Wave Intensity Analysis Research Articles

Non-invasive assessment of ventriculo-arterial coupling using aortic wave intensity analysis combining central blood pressure and phase-contrast cardiovascular magnetic resonance.

Wave intensity analysis (WIA) in the aorta offers important clinical and mechanistic insight into ventriculo-arterial coupling, but is difficult to measure non-invasively. We performed WIA by combining standard cardiovascular magnetic resonance (CMR) flow-velocity and non-invasive central blood pressure (cBP) waveforms. Two hundred and six healthy volunteers (age range 21-73 years, 47% male) underwent sequential phase contrast CMR (Siemens Aera 1.5 T, 1.97 × 1.77 mm2, 9.2 ms temporal resolution) and supra-systolic oscillometric cBP measurement (200 Hz). Velocity (U) and central pressure (P) waveforms were aligned using the waveform foot, and local wave speed was calculated both from the PU-loop (c) and the sum of squares method (cSS). These were compared with CMR transit time derived aortic arch pulse wave velocity (PWVtt). Associations were examined using multivariable regression. The peak intensity of the initial compression wave, backward compression wave, and forward decompression wave were 69.5 ± 28, -6.6 ± 4.2, and 6.2 ± 2.5 × 104 W/m2/cycle2, respectively; reflection index was 0.10 ± 0.06. PWVtt correlated with c or cSS (r = 0.60 and 0.68, respectively, P < 0.01 for both). Increasing age decade and female sex were independently associated with decreased forward compression wave (-8.6 and -20.7 W/m2/cycle2, respectively, P < 0.01) and greater wave reflection index (0.02 and 0.03, respectively, P < 0.001). This novel non-invasive technique permits straightforward measurement of wave intensity at scale. Local wave speed showed good agreement with PWVtt, and correlation was stronger using the cSS than the PU-loop. Ageing and female sex were associated with poorer ventriculo-arterial coupling in healthy individuals.

Large vessels as a tree of transmission lines incorporated in the CircAdapt whole-heart model: A computational tool to examine heart-vessel interaction.

We developed a whole-circulation computational model by integrating a transmission line (TL) model describing vascular wave transmission into the established CircAdapt platform of whole-heart mechanics. In the present paper, we verify the numerical framework of our TL model by benchmark comparison to a previously validated pulse wave propagation (PWP) model. Additionally, we showcase the integrated CircAdapt–TL model, which now includes the heart as well as extensive arterial and venous trees with terminal impedances. We present CircAdapt–TL haemodynamics simulations of: 1) a systemic normotensive situation and 2) a systemic hypertensive situation. In the TL–PWP benchmark comparison we found good agreement regarding pressure and flow waveforms (relative errors ≤ 2.9% for pressure, and ≤ 5.6% for flow). CircAdapt–TL simulations reproduced the typically observed haemodynamic changes with hypertension, expressed by increases in mean and pulsatile blood pressures, and increased arterial pulse wave velocity. We observed a change in the timing of pressure augmentation (defined as a late-systolic boost in aortic pressure) from occurring after time of peak systolic pressure in the normotensive situation, to occurring prior to time of peak pressure in the hypertensive situation. The pressure augmentation could not be observed when the systemic circulation was lumped into a (non-linear) three-element windkessel model, instead of using our TL model. Wave intensity analysis at the carotid artery indicated earlier arrival of reflected waves with hypertension as compared to normotension, in good qualitative agreement with findings in patients. In conclusion, we successfully embedded a TL model as a vascular module into the CircAdapt platform. The integrated CircAdapt–TL model allows detailed studies on mechanistic studies on heart-vessel interaction.

The speed, reflection and intensity of waves propagating in flexible tubes with aneurysm and stenosis: Experimental investigation.

