cognitive impairment and neurodegenerative diseases. Furthermore, physical activity (PA), which has been associated with improved cognitive function and holds therapeutic effects for cardiovascular function, may be linked with lower cerebral pulsatility, especially in postmenopausal women (PMW). PURPOSE: To investigate the relationship between PA and PI in PMW and determine if these relationships are maintained in age-matched men. We hypothesized that there would be an inverse relationship between PA and PI in PMW, and that this relationship would diminish in age-matched men. METHODS: Fifty-two healthy PMW (age 63 ± 4 years) and 25 age-matched men (63 ± 4 years) were recruited for this study. PA was self-reported via the Godin Questionnaire (Godin Score) and using the metabolic equivalent to exercise in minutes per week (MET-Min). Cerebral blood flow was measured through the internal carotid arteries (ICAs), middle cerebral arteries (MCAs), and the basilar artery using 4D Flow MRI. PI was calculated as (maximum flow – minimum flow)/mean flow. RESULTS: There were no significant differences in PA between groups via Godin Score (PMW: 37 ± 21 vs. Men 37 ± 13, p = 1.00) or MET-Min (PMW: 1586 ± 901 vs. Men: 1831 ± 901, p = 0.28). When combined, there was a significant inverse association between MET-Min and basilar PI (r = -0.24, p = 0.04). In PMW, there was a trend for greater MET-Min to be associated with lower basilar PI (r = -0.24, p = 0.08), however this trend was not observed in men (r = -0.25, p = 0.25). Interestingly, in men, there was a significant positive association between MET-Min and MCA PI (r = 0.46, p = 0.03). There were no significant associations observed between PA and ICA PI. CONCLUSION: Greater PA may be linked to lower PI in PMW, but not in in age-matched men. The influence of regular physical activity on cerebral PI may be specific to certain cerebral vessels. This study was funded by the Virginia Horn Henry Research Grant, NIH grant (AG070469-01), and the Wisconsin Alzheimer's Disease Research Center (P30-AG062715). This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Central arterial stiffness, brain white matter hyperintensity and total brain volume across the adult lifespan.

Mounting evidence suggests that central arterial stiffening is associated with brain ageing in older adults. The purpose of this study was to determine the associations of age with carotid arterial stiffness and carotid-femoral pulse wave velocity (cfPWV), both measurements of central arterial stiffness, the relationship between age-related arterial stiffness, brain white matter hyperintensity (WMH) and total brain volume (TBV), and whether effects of central arterial stiffness on WMH volume and TBV are mediated by pulsatile cerebral blood flow (CBF). One hundred and seventy-eight healthy adults (21-80 years) underwent measurements of central arterial stiffness using tonometry and ultrasonography, WMH and TBV via MRI, and pulsatile CBF at the middle cerebral artery via transcranial Doppler. Advanced age was associated with increases in both carotid arterial stiffness and cfPWV, increases in WMH volume and decreases in TBV (all P < 0.01). Multiple linear regression analysis showed that carotid β-stiffness was positively associated with WMH volume (B = 0.015, P = 0.017) and cfPWV negatively with TBV (B = -0.558, P < 0.001) after adjustment for age, sex and arterial pressure. Pulsatile CBF mediates the associations between carotid β-stiffness and WMH (95% confidence interval: 0.0001-0.0079). These findings suggest that age-related central arterial stiffness is associated with increased WMH volume and decreased TBV, which is likely mediated by increased arterial pulsation.

Cerebral blood flow pulsatility and cerebral artery stiffness acutely decrease during hemodialysis.

