Noninvasive pulmonary artery wave intensity analysis in pulmonary hypertension

Characterization of pulmonary arterial stiffness using cardiac MRI

Pulmonary arterial stiffness (PAS) is a pathologic hallmark of all types of pulmonary hypertension (PH). Cardiac MRI (CMR), a gold-standard imaging modality for the evaluation of pulmonary flow, biventricular morphology and function has been historically reserved for the longitudinal clinical follow-up, PH phenotyping purposes, right ventricular evaluation, and research purposes. Over the last two decades, numerous indices combining invasive catheterization and non-invasive CMR have been utilized to phenotype the character and severity of PAS in different types of PH and to assess its clinically prognostic potential with encouraging results. Many recent studies have demonstrated a strong role of CMR derived PAS markers in predicting long-term clinical outcomes and improving currently gold standard risk assessment provided by the REVEAL calculator. With the utilization of a machine learning strategies, strong diagnostic and prognostic performance of CMR reported in multicenter studies, and ability to detect PH at early stages, the non-invasive assessment of PAS is on verge of routine clinical utilization. In this review, we focus on appraising important CMR studies interrogating PAS over the last 20 years, describing the benefits and limitations of different PAS indices, and their pathophysiologic relevance to pulmonary vascular remodeling. We also discuss the role of CMR and PAS in clinical surveillance and phenotyping of PH, and the long-term future goal to utilize PAS as a biomarker to aid with more targeted therapeutic management.

Assessment of pulmonary artery stiffness by multiparametric cardiac magnetic resonance-surrogate for right heart catheterization

Background

Cardiac magnetic resonance (CMR) imaging allows for multiparametric assessment of healthy pulmonary artery (PA) hemodynamics. Gender- and aging-associated PA stiffness and pressure alterations have remained clinically unestablished, however may demonstrate epidemiological differences in disease development. The aim of this study is to evaluate the role of CMR as a surrogate for catheter examinations by providing a comprehensive CMR assessment of sex- and age-related reference values for PA stiffness, flow, and pressure.

Methods and Results

PA hemodynamics were studied between gender and age groups (>/<50 years) using phase-contrast CMR. Corresponding correlation analyses were performed. 179 healthy volunteers with a median age of 32.6 years (range 11.3-68.2) were examined. Males demonstrated increased PA compliance (median [interquartile range] or mean ± standard deviation) (20.8 mm2/mmHg [16.6; 25.8] vs. 19.2 ± 7.1 mm2/mmHg; P < 0.033), higher pulse wave velocity (2.00 m/s [1.35; 2.87] vs. 1.73 m/s [1.19; 2.34]; P = 0.018) and a reduced full width half maximum (FWHM) (219 ± 22 ms vs. 235 ± 23 ms; P < 0.001) than females. Mean, systolic, diastolic PA pressure and pulmonary proportional pulse pressure were significantly elevated for males compared to females (P < 0.001). Older subjects (>50 years) exhibited reduced PA elasticity (41.7% [31.0; 52.9] vs. 66.4% [47.7; 83.0]; P < 0.001), reduced PA compliance (15.4 mm2/mmHg [12.3; 20.7] vs. 21.3 ± 6.8 mm2/mmHg; P < 0.001), higher pulse wave velocity (2.59 m/s [1.57; 3.59] vs. 1.76 m/s [1.24; 2.34]; P < 0.001) and a reduced FWHM (218 ± 29 ms vs. 231 ± 21 ms; P < 0.001) than younger subjects.

Conclusions

Velocity-time profiles are dependent on age and gender. PA stiffness indices deteriorate with age. CMR has potential to serve as a surrogate for right heart catheterization.

Aortic shape variation after frozen elephant trunk procedure predicts aortic events: Principal component analysis study

Objective

The frozen elephant trunk procedure is a well-established technique for the repair of type A ascending aortic dissection and complex aortic arch pathology. The ultimate shape created by the repair may have consequences in long-term complications. The purpose of this study was to apply a machine learning technique to comprehensively describe 3-dimensional aortic shape variations after the frozen elephant trunk procedure and associate these variations with aortic events.

Methods

Computed tomography angiography acquired before discharge of patients (n = 93) who underwent the frozen elephant trunk procedure for type A ascending aortic dissection or ascending aortic arch aneurysm was preprocessed to yield patient-specific aortic models and centerlines. Aortic centerlines were subjected to principal component analysis to describe principal components and aortic shape modulators. Patient-specific shape scores were correlated with outcomes defined by composite aortic event, including aortic rupture, aortic root dissection or pseudoaneurysm, new type B dissection, new thoracic or thoracoabdominal pathologies, residual descending aortic dissection with residual false lumen flow, or thoracic endovascular aortic repair complications.

Results

The first 3 principal components accounted for 36.4%, 26.4%, and 11.6% of aortic shape variance, respectively, and cumulatively for 74.5% of the total shape variation in all patients. The first principal component described variation in arch height-to-length ratio, the second principal component described angle at the isthmus, and the third principal component described variation in anterior-to-posterior arch tilt. Twenty-one aortic events (22.6%) were encountered. The degree of aortic angle at the isthmus described by the second principal component was associated with aortic events in logistic regression (hazard ratio, 0.98; 95% confidence interval, 0.97-0.99; P = .046).

Conclusions

The second principal component, describing angulation at the region of the aortic isthmus, was associated with adverse aortic events. Observed shape variation should be evaluated in the context of aortic biomechanical properties and flow hemodynamics.

Pulmonary artery wave reflection and right ventricular function after lung resection

BACKGROUND

Lung resection has been shown to impair right ventricular function. Although conventional measures of afterload do not change, surgical ligation of a pulmonary artery branch, as occurs during lobectomy, can create a unilateral proximal reflection site, increasing wave reflection (pulsatile component of afterload) and diverting blood flow through the contralateral pulmonary artery. We present a cardiovascular magnetic resonance imaging (MRI) observational cohort study of changes in wave reflection and right ventricular function after lung resection.

METHODS

Twenty-seven patients scheduled for open lobectomy for suspected lung cancer underwent cardiovascular MRI preoperatively, on postoperative Day 2, and at 2 months. Wave reflection was assessed in the left and right pulmonary arteries (operative and non-operative, as appropriate) by wave intensity analysis and calculation of wave reflection index. Pulmonary artery blood flow distribution was calculated as percentage of total blood flow travelling in the non-operative pulmonary artery. Right ventricular function was assessed by ejection fraction and strain analysis.

RESULTS

Operative pulmonary artery wave reflection increased from 4.3 (2.1-8.8) % preoperatively to 9.5 (4.9-14.9) % on postoperative Day 2 and 8.0 (2.3-11.7) % at 2 months (P<0.001) with an associated redistribution of blood flow towards the nonoperative pulmonary artery (r>0.523; P<0.010). On postoperative Day 2, impaired right ventricular ejection fraction was associated with increased operative pulmonary artery wave reflection (r=-0.480; P=0.028) and pulmonary artery blood flow redistribution (r=-0.545; P=0.011). At 2 months, impaired right ventricular ejection fraction and right ventricular strain were associated with pulmonary artery blood flow redistribution (r=-0.634, P=0.002; r=0.540, P=0.017).

CONCLUSIONS

Pulsatile afterload increased after lung resection. The unilateral increase in operative pulmonary artery wave reflection resulted in redistribution of blood flow through the nonoperative pulmonary artery and was associated with right ventricular dysfunction.

CLINICAL TRIAL REGISTRATION

NCT01892800.

Quantitative cardiopulmonary magnetic resonance imaging in neonatal congenital diaphragmatic hernia

BACKGROUND

Pulmonary arterial hypertension, impaired cardiac function and lung hypoplasia are common in infants with congenital diaphragmatic hernia (CDH) and are associated with increased morbidity and mortality. Robust noninvasive methods to quantify these abnormalities in early infancy are lacking.

OBJECTIVE

To determine the feasibility of MRI to quantify cardiopulmonary hemodynamics and function in infants with CDH and to investigate left-right blood flow and lung volume discrepancies.

MATERIALS AND METHODS

We conducted a prospective MRI study of 23 neonates (isolated left CDH: 4 pre-repair, 7 post-repair, 3 pre- and post-repair; and 9 controls) performed on a small-footprint 1.5-tesla (T) scanner. We calculated MRI-based pulmonary arterial blood flow, left ventricular eccentricity index, cardiac function and lung volume. Using the Wilcoxon rank sum test for continuous data and Fisher exact test for categorical data, we made pairwise group comparisons.

RESULTS

The right-to-left ratios for pulmonary artery blood flow and lung volume were elevated in pre-repair and post-repair CDH versus controls (flow: P&lt;0.005; volume: P&lt;0.05 pre-/post-repair). Eccentricity index at end-systole significantly differed between pre-repair and post-repair CDH (P&lt;0.01) and between pre-repair CDH and controls (P&lt;0.001).