A localized stenosis or aneurysm is a discontinuity that presents the pulse wave produced by the contracting heart with a reflection site. However, neither wave speed (c) in these discontinuities nor the size of reflection in relation to the size of the discontinuity has been adequately studied before. Therefore, the aim of this work is to study the propagation of waves traversing flexible tubes in the presence of aneurysm and stenosis in vitro. We manufactured different sized four stenosis and four aneurysm silicone sections, connected one at a time to a flexible ‘mother’ tube, at the inlet of which a single semi-sinusoidal wave was generated. Pressure and velocity were measured simultaneously 25 cm downstream the inlet of the respective mother tube. The wave speed was measured using the PU-loop method in the mother tube and within each discontinuity using the foot-to-foot technique. The stenosis and aneurysm dimensions and c were used to determine the reflection coefficient (R) at each discontinuity. Wave intensity analysis was used to determine the size of the reflected wave. The reflection coefficient increased with the increase and decrease in the size of the aneurysm and stenosis, respectively. c increased and decreased within stenosis and aneurysms, respectively, compared to that of the mother tube. Stenosis and aneurysm induced backward compression and expansion waves, respectively; the size of which was related to the size of the reflection coefficient at each discontinuity, increases with smaller stenosis and larger aneurysms. Wave speed is inversely proportional to the size of the discontinuity, exponentially increases with smaller stenosis and aneurysms and always higher in the stenosis. The size of the compression and expansion reflected wave depends on the size of R, increases with larger aneurysms and smaller stenosis.

A One-Dimensional Hemodynamic Model of the Coronary Arterial Tree.

One-dimensional (1D) hemodynamic models of arteries have increasingly been applied to coronary circulation. In this study, we have adopted flow and pressure profiles in Olufsen's 1D structured tree as coronary boundary conditions, with terminals coupled to the dynamic pressure feedback resulting from the intra-myocardial stress because of ventricular contraction. We model a trifurcation structure of the example coronary tree as two adjacent bifurcations. The estimated results of blood pressure and flow rate from our simulation agree well with the clinical measurements and published data. Furthermore, the 1D model enables us to use wave intensity analysis to simulate blood flow in the developed coronary model. Six characteristic waves are observed in both left and right coronary flows, though the waves' magnitudes differ from each other. We study the effects of arterial wall stiffness on coronary blood flow in the left circumflex artery (LCX). Different diseased cases indicate that distinct pathological reactions of the cardiovascular system can be better distinguished through Wave Intensity analysis, which shows agreement with clinical observations. Finally, the feedback pressure in terminal vessels and measurement deviation are also investigated by changing parameters in the LCX. We find that larger feedback pressure increases the backward wave and decreases the forward one. Although simplified, this 1D model provides new insight into coronary hemodynamics in healthy and diseased conditions. We believe that this approach offers reference resources for studies on coronary circulation disease diagnosis, treatment and simulation.

Wave Intensity Analysis of Right Ventricular Function during Pulsed Operation of Rotary Left Ventricular Assist Devices.

Changing the speed of left ventricular assist devices (LVADs) cyclically may be useful to restore aortic pulsatility; however, the effects of this pulsation on right ventricular (RV) function are unknown. This study investigates the effects of direct ventricular interaction by quantifying the amount of wave energy created by RV contraction when axial and centrifugal LVADs are used to assist the left ventricle. In 4 anesthetized pigs, pressure and flow were measured in the main pulmonary artery and wave intensity analysis was used to identify and quantify the energy of waves created by the RV. The axial pump depressed the intensity of waves created by RV contraction compared with the centrifugal pump. In both pump designs, there were only minor and variable differences between the continuous and pulsed operation on RV function. The axial pump causes the RV to contract with less energy compared with a centrifugal design. Diminishing the ability of the RV to produce less energy translates to less pressure and flow produced, which may lead to LVAD-induced RV failure. The effects of pulsed LVAD operation on the RV appear to be minimal during acute observation of healthy hearts. Further study is necessary to uncover the effects of other modes of speed modulation with healthy and unhealthy hearts to determine if pulsed operation will benefit patients by reducing LVAD complications.

Impact of pulmonary endarterectomy on pulmonary arterial wave propagation and reservoir function.