End-stage kidney disease (ESKD) is associated with increased arterial stiffness and cognitive impairment. Cognitive decline is accelerated in ESKD patients on hemodialysis and may result from repeatedly inappropriate cerebral blood flow (CBF). The aim of this study was to examine the acute effect of hemodialysis on pulsatile components of CBF and their relation to acute changes in arterial stiffness. In eight participants (age: 63 ± 18 years, men: 5), CBF was estimated using middle cerebral artery blood velocity (MCAv) assessed with transcranial Doppler ultrasound before, during, and after a single hemodialysis session. Brachial and central blood pressure, along with estimated aortic stiffness (eAoPWV) were measured using an oscillometric device. Arterial stiffness from heart to MCA was measured as the pulse arrival time (PAT) between electrocardiogram (ECG) and transcranial Doppler ultrasound waveforms (cerebral PAT). During hemodialysis, there was a significant reduction in mean MCAv (-3.2cm/s, p< 0.001), and systolic MCAv (-13.0cm/s, p< 0.001). While baseline eAoPWV (9.25 ± 0.80 m/s) did not significantly change during hemodialysis, cerebral PAT increased significantly (+0.027 , p< 0.001) and was associated with reduced pulsatile components of MCAv. This study shows that hemodialysis acutely reduces stiffness of arteries perfusing the brain along with pulsatile components of blood velocity.

Aerobic exercise training reduces central arterial stiffness and improves cerebral blood flow in older adults

Background: Evidence of the benefits of aerobic exercise training (AET) on brain structure, function, and perfusion in older adults is inconclusive.&#x0D; Methods: We conducted two randomized controlled trials (RCT) in sedentary older adults with or without mild cognitive impairment (MCI) to address this question.1-3 The trial’s intervention arm was a progressive moderate-to-vigorous intensity AET, and the active control arm was stretching-and-toning (SAT). Outcome measures included neurocognitive function focused on memory and executive function, global and regional brain volume and cortical thickness measured with structural magnetic resonance imaging (MRI), cerebral blood flow (CBF) and CBF pulsatility measured in the large cerebral arteries (the internal carotid artery, the vertebral artery, and the middle cerebral artery) with 2D duplex ultrasonography and transcranial Doppler, central arterial stiffness measured with arterial applanation tonometry, and cardiorespiratory fitness measured with treadmill peak oxygen consumption (V̇O2peak). The duration of both trials was one year.&#x0D; Results: In both studies, we observed that AET increased V̇O2peak significantly by ∼10% while it did not change with SAT. Cognitive composite scores and domain-specific scores improved in both the AET and SAT groups, although no group differences were observed (likely reflected by cognitive test practice effects). Total brain and hippocampal volume and mean cortical thickness decreased in both groups over one year. Conversely, AET increased CBF, and decreased central arterial stiffness and CBF pulsatility. Increases in V̇O2peak with AET were correlated with increases in CBF and decreases in cerebrovascular resistance (CVR). Further, the improved memory score in the AET group was associated with decreased CVR and central arterial stiffness measured with carotid β-stiffness index.&#x0D; Conclusions: Taken together, these findings demonstrated that one-year moderate-to-vigorous intensity AET increased CBF and decreased central arterial stiffness in older adults with or without MCI. We speculate that improvement in cerebrovascular function with AET may precede its potential effects on brain structure and neurocognitive function in older adults. (The research findings presented herein were supported by the National Institutes of Health R01AG033106 and R01HL102457)

Human intracranial pulsatility during the cardiac cycle: a computational modelling framework

