Pulsatile Blood Research Articles

Measuring global cerebrovascular pulsatility transmission using 4D flow MRI

Pulse wave encephalopathy (PWE) is hypothesised to initiate many forms of dementia, motivating its identification and risk assessment. As candidate pulsatility based biomarkers for PWE, pulsatility index and pulsatility damping have been studied and, currently, do not adequately stratify risk due to variability in pulsatility and spatial bias. Here, we propose a locus-independent pulsatility transmission coefficient computed by spatially tracking pulsatility along vessels to characterise the brain pulse dynamics at a whole-organ level. Our preliminary analyses in a cohort of 20 subjects indicate that this measurement agrees with clinical observations relating blood pulsatility with age, heart rate, and sex, making it a suitable candidate to study the risk of PWE. We identified transmission differences between vascular regions perfused by the basilar and internal carotid arteries attributed to the identified dependence on cerebral blood flow, and some participants presented differences between the internal carotid perfused regions that were not related to flow or pulsatility burden, suggesting underlying mechanical differences. Large populational studies would benefit from retrospective pulsatility transmission analyses, providing a new comprehensive arterial description of the hemodynamic state in the brain. We provide a publicly available implementation of our tools to derive this coefficient, built into pre-existing open-source software.

A real-time method for ventilation and blood pulsatility separation in functional images of the chest

A real-time method for ventilation and blood pulsatility separation in functional images of the chest

Unsteady nano-magnetic drug dispersion for pulsatile Darcy flow through microvessel with drug elimination phenomena

Drug delivery by nano-drug carriers in magnetic drug targeting has shown a promising future in various cancer tumor treatments. The distinguishing properties of nanocarriers, such as small size, selective targeting, controlled release, and others, have made them more effective than the existing conventional treatments. However, several factors affect its delivery. In the present problem, we study the unsteady dispersion of drug-loaded magnetic nanocarriers in microvessels driven by a pulsatile pressure gradient derived from the unsteady Darcy law. Both fluid flow rate and mean velocity are computed analytically. The finite difference method is used to obtain the numerical solution of the solute transport equation, and the results are presented in graphs. Our results show that not only does the Womersley number influence the pulsatility dispersion of nanocarrier particles but also the microvessel permeability, magnetic-tumor distance, magnetization number, and volume fraction of magnetic nanoparticles. We found a drop in drug-loaded magnetic nanocarriers' concentration at the targeted site with decreasing blood pulsatility in the microvessel as portrayed by the Womersley parameter. In contrast, the descending magnetic tumor distance promotes nanoparticle concentration in the tumor tissue. Furthermore, the effects of other parameters, such as permeability, magnetization, volume fraction of magnetic nanoparticles, source term, elimination parameter, and nanocarrier radius, are discussed. To sum up, based on the Womersley frequency parameter coefficient used to describe blood pulsatility resulting from forceful heartbeat, flow pulsatility and nanocarrier particle dispersion are positively correlated, while magnetic-tumor distance is negatively correlated with both pulsatility and nanoparticle concentration.

NEUROVASCULAR COUPLING AND CEREBROVASCULAR HAEMODYNAIMCS ARE MODIFIED BY EXERCISE TRAINING STATUS AT DIFFERENT STAGES OF MATURATION DURING YOUTH.

Neurovascular coupling (NVC) is mediated via nitric oxide signalling, which is independently influenced by sex hormones and exercise training. Whether exercise training differentially modifies NVC pre- vs. post-puberty, where levels of circulating sex hormones will differ greatly within- and between-sexes, remains to be determined. Therefore, we investigated the influence of exercise training-status on resting intra-cranial haemodynamics and NVC at different stages of maturation. Posterior and middle cerebral artery velocities (PCAv and MCAv) and pulsatility index (PCAPI and MCAPI) were assessed via trans-cranial Doppler ultrasound at rest and during visual NVC stimuli. N=121 exercise-trained (males: n=32, females: n=32) and untrained (males: n=28, females: n=29) participants were characterised as pre- (males: n=33, females: n=29) or post- (males: n=27, females: n=32) peak height velocity (PHV). Exercise-trained youth demonstrated higher resting MCAv (P=0.010). Maturity- and training-status did not affect the ∆PCAv and ∆MCAv during NVC. However, pre-PHV untrained males (19.4±13.5 vs. 6.8±6.0%; P≤0.001) and females (19.3±10.8 vs. 6.4±7.1%; P≤0.001) had a higher ∆PCAPI during NVC than post-PHV untrained counterparts, while the ∆PCAPI was similar in pre- and post-PHV trained youth. Pre-PHV untrained males (19.4±13.5 vs. 7.9±6.0%; P≤0.001) and females (19.3±10.8 vs 11.1±7.3%; P=0.016) also had a larger ∆PCAPI than their pre-PHV trained counterparts during NVC, but the ∆PCAPI was similar in trained and untrained post-PHV youth. Collectively, our data indicate that exercise training elevates regional cerebral blood velocities during youth, but training-mediated adaptations in NVC are only attainable during early stages of adolescence. Therefore, childhood provides a unique opportunity for exercise-mediated adaptations in NVC.