CONCLUSION

Cardiopulmonary MRI is a viable method to serially evaluate cardiopulmonary hemodynamics and function in critically ill infants and is useful for capturing left-right asymmetries in pulmonary blood flow and lung volume.

Evaluating cardiopulmonary function following acute pulmonary embolism

INTRODUCTION

Pulmonary embolism is a common cause of cardiopulmonary mortality and morbidity worldwide. Survivors of acute pulmonary embolism may experience dyspnea, report reduced exercise capacity, or develop overt pulmonary hypertension. Clinicians must be alert for these phenomena and appreciate the modalities and investigations available for evaluation.

AREAS COVERED

In this review, the current understanding of available contemporary imaging and physiologic modalities is discussed, based on available literature and professional society guidelines. The purpose of the review is to provide clinicians with an overview of these modalities, their strengths and disadvantages, and how and when these investigations can support the clinical work-up of patients post-pulmonary embolism.

EXPERT OPINION

Echocardiography is a first test in symptomatic patients post-pulmonary embolism, with ventilation/perfusion scanning vital to determination of whether there is chronic residual emboli. The role of computed tomography and magnetic resonance in assessing the pulmonary arterial tree in post-pulmonary embolism patients is evolving. Functional testing, in particular cardiopulmonary exercise testing, is emerging as an important modality to quantify and determine cause of functional limitation. It is possible that future investigations of the post-pulmonary embolism recovery period will better inform treatment decisions for acute pulmonary embolism patients.

When right ventricular pressure meets volume: the impact of arrival time of reflected waves on right ventricle load in pulmonary arterial hypertension

Abstract

Right ventricular (RV) wall tension in pulmonary arterial hypertension (PAH) is determined not only by pressure, but also by RV volume. A larger volume at a given pressure generates more wall tension. Return of reflected waves early after the onset of contraction, when RV volume is larger, may augment RV load. We aimed to elucidate: (1) the distribution of arrival times of peak reflected waves in treatment‐naïve PAH patients; (2) the relationship between time of arrival of reflected waves and RV morphology; and (3) the effect of PAH treatment on the arrival time of reflected waves. Wave separation analysis was conducted in 68 treatment‐naïve PAH patients. In the treatment‐naïve condition, 54% of patients had mid‐systolic return of reflected waves (defined as 34–66% of systole). Despite similar pulmonary vascular resistance (PVR), patients with mid‐systolic return had more pronounced RV hypertrophy compared to those with late‐systolic or diastolic return (RV mass/body surface area; mid‐systolic return 54.6 ± 12.6 g m^–2, late‐systolic return 44.4 ± 10.1 g m^–2, diastolic return 42.8 ± 13.1 g m^–2). Out of 68 patients, 43 patients were further examined after initial treatment. At follow‐up, the stiffness of the proximal arteries, given as characteristic impedance, decreased from 0.12 to 0.08 mmHg s mL^–1. Wave speed was attenuated from 13.3 to 9.1 m s^–1, and the return of reflected waves was delayed from 64% to 71% of systole. In conclusion, reflected waves arrive at variable times in PAH. Early return of reflected waves was associated with more RV hypertrophy. PAH treatment not only decreased PVR, but also delayed the timing of reflected waves.

Key points

Right ventricular (RV) wall tension in pulmonary arterial hypertension (PAH) is determined not only by pressure, but also by RV volume. Larger volume at a given pressure causes larger RV wall tension.

Early return of reflected waves adds RV pressure in early systole, when RV volume is relatively large. Thus, early return of reflected waves may increase RV wall tension. Wave reflection can provide a description of RV load.

In PAH, reflected waves arrive back at variable times. In over half of PAH patients, the RV is exposed to mid‐systolic return of reflected waves. Mid‐systolic return of reflected waves is related to RV hypertrophy.

PAH treatment acts favourably on the RV not only by reducing resistance, but also by delaying the return of reflected waves.

Arrival timing of reflected waves is an important parameter for understanding the relationship between RV load and its function in PAH.

Integrated Cardiopulmonary MRI Assessment of Pulmonary Hypertension

Pulmonary hypertension (PH) is a heterogeneous condition that can affect the lung parenchyma, pulmonary vasculature, and cardiac chambers. Accurate diagnosis often requires multiple complex assessments of the cardiac and pulmonary systems. MRI is able to comprehensively assess cardiac structure and function, as well as lung parenchymal, pulmonary vascular, and functional lung changes. Therefore, MRI has the potential to provide an integrated functional and structural assessment of the cardiopulmonary system in a single exam. Cardiac MRI is used in the assessment of PH in most large PH centers, whereas lung MRI is an emerging technique in patients with PH. This article reviews the current literature on cardiopulmonary MRI in PH, including cine MRI, black-blood imaging, late gadolinium enhancement, T₁ mapping, myocardial strain analysis, contrast-enhanced perfusion imaging and contrast-enhanced MR angiography, and hyperpolarized gas functional lung imaging. This article also highlights recent developments in this field and areas of interest for future research including cardiac MRI-based diagnostic models, machine learning in cardiac MRI, oxygen-enhanced ¹ H imaging, contrast-free ¹ H perfusion and ventilation imaging, contrast-free angiography and UTE imaging. EVIDENCE LEVEL: 5 TECHNICAL EFFICACY: Stage 3.

Estimation of Pulmonary Arterial Wave Reflection by Echo-Doppler: A Preliminary Study in Dogs With Experimentally-Induced Acute Pulmonary Embolism

Background: Pulmonary arterial (PA) wave reflection provides additional information for assessing right ventricular afterload, but its applications is hampered by the need for invasive pressure and flow measurements. We tested the hypothesis that PA pressure and flow waveforms estimated by Doppler echocardiography could be used to quantify PA wave reflection.

Methods: Doppler echocardiographic images of tricuspid regurgitation and right ventricular outflow tract flow used to estimate PA pressure and flow waveforms were acquired simultaneously with direct measurements with a dual sensor-tipped catheter under various hemodynamic conditions in a canine model of pulmonary hypertension (n = 8). Wave separation analysis was performed on echo-Doppler derived as well as catheter derived waveforms to separate PA pressure into forward (Pf) and backward (Pb) pressures and derive wave reflection coefficient (RC) defined as the ratio of peak Pb to peak Pf.

Results: Wave reflection indices by echo-Doppler agreed well with corresponding indices by catheter (Pb: mean difference = 0.4 mmHg, 95% limits of agreement = −4.3 to 5.0 mmHg; RC: bias = 0.13, 95% limits of agreement = −0.25 to 0.26). RC correlated negatively with PA compliance.

Conclusion: This echo-Doppler method yields reasonable measurement of reflected wave in the pulmonary circulation, paving the way to a more integrative assessment of pulmonary hemodynamics in the clinical setting.

Measurement of Pulmonary Artery Wave Reflection Before and After Mitral Valvuloplasty in Canine Patients With Pulmonary Hypertension Caused by Myxomatous Mitral Valve Disease

Background: Pulmonary arterial wave reflection provides novel information about pulmonary artery hemodynamics in pulmonary hypertension (PH). PH is common in dogs with myxomatous mitral valve disease (MMVD), though research examining the relationship between pulmonary arterial wave reflection and MMVD with PH is lacking. Hypothesis/Objective: This study investigated conventional echocardiographic parameters and pulmonary artery wave reflection parameters before and after mitral valvuloplasty in canine patients with PH due to MMVD. The parameters were backward pressure (Pb), forward pressure (Pf), and the reflection coefficient calculated as the ratio of peak Pb to peak Pf (RC). Animals: The study subjects were 10 client-owned dogs receiving mitral valvuloplasty for MMVD with PH. Methods: Conventional echocardiographic parameters and pulmonary artery wave reflection parameters were measured before and after mitral valvuloplasty. The relationships between pulmonary artery wave reflection parameters and echocardiographic parameters, estimation of pulmonary artery systolic pressure, and right atrium pressure (RAP) gained by catheter in mitral valvuloplasty were also investigated. Post-operative echocardiography and the measurement of pulmonary arterial wave reflection were performed 2 weeks after mitral valvuloplasty. Results: The parameters of normalized left ventricular internal diameter at end-diastole (LVIDDN), E velocity, and the estimation of pulmonary artery systolic pressure were significantly reduced post-operatively compared with baseline measurements (p < 0.05). Post-operative Pb decreased significantly compared with pre-operative measurements (8.8 ± 5.9 to 5.0 ± 3.2 mmHg, p = 0.037) as did RC (0.37 ± 0.15 to 0.22 ± 0.11, p < 0.01). A statistically significant positive correlation existed between wave reflection parameters and RAP, an estimation of pulmonary artery systolic pressure. Conclusions: Results demonstrate that mitral valvuloplasty can be used to treat secondary PH caused by MMVD, resulting in the improvement of post-operative echocardiographic and wave reflection parameters and a decrease in the right afterload. In some patients, some degree of vascular admittance mismatch persisted, despite the improvement of left atrial pressure. This may be indicative of residual pulmonary arterial disease, which may continue to adversely affect interactions between the right ventricle and the vasculature.