High wave speed and large wave reflection in the pulmonary artery have previously been reported in patients with chronic thromboembolic pulmonary hypertension (CTEPH). We assessed the impact of pulmonary endarterectomy (PEA) on pulmonary arterial wave propagation and reservoir function in patients with CTEPH. Right heart catheterization was performed using a combined pressure and Doppler flow sensor-tipped guidewire to obtain simultaneous pressure and flow velocity measurements in the pulmonary artery in eight patients with CTEPH before and 3 mo after PEA. Wave intensity and reservoir-excess pressure analyses were then performed. Following PEA, mean pulmonary arterial pressure (PAPm; ∼49 vs. ∼32 mmHg), pulmonary vascular resistance (PVR; ∼11.1 vs. ∼5.1 Wood units), and wave speed (∼16.5 vs. ∼8.1 m/s), i.e., local arterial stiffness, markedly decreased. The changes in the intensity of the reflected arterial wave and wave reflection index (pre: ∼28%; post: ∼22%) were small, and patients post-PEA with and without residual pulmonary hypertension (i.e., PAPm ≥ 25 mmHg) had similar wave reflection index (∼20 vs. ∼23%). The reservoir and excess pressure decreased post-PEA, and the changes were associated with improved right ventricular afterload, function, and size. In conclusion, although PVR and arterial stiffness decreased substantially following PEA, large wave reflection persisted, even in patients without residual pulmonary hypertension, indicating lack of improvement in vascular impedance mismatch. This may continue to affect the optimal ventriculoarterial interaction, and further studies are warranted to determine whether this contributes to persistent symptoms in some patients.NEW & NOTEWORTHY We performed wave intensity analysis in the pulmonary artery in patients with chronic thromboembolic pulmonary hypertension before and 3 mo after pulmonary endarterectomy. Despite substantial reduction in pulmonary arterial pressures, vascular resistance, and arterial stiffness, large pulmonary arterial wave reflection persisted 3 mo postsurgery, even in patients without residual pulmonary hypertension, suggestive of lack of improvement in vascular impedance mismatch.

Quantification of Pulsed Operation of Rotary Left Ventricular Assist Devices with Wave Intensity Analysis.

The current generation of left ventricular assist devices (LVADs) provides continuous flow and has the capacity to reduce aortic pulsatility, which may be related to a range of complications associated with these devices. Pulsed LVAD operation using speed modulation presents a mechanism to restore aortic pulsatility and potentially mitigate complications. We sought to investigate the interaction of axial and centrifugal LVADs with the LV and quantify the effects of continuous and pulsed LVAD operations on LV generated wave patterns under different physiologic conditions using wave intensity analysis (WIA) method. The axial LVAD created greater wave intensity associated with LV relaxation. In both LVADs, there were only minor and variable differences between the continuous and pulsed operations. The response to physiologic stress was preserved with LVAD implantation as wave intensity increased marginally with volume loading and significantly with infusion of norepinephrine. Our findings and a new approach of investigating aortic wave patterns based on WIA are expected to provide useful clinical insights to determine the ideal operation of LVADs.

Carotid artery wave intensity in mid- to late-life predicts cognitive decline: the Whitehall II study.

AimsExcessive arterial pulsatility may contribute to cognitive decline and risk of dementia via damage to the fragile cerebral microcirculation. We hypothesized that the intensity of downstream-travelling pulsatile waves measured by wave intensity analysis in the common carotid artery during mid- to late-life would be associated with subsequent cognitive decline.Methods and resultsDuplex Doppler ultrasound was used to calculate peak forward-travelling compression wave intensity (FCWI) within the common carotid artery in 3191 individuals [mean ± standard deviation (SD), age = 61 ± 6 years; 75% male] assessed as part of the Whitehall II study in 2003–05. Serial measures of cognitive function were taken between 2002–04 and 2015–16. The relationship between FCWI and cognitive decline was adjusted for sociodemographic variables, genetic and health-related risk factors, and health behaviours. Mean (SD) 10-year change in standardized global cognitive score was -0.39 (0.18). Higher FCWI at baseline was associated with accelerated cognitive decline during follow-up [difference in 10-year change of global cognitive score per 1 SD higher FCWI = −0.02 (95% confidence interval −0.04 to −0.00); P = 0.03]. This association was largely driven by cognitive changes in individuals with the highest FCWI [Q4 vs. Q1–Q3 = −0.05 (−0.09 to −0.01), P = 0.01], equivalent to an age effect of 1.9 years. Compared to other participants, this group was ∼50% more likely to exhibit cognitive decline (defined as the top 15% most rapid reductions in cognitive function during follow-up) even after adjustments for multiple potential confounding factors [odds ratio 1.49 (1.17–1.88)].ConclusionElevated carotid artery wave intensity in mid- to late-life predicts faster cognitive decline in long-term follow-up independent of other cardiovascular risk factors.