Influence of pulsating intracardiac blood flow on radiofrequency catheter ablation outcomes in an anatomy-based atrium model

Background Highly consistent cardiac ablation outcomes through radiofrequency catheter ablation (RFCA) under pulsatile and constant flow profiles (PP&CP) of intracardiac blood were previously indicated by computer modeling, with simplified geometry and lossless receipt of inflow for ablation catheters. This study aimed to further investigate the effects of intracardiac blood pulsatility in an anatomy-based atrium model. Methods Four pulmonary veins were blood inflows at 10 mm Hg. The mitral valve was the outflow, with PP based on pulsatile velocity curve from clinical measurements, and CP was obtained by averaging the velocity curve under PP over an ablation time of 30 s. A numerical comparison between ablation results under PP and CP, without experimental validation, was performed. Results Temperature fluctuations persisted in mid-myocardium, and most clearly in blood and endocardium under PP. At a constant power of 20 W, marked differences in ablation outcome between PP and CP occurred in the middle of unilateral pulmonary veins and the posterior wall of the left atrium (LA) where the blood velocities were significantly decreased under CP. The mid-myocardial, blood and endocardial temperatures, as well as the effective lesion volume at the former position, were decreased by 4.1%, 15%, 13.6%, and 13.8%, respectively under PP. The extents for the latter position were 11%, 22%, 22.5%, and 55.6%, respectively. Conclusion Intracardiac flow pulsatility causes a greater reduction in blood and endocardial temperatures at ablation sites away from the main bloodstream, effective cooling of which is more likely to rely on blood velocities approaching peak PP values.

Association Between Homocysteine, Frailty and Biomechanical Response of the CNS in NPH-Suspected Patients.

Frailty is a geriatric syndrome that combines physiological decline, disruptions of homeostatic mechanisms across multiple physiologic systems and thus, strong vulnerability to further pathological stress. Previously, we provided the first evidence that increased risk of poor health outcomes, as quantified by a frailty index (FI), is associated with an alteration of the central nervous system (CNS) biomechanical response to blood pulsatility. In this study, we explored correlation between 14 biological parameters, the CNS elastance coefficient and FI. We included 60 adults (52-92 years) suspected of normal pressure hydrocephalus and presenting with markers of multiple coexisting brain pathologies, including Parkinson disease, Alzheimer disease, and vascular dementia. We showed that the homocysteine (Hcy) level was independently and positively associated with both the FI and the CNS elastance coefficient (adjusted R² of 10% and 6%). We also demonstrated that creatinine clearance and folate level were independently associated with Hcy level. Based on previous literature results describing the involvement of Hcy in endothelial dysfunction, glial activation, and neurodegeneration, we discuss how Hcy could contribute to the altered biomechanical response of the CNS and frailty.

Optical Coherence Tomography Based Biomechanical Fluid-Structure Interaction Analysis of Coronary Atherosclerosis Progression.