A computational model of contributors to pulmonary hypertensive disease: impacts of whole lung and focal disease distributions

Pulmonary hypertension has multiple etiologies and so can be difficult to diagnose, prognose, and treat. Diagnosis is typically made via invasive hemodynamic measurements in the main pulmonary artery and is based on observed elevation of mean pulmonary artery pressure. This static mean pressure enables diagnosis, but does not easily allow assessment of the severity of pulmonary hypertension, nor the etiology of the disease, which may impact treatment. Assessment of the dynamic properties of pressure and flow data obtained from catheterization potentially allows more meaningful assessment of the strain on the right heart and may help to distinguish between disease phenotypes. However, mechanistic understanding of how the distribution of disease in the lung leading to pulmonary hypertension impacts the dynamics of blood flow in the main pulmonary artery and/or the pulmonary capillaries is lacking. We present a computational model of the pulmonary vasculature, parameterized to characteristic features of pulmonary arterial hypertension and chronic thromboembolic pulmonary hypertension to help understand how the two conditions differ in terms of pulmonary vascular response to disease. Our model incorporates key features known to contribute to pulmonary vascular function in health and disease, including anatomical structure and multiple contributions from gravity. The model suggests that dynamic measurements obtained from catheterization potentially distinguish between distal and proximal vasculopathy typical of pulmonary arterial hypertension and chronic thromboembolic pulmonary hypertension. However, the model suggests a non-linear relationship between these data and vascular structural changes typical of pulmonary arterial hypertension and chronic thromboembolic pulmonary hypertension which may impede analysis of these metrics to distinguish between cohorts.

Role of cardiovascular magnetic resonance in pediatric pulmonary hypertension-novel concepts and imaging biomarkers

Pulmonary hypertension (PH) in children is a heterogenous disease of the small pulmonary arteries characterized by a progressive increase in pulmonary vascular resistance. Despite adequate medical therapy, long-term pressure overload is frequently associated with a progressive course leading to right ventricular failure and ultimately death. Invasive hemodynamic assessment by cardiac catheterization is crucial for initial diagnosis, risk stratification and therapeutic strategy. Although echocardiography remains the most important imaging modality for the assessment of right ventricular function and pulmonary hemodynamics, cardiovascular magnetic resonance (CMR) has emerged as a valuable non-invasive imaging technique that enables comprehensive evaluation of biventricular performance, blood flow, morphology and the myocardial tissue. In this review, we summarize the principles and applications of CMR in the evaluation of pediatric PH patients and present an update about novel CMR based concepts and imaging biomarkers that may provide further diagnostic, therapeutic and prognostic information.

Limited value of pulse wave analysis in assessing arterial wave reflection and stiffness in the pulmonary artery

We explored the use of the augmentation index (AI) based on pulse wave analysis (PWA) in the pulmonary circulation as a measure of wave reflection and arterial stiffness in individuals with and without pulmonary arterial hypertension (PAH) and chronic thromboembolic pulmonary hypertension (CTEPH). Right heart catheterization was performed using a pressure and Doppler flow sensor-tipped catheter to obtain simultaneous pressure and flow velocity measurements in the pulmonary artery in 10 controls, 11 PAH patients, and 11 CTEPH patients. PWA was applied to the measured pressure, while wave intensity analysis (WIA) and wave separation analysis (WSA) were performed using both the pressure and velocity to determine the magnitudes and timings of reflected waves. Type C (AI < 0) pressure waveform dominated in controls and type A (AI > 12%) waveform dominated in PAH patients, while there was a mixture of types A, B, and C among CTEPH patients. AI was greater and the inflection time shorter in CTEPH compared to PAH patients. There was a poor correlation between AI and arterial wave speed as well as measures of wave reflection derived from WIA and WSA. The infection point did not match the timing of the backward compression wave in ~50% of the cases. In patients with type C waveforms, the inflection time correlated well to the timing of the late systolic forward decompression wave caused by ventricular relaxation. In conclusion quantifying pulmonary arterial wave reflection and stiffness using AI based on PWA may be inaccurate and should therefore be discouraged.

Non-invasive Assessment of Pulmonary Artery Wave Reflection in Dogs With Suspected Pulmonary Hypertension

Background: Pulmonary arterial wave reflection (PAWR) occurs when the forward blood flow out the right ventricle is reflected by the pulmonary arterial tree, generating a backward wave. PAWR assessed by cardiac catheterization has been used to obtain information regarding pulmonary artery hemodynamics in pulmonary hypertension (PH) in people. However, diagnostic cardiac catheterization is not commonly used in small animal medicine because it is invasive and requires anesthesia.

Hypothesis/Objective: To investigate whether PAWR can be assessed non-invasively in dogs with suspected PH using Doppler echocardiography, based on wave intensity analysis (WIA). In addition, the method was validated in a dog model of acute pulmonary embolism.

Animals: Fifty-one client-owned dogs with tricuspid valve regurgitation were included in the clinical study (35 with suspected PH and 16 without echocardiographic evidence of PH) and eight healthy beagle dogs were included in the validation study.

Methods: PAWR was assessed by separating pulmonary artery pulse pressure waveforms, which were estimated from the flow profile of tricuspid regurgitation, into forward (Pf) and backward pressures (Pb) using WIA. Reflection coefficient (RC) was defined as the ratio of peak Pb to peak Pf. We investigated the relationships between RC, cause, and survival time in dogs with suspected PH. In addition, we performed a validation study to compare PAWR obtained by cardiac catheterization and PAWR by Doppler echocardiography in dogs with experimentally-induced PH.

Results: RC was significantly higher in dogs with suspected PH than in dogs without echocardiographic evidence of PH (0.18 ± 0.13 vs. 0.59 ± 0.21, P < 0.001). A characteristic reflected waveform appeared depending on the cause of PH. Kaplan-Meier survival curves showed that dogs with RC > 0.48 had a significantly shorter survival time than dogs with RC <0.48 (x² = 9.8, log-rank test, p = 0.0018, median survival time 353 days vs. 110 days). In the validation study, RC obtained by Doppler echocardiography was significantly correlated with RC obtained by cardiac catheterization (r = 0.81, P < 0.001).

Conclusions: PAWR analysis performed by echocardiography seems feasible in dogs and could provide useful information for classification and prognosis in canine PH.

Changes in the Pulmonary Artery Wave Reflection in Dogs with Experimentally-Induced Acute Pulmonary Embolism and the Effect of Vasodilator

Simple Summary

Pulmonary hypertension (PH) remains a fatal disease, despite the advances in disease-specific therapies. This may be because the assessment of pulmonary hemodynamics in PH has not been established. Recently, several studies have reported that the pulmonary arterial wave reflection (PAWR) might influence the right ventricular afterload and could provide additional information regarding the severity and progression of PH. However, the pathophysiology of PAWR has some unclear points particularly in the case of acute pulmonary embolism (APE). The objective of this study was to investigate, for the first time, the characteristics of PAWR in a dog model of APE using dual-tipped sensor wire. From the result of the present study, after dogs developed PH by injections of dextran microsphere, PAWR was increased significantly along with the pulmonary vascular resistance (PVR) and reduced after vasodilator administration. In addition, PAWR was significantly correlated with PVR and right ventricular fractional area of change (FAC). These results indicating that PAWR may be useful as a new evaluation method in PH and may detect changes related to right ventricular afterload earlier than pulmonary artery pressure (PAP).

Abstract

Pulmonary hypertension (PH) is a complex syndrome that has been frequently diagnosed in dogs and humans and can be detected by Doppler echocardiography and invasive catheterization. Recently, PAWR attracts much attention as a noninvasive approach for the early detection of PH. The present study aims to investigate the PAWR changes in acute pulmonary embolism (APE) and highlight the response of PAWR variables to vasodilator therapy in dogs. For this purpose, anesthesia and catheterization were performed in 6 Beagle dogs. After that, APE was experimentally conducted by Dextran microsphere administration, followed by vasodilator (Nitroprusside; 1μg/kg/min/IV) administration. The hemodynamics, echocardiography, PVR and PAWR variables were evaluated at the baseline, after APE and after administration of nitroprusside. The result showed a significant increase in PVR, PAP, tricuspid regurgitation (TR) as well as PAWR variables following APE induction compared with the baseline (p < 0.05). Vasodilation caused by administration of nitroprusside reduced the mean atrial pressure, PVR and PAWR parameters. There were a significant correlation and linear regression between PAWR indices and PVR as well as right ventricular function parameters. In conclusion, PAWR is not only correlated with PVR but also the right ventricular function parameter, which indicates that PAWR may be useful as a new evaluation method in PH, considering that PAWR can assess both right ventricular afterload and right ventricular function.

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

BACKGROUND

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.

METHODS AND RESULTS

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).

CONCLUSION

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.