Altered Wave Reflection in Patients with Duchenne Muscular Dystrophy (DMD)

Cardiovascular complications are progressive in Duchenne Muscular Dystrophy (DMD) with cardiomyopathy/heart failure characterized as the leading cause of death in these young patients. Increased wave reflection augments pulsatile load on the heart and is known to be predictive of new onset heart failure in adults. Patients with DMD may have higher wave reflection as measured by augmentation index (AIx) but this has yet to be comprehensively studied in these patients. Given the incidence of dilated cardiomyopathy in DMD, a better understanding of the pulsatile load and ventricular‐arterial interactions could provide valuable insight into disease progression and management.PURPOSEThus, the purpose of this study was to characterize wave reflectance and pulsatile load with wave separation and wave intensity analyses in a group of patients with DMD compared to typically‐developing controls.METHODSAssessments were performed on 23 boys (10 DMD and 13 typically‐developing controls (CON)) between the ages of 8 and 18 years. A brachial artery oscillometric‐cuff device was used to record brachial artery pressure waveforms that were calibrated and synthesized to central pressure waves using a generalized transfer function. Pulse wave analysis (PWA) was performed to determine central blood pressures and AIx. Wave separation analysis was also used to determine the relative contributions of forward (Pf) and backward (Pb) pressure waves and reflection magnitude (RM=Pb/Pf).RESULTSPatients with DMD had a significantly higher augmentation index (AI) as measured by PWA (DMD: 21.2 ± 5 vs CON: 0.9 ± 2 %, p&lt;0.05) but no difference in central pulse pressure (DMD: 34 ± 3 vs CON: 30 ± 1 mmHg). There was also no difference in Pf between groups (DMD: 27 ± 2 vs CON: 26 ± 2 mmHg). However, both Pb (DMD: 14.0 ± 1 vs CON: 11.7 ± 1 mmHg, p&lt;0.05) and RM (DMD: 52.0 ± 1 vs CON: 43.5 ± 2 %, p&lt;0.05) were significantly elevated in the children with DMD.CONCLUSIONThese preliminary data suggest that patients with DMD have higher wave reflection, which may indicate increased arterial stiffness and increased pulsatile load on the heart.Support or Funding InformationGrant support: NIH P20GM113125This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Vascular Contributions to Intracranial Hemodynamic Pulsatility and Pulsatile Dampening in Adults

The brain is a high‐flow organ that requires continuous, non‐pulsatile blood flow. Intracranial blood flow pulsatility depends on the ability of the large elastic arteries and cerebrovasculature to dampen pulsatile hemodynamics transmitted from the heart. Aging is accompanied by large artery stiffening and reductions in cerebrovascular dampening, ultimately increasing intracranial pulsatility. It is unclear what hemodynamic forces may be responsible for these age‐related changes in the transmission and dampening of intracranial pulsatility across the lifespan. The purpose of this study was to explore hemodynamic contributors to intracranial pulsatility and pulsatile dampening in 244 adults between 35–85 yr (49% female, 56±12 yr, 27±4.2 kg/m2). Intracranial pulsatile dampening was calculated as the ratio between common carotid and middle cerebral artery (MCA) blood velocity pulsatility index (PI) measured via Doppler. Carotid ultrasound and wave intensity analysis were used to measure carotid diameter, forward compression wave energy (W1), wave reflection index (RIx), and forward traveling expansion wave (W2). Aortic (carotid‐femoral) and carotid pulse wave velocity (PWV) were assessed via tonometry and carotid ultrasound, respectively, and expressed as a ratio (aortic:carotid PWV). Carotid pulse pressure (PP) was measured via tonometry. Multiple regression was used to examine the contributions of 1) age, sex, BMI, aortic:carotid PWV, carotid diameter, PP, and W1 to intracranial pulsatility (MCA PI); and 2) age, sex, BMI, aortic:carotid PWV, carotid diameter, RIx, and W2 to intracranial pulsatile dampening. After entering all variables, significant predictors of MCA PI included age (β,0.44), aortic:carotid PWV (β,0.16), PP (β,0.29), and W1 (β,0.20; R2=0.50, p&lt;0.01). Significant predictors of intracranial pulsatile dampening included age (β,−0.47), sex (β,−0.43), and RIx (β,0.26; R2=0.53, p&lt;0.01). Our data confirms recent literature linking age, exaggerated stiffening of the aorta compared to carotid artery, and extracranial hemodynamics to intracranial pulsatility in the MCA. Moreover, our findings indicate age, sex, and wave reflections in the carotid artery impact the ability of the cerebrovasculature to dampen transmission of pulsatile hemodynamics. These data highlight the potential utility of the large extracranial arteries as therapeutic targets to reduce intracranial pulsatility and importance of carotid wave reflections in dampening intracranial pulsatility.Support or Funding InformationFunded in part by an ACSM Foundation Research Grant (WKL), AHA Predoctoral Fellowship (WKL), and Dairy Research Institute/Dairy management Inc. Grant 1154 (KSH).This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Intra-aortic Balloon Counterpulsation for High-Risk Percutaneous Coronary Intervention: Defining Coronary Responders