In this paper, we present a complete workflow for the biomechanical analysis of atherosclerotic plaque in the coronary vasculature. With atherosclerosis as one of the leading causes of global death, morbidity and economic burden, novel ways of analyzing and predicting its progression are needed. One such computational method is the use of fluid-structure interaction (FSI) to analyze the interaction between the blood flow and artery/plaque domains. Coupled with in vivo imaging, this approach could be tailored to each patient, assisting in differentiating between stable and unstable plaques. We outline the three-dimensional reconstruction process, making use of intravascular Optical Coherence Tomography (OCT) and invasive coronary angiography (ICA). The extraction of boundary conditions for the simulation, including replicating the three-dimensional motion of the artery, is discussed before the setup and analysis is conducted in a commercial finite element solver. The procedure for describing the highly nonlinear hyperelastic properties of the artery wall and the pulsatile blood velocity/pressure is outlined along with setting up the system coupling between the two domains. We demonstrate the procedure by analyzing a non-culprit, mildly stenotic, lipid-rich plaque in a patient following myocardial infarction. Established and emerging markers related to atherosclerotic plaque progression, such as wall shear stress and local normalized helicity, respectively, are discussed and related to the structural response in the artery wall and plaque. Finally, we translate the results to potential clinical relevance, discuss limitations, and outline areas for further development. The method described in this paper shows promise for aiding in the determination of sites at risk of atherosclerotic progression and, hence, could assist in managing the significant death, morbidity, and economic burden of atherosclerosis.

Arterial Function after a 246 km Ultra-marathon Running Race.

There is little research about the effects of ultra-endurance exercise on arterial morphological and functional properties. The aim was to assess the acute changes of the carotid-femoral pulse wave velocity and carotid doppler-derived parameters following an ultra-marathon race as well as the intima-media thickness of the carotid artery in ultra-marathon runners. Twenty athletes were examined at baseline and within 10 mins after a 246 km running race. Measurements included carotid-femoral pulse wave velocity, peak-systolic and end-diastolic velocities of carotid artery blood flow, pulsatility and resistivity indices and blood biochemical parameters. The intima-media thickness of the right and left carotid artery was measured before the race. Arterial stiffness and carotid artery intima media thickness at rest remained within known normal limits. The ultra-marathon race significantly increased carotid-femoral pulse wave velocity by 22.6% and pulsatility index by 10.2%. There was a decrease in body weight by 3.35% and an increase of all biochemical markers of muscle damage after the race. Additionally, C-reactive protein was correlated with both pulsatility and resistivity indices post-race. This study shows that immediately after a 246 km ultra-marathon running race, acute increase of arterial stiffness and vascular resistance were evident. The carotid artery thickness of ultra-marathon runners was within normal range.

Natural shear wave imaging using vocal tract vibrations: Introducing vocal passive elastography (V-PE) to thyroid elasticity mapping

We present a shear wave elastography (SWE) approach for thyroid characterization that is inspired by passive elastography, which extracts elasticity from the natural vibrations in living tissues that are caused by cardiac motion, blood pulsatility, and muscle activity. On thyroid, this physiological noise is mainly due to the carotid pulsation, which is in the 1–10 Hz bandwidth and is located right next to the gland. In order to decrease the shear wavelength and increase the signal to noise ratio, we propose to create in the thyroid a complex shear wave field by using natural vocal tract vibrations. The nature of the sound can be easily modified to be narrow or broad band, with small or large amplitude. Using correlation-based algorithm and a sound sustained at 150 Hz, we have developed an innovative technique using ultrasound, allowing us to compute a 2D shear wave velocity map, superposed onto a B-mode ultrasound image of a volunteer's thyroid. Using our vocal passive elastography method, shear wave velocity was measured at every point within a mask surrounding the thyroid with a pixel resolution of 150 × 150 μm2. The mean shear wave speed value measured is 3.2 m/s, taking its value from 0.7 m/s to 8.8 m/s. The values obtained were in good agreement with comparative shear wave elastography (SWE) measurements.

Effect of intracardiac blood flow pulsatility during radiofrequency cardiac ablation: computer modeling study

Purpose To assess the effect of intracardiac blood flow pulsatility on tissue and blood distributions during radiofrequency (RF) cardiac ablation (RFCA). Methods A three-dimensional computer model was used to simulate constant power ablations with an irrigated-tip electrode and three possible catheter orientations (perpendicular, parallel and 45°). Continuous flow and three different pulsatile flow profiles were considered, with four average blood velocity values: 3, 5.5, 8.5 and 24.4 cm/s. The 50 °C contour was used to assess thermal lesion size. Results The differences in lesion size between continuous flow and the different pulsatile flow profiles were always less than 1 mm. As regards maximum tissue temperature, the differences between continuous and pulsatile flow were always less than 1 °C, with slightly higher differences in maximum blood temperature, but never over 6 °C. While the progress of maximum tissue temperature was identical for continuous and pulsatile flow, maximum blood temperature with the pulsatile profile showed small amplitude oscillations associated with blood flow pulsatility. Conclusions The findings show that intracardiac blood pulsatility has a negligible effect on lesion size and a very limited impact on maximum tissue and blood temperatures, which suggests that future experimental studies based on ex vivo or in silico models can ignore pulsatility in intracardiac blood flow.