A multiscale model of vascular function in chronic thromboembolic pulmonary hypertension

Chronic thromboembolic pulmonary hypertension (CTEPH) is caused by recurrent or unresolved pulmonary thromboemboli, leading to perfusion defects and increased arterial wave reflections. CTEPH treatment aims to reduce pulmonary arterial pressure and reestablish adequate lung perfusion, yet patients with distal lesions are inoperable by standard surgical intervention. Instead, these patients undergo balloon pulmonary angioplasty (BPA), a multisession, minimally invasive surgery that disrupts the thromboembolic material within the vessel lumen using a catheter balloon. However, there still lacks an integrative, holistic tool for identifying optimal target lesions for treatment. To address this insufficiency, we simulate CTEPH hemodynamics and BPA therapy using a multiscale fluid dynamics model. The large pulmonary arterial geometry is derived from a computed tomography (CT) image, whereas a fractal tree represents the small vessels. We model ring- and web-like lesions, common in CTEPH, and simulate normotensive conditions and four CTEPH disease scenarios; the latter includes both large artery lesions and vascular remodeling. BPA therapy is simulated by simultaneously reducing lesion severity in three locations. Our predictions mimic severe CTEPH, manifested by an increase in mean proximal pulmonary arterial pressure above 20 mmHg and prominent wave reflections. Both flow and pressure decrease in vessels distal to the lesions and increase in unobstructed vascular regions. We use the main pulmonary artery (MPA) pressure, a wave reflection index, and a measure of flow heterogeneity to select optimal target lesions for BPA. In summary, this study provides a multiscale, image-to-hemodynamics pipeline for BPA therapy planning for patients with inoperable CTEPH. NEW & NOTEWORTHY This article presents novel computational framework for predicting pulmonary hemodynamics in chronic thromboembolic pulmonary hypertension. The mathematical model is used to identify the optimal target lesions for balloon pulmonary angioplasty, combining simulated pulmonary artery pressure, wave intensity analysis, and a new quantitative metric of flow heterogeneity.

Metalloproteinases and their inhibitors are associated with pulmonary arterial stiffness and ventricular function in pediatric pulmonary hypertension

Disturbed balance between matrix metalloproteinases (MMPs) and their respective tissue inhibitors (TIMPs) is a well-recognized pathophysiological component of pulmonary arterial hypertension (PAH). Both classes of proteinases have been associated with clinical outcomes as well as with specific pathological features of ventricular dysfunction and pulmonary arterial remodeling. The purpose of this study was to evaluate the circulating levels of MMPs and TIMPs in children with PAH undergoing the same-day cardiac magnetic resonance imaging (MRI) and right heart catheterization. Children with PAH (n = 21) underwent a same-day catheterization, comprehensive cardiac MRI evaluation, and blood sample collection for proteomic analysis. Correlative analysis was performed between protein levels and 1) standard PAH indices from catheterization, 2) cardiac MRI hemodynamics, and 3) pulmonary arterial stiffness. MMP-8 was significantly associated with the right ventricular end-diastolic volume (R = 0.45, P = 0.04). MMP-9 levels were significantly associated with stroke volume (R = -0.49, P = 0.03) and pulmonary vascular resistance (R = 0.49, P = 0.03). MMP-9 was further associated with main pulmonary arterial stiffness evaluated by relative area change (R = -0.79, P < 0.01).TIMP-2 and TIMP-4 levels were further associated with the right pulmonary artery pulse wave velocity (R = 0.51, P = 0.03) and backward compression wave (R = 0.52, P = 0.02), respectively. MMPs and TIMPs warrant further clinically prognostic evaluation in conjunction with the conventional cardiac MRI hemodynamic indices.NEW & NOTEWORTHY Metalloproteinases have been associated with clinical outcomes in pulmonary hypertension and with specific pathological features of ventricular dysfunction and pulmonary arterial remodeling. In this study, we demonstrated that plasma circulating levels of metalloproteinases and their inhibitors are associated with standard cardiac MRI hemodynamic indices and with the markers of proximal pulmonary arterial stiffness. Particularly, MMP-9 and TIMP-2 were associated with several different markers of pulmonary arterial stiffness. These findings suggest the interplay between the extracellular matrix (ECM) remodeling and overall hemodynamic status in children with PAH might be assessed using the peripheral circulating MMP and TIMP levels.

The composition of vulnerable plaque and its effect on arterial waveforms

Carotid plaque composition is a key factor of plaque stability and it carries significant prognostic information. The carotid unstable plaques are characterized by a thin fibrous cap (FC) ≤65μm with large lipid core (LC), while stable plaques have a thicker FC and less LC. Identifying the percentage of plaque compositions could help surgeons to make a precise decision for their patients' treatment protocol. This study aims to distinguish between stable and unstable plaque by defining the relationship between plaque composition and arterial waveform non-invasively. An in-vitro arterial system, composed of a Harvard pulsatile flow pump and artificial circulation system, was used to investigate the effect of the plaque compositions on the pulsatile arterial waveforms. Five types of arterial plaques, composed of the LC, FC, Collagen (Col) and Calcium (Ca), were implemented into the artificial carotid artery to represent the diseased arterial system with 30% of blockage. The pulsatile pressure, velocity and arterial wall movement were measured simultaneously at the site proximal to the plaque. Non-invasive wave intensity analysis (Non-WIA) was used to separate the waves into forward and backward components. The correlation between the plaque compositions and the reflected waveforms was quantitatively analysed. The experimental results indicate that the reflected waveforms are strongly correlated with the plaque compositions, where the percentages of the Col are linearly correlated with the amplitude of the backward diameter (correlation coefficient, r = 0.74) and the lipid content has a strong negative correlation with the backward diameter (r = 0.82). A slight weak correlation exists between the reflected waveform and the percentage of Ca. The strong correlation between the compositions of the plaques with the backward waveforms observed in this study demonstrates that the components of the arterial plaques could be distinguished by the arterial waveforms. This finding might lead to a potential novel non-invasive clinical tool to determine the composition of the plaques and distinguish between stable and vulnerable arterial plaques at the early stage.

Early return of reflected waves increases right ventricular wall stress in chronic thromboembolic pulmonary hypertension

Pulmonary vascular resistance (PVR) and compliance are comparable in proximal and distal chronic thromboembolic pulmonary hypertension (CTEPH). However, proximal CTEPH is associated with inferior right ventricular (RV) adaptation. Early wave reflection in proximal CTEPH may be responsible for altered RV function. The aims of the study are as follows: 1) to investigate whether reflected pressure returns sooner in proximal than in distal CTEPH and 2) to elucidate whether the timing of reflected pressure is related to RV dimensions, ejection fraction (RVEF), hypertrophy, and wall stress. Right heart catheterization and cardiac MRI were performed in 17 patients with proximal CTEPH and 17 patients with distal CTEPH. In addition to the determination of PVR, compliance, and characteristic impedance, wave separation analysis was performed to determine the magnitude and timing of the peak reflected pressure (as %systole). Findings were related to RV dimensions and time-resolved RV wall stress. Proximal CTEPH was characterized by higher RV volumes, mass, and wall stress, and lower RVEF. While PVR, compliance, and characteristic impedance were similar, proximal CTEPH was related to an earlier return of reflected pressure than distal CTEPH (proximal 53 ± 8% vs. distal 63 ± 15%, P < 0.05). The magnitude of the reflected pressure waves did not differ. RV volumes, RVEF, RV mass, and wall stress were all related to the timing of peak reflected pressure. Poor RV function in patients with proximal CTEPH is related to an early return of reflected pressure wave. PVR, compliance, and characteristic impedance do not explain the differences in RV function between proximal and distal CTEPH.NEW & NOTEWORTHY In chronic thromboembolic pulmonary hypertension (CTEPH), proximal localization of vessel obstructions is associated with poor right ventricular (RV) function compared with distal localization, though pulmonary vascular resistance, vascular compliance, characteristic impedance, and the magnitude of wave reflection are similar. In proximal CTEPH, the RV is exposed to an earlier return of the reflected wave. Early wave reflection may increase RV wall stress and compromise RV function.

Measurement, Analysis and Interpretation of Pressure/Flow Waves in Blood Vessels

The optimal performance of the cardiovascular system, as well as the break-down of this performance with disease, both involve complex biomechanical interactions between the heart, conduit vascular networks and microvascular beds. ‘Wave analysis’ refers to a group of techniques that provide valuable insight into these interactions by scrutinizing the shape of blood pressure and flow/velocity waveforms. The aim of this review paper is to provide a comprehensive introduction to wave analysis, with a focus on key concepts and practical application rather than mathematical derivations. We begin with an overview of invasive and non-invasive measurement techniques that can be used to obtain the signals required for wave analysis. We then review the most widely used wave analysis techniques—pulse wave analysis, wave separation and wave intensity analysis—and associated methods for estimating local wave speed or characteristic impedance that are required for decomposing waveforms into forward and backward wave components. This is followed by a discussion of the biomechanical phenomena that generate waves and the processes that modulate wave amplitude, both of which are critical for interpreting measured wave patterns. Finally, we provide a brief update on several emerging techniques/concepts in the wave analysis field, namely wave potential and the reservoir-excess pressure approach.