The effect of intra-aortic balloon counterpulsation (IABC) varies, and it is unknown whether this is due to a heterogeneous coronary physiological response. This study aimed to characterise the coronary and left ventricular (LV) effects of IABC and define responders in terms of their invasive physiology. Twenty-seven patients (LVEF 31 ± 9%) underwent coronary pressure and Doppler flow measurements in the target vessel and acquisition of LV pressure volume loops after IABC supported PCI, with and without IABC assistance. Through coronary wave intensity analysis, perfusion efficiency (PE) was calculated as the proportion of total wave energy comprised of accelerating waves, with responders defined as those with an increase in PE with IABC. The myocardial supply/demand ratio was defined as the ratio between coronary flow and LV pressure volume area (PVA). Responders (44.4%) were more likely to have undergone complex PCI (p = 0.03) with a higher pre-PCI disease burden (p = 0.02) and had lower unassisted mean arterial (87.4 ± 11.0 vs. 77.8 ± 11.6 mmHg, p = 0.04) and distal coronary pressures (88.0 ± 11.0 vs. 71.6 ± 12.4 mmHg, p < 0.001). There was no effect overall of IABC on the myocardial supply/demand ratio (p = 0.34). IABC has minimal effect on demand, but there is marked heterogeneity in the coronary response to IABC, with the greatest response observed in those patients with the most disordered autoregulation.

Proximal pressure reducing effect of wave reflection in the pulmonary circulation disappear in obstructive disease: insight from a rabbit model

Locating the site of increased resistance within the vascular tree in pulmonary arterial hypertension could assist in both patient diagnosis and tailoring treatment. Wave intensity analysis (WIA) is a wave analysis method that may be capable of localizing the major site of reflection within a vascular system. We investigated the contribution of WIA to the analysis of the pulmonary circulation in a rabbit model with animals subjected to variable occlusive pulmonary disease. Animals were embolized with different sized microspheres for 6 wk ( n = 10) or underwent pulmonary artery (PA) ligation for 6 wk ( n = 3). These animals were compared with a control group ( n = 6) and acutely embolized animals ( n = 4). WIA was performed and compared with impedance-based methods to analyze wave reflections. The control group showed a relatively high extent of reflected waves (15.7 ± 10.6%); reflections had a net effect of pressure reduction during systole, suggesting an open-end reflector. The pattern of wave reflection was not different in the group with partial PA ligation (12.4 ± 4.1%). In the chronically embolized group, wave reflection was not observed (3.6 ± 1.5%). In the acute embolization group, wave reflection was more prominent (37.3 ± 12.6%), with the appearance of a novel wave increasing pressure, suggesting the appearance of a closed-end reflector. Wave reflections of an open-end type are present in the normal rabbit pulmonary circulation. However, the pattern and nature of reflections vary according to the extent of pulmonary vascular occlusion. NEW & NOTEWORTHY The study proposes an original framework of a complementary analysis of wave reflections in the time domain and in the frequency domain. The methodology was used in the pulmonary circulation with different forms of chronic obstructions. The results suggest that the pulmonary vascular tree generates a reflection pattern that could actually assist the heart during ejection, and chronic obstruction significantly modifies the pattern.

Alterations in Carotid Parameters in ApoE–/– Mice Treated with a High-Fat Diet: A Micro-ultrasound Analysis