BackgroundToday’s availability of medical imaging and computational resources set the scene for high-fidelity computational modelling of brain biomechanics. The brain and its environment feature a dynamic and complex interplay between the tissue, blood, cerebrospinal fluid (CSF) and interstitial fluid (ISF). Here, we design a computational platform for modelling and simulation of intracranial dynamics, and assess the models’ validity in terms of clinically relevant indicators of brain pulsatility. Focusing on the dynamic interaction between tissue motion and ISF/CSF flow, we treat the pulsatile cerebral blood flow as a prescribed input of the model.MethodsWe develop finite element models of cardiac-induced fully coupled pulsatile CSF flow and tissue motion in the human brain environment. The three-dimensional model geometry is derived from magnetic resonance images (MRI) and features a high level of detail including the brain tissue, the ventricular system, and the cranial subarachnoid space (SAS). We model the brain parenchyma at the organ-scale as an elastic medium permeated by an extracellular fluid network and describe flow of CSF in the SAS and ventricles as viscous fluid movement. Representing vascular expansion during the cardiac cycle, a prescribed pulsatile net blood flow distributed over the brain parenchyma acts as the driver of motion. Additionally, we investigate the effect of model variations on a set of clinically relevant quantities of interest.ResultsOur model predicts a complex interplay between the CSF-filled spaces and poroelastic parenchyma in terms of ICP, CSF flow, and parenchymal displacements. Variations in the ICP are dominated by their temporal amplitude, but with small spatial variations in both the CSF-filled spaces and the parenchyma. Induced by ICP differences, we find substantial ventricular and cranial-spinal CSF flow, some flow in the cranial SAS, and small pulsatile ISF velocities in the brain parenchyma. Moreover, the model predicts a funnel-shaped deformation of parenchymal tissue in dorsal direction at the beginning of the cardiac cycle.ConclusionsOur model accurately depicts the complex interplay of ICP, CSF flow and brain tissue movement and is well-aligned with clinical observations. It offers a qualitative and quantitative platform for detailed investigation of coupled intracranial dynamics and interplay, both under physiological and pathophysiological conditions.

Effects of changes in large arterial compliance and small arterial buffer function with resistance training on cerebral blood flow pulsatility

article: Effects of changes in large arterial compliance and small arterial buffer function with resistance training on cerebral blood flow pulsatility - Gazzetta Medica Italiana - Archivio per le Scienze Mediche 2021 December;180(12):805-14 - Minerva Medica - Journals

Cerebral Blood Flow Pulsatility Index is Unchanged during Superimposed Lower‐Body Negative Pressure in Head‐Up Tilt in Anterior and Posterior Cerebral Circulations

Lower body negative pressure (LBNP) chambers can be utilized to experimentally-elicit reductions in blood pressure, cerebral blood flow (CBF) and associated symptoms of presyncope. There is high between-individual variability in tolerance to LBNP, however the underlying physiological responses affecting tolerance remains unclear. Pulsatility in CBF may affect LBNP tolerance, as more pulsatile flow may protect the delivery of oxygen to cerebral tissues in hypotension. We aimed to assess the pulsatility index (PI) in anterior and posterior cerebral circulations during LBNP in superimposed head-up tilt (HUT), where gravitational-induced blood volume re-distribution augments volume unloading during LBNP. We recruited and included 12 healthy male participants, and instrumented them in a custom-build integrated 45° HUT-LBNP chamber. Participants were instrumented for heart rate (HR; ECG), end-tidal CO2 (PETCO2; mouthpiece and gas analyzer),beat-by-beat mean arterial pressure (MAP; finometer), and middle and posterior cerebral artery velocity (MCAv, PCAv; transcranial Doppler ultrasound). All measures were recorded during baseline (BL) and during -50 mmHg LBNP exposure up to a maximum of 10-minutes (600s). Presyncope was defined as a 30% reduction in systolic blood pressure (i.e., investigator stop) or onset subjective symptoms (i.e., participant stop). We quantified all variables as a 30-sec mean bin during BL and the final 30-sec of LBNP prior to presyncope. MAP, MCAv and PCAv PI was calculated as systolic-diastolic/mean. LBNP tolerance time was 480.9±134.3 sec. HR increased from 72.3±10.3 (BL) to 103.0±18.2 bpm (P<0.01) during LBNP, suggesting a baroreflex response, and PETCO2 was reduced from 32.0±2.9 (BL) to 28.7±2.9 Torr (P<0.01) during LBNP, suggesting mild hyperventilation. MAP decreased from 84.8±11.3 (BL) to 76.2±14.7 mmHg (P<0.01) during LBNP, with associated reductions in mean MCAv from 52.1±15.0 to 44.3±14.5 cm/s (P<0.01), and mean PCAv from 35.5±12.6 to 29.0±9.9 cm/s (P<0.01) during LBNP. MAP PI was reduced from 0.76±0.2 to 0.59±0.02 (P<0.01) during LBNP. However, MCAv and PCAv PI were unchanged during LBNP (P=0.6 and P=0.9, respectively). Our results suggest that although MAP and MAP PI were both reduced during LBNP at pre-syncope, with associated reductions in mean MCAv and PCAv, MCAv and PCAv PI remained stable with LBNP in HUT. These findings suggest that PI in CBF variables at the cardiac frequency are not related to LBNP tolerance in healthy men.