Patients with Fontan circulation have abnormal aortic wave propagation patterns: A wave intensity analysis study

BACKGROUND

Elevated systemic afterload in patients with Fontan circulation may lead to impaired single ventricular function. Wave intensity analysis (WIA) enables evaluation of compression and expansion waves traveling through vasculature. We aimed to investigate the unfavorable wave propagation causing excessive afterload may be an important contributor to the overall single ventricle function and to the limited functional capacity in this patient population.

METHODS

Patients with hypoplastic left heart syndrome (HLHS) (n = 25), single left ventricle (SLV) (n = 24), and normal controls (n = 10) underwent phase-contrast MRI based WIA analysis evaluated in the ascending aorta. Forward compression wave (FCW) representing dP/dt, backward compression wave (BCW) reflecting vascular stiffness, and forward decompression wave (FDW) representing LV relaxation were recorded and indexed to each other.

RESULTS

FCW was lowest in HLHS patients (1098 mm⁵/s), and higher in the SLV group (1457 mm5/s), and controls (6457 mm5/s) (P < 0.001). BCW/FCW was increased in HLHS (0.22) and SLV (0.14) groups compared to controls (0.08) (P = 0.003). Peak VO2 correlated with FCW (R = 0.50, P = 0.015), stroke volume (R = 0.72, P < 0.001), and cardiac output (R = 0.44, P = 0.034).

CONCLUSIONS

Patients with HLHS and SLV have unfavorable aortic WIA patterns with increased BCW/FCW ratio indicating increased systemic afterload due to retrograde compression waves. Reduced FCW and systolic MRI indices correlated with peak VO2 suggesting that abnormal systolic wave propagation may play a role in exercise intolerance for Fontan patients.

How to Measure Arterial Stiffness in Humans

Despite the wide recognition of larger artery stiffness as a highly clinically relevant and independent prognostic biomarker, it has yet be incorporated into routine clinical practice and to take a more prominent position in clinical guidelines. An important reason may be the plethora of methods and devices claiming to measure arterial stiffness in humans. This brief review provides a concise overview of methods in use, indicating strengths and weaknesses. We classified and graded methods, highly weighing their scrutiny and purity in quantifying arterial stiffness, rather than focusing on their ease of application or the level at which methods have demonstrated their prognostic and diagnostic potential.

Stiffening and ventricular-arterial interaction in the ascending aorta using MRI: ageing effects in healthy humans

Supplemental Digital Content is available in the text

Objectives:

The aim of this study was to investigate the effect of age and sex on _nPWV and _ndI in the ascending aorta of healthy humans.

Background:

Local pulse wave velocity (_nPWV) and wave intensity (_ndI) in the human ascending aorta have not been studied adequately, because of the need for invasive pressure measurements. However, a recently developed technique made the noninvasive determination of _nPWV and _ndI possible using measurements of flow velocity and arterial diameter.

Methods:

Diameter and flow velocity were measured at the level of the ascending aorta in 144 healthy participants (aged 20–77 years, 66 men), using MRI. _nPWV, _ndI parameters; forward (FCW); backward (BCW) compression waves, forward decompression wave (FDW), local aortic distensibility (_nD_s) and reflection index (_nRI) were calculated.

Results:

_nPWV increased significantly with age from 4.7 ± 0.3 m/s for those 20–30 years to 6.4 ± 0.2 m/s for those 70–80 years (P < 0.001) and did not differ between sexes. _nD_s decreased with age (5.3 ± 0.5 vs. 2.6 ± 0.2 10⁻⁵ 1/Pa, P < 0.001) and _nRI increased with age (0.17 ± 0.03 vs. 0.39 ± 0.06, P < 0.01) for those 20–30 and 70–80 years, respectively. FCW, BCW and FDW decreased significantly with age by 86.3, 71.3 and 74.2%, respectively (P < 0.001), all compared to the lowest age-band.

Conclusion:

In healthy humans, ageing results in stiffer ascending aorta, with increase in _nPWV and decrease in _nD_s. A decrease in FCW and FDW indicates decline in left ventricular early and late systolic functions with age in healthy humans with no differences between sexes. _nRI is more sensitive than BCW in establishing the effects of ageing on reflected waves measured in the ascending aorta.

On the accuracy of displacement-based wave intensity analysis: Effect of vessel wall viscoelasticity and nonlinearity

Recent studies showed that wave intensity analysis (WIA) provides clinically valuable information about local and global cardiovascular function. Wave intensity (WI) is computed as the product of the pressure change and the velocity change during short time intervals. The major limitation of WIA in clinical practice is the need for invasive pressure measurement. Since vessel wall displacement can be measured non-invasively, the usage of WI will be expanded if the vessel wall dilation is used instead of pressure in derivation of WI waveform. Our goal in this study is to investigate the agreement between wall displacement-based WI and the pressure-based WI for different vessel wall models including linear elastic, nonlinear and viscoelastic cases. The arbitrary Eulerian Lagrangian finite element method is employed to solve the coupled fluid-structure interaction (FSI). Our computational models also include two types of vascular disease-related cases with geometrical irregularities, aneurysm and stenosis. Our results show that for vessels with linear elastic wall, the displacement-based WI is almost identical to the pressure-based WI. The existence of vessel irregularities does not impact the accuracy of displacement-based WI. However, in a viscoelastic wall where there is a phase difference between pressure and vessel wall dilation, displacement-based WI deviated from pressure-based WI. The error associated with this phase difference increased nonlinearly with increasing viscosity. This results in a maximum error of 6.8% and 7.13% for a regular viscoelastic vessel wall and an irregular viscoelastic vessel wall, respectively. A separate analysis has also been performed on the agreement of backward and forward running waves extracted from a decomposition of the displacement-based and pressure-based WI. Our findings suggest that displacement-based WI is a reliable method of WIA for large central arteries that do not show viscoelastic behaviors. This can be clinically significant since the required information can be measured non-invasively.

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.

Proximal pulmonary vascular stiffness as a prognostic factor in children with pulmonary arterial hypertension

Aims

Main pulmonary artery (MPA) stiffness and abnormal flow haemodynamics in pulmonary arterial hypertension (PAH) are strongly associated with elevated right ventricular (RV) afterload and associated with disease severity and poor clinical outcomes in adults with PAH. However, the long-term effects of MPA stiffness on RV function in children with PAH remain poorly understood. This study is the first comprehensive evaluation of MPA stiffness in children with PAH, delineating the mechanistic relationship between flow haemodynamics and MPA stiffness as well as the prognostic ability of these measures regarding clinical outcomes.

Methods and results

Fifty-six children diagnosed with PAH underwent baseline cardiac magnetic resonance (CMR) acquisition and were compared with 23 control subjects. MPA stiffness and wall shear stress (WSS) were evaluated using phase contrast CMR and were evaluated for prognostic potential along with standard RV volumetric and functional indices. Pulse wave velocity (PWV) was significantly increased (2.8 m/s vs. 1.4 m/s, P < 0.0001) and relative area change (RAC) was decreased (25% vs. 37%, P < 0.0001) in the PAH group, correlating with metrics of RV performance. Decreased WSS was associated with a decrease in RAC over time (r = 0.679, P < 0.001). For each unit increase in PWV, there was approximately a 3.2-fold increase in having a moderate clinical event.

Conclusion

MPA stiffness assessed by non-invasive CMR was increased in children with PAH and correlated with RV performance, suggesting that MPA stiffness is a major contribution to RV dysfunction. PWV is predictive of moderate clinical outcomes, and may be a useful prognostic marker of disease activity in children with PAH.

4D Flow MRI Estimation of Boundary Conditions for Patient Specific Cardiovascular Simulation

Accurate image based cardiovascular simulations require patient specific boundary conditions (BCs) for inlets, outlets and vessel wall mechanical properties. While inlet BCs are typically determined non-invasively, invasive pressure catheterization is often used to determine patient specific outlet BCs and vessel wall mechanical properties. A method using 4D Flow MRI to non-invasively determine both patient specific outlet BCs and vessel wall mechanical properties is presented and results for both in vitro validation with a latex tube and an in vivo pulmonary artery stenosis (PAS) stent intervention are presented. For in vitro validation, acceptable agreement is found between simulation using BCs from 4D Flow MRI and benchtop measurements. For the PAS virtual intervention, simulation correctly predicts flow distribution with 9% error compared to MRI. Using 4D Flow MRI to noninvasively determine patient specific BCs increases the ability to use image based simulations as pressure catheterization is not always performed.

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.

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

BACKGROUND

Aortic 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.

METHODS

Sixty 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.

RESULTS

There 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.

CONCLUSIONS

There 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.