Information on the common carotid artery and cerebral microcirculation can be obtained by micro-ultrasound (µUS). The aim of the study described here was to investigate high-fat diet-induced alterations in vascular parameters in ApoE–/– mice. Twenty-two ApoE–/– male mice were examined by µUS and divided into the standard diet (ApoE–/–SD) and high-fat diet (ApoE–/–HF) groups. The µUS examination was repeated after 4 mo (T1). Carotid stiffness, reflection magnitude and reflection index were measured; the amplitudes of the first (W1) and second (W2) local maxima, the local minimum (Wb) and the reflection index (RIWIA = Wb/W1) were assessed with wave intensity analysis. At T1, ApoE–/–HF mice had increased carotid stiffness (1.48 [0.36] vs. 1.88 [0.51]) and reflection magnitude (0.89 [0.07] vs. 0.94 [0.07]) values. Longitudinal comparisons highlighted increases in carotid stiffness for ApoE–/–HF mice (from 1.37 [0.25] to 1.88 [0.51] m/s) but not for ApoE–/–SD mice (from 1.40 [0.62] to 1.48 [0.36] m/s). ApoE–/–HF mice exhibited carotid artery stiffening and increased wave reflections.

Distinguish the Stable and Unstable Plaques Based on Arterial Waveform Analysis

The rupturing of unstable plaques, formed by atherosclerosis, is the main factor contributing to the stroke event. According to stroke association in 2017, the stroke is the fourth leading cause of death in the UK. The percentage of plaque composition plays an important role for plaque stability and can be considered as important information to determine whether the patients need surgery or not. The main aim of this work is to determine the relationship that exists between plaque composition and arterial waveform for distinguishing stable and vulnerable plaques. An in-vitro experiment, representing the arterial system, is used to investigate the effect of the composition of the atherosclerosis on the propagation of the arterial waveforms. Different types of the artificial plaque, fabricated manually, were implemented into the artificial carotid artery. The pressure, velocity and arterial vessel wall movement were measured simultaneously proximal to the site of the arterial plaques. Wave intensity analysis (WIA) was used to separate the waves into forward and backward waves to identify how the plaque compositions will affect the reflected arterial waveforms. Our results indicated that stable plaques caused the stronger reflected waves, leading to the higher amplitude of the arterial diameter waveform. In general, this study demonstrated that the arterial waveforms are strongly associated with the compositions of the arterial plaques, implying the arterial waveform could provide the information to characterize the types of the plaques, then leading to a novel approach to stratify the atherosclerosis patients and determine if the interventional vascular surgery is needed.

The aorta after coarctation repair \u2013 effects of calibre and curvature on arterial haemodynamics

BackgroundAortic shape has been proposed as an important determinant of adverse haemodynamics following coarctation repair. However, previous studies have not demonstrated a consistent relationship between shape and vascular load. In this study, 3D aortic shape was evaluated using principal component analysis (PCA), allowing investigation of the relationship between 3D shape and haemodynamics.MethodsSixty subjects (38 male, 25.0 ± 7.8 years) with repaired coarctation were recruited. Central aortic haemodynamics including wave intensity analysis were measured noninvasively using a combination of blood pressure and phase contrast cardiovascular magnetic resonance (CMR). 3D curvature and radius data were derived from CMR angiograms. PCA was separately performed on 3D radius and curvature data to assess the role of arch geometry on haemodynamics. Clinical findings were corroborated using 1D vascular models.ResultsThere were no independent associations between 3D curvature and any hemodynamic parameters. However, the magnitude of the backwards compression wave was related to the 1st (r = − 0.36, p = 0.005), 3rd (r = 0.27, p = 0.036) and 4th (r = − 0.31, p = 0.017) principle components of radius. The 4th principle componentof radius also correlated with central aortic systolic pressure. These aortas had larger aortic roots, more transverse arch hypoplasia and narrower aortic isthmuses.ConclusionsThere are major modes of variation in 3D aortic shape after coarctation repair witha modest association between variation in aortic radius and pathological wave reflections, but not with 3D curvature. Taken together, these data suggest that shape is not the major determinant of vascular load following coarctation repair, and calibre is more important than curvature.

Effects of carotid pressure waveform obtained in different ways on the results of wave separation, wave intensity and reservoir pressure analysis