Arterial stiffness as a vascular contribution to cognitive impairment: a fluid dynamics perspective

A model of cerebral pulsatile blood flow through multiple arterial bifurcations is developed, based on the physics of wave propagation in compliant vessels. The model identifies the conditions for the optimum antegrade flow of blood into the arterioles as a function of the areas and stiffnesses of the arteries. The model predicts and quantifies the reduction in vessel diameter which occurs in progressing from the large central arteries into the arterioles. It also predicts and quantifies the change in vessel compliance which occurs in progressing from the large central arteries, through the small arteries, into the arterioles. Physics predicts that the clinically observed compliance changes are consistent with the efficient delivery of blood to the cerebral capillary bed. The model predicts that increasing arterial stiffening with age, reduces pulsatile cerebral blood flow substantially, potentially resulting in ischemia, hypoperfusion and hypoxia, with attendant neurological and cognition consequences. The model predicts that while central pulse pressure increases with aging, small vessel pulse pressure reduces, contrary to the concept of a pressure wave tsunami in the small vessels. The model also predicts that increased luminal diameters with increasing age, mitigate, somewhat the negative consequences of arterial stiffening, a form of adaptive arterial remodelling.

One-Year Aerobic Exercise Reduced Carotid Arterial Stiffness and Increased Cerebral Blood Flow in Amnestic Mild Cognitive Impairment.

Central arterial stiffness and brain hypoperfusion are emerging risk factors of Alzheimer's disease (AD). Aerobic exercise training (AET) may improve central arterial stiffness and brain perfusion. To investigate the effects of AET on central arterial stiffness and cerebral blood flow (CBF) in patients with amnestic mild cognitive impairment (MCI), a prodromal stage of AD. This is a proof-of-concept, randomized controlled trial that assigned 70 amnestic MCI patients into a 12-month program of moderate-to-vigorous AET or stretching-and-toning (SAT) intervention. Carotid β-stiffness index and CBF were measured by color-coded duplex ultrasonography and applanation tonometry. Total CBF was measured as the sum of CBF from both the internal carotid and vertebral arteries, and divided by total brain tissue mass assessed with MRI to obtain normalized CBF (nCBF). Episodic memory and executive function were assessed using standard neuropsychological tests (CVLT-II and D-KEFS). Changes in cardiorespiratory fitness were measured by peak oxygen uptake (VO2peak). Total 48 patients (29 in SAT and 19 in AET) were completed one-year training. AET improved VO2peak, decreased carotid β-stiffness index and CBF pulsatility, and increased nCBF. Changes in VO2peak were associated positively with changes in nCBF (r = 0.388, p = 0.034) and negatively with carotid β-stiffness index (r = -0.418, p = 0.007) and CBF pulsatility (r = -0.400, p = 0.014). Decreases in carotid β-stiffness were associated with increases in cerebral perfusion (r = -0.494, p = 0.003). AET effects on cognitive performance were minimal compared with SAT. AET reduced central arterial stiffness and increased CBF which may precede its effects on neurocognitive function in patients with MCI.

P.18 Carotid Stiffness Parameters and Cerebral Blood Flow Pulsatility in Young Healthy Individuals across Races