Imaging video plethysmography shows reduced signal amplitude in glaucoma patients in the area of the microvascular tissue of the optic nerve head

PurposeTo measure parameters of the cardiac cycle-induced pulsatile light absorption signal (plethysmography signal) of the optic nerve head (ONH) and to compare parameters between normal subjects and patients with different stages of glaucoma.Patients and methodsA recently developed video ophthalmoscope was used to acquire short video sequences (10 s) of the ONH. After image registration and trend correction, the pulsatile changing light absorption at the ONH tissue (excluding large vessels) was calculated. The changing light absorption depends on the pulsatile changing blood volume. Various parameters, including peak amplitude, steepness, time-to-peak, full width at half maximum (FWHM), and pulse duration, were calculated for averaged individual pulses (heartbeats) of the plethysmography signal. This method was applied to 19 healthy control subjects and 91 subjects with ocular hypertension, as well as different stages of primary open-angle glaucoma (17 subjects with ocular hypertension, 24 with preperimetric glaucoma, and 50 with perimetric glaucoma).ResultsCompared to the normal subjects, significant reductions (p < 0.001) in peak amplitude and steepness were observed in the group of perimetric glaucoma patients, but no significant difference was found for time-to-peak, FWHM, and pulse duration. Peak amplitude and steepness showed high correlations with RNFL thickness (p < 0.001).ConclusionsThe presented low-cost video-ophthalmoscope permits measurement of the plethysmographic signal of the ONH tissue and calculation of different blood flow-related parameters. The reduced values of the amplitude and steepness parameters in perimetric glaucoma patients suggest decreased ONH perfusion and blood volume. This outcome is in agreement with results from other studies using OCT angiography and laser speckle flowgraphy, which confirm reduced capillary density in these patients.Registration site: www.clinicaltrials.gov, Trial registration number: NCT00494923

Understanding the interplay between baroreflex gain, low frequency oscillations, and pulsatility in the neural baroreflex

The neural baroreflex, which regulates mean arterial pressure (MAP) via the action of the brain, consists of baroreceptors which measure MAP, and actuators that can produce a change in MAP, such as the heart and parts of the peripheral resistance containing innervated smooth muscle. The brain is the controlling unit, maintaining an appropriate MAP in spite of various disturbances. Under certain circumstances, including haemorrhage and other states of distress, the gain of the neural baroreflex can change, causing low frequency (LF) oscillations (sometimes termed Mayer waves) in blood pressure (BP). Though their purpose is unclear, the origins of these LF oscillations has previously been explained via a nonlinear feedback model, though focusing on the peripheral resistance as an MAP actuator only. The present paper now includes analytical and simulation results explaining the LF oscillation phenomenon for the full neural baroreflex, containing both peripheral resistance (PR) and cardiac branches. However, the main contribution of the paper is to examine the effect of blood pulsatility, or a lack of pulsatility, on the neural baroreflex, and how it's effect can manifest in the presence of LF oscillations. This may have importance in cases where pulsatility is reduced (for example where left-ventricular assist devices are present), or completely absent (for example in turbine-based artificial hearts).