Purpose/Background/ObjectivesRecently great attention has been placed on innovative cardiovascular biomarkers obtained from wave separation (WS), wave intensity analysis (WIA) and the reservoir-wave (RW) concept. Pressure waveforms needed to implement these techniques can be obtained in different ways. Aim of this study was to evaluate differences in WS, WIA and RW parameters obtained deriving pressure curves in different ways.MethodsTwenty-two individuals (49 ± 17 years, 59% males) were examined. Common carotid blood flow waveforms were obtained from Pulsed-Wave Doppler images. Carotid pressure waveforms were obtained in four different ways: 1) standard method, i.e., with applanation tonometry; 2) linear scaling from ultrasound (US)-derived diameter curve; 3) exponential scaling from US-derived diameter curve; 4) linear scaling from an accelero-metric-derived diameter signal. In each case, reflection magnitude (RM) and reflection index (RI) were obtained from WS. The amplitude of the first positive peak (W1), of the second positive peak (W2) and of the negative one (Wb) were calculated from WIA; the maximum of the reservoir (maxPr) and the excess (maxPex) pressure were achieved from RW.ResultsAccording to the intra-class coefficient values, the agreement between the standard method and all the others was excellent in case of RM, RI, maxPrand maxPex(0.82–0.97), while reached only a fair/good level in case of W1, W2and Wb(0.44–0.82).ConclusionsThe use of alternative carotid pressure waveforms does not influence the cardiovascular parameters obtained by WS and RW, while those derived by WIA are affected by the carotid pressure curve employed.

Feasibility of aortic wave intensity analysis from sequentially acquired cardiac mri and non-invasive central blood pressure

BackgroundWave intensity analysis (WIA) in the aorta offers important clinical and mechanistic insights but is difficult non-invasively. We performed WIA by combining high temporal resolution cardiovascular magnetic resonance (CMR) flow velocity and non-invasive central blood pressure (BP) waveform data.Method206 healthy volunteers (36 ± 11 years, 47% male) underwent sequential phase contrast CMR (Siemens Aera 1.5T, 1.97 × 1.77 mm2, ~9 ms temporal resolution) and supra-systolic oscillometric central BP (Uscom Ltd BP+) measurement. Velocity (U) and central pressure (P) waveforms (200 Hz) were aligned using the wave foot, and local wave speed was calculated both from the P-U slope during early systole (c) and the sum of squares method (cSS) (Figure 1), and compared with CMR aortic arch pulse wave velocity (PWV) by transit time.ResultsThe peak intensity of the initial compression wave (dI+1), backward compression wave (dI-) and protodiastolic decompression wave (dI + 2) were 69.5 ± 28, −6.6 ± 4.2 and 6.2 ± 2.5 W/m2 respectively. PWV correlated with c or cSS (r = 0.60, and 0.68 respectively; bias −1.3 [limits of agreement: −3.8 to 1.2 m/s], and bias −0.64 [limits of agreement: −3.0 to 1.7 m/s] respectively), Figure 1.ConclusionWave intensity patterns and values are similar to those measured using invasive methods. Local wave speed showed good agreement with PWV. CMR and central blood pressure provides a novel non-invasive technique for performing wave intensity analysis and is feasible for large scale studies.Figure 1Calculation of wave speed from a pressure - velocity (P-U) loop and comparison with pulse wave velocity by transit time. Top left: alignment of scaled pressure (blue) and velocity (red) waveforms and example of wave intensity analysis showing initial compression (dl+1), backward compression (dl-)and protodiastolic decompression (dl+2) waves. Top right: P-U loop showing wave speed measurement in early systole (c); and using sum of squares (cSS). Bottom left and Bottom right: Correlation and Bland-Altman analysis of cSS and PWV from phase-contrast MRI showing good correlation and slight underestimation

Effects of carotid pressure waveforms on the results of wave separation, wave intensity and reservoir pressure analysis

Objective: Recently great attention has been paid to innovative cardiovascular biomarkers obtained from wave separation (WS), wave intensity (WI) and reservoir-wave (RW) theories. All these approaches share a requirement for pressure information. The aim of this study was to evaluate differences in WS-, WI- and RW-derived parameters obtained achieving pressure waveforms in different ways. Approach: Twenty-two individuals (49 ± 17 years, 59% males) were examined. Common carotid blood flow waveforms were obtained from pulsed-wave Doppler images. Carotid pressure waveforms were achieved in four different ways: (1) with applanation tonometry, used as a reference method; (2) linear scaling from an ultrasound (US)-derived diameter curve; (3) exponential scaling from a US-derived diameter curve; and (4) linear scaling from an accelerometric-derived diameter signal. For each case, the reflection magnitude (RM) and index (RI) were obtained from the WS. The amplitude of the first positive peak (W1), of the second positive peak (W2) and of the negative peak (Wb) were calculated from the WI, while the maximum of the reservoir (maxPr) and the excess (maxPex) pressure were achieved from the RW. Main results: According to the intra-class coefficient values, the agreement between the standard method and all the others was excellent for the RM (linear: 0.82; exponential: 0.83; accelerometric: 0.86), RI (linear: 0.84; exponential: 0.85; accelerometric: 0.87), maxPr (linear: 0.97; exponential: 0.96; accelerometric: 0.97) and maxPex (linear: 0.85; exponential: 0.87; accelerometric: 0.89), while only a fair/good level was reached for W1 (linear: 0.67; exponential: 0.77; accelerometric: 0.52), W2 (linear: 0.52; exponential: 0.69; accelerometric: 0.83) and Wb (linear: 0.60; exponential: 0.44; accelerometric: 0.50). Significance: Measuring carotid pressure waveforms with different approaches does not influence the cardiovascular parameters obtained by WS and RW; those derived by WI are affected by the carotid pressure curve employed.