BackgroundHigher cerebral blood flow (CBF) pulsatility was found to be associated with severer brain white matter lesions in the elderly [1]. It was hypothesized that the central/elastic arterial stiffness/compliance may directly affect CBF pulsatility. However, it is still unclear which carotid stiffness parameters may better reflect this impact, and whether race and sex differences are present.MethodsTo study the correlations among those parameters with comparisons between different races and sexes, we enrolled 35 young healthy subjects (19 females), aged 29 ± 5 (18~40) years, with three races of comparable age and sex ratio, i.e. White (n = 16), Black (n = 7), and Asian (n = 12). All subjects were in resting seated position, with continuous transcranial Doppler recording of CBF velocity at middle cerebral artery (MCA), simultaneous 1-min ultrasound echo-tracking on bilateral common carotid arteries, and multiple measurements of brachial blood pressure (BP).ResultsAll derived parameters [2], including MCA pulsatility index (PI), showed no significant racial differences but with significantly (p < 0.05) higher carotid stiffness index (β), Peterson’s pressure modulus (Ep), BP pulsatility index (mostly driven by higher systolic BP but similar diastolic BP), and lower arterial compliance (AC, p = 0.07) in males than in females. Only AC (but not β and Ep) showed a significant correlation with PI (r = 0.49, p = 0.004) even after controlling for BP pulsatility index, which negatively correlated with AC (β = −0.35, p = 0.038).ConclusionsHigher carotid AC (i.e. decreased stiffness) seems to enhance CBF pulsatility in young healthy populations, which might differ from the elderly.

Effects of 1‐year Aerobic Exercise Training on Cerebral Blood Flow and Arterial Siffness in Amnestic Mild Cognitive Impairment

Aerobic exercise training (AET) may improve cerebralperfusion and reduce the risk of dementia. Changes in central arterialstiffness and pulsatile cerebral blood flow (CBF) associated with exercise training may be one of the underlying pathophysiological mechanism. The purpose of this study was to investigate: (1) The effects of AET on central arterialstiffness and CBF, and (2) whether pulsatile CBF mediates the association between changes in arterial stiffness and cerebral perfusion in amnestic mildcognitive impairment (aMCI), a prodromal stage of Alzheimer disease. Seventy aMCI patients were randomized to 12 months of moderate‐intensity AET (n=31) or stretching program (n=39). CBF and carotid β‐stiffness index were assessed by ultrasonography and applanation tonometry. Cerebral perfusion was calculated by normalizing total CBF to brain tissue mass measured by magnetic resonance imaging. Pulsatile CBF was measured from the middle cerebralartery using transcranial Doppler. Cardiorespiratory fitness was assessed by peak oxygen uptake (VO2peak). VO2peak and cerebralperfusion increased and carotid β‐stiffness index decreased in the AET group, while remained unchanged in the stretching group. The change in VO2peak was significantly associated with the change in cerebral perfusion, carotidβ‐stiffness index, and pulsatile CBF (Fig. 1). The decrease in carotidβ‐stiffness was associated with increased in cerebral perfusion (Fig. 2). Mediation analysis showed that changes in pulsatile CBF mediates the association between carotidβ‐stiffness index and cerebral perfusion (Fig. 2). These results suggest that AET decreases arterial stiffness and increases cerebral perfusion, which is mediated by pulsatile CBF in aMCI patients.Support or Funding InformationThis work was funded by the National Institutes of Health ((R01AG033106, R01HL102457, P30AG012300)Associations between the change (Δ) in relative peak oxygen uptake (VO2) and the change in cerebral perfusion, carotid β‐stiffness index and pulsatile cerebral blood flow (CBF).Figure 1Mediation analysis diagram of the effect of the change (Δ) in carotid β‐stiffness index on the change in cerebral perfusion through the change in pulsatile cerebral blood flow (CBF).Figure 2

Estimating intracranial pressure using pulsatile cerebral blood flow measured with diffuse correlation spectroscopy.

Measuring intracranial pressure (ICP) is necessary for the treatment of severe head injury but measurement systems are highly invasive and introduce risk of infection and complications. We developed a non-invasive alternative for quantifying ICP using measurements of cerebral blood flow (CBF) by diffuse correlation spectroscopy. The recorded cardiac pulsation waveform in CBF undergoes morphological changes in response to ICP changes. We used the pulse shape to train a randomized regression forest to estimate the underlying ICP and demonstrate in five non-human primates that DCS-based estimation can explain over 90% of the variance in invasively measured ICP.