EXPRESS: Statement on imaging and pulmonary hypertension from the Pulmonary Vascular Research Institute (PVRI)

Pulmonary hypertension (PH) is highly heterogeneous and despite treatment advances it remains a life-shortening condition. There have been significant advances in imaging technologies, but despite evidence of their potential clinical utility, practice remains variable, dependent in part on imaging availability and expertise. This statement summarizes current and emerging imaging modalities and their potential role in the diagnosis and assessment of suspected PH. It also includes a review of commonly encountered clinical and radiological scenarios, and imaging and modeling-based biomarkers. An expert panel was formed including clinicians, radiologists, imaging scientists, and computational modelers. Section editors generated a series of summary statements based on a review of the literature and professional experience and, following consensus review, a diagnostic algorithm and 55 statements were agreed. The diagnostic algorithm and summary statements emphasize the key role and added value of imaging in the diagnosis and assessment of PH and highlight areas requiring further research.

The right ventricular response to lung resection

OBJECTIVES

Lung cancer is a leading cause of cancer death and in suitable cases the best chance of cure is offered by surgery. Lung resection is associated with significant postoperative cardiorespiratory morbidity, with dyspnea and reduced functional capacity as dominant features. These changes are poorly associated with deterioration in pulmonary function and a potential role of right ventricular (RV) dysfunction has been hypothesized. Cardiovascular magnetic resonance imaging is a reference method for noninvasive assessment of RV function and has not previously been applied to this population.

METHODS

We used cardiovascular magnetic resonance imaging to assess the RV response to lung resection. Cardiovascular magnetic resonance imaging with volume and flow analysis was performed on 27 patients preoperatively, on postoperative day 2 and at 2 months. Left ventricular ejection fraction and RV ejection fraction, the ratio of stroke volume to end systolic volume, pulmonary artery acceleration time, and distensibility of main and branch pulmonary arteries were studied.

RESULTS

Mean ± standard deviation RV ejection fraction deteriorated from 50.5% ± 6.9% preoperatively to 45.6% ± 4.5% on postoperative day 2 and remained depressed at 44.9% ± 7.7% by 2 months (P = .003). The ratio of stroke volume to end systolic volume deteriorated from median 1.0 (quartile 1, quartile 3: 0.9, 1.2) preoperatively to median 0.8 (quartile 1, quartile 3: 0.7, 1.0) on postoperative day 2 (P = .011). On postoperative day 2 there was a decrease in pulmonary artery acceleration time and operative pulmonary artery distensibility (P < .030 for both). There were no changes in left ventricular ejection fraction during the study period (P = .621).

CONCLUSIONS

These findings suggest RV dysfunction occurs following lung resection and persists 2 months after surgery. The deterioration in the ratio of stroke volume to end systolic volume suggests a mismatch between afterload and contractility. There is an increase in indices of pulsatile afterload resulting from the operative pulmonary artery.

Noninvasive wave intensity analysis predicts functional worsening in children with pulmonary arterial hypertension

The purpose of the present study was to characterize pulmonary vascular stiffness using wave intensity analysis (WIA) in children with pulmonary arterial hypertension (PAH), compare the WIA indexes with catheterization- and MRI-derived hemodynamics, and assess the prognostic ability of WIA-derived biomarkers to predict the functional worsening. WIA was performed in children with PAH ( n = 40) and healthy control subjects ( n = 15) from phase-contrast MRI-derived flow and area waveforms in the main pulmonary artery (MPA). From comprehensive WIA spectra, we collected and compared with healthy control subjects forward compression waves (FCW), backward compression waves (BCW), forward decompression waves (FDW), and wave propagation speed ( c-MPA). There was no difference in the magnitude of FCW between PAH and control groups (88 vs. 108 mm⁵·s^-1·ml^-1, P = 0.239). The magnitude of BCW was increased in patients with PAH (32 vs. 5 mm⁵·s^-1·ml^-1, P < 0.001). There was no difference in magnitude of indexed FDW (32 vs. 28 mm⁵·s^-1·ml^-1, P = 0.856). c-MPA was increased in patients with PAH (3.2 vs. 1.6 m/s, P < 0.001). BCW and FCW correlated with mean pulmonary arterial pressure, right ventricular volumes, and ejection fraction. Elevated indexed BCW [heart rate (HR) = 2.91, confidence interval (CI): 1.18-7.55, P = 0.019], reduced indexed FDW (HR = 0.34, CI: 0.11-0.90, P = 0.030), and increased c-MPA (HR = 3.67, CI: 1.47-10.20, P = 0.004) were strongly associated with functional worsening of disease severity. Our results suggest that noninvasively derived biomarkers of pulmonary vascular resistance and stiffness may be helpful for determining prognosis and monitoring disease progression in children with PAH. NEW & NOTEWORTHY Wave intensity analysis (WIA) studies are lacking in children with pulmonary arterial hypertension (PAH) partially because WIA, which is necessary to assess vascular stiffness, requires an invasive pressure-derived waveform along with simultaneous flow measurements. We analyzed vascular stiffness using WIA in children with PAH who underwent phase-contrast MRI and observed significant differences in WIA indexes between patients with PAH and control subjects. Furthermore, WIA indexes were predictive of functional worsening and were associated with standard catheterization measures.

Impact of chronic hypoxia on proximal pulmonary artery wave propagation and mechanical properties in rats

Arterial stiffness and wave reflection are important components of the ventricular afterload. Therefore, we aimed to assess the arterial wave characteristics and mechanical properties of the proximal pulmonary arteries (PAs) in the hypoxic pulmonary hypertensive rat model. After 21 days in normoxic or hypoxic chambers (24 animals/group), animals underwent transthoracic echocardiography and PA catheterization with a dual-tipped pressure and Doppler flow sensor wire. Wave intensity analysis was performed. Artery rings obtained from the pulmonary trunk, right and left PAs, and aorta were subjected to a tensile test to rupture. Collagen and elastin content were determined. In hypoxic rats, proximal PA wall thickness, collagen content, tensile strength per unit collagen, maximal elastic modulus, and wall viscosity increased, whereas the elastin-to-collagen ratio and arterial distensibility decreased. Arterial pulse wave velocity was also increased, and the increase was more prominent in vivo than ex vivo. Wave intensity was similar in hypoxic and normoxic animals with negligible wave reflection. In contrast, the aortic maximal elastic modulus remained unchanged, whereas wall viscosity decreased. In conclusion, there was no evidence of altered arterial wave propagation in proximal PAs of hypoxic rats while the extracellular matrix protein composition was altered and collagen tensile strength increased. This was accompanied by altered mechanical properties in vivo and ex vivo. NEW & NOTEWORTHY In rats exposed to chronic hypoxia, we have shown that pulse wave velocity in the proximal pulmonary arteries increased and pressure dependence of the pulse wave velocity was steeper in vivo than ex vivo leading to a more prominent increase in vivo.

Children with kawasaki disease present elevated stiffness of great arteries: Phase-contrast MRI study

BACKGROUND

Patients with diagnosed Kawasaki disease (KD) are known to develop extracardiac vascular lesions and are prone to accelerated stiffening of medium-size arteries.

PURPOSE

To noninvasively evaluate great vessel (central aorta and main pulmonary artery (MPA)) stiffness using phase-contrast MRI (PC-MRI).

STUDY TYPE

Retrospective review.

SUBJECTS

Thirty-three patients with previously diagnosed KD and 15 control subjects underwent PC-MRI evaluation.

FIELD STRENGTH/SEQUENCE

A free-breathing PC-MRI sequence was applied with Cartesian encoding and retrospective sorting using a 1.5 or 3.0T system.

ASSESSMENT

We evaluated regionally specific vessel stiffness using pulse-wave velocity (PWV) and relative area change (RAC) at the ascending aorta, descending aorta, and MPA.

STATISTICAL TESTS

Hemodynamics among patients with KD and controls were compared using Student's t-test, Wilcoxon Rank-sum, and χ² . Additional group-specific comparisons were performed using Kruskal-Wallis or one-way analysis of variance (ANOVA).

RESULTS

Patients with KD showed elevated PWV in both ascending (5.0 ± 1.2 vs. 2.4 ± 0.5, P < 0.001) and descending aorta (4.4 ± 2.1 vs. 2.8 ± 0.8, P < 0.001). RAC was correspondingly reduced in both segments (both P < 0.01). PWV measured in MPA was increased in KD patients (2.2 ± 0.5 vs. 1.5 ± 0.6, P = 0.045) while the RAC was reduced (34 ± 6 vs. 47 ± 3, P = 0.045). There were no associations between considered vessel stiffness indices and respective ventricular size and function, functional indices, and no correlations were observed with KD severity markers.

DATA CONCLUSION

Patients with KD have elevated great vessel stiffness measured at the chronic stage of the disease. Accelerated stiffness process does not appear to affect biventricular function in youth Level of Evidence: 1 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2018;47:1228-1236.