Wave intensity analysis in the internal carotid artery of hypertensive subjects using phase-contrast MR angiography and preliminary assessment of the effect of vessel morphology on wave dynamics

Objective: Hypertension is associated with reduced cerebral blood flow, but it is not known how this impacts on wave dynamics or potentially relates to arterial morphology. Given the location of the internal carotid artery (ICA) and risks associated with invasive measurements, wave dynamics in this artery have not been extensively assessed in vivo. This study explores the feasibility of studying wave dynamics in the internal carotid artery non-invasively. Approach: Normotensive, uncontrolled and controlled hypertensive participants were recruited (daytime ambulatory blood pressure <135/85 mmHg and >135/85 mmHg, respectively; n = 38). Wave intensity, reservoir pressure and statistical shape analyses were performed on the right ICA and ascending aorta high-resolution phase-contrast magnetic resonance angiography data. Main results: Wave speed in the aorta was significantly lower in normotensive compared to hypertensive participants (6.7 ± 1.8 versus 11.2 ± 6.2 m s−1 for uncontrolled and 11.8 ± 4.6 m s−1 for controlled hypertensives, p = 0.02), whilst there were no differences in wave speed in the ICA. There were no significant differences between the groups for the wave intensity or reservoir pressure. Interestingly, a significant association between the anatomy of the ICA and wave energy (FCW and size, r2 = 0.12, p = 0.04) was found. Significance: This study shows it is feasible to study wave dynamics in the ICA non-invasively. Whilst changes in aortic wave speed confirmed an expected increase in arterial stiffness, this was not observed in the ICA. This might suggest a protective mechanism in the cerebral circulation, in conjunction with the effect of vessel tortuosity. Furthermore, it was observed that ICA shape correlated with wave energy but not wave speed.

Effects of acute aerobic exercise on arterial stiffness and cerebrovascular pulsatility in adults with and without hypertension.

Stiffer central arteries, as seen in hypertension (HTN), foster transmission of pulsatile hemodynamics into fragile cerebral vessels. Aerobic exercise is recommended for adults with HTN, but its effects on arterial stiffness and pulsatility in this group are unclear. This study sought to investigate the effect of acute aerobic exercise on arterial stiffness and cerebrovascular pulsatility in 30 adults with treated HTN and 30 age, sex, and BMI-matched adults without HTN (56 ± 6 years, BMI 28.2 ± 2.9 kg/m; 28 women). Patients underwent hemodynamic measures before/after 30-min cycling (≈55% peak oxygen consumption). Aortic stiffness was measured using carotid-femoral pulse wave velocity, and carotid artery stiffness was assessed with β-stiffness via ultrasound. Aortic/carotid pulse pressure (aortic via radial generalized transfer function) was measured by tonometry and calibrated to brachial mean pressure and diastolic pressure. Carotid/middle cerebral artery (MCA) blood velocity pulsatility indices were measured using Doppler. Carotid wave intensity analysis was used to derive forward wave intensity (W1). Exercise impacted hemodynamics similarly in HTN compared to no-HTN. Carotid-femoral pulse wave velocity, MCA pulsatility index, carotid pulsatility index, and W1 increased similarly after exercise in both groups (P < 0.05). Carotid pulse pressure and β-stiffness were unaltered after exercise. Postexercise changes in W1 were positively associated with carotid pulsatility index, which was further associated with MCA pulsatility index. These data suggest adults with treated HTN experience similar increases in aortic stiffness and cerebrovascular hemodynamic pulsatility during early recovery from acute aerobic exercise as their counterparts without HTN.