Ocular Blood Volume Index Based on Scattering Properties of Retinal Vessels Using Spectral Domain Optical Coherence Tomography

ABSTRACTIntroduction: The evaluation of retinal vessels and the retinal blood flow is important for ocular diseases. We introduce a spectral domain optical coherence tomography (SD-OCT) based method for facilitating a retinal blood vessel analysis using the scattering properties of retinal vessels. The intensity of the distal shadow of vessels caused by the scattered signal is measured, correlated with the pulsatile ocular blood flow (POBF), and its repeatability is analyzed.Methods: About 20 eyes of 20 healthy, young participants (mean age 23.15 years, standard deviation 2.3 years) were included in the analysis. Participants underwent ophthalmic diagnostics including three repeated SD-OCT examinations and measurement of POBF. The vessel shadow intensity analysis is based on peripapillary SD-OCT scans and automatically analyses the intensity of the distal vessel shadow compared to its surroundings.Results: The distal shadow of arteries in SD-OCT scans correlated with the POBF (r = 0.647, p = 0.002). Furthermore, the shadow intensity correlated with the established morphological arterio-venous ratio. The evaluation of repeatability was performed using the interclass correlation coefficient (ICC), showing good repeatability for individual vessels (ICC = 0.825) and arteries (ICC = 0.820).Conclusions: In summary, we indicate that the scattering properties of retinal vessels in SD-OCT images might correlate with the vessel morphology and for retinal arteries with the retinal blood flow volume as well. Further studies are needed to establish this method’s sensitivity and specificity in participants with retinal and cardiovascular diseases.

Coronary Blood Flow Is Increased in RV Hypertrophy, but the Shape of Normalized Waves Is Preserved Throughout the Arterial Tree.

A pulsatile hemodynamic analysis was carried out in the right coronary arterial (RCA) tree of control and RV hypertrophy (RVH) hearts. The shape of flow and wall shear stress (WSS) waves was hypothesized to be maintained throughout the RCA tree in RVH (i.e., similar patterns of normalized flow and WSS waves in vessels of various sizes). Consequently, we reconstructed the entire RCA tree down to the first capillary bifurcation of control and RVH hearts based on measured morphometric data. A Womersley-type model was used to compute the flow and WSS waves in the tree. The hemodynamic parameters obtained from experimental measurements were incorporated into the numerical model. Given an increased number of arterioles, the mean and amplitude of flow waves at the inlet of RCA tree in RVH was found to be two times larger than that in control, but no significant differences (p > 0.05) were found in precapillary arterioles. The increase of stiffness in RCA of RVH preserved the shape of normalized flow and WSS waves, but increased the PWV in coronary arteries and reduced the phase angle difference for the waves between the most proximal RCA and the most distal precapillary arteriole. The study is important for understanding pulsatile coronary blood flow in ventricular hypertrophy.

FEATURES OF DIURNAL BLOOD PRESSURE PROFILE, ARTERIAL STIFFNESS AND CENTRAL AORTIC PRESSURE IN PATIENTS WITH ARTERIAL HYPERTENSION AND PREDIABETES

Aim. To assess the features of diurnal blood profile, arterial stiffness and central aortic in patients with arterial hypertension (AH) and prediabetes. Materials and methods. The study included 118 patients with AH, 38 without prediabetes, 80 with prediabetes, 48 of them patients with impaired fasting glucose and 32 patients with impaired glucose tolerance. Prediabetes was determined by the results of an oral glucose tolerance test. All patients underwent 24-hour blood monitoring the main parameters of arterial stiffness and central aortic were determined using the BPLab Vasotens complex of OOO «Petr Telegin» (Russia). Results. The obtained data showed that in patients with hypertension and prediabetes there were recorded increased levels of systolic and pulsatile blood in the brachial artery and aorta, a more pronounced pressure load was detected compared to patients without prediabetes. At night, the level of diastolic blood in the brachial artery and aorta, the diastolic time index was higher than in patients with AH without prediabetes. Pathological type of the non-dipper curve was detected 2.5 times more often in patients with AH and prediabetes. Moreover, the pulse wave velocity, the augmentation index in the brachial artery and aorta characterizing the stiffness of the vessel wall were significantly higher in hypertensive patients with prediabetes. Conclusion. Thereby, in patients with AH in combination with prediabetes, unlike patients without prediabetes, there were more pronounced changes in the parameters of the diurnal blood profile, arterial stiffness and central aortic including the pulse wave velocity, the augmentation index and pulsatile which are known to be sensitive indicators of target organ damage and are associated with an increased risk of developing cardiovascular and cerebrovascular complications.