Dissociation of Cerebral Blood Flow and Femoral Artery Blood Pressure Pulsatility After Cardiac Arrest and Resuscitation in a Rodent Model: Implications for Neurological Recovery.

BackgroundImpaired neurological function affects 85% to 90% of cardiac arrest (CA) survivors. Pulsatile blood flow may play an important role in neurological recovery after CA. Cerebral blood flow (CBF) pulsatility immediately, during, and after CA and resuscitation has not been investigated. We characterized the effects of asphyxial CA on short‐term (<2 hours after CA) CBF and femoral arterial blood pressure (ABP) pulsatility and studied their relationship to cerebrovascular resistance (CVR) and short‐term neuroelectrical recovery.Methods and ResultsMale rats underwent asphyxial CA followed by cardiopulmonary resuscitation. A multimodal platform combining laser speckle imaging, ABP, and electroencephalography to monitor CBF, peripheral blood pressure, and brain electrophysiology, respectively, was used. CBF and ABP pulsatility and CVR were assessed during baseline, CA, and multiple time points after resuscitation. Neuroelectrical recovery, a surrogate for neurological outcome, was assessed using quantitative electroencephalography 90 minutes after resuscitation. We found that CBF pulsatility differs significantly from baseline at all experimental time points with sustained deficits during the 2 hours of postresuscitation monitoring, whereas ABP pulsatility was relatively unaffected. Alterations in CBF pulsatility were inversely correlated with changes in CVR, but ABP pulsatility had no association to CVR. Interestingly, despite small changes in ABP pulsatility, higher ABP pulsatility was associated with worse neuroelectrical recovery, whereas CBF pulsatility had no association.ConclusionsOur results reveal, for the first time, that CBF pulsatility and CVR are significantly altered in the short‐term postresuscitation period after CA. Nevertheless, higher ABP pulsatility appears to be inversely associated with neuroelectrical recovery, possibly caused by impaired cerebral autoregulation and/or more severe global cerebral ischemia.

Assessment of Cerebral Blood Flow Pulsatility and Cerebral Arterial Compliance With 4D Flow MRI.

BackgroundFour‐dimensional flow magnetic resonance imaging (4D flow MRI) enables efficient investigation of cerebral blood flow pulsatility in the cerebral arteries. This is important for exploring hemodynamic mechanisms behind vascular diseases associated with arterial pulsations.PurposeTo investigate the feasibility of pulsatility assessments with 4D flow MRI, its agreement with reference two‐dimensional phase‐contrast MRI (2D PC‐MRI) measurements, and to demonstrate how 4D flow MRI can be used to assess cerebral arterial compliance and cerebrovascular resistance in major cerebral arteries.Study TypeProspective.SubjectsThirty‐five subjects (20 women, 79 ± 5 years, range 70–91 years).Field Strength/Sequence4D flow MRI (PC‐VIPR) and 2D PC‐MRI acquired with a 3T scanner.AssessmentTime‐resolved flow was assessed in nine cerebral arteries. From the pulsatile flow waveform in each artery, amplitude (ΔQ), volume load (ΔV), and pulsatility index (PI) were calculated. To reduce high‐frequency noise in the 4D flow MRI data, the flow waveforms were low‐pass filtered. From the total cerebral blood flow, total PI (PItot), total volume load (ΔVtot), cerebral arterial compliance (C), and cerebrovascular resistance (R) were calculated.Statistical TestsTwo‐tailed paired t‐test, intraclass correlation (ICC).ResultsThere was no difference in ΔQ between 4D flow MRI and the reference (0.00 ± 0.022 ml/s, mean ± SEM, P = 0.97, ICC = 0.95, n = 310) with a cutoff frequency of 1.9 Hz and 15 cut plane long arterial segments. For ΔV, the difference was –0.006 ± 0.003 ml (mean ± SEM, P = 0.07, ICC = 0.93, n = 310) without filtering. Total R was 11.4 ± 2.41 mmHg/(ml/s) (mean ± SD) and C was 0.021 ± 0.009 ml/mmHg (mean ± SD). ΔVtot was 1.21 ± 0.29 ml (mean ± SD) with an ICC of 0.82 compared with the reference. PItot was 1.08 ± 0.21 (mean ± SD).Data ConclusionWe successfully assessed 4D flow MRI cerebral arterial pulsatility, cerebral arterial compliance, and cerebrovascular resistance. Averaging of multiple cut planes and low‐pass filtering was necessary to assess accurate peak‐to‐peak features in the flow rate waveforms. Level of Evidence: 2 Technical Efficacy Stage: 2J. Magn. Reson. Imaging 2020;51:1516–1525.