Pulmonary arterial stiffening in COPD and its implications for right ventricular remodelling

Background

Pulmonary pulse wave velocity (PWV) allows the non-invasive measurement of pulmonary arterial stiffening, but has not previously been assessed in COPD. The aim of the current study was to assess PWV in COPD and its association with right ventricular (RV) remodelling.

Methods

Fifty-eight participants with COPD underwent pulmonary function tests, 6-min walk test and cardiac MRI, while 21 healthy controls (HCs) underwent cardiac MRI. Thirty-two COPD patients underwent a follow-up MRI to assess for longitudinal changes in RV metrics. Cardiac MRI was used to quantify RV mass, volumes and PWV. Differences in continuous variables between the COPD and HC groups was tested using an independent t-test, and associations between PWV and right ventricular parameters was examined using Pearson’s correlation coefficient.

Results

Those with COPD had reduced pulsatility (COPD (mean±SD):24.88±8.84% vs. HC:30.55±11.28%, p=0.021), pulmonary acceleration time (COPD:104.0±22.9ms vs. HC: 128.1±32.2ms, p<0.001), higher PWV (COPD:2.62±1.29ms^-1 vs. HC:1.78±0.72ms^-1, p=0.001), lower RV end diastolic volume (COPD:53.6±11.1ml vs. HC:59.9±13.0ml, p=0.037) and RV stroke volume (COPD:31.9±6.9ml/m² vs. HC:37.1±6.2ml/m², p=0.003) with no difference in mass (p=0.53). PWV was not associated with right ventricular parameters.

Conclusions

While pulmonary vascular remodelling is present in COPD, cardiac remodelling favours reduced filling rather than increased afterload. Treatment of obstructive lung disease may have greater effect on cardiac function than treatment of pulmonary vascular disease in most COPD patients

Key Points

• Pulmonary pulse wave velocity (PWV) is elevated in COPD.

• Pulmonary PWV is not associated with right ventricular remodelling.

• Right ventricular remodelling is more in keeping with that of reduced filling.

Electronic supplementary material

The online version of this article (10.1007/s00330-018-5346-x) contains supplementary material, which is available to authorized users.

Wave Intensity Analysis Provides Novel Insights Into Pulmonary Arterial Hypertension and Chronic Thromboembolic Pulmonary Hypertension

Background

In contrast to systemic hypertension, the significance of arterial waves in pulmonary hypertension (PH) is not well understood. We hypothesized that arterial wave energy and wave reflection are augmented in PH and that wave behavior differs between patients with pulmonary arterial hypertension (PAH) and chronic thromboembolic pulmonary hypertension (CTEPH).

Methods and Results

Right heart catheterization was performed using a pressure and Doppler flow sensor–tipped catheter to obtain simultaneous pressure and flow velocity measurements in the pulmonary artery. Wave intensity analysis was subsequently applied to the acquired data. Ten control participants, 11 patients with PAH, and 10 patients with CTEPH were studied. Wave speed and wave power were significantly greater in PH patients compared with controls, indicating increased arterial stiffness and right ventricular work, respectively. The ratio of wave power to mean right ventricular power was lower in PAH patients than CTEPH patients and controls. Wave reflection index in PH patients (PAH: ≈25%; CTEPH: ≈30%) was significantly greater compared with controls (≈4%), indicating downstream vascular impedance mismatch. Although wave speed was significantly correlated to disease severity, wave reflection indexes of patients with mildly and severely elevated pulmonary pressures were similar.

Conclusions

Wave reflection in the pulmonary artery increased in PH and was unrelated to severity, suggesting that vascular impedance mismatch occurs early in the development of pulmonary vascular disease. The lower wave power fraction in PAH compared with CTEPH indicates differences in the intrinsic and/or extrinsic ventricular load between the 2 diseases.

Pulmonary artery wave propagation and reservoir function in conscious man: impact of pulmonary vascular disease, respiration and dynamic stress tests

KEY POINTS

Wave travel plays an important role in cardiovascular physiology. However, many aspects of pulmonary arterial wave behaviour remain unclear. Wave intensity and reservoir-excess pressure analyses were applied in the pulmonary artery in subjects with and without pulmonary hypertension during spontaneous respiration and dynamic stress tests. Arterial wave energy decreased during expiration and Valsalva manoeuvre due to decreased ventricular preload. Wave energy also decreased during handgrip exercise due to increased heart rate. In pulmonary hypertension patients, the asymptotic pressure at which the microvascular flow ceases, the reservoir pressure related to arterial compliance and the excess pressure caused by waves increased. The reservoir and excess pressures decreased during Valsalva manoeuvre but remained unchanged during handgrip exercise. This study provides insights into the influence of pulmonary vascular disease, spontaneous respiration and dynamic stress tests on pulmonary artery wave propagation and reservoir function.

ABSTRACT

Detailed haemodynamic analysis may provide novel insights into the pulmonary circulation. Therefore, wave intensity and reservoir-excess pressure analyses were applied in the pulmonary artery to characterize changes in wave propagation and reservoir function during spontaneous respiration and dynamic stress tests. Right heart catheterization was performed using a pressure and Doppler flow sensor tipped guidewire to obtain simultaneous pressure and flow velocity measurements in the pulmonary artery in control subjects and patients with pulmonary arterial hypertension (PAH) at rest. In controls, recordings were also obtained during Valsalva manoeuvre and handgrip exercise. The asymptotic pressure at which the flow through the microcirculation ceases, the reservoir pressure related to arterial compliance and the excess pressure caused by arterial waves increased in PAH patients compared to controls. The systolic and diastolic rate constants also increased, while the diastolic time constant decreased. The forward compression wave energy decreased by ∼8% in controls and ∼6% in PAH patients during expiration compared to inspiration, while the wave speed remained unchanged throughout the respiratory cycle. Wave energy decreased during Valsalva manoeuvre (by ∼45%) and handgrip exercise (by ∼27%) with unaffected wave speed. Moreover, the reservoir and excess pressures decreased during Valsalva manoeuvre but remained unaltered during handgrip exercise. In conclusion, reservoir-excess pressure analysis applied to the pulmonary artery revealed distinctive differences between controls and PAH patients. Variations in the ventricular preload and afterload influence pulmonary arterial wave propagation as demonstrated by changes in wave energy during spontaneous respiration and dynamic stress tests.

Cardiovascular mechanics in the early stages of pulmonary hypertension: a computational study

We formulate and study a new mathematical model of pulmonary hypertension. Based on principles of fluid and elastic dynamics, we introduce a model that quantifies the stiffening of pulmonary vasculature (arteries and arterioles) to reproduce the hemodynamics of the pulmonary system, including physiologically consistent dependence between compliance and resistance. This pulmonary model is embedded in a closed-loop network of the major vessels in the body, approximated as one-dimensional elastic tubes, and zero-dimensional models for the heart and other organs. Increasingly severe pulmonary hypertension is modeled in the context of two extreme scenarios: (1) no cardiac compensation and (2) compensation to achieve constant cardiac output. Simulations from the computational model are used to estimate cardiac workload, as well as pressure and flow traces at several locations. We also quantify the sensitivity of several diagnostic indicators to the progression of pulmonary arterial stiffening. Simulation results indicate that pulmonary pulse pressure, pulmonary vascular compliance, pulmonary RC time, luminal distensibility of the pulmonary artery, and pulmonary vascular impedance are much better suited to detect the early stages of pulmonary hypertension than mean pulmonary arterial pressure and pulmonary vascular resistance, which are conventionally employed as diagnostic indicators for this disease.

A Mock Circulatory System Incorporating a Compliant 3D-Printed Anatomical Model to Investigate Pulmonary Hemodynamics

A realistic mock circulatory system (MCS) could be a valuable in vitro testbed to study human circulatory hemodynamics. The objective of this study was to design a MCS replicating the pulmonary arterial circulation, incorporating an anatomically representative arterial model suitable for testing clinically relevant scenarios. A second objective of the study was to ensure the system's compatibility with magnetic resonance imaging (MRI) for additional measurements. A latex pulmonary arterial model with two generations of bifurcations was manufactured starting from a 3D-printed mold reconstructed from patient data. The model was incorporated into a MCS for in vitro hydrodynamic measurements. The setup was tested under physiological pulsatile flow conditions and results were evaluated using wave intensity analysis (WIA) to investigate waves traveling in the arterial system. Increased pulmonary vascular resistance (IPVR) was simulated as an example of one pathological scenario. Flow split between right and left pulmonary artery was found to be realistic (54 and 46%, respectively). No substantial difference in pressure waveform was observed throughout the various generations of bifurcations. Based on WIA, three main waves were identified in the main pulmonary artery (MPA), that is, forward compression wave, backward compression wave, and forward expansion wave. For IPVR, a rise in mean pressure was recorded in the MPA, within the clinical range of pulmonary arterial hypertension. The feasibility of using the MCS in the MRI scanner was demonstrated with the MCS running 2 h consecutively while acquiring preliminary MRI data. This study shows the development and verification of a pulmonary MCS, including an anatomically correct, compliant latex phantom. The setup can be useful to explore a wide range of hemodynamic questions, including the development of patient- and pathology-specific models, considering the ease and low cost of producing rapid prototyping molds, and the versatility of the setup for invasive and noninvasive (i.e., MRI) measurements.