BS09. Latency of the skin vasomotor reflex of the finger to an electrical stimulus to the median nerve

Introduction An electrical pulse to a sensory or mixed peripheral nerve elicits activation of the skin sympathetic response (SSR) and the latency and the duration of the response can thereby be attained. We reasoned that an electrical stimulus may also activate the sympathetic C fibers to the skin blood vessels of the hand and the latency and duration of the skin vasomotor reflexes (VSRs) could also be obtained. Methods We evaluated 30 healthy subjects aged 20–35 years. The subjects had no history of peripheral or central nervous system disease. A 0.5 ms pulse with an intensity four times the threshold was delivered to the right median nerve at the wrist. The stimulus was given at random every 40–60 s. We gave three stimuli to each subject. We recorded the SSR in the palm of the left hand and the VSRs in the tip of the left index finger. The pulsatile skin blood flow (SBF) was recorded with an infrared photoplethysmograph located at the pad of the right index finger. Results All subjects displayed both a SSR and a VSR. The mean latency of the SSR was 1.3 ± 0.3 s with a mean duration of 5.9 ± 0.6 s. The mean latency of the VSR (first decreased pulse) was 3 ± 0.5 s and the mean duration of the VSR was 9.5 ± 2 s. The VSR had a longer latency and lasted more than the SSR. The decrease in the amplitude of the SBF had a mean or 50 ± 8 per cent of the basal flow. Conclusion The SSR and VSRs reflect sympathetic C fibers traffic to the eccrine sweat glands and the skin microcirculation, respectively. The longer latency of the VSRs, compared to the SSR, may reflect a slower conduction time of the sympathetic C fibers to the skin blood vessels or be the consequence of the physiological properties of the response of the neuro-effector junction of the skin blood vessels. This technique allows a quantitative measurement of the latency and duration of the VSRs and is potentially useful for the study of peripheral and central autonomic disorders.

AB091. A novel method for the measurement of pulsatile choroidal blood flow based on video-rate OCT imaging and automated segmentation of the choroid: description and reproducibility

AB091. A novel method for the measurement of pulsatile choroidal blood flow based on video-rate OCT imaging and automated segmentation of the choroid: description and reproducibility

AB036. Pulsatile choroidal blood flow (PCBF) in the glaucoma spectrum—preliminary results obtained with a novel optical method

AB036. Pulsatile choroidal blood flow (PCBF) in the glaucoma spectrum—preliminary results obtained with a novel optical method

A time-dependent non-Newtonian extension of a 1D blood flow model

Blood pulsatility, aneurysms, stenoses and general low shear stress hemodynamics enhance non-Newtonian blood effects which generate local changes in the space-time evolution of the blood pressure, flow rate and cross-sectional area of elastic vessels. Even though these local changes are known to cause global unexpected hemodynamical behaviors, all one-dimensional (1D) blood flow models are built under Newtonian fluid hypothesis.In this work, we present a time-dependent non-Newtonian extension of a 1D blood flow model, able to describe local space-time variations of the viscous behavior of blood. The rheological model is based on a simplified Maxwell viscoelastic equation for the shear stress with structure dependent coefficients. We compare the numerical predictions of the 1D non-Newtonian model to experimental rheological data available in the literature. Specifically, we explore four well documented shear stress protocols and we show that the results predicted by the 1D non-Newtonian model in a single artery accurately compare, both qualitatively and quantitatively, to the steady and unsteady shear stresses measured experimentally. We then use the 1D non-Newtonian model to compute the flow in idealized healthy and pathological symmetric and asymmetric networks of increasing size. We show that aggregation occurs in such networks occurs, leading to non-Newtonian blood behaviors especially in the presence of pathologies.This non-Newtonian extension of a 1D blood flow model will be useful in the future to improve our understanding of the large-scale hemodynamics in micro- and macro-circulation networks.

Application value of regional cerebral oxygenation monitoring in early neonates

Regional cerebral oxygenation(rSO2) is widely used in the monitoring of cerebral blood flow, which is not affected by temperature and pulsatile blood flow.rSO2 monitoring gives us a new way to monitor the oxygenation status of brain regions.But, currently, rSO2 research in the neonates is rare.This paper summarized the different pathological conditions influence on early neonatal rSO2, clarified the important clinical significance of monitoring of neonatal rSO2 and the future application was prospected. Key words: Neonate; Early postnatal; Regional cerebral oxygenation