Aortic Stiffness is Associated with Cardiac Function and Cerebral Blood Flow Pulsatility in Type2 Diabetes Mellitus

&#x0D; &#x0D; &#x0D; &#x0D; &#x0D; &#x0D; &#x0D; &#x0D; &#x0D; &#x0D; &#x0D; &#x0D; &#x0D; &#x0D; &#x0D; &#x0D; &#x0D; &#x0D; &#x0D; &#x0D; &#x0D; &#x0D; &#x0D; Introduction&#x0D; Central hemodynamics has an important role in maintaining appropriate cerebral and other end-organ perfusion and is altered in type2DM. Arterial stiffening is an early phenomenon in patients with type2DM, affecting cardiac function by increasing the cardiac afterload and reducing diastolic coronary artery perfusion, also involving small vessel disease in the brain and subsequent hypoperfusion.&#x0D; Aims and Objectives&#x0D; The aim of present study was to determine whether aortic stiffness affects cardiac function and whether central elastic artery stiffness was associated with cerebral blood flow pulsatility and subsequent, cerebral perfusion in type 2 DM patients.&#x0D; Materials and Method&#x0D; Fifty six patients with type2DM and 60 age-matched healthy volunteers were enrolled. Aortic PWV was measured using non-invasive cardiovascular risk analysis system (Periscope). Cerebral blood flow was measured by using Trans-Cranial Doppler.&#x0D; Results&#x0D; CFPWV of diabetic group showed significantly higher mean values (Group 1=931.00±215.98cm/s Group 2=1241±152.03cm/s) than control subjects (758±151.82). CFPWV was significantly (p value &lt;0.01) increased between two diabetic groups. HbA1c was most significantly correlated to CFPWV (r=1.00, p&lt;0.001) followed by weak correlation between central aortic stiffness quantified by PWV and PI (r=0.5, p&gt;0.01).&#x0D; Conclusion&#x0D; In patients with type2DM, aortic stiffness is significantly associated with pulse pressure, aortic pulse pressure, aortic augmentation pressure as well as with cerebral blood flow pulsatility and subsequent cerebral perfusion, contributing to decreased cardiac function and cerebral hypoperfusion. Aortic PWV and TCD measurement might be useful prognostic marker of cardiac and cerebrovascular disease in type2DM.&#x0D; &#x0D; &#x0D; &#x0D; &#x0D; &#x0D; &#x0D; &#x0D; &#x0D; &#x0D; &#x0D; &#x0D; &#x0D; &#x0D; &#x0D; &#x0D; &#x0D; &#x0D; &#x0D; &#x0D; &#x0D; &#x0D; &#x0D;

Objective Assessment of Beat Quality in Transcranial Doppler Measurement of Blood Flow Velocity in Cerebral Arteries.

Transcranial Doppler (TCD) ultrasonography measures pulsatile cerebral blood flow velocity in the arteries and veins of the head and neck. Similar to other real-time measurement modalities, especially in healthcare, the identification of high-quality signals is essential for clinical interpretation. Our goal is to identify poor quality beats and remove them prior to further analysis of the TCD signal. We selected objective features for this purpose including Euclidean distance between individual and average beat waveforms, cross-correlation between individual and average beat waveforms, ratio of the high-frequency power to the total beat power, beat length, and variance of the diastolic portion of the beat waveform. We developed an iterative outlier detection algorithm to identify and remove the beats that are different from others in a recording. Finally, we tested the algorithm on a dataset consisting of more than 15 h of TCD data recorded from 48 stroke and 34 in-hospital control subjects. We assessed the performance of the algorithm in the improvement of estimation of clinically important TCD parameters by comparing them to that of manual beat annotation. The results show that there is a strong correlation between the two, that demonstrates the algorithm has successfully recovered the clinically important features. We obtained significant improvement in estimating the TCD parameters using the algorithm accepted beats compared to using all beats. Our algorithm provides a valuable tool to clinicians for automated detection of the reliable portion of the data. Moreover, it can be used as a pre-processing tool to improve the data quality for automated diagnosis of pathologic beat waveforms using machine learning.

Aortic Stiffness is Associated with Cardiac Function and Cerebral Blood Flow Pulsatility in Type2 Diabetes Mellitus

Aortic Stiffness is Associated with Cardiac Function and Cerebral Blood Flow Pulsatility in Type2 Diabetes Mellitus

The effect of mild decrement in plasma volume simulating short-duration spaceflight on intracranial pressure

Short-duration spaceflight induces an approximately 10% reduction in plasma volume, which leads to mild volume depletion. In a previous study, we found that mild volume depletion improved dynamic cerebral autoregulation. However, the effect of mild volume depletion on intracranial pressure (ICP) remains unknown. Therefore, we estimated ICP noninvasively (nICP), and calculated two indices relating to ICP, the cerebral artery compliance and the cerebral blood flow pulsatility index (PI), to examine whether ICP would decrease due to a mild decrement in plasma volume. In our previous experiment, fourteen subjects were administered 0.2 mg/kg of furosemide in a supine position to simulate an approximately 10% reduction in plasma volume induced by short-duration spaceflight. We re-analyzed the cerebral blood flow velocity waveform from the middle cerebral artery obtained by transcranial Doppler and the arterial blood pressure waveform at the radial artery obtained by tonometry to estimate nICP and to calculate cerebral artery compliance and PI using mathematical analysis based on an intracranial hydraulic model. All indices were compared between before and after furosemide administration. There were no significant changes in nICP and cerebral artery compliance. However, PI decreased significantly from before to after furosemide administration (0.78 ± 0.10 to 0.74 ± 0.09, p = 0.009). Decreases in ICP were not observed during the 10% reduction in plasma volume. Although cerebral artery compliance did not change, PI decreased significantly. These findings suggest that the impedance of distal cerebral arteries would be reduced in response to mild decreases in plasma volume induced by short-duration spaceflight.

Ultrasound Measures of Brain Pulsatility Correlate with Subcortical Brain Volumes in Healthy Young Adults

Increasing evidence suggests that brain pulsatility is involved in the pathophysiology of various neurological and psychiatric disorders. However, it remains unclear whether high brain pulsatility is damaging to or protective of the brain in normal conditions, and this could depend on the age of the individual and the methods used to measure brain pulsatility. The goal of our study was to investigate associations between subcortical volumes and brain pulsatility as assessed with ultrasound in healthy young adults using both a conventional method (transcranial Doppler pulsatility index [TCD-PI]) and the innovative method of tissue pulsatility imaging (TPI), which allows a high level of detection of small brain movements (micrometers). Twenty-five females aged 18–55 with no history of significant medical disorder underwent magnetic resonance imaging and ultrasound assessment. The volumes of six subcortical regions known to be particularly sensitive to change in cerebral blood flow were measured and compared with brain pulsatility as assessed with TCD-PI and TPI. TCD-PI and TPI measures positively correlated with all subcortical regions, with the caudate nucleus having the strongest association. Linear regressions found that TCD-PI and TPI measures of brain pulsatility explained 16% to 67% of the variance of the subcortical volumes. Our results suggest that a greater pulsatility as assessed with ultrasound in healthy young adults may constitute a protective factor for brain structure. Ultrasound measures of brain pulsatility may be appropriate to provide costless, non-invasive, portable and highly sensitive markers of cerebral blood flow pulsatility related to brain structure.