Abnormal Wave Reflections and Left Ventricular Hypertrophy Late After Coarctation of the Aorta Repair

Patients with repaired coarctation of the aorta are thought to have increased afterload due to abnormalities in vessel structure and function. We have developed a novel cardiovascular magnetic resonance protocol that allows assessment of central hemodynamics, including central aortic systolic blood pressure, resistance, total arterial compliance, pulse wave velocity, and wave reflections. The main study aims were to (1) characterize group differences in central aortic systolic blood pressure and peripheral systolic blood pressure, (2) comprehensively evaluate afterload (including wave reflections) in the 2 groups, and (3) identify possible biomarkers among covariates associated with elevated left ventricular mass (LVM). Fifty adult patients with repaired coarctation and 25 age- and sex-matched controls were recruited. Ascending aorta area and flow waveforms were obtained using a high temporal-resolution spiral phase-contrast cardiovascular magnetic resonance flow sequence. These data were used to derive central hemodynamics and to perform wave intensity analysis noninvasively. Covariates associated with LVM were assessed using multivariable linear regression analysis. There were no significant group differences (P≥0.1) in brachial systolic, mean, or diastolic BP. However central aortic systolic blood pressure was significantly higher in patients compared with controls (113 versus 107 mm Hg, P=0.002). Patients had reduced total arterial compliance, increased pulse wave velocity, and larger backward compression waves compared with controls. LVM index was significantly higher in patients than controls (72 versus 59 g/m², P<0.0005). The magnitude of the backward compression waves was independently associated with variation in LVM (P=0.01). Using a novel, noninvasive hemodynamic assessment, we have shown abnormal conduit vessel function after coarctation of the aorta repair, including abnormal wave reflections that are associated with elevated LVM.

Feasibility of cardiovascular magnetic resonance derived coronary wave intensity analysis

BACKGROUND

Wave intensity analysis (WIA) of the coronary arteries allows description of the predominant mechanisms influencing coronary flow over the cardiac cycle. The data are traditionally derived from pressure and velocity changes measured invasively in the coronary artery. Cardiovascular magnetic resonance (CMR) allows measurement of coronary velocities using phase velocity mapping and derivation of central aortic pressure from aortic distension. We assessed the feasibility of WIA of the coronary arteries using CMR and compared this to invasive data.

METHODS

CMR scans were undertaken in a serial cohort of patients who had undergone invasive WIA. Velocity maps were acquired in the proximal left anterior descending and proximal right coronary artery using a retrospectively-gated breath-hold spiral phase velocity mapping sequence with high temporal resolution (19 ms). A breath-hold segmented gradient echo sequence was used to acquire through-plane cross sectional area changes in the proximal ascending aorta which were used as a surrogate of an aortic pressure waveform after calibration with brachial blood pressure measured with a sphygmomanometer. CMR-derived aortic pressures and CMR-measured velocities were used to derive wave intensity. The CMR-derived wave intensities were compared to invasive data in 12 coronary arteries (8 left, 4 right). Waves were presented as absolute values and as a % of total wave intensity. Intra-study reproducibility of invasive and non-invasive WIA was assessed using Bland-Altman analysis and the intraclass correlation coefficient (ICC).

RESULTS

The combination of the CMR-derived pressure and velocity data produced the expected pattern of forward and backward compression and expansion waves. The intra-study reproducibility of the CMR derived wave intensities as a % of the total wave intensity (mean ± standard deviation of differences) was 0.0 ± 6.8%, ICC = 0.91. Intra-study reproducibility for the corresponding invasive data was 0.0 ± 4.4%, ICC = 0.96. The invasive and CMR studies showed reasonable correlation (r = 0.73) with a mean difference of 0.0 ± 11.5%.

CONCLUSION

This proof of concept study demonstrated that CMR may be used to perform coronary WIA non-invasively with reasonable reproducibility compared to invasive WIA. The technique potentially allows WIA to be performed in a wider range of patients and pathologies than those who can be studied invasively.

The reservoir-wave approach to characterize pulmonary vascular-right ventricular interactions in humans

Using the reservoir-wave approach (RWA) we previously characterized pulmonary vasculature mechanics in a normal canine model. We found reflected backward-traveling waves that decrease pressure and increase flow in the proximal pulmonary artery (PA). These waves decrease right ventricular (RV) afterload and facilitate RV ejection. With pathological alterations to the pulmonary vasculature, these waves may change and impact RV performance. Our objective in this study was to characterize PA wave reflection and the alterations in RV performance in cardiac patients, using the RWA. PA pressure, Doppler-flow velocity, and pulmonary arterial wedge pressure were measured in 11 patients with exertional dyspnea. The RWA was employed to analyze PA pressure and flow; wave intensity analysis characterized PA waves. Wave-related pressure was partitioned into two components: pressures due to forward-traveling and to backward-traveling waves. RV performance was assessed by examining the work done in raising reservoir pressure and that associated with the wave components of systolic PA pressure. Wave-related work, the mostly nonrecoverable energy expended by the RV to eject blood, tended to vary directly with mean PA pressure. Where PA pressures were lower, there were pressure-decreasing/flow-increasing backward waves that aided RV ejection. Where PA pressures were higher, there were pressure-increasing/flow-decreasing backward waves that impeded RV ejection. Pressure-increasing/flow-decreasing backward waves were responsible for systolic notches in the Doppler flow velocity profiles in patients with the highest PA pressure. Pulmonary hypertension is characterized by reflected waves that impede RV ejection and an increase in wave-related work. The RWA may facilitate the development of therapeutic strategies.

A review of wave mechanics in the pulmonary artery with an emphasis on wave intensity analysis

Mean pulmonary arterial pressure and pulmonary vascular resistance (PVR) remain the most common haemodynamic measures to evaluate the severity and prognosis of pulmonary hypertension. However, PVR only captures the non-oscillatory component of the right ventricular hydraulic load and neglects the dynamic compliance of the pulmonary arteries and the contribution of wave transmission. Wave intensity analysis offers an alternative way to assess the pulmonary vasculature in health and disease. Wave speed is a measure of arterial stiffness, and the magnitude and timing of wave reflection provide information on the degree of impedance mismatch between the proximal and distal circulation. Studies in the pulmonary artery have demonstrated distinct differences in arterial wave propagation between individuals with and without pulmonary vascular disease. Notably, greater wave speed and greater wave reflection are observed in patients with pulmonary hypertension and in animal models exposed to hypoxia. Studying wave propagation makes a valuable contribution to the assessment of the arterial system in pulmonary hypertension, and here, we briefly review the current state of knowledge of the methods used to evaluate arterial waves in the pulmonary artery.

Assessment of proximal pulmonary arterial stiffness using magnetic resonance imaging: effects of technique, age and exercise

Introduction

To compare the reproducibility of pulmonary pulse wave velocity (PWV) techniques, and the effects of age and exercise on these.

Methods

10 young healthy volunteers (YHV) and 20 older healthy volunteers (OHV) with no cardiac or lung condition were recruited. High temporal resolution phase contrast sequences were performed through the main pulmonary arteries (MPAs), right pulmonary arteries (RPAs) and left pulmonary arteries (LPAs), while high spatial resolution sequences were obtained through the MPA. YHV underwent 2 MRIs 6 months apart with the sequences repeated during exercise. OHV underwent an MRI scan with on-table repetition. PWV was calculated using the transit time (TT) and flow area techniques (QA). 3 methods for calculating QA PWV were compared.

Results

PWV did not differ between the two age groups (YHV 2.4±0.3/ms, OHV 2.9±0.2/ms, p=0.1). Using a high temporal resolution sequence through the RPA using the QA accounting for wave reflections yielded consistently better within-scan, interscan, intraobserver and interobserver reproducibility. Exercise did not result in a change in either TT PWV (mean (95% CI) of the differences: −0.42 (−1.2 to 0.4), p=0.24) or QA PWV (mean (95% CI) of the differences: 0.10 (−0.5 to 0.9), p=0.49) despite a significant rise in heart rate (65±2 to 87±3, p<0.0001), blood pressure (113/68 to 130/84, p<0.0001) and cardiac output (5.4±0.4 to 6.7±0.6 L/min, p=0.004).

Conclusions

QA PWV performed through the RPA using a high temporal resolution sequence accounting for wave reflections yields the most reproducible measurements of pulmonary PWV.

MR phase-contrast imaging in pulmonary hypertension

Pulmonary hypertension (PH) is a life-threatening, multifactorial pathophysiological haemodynamic condition, diagnosed when the mean pulmonary arterial pressure equals or exceeds 25 mmHg at rest during right heart catheterization. Cardiac MRI, in general, and MR phase-contrast (PC) imaging, in particular, have emerged as potential techniques for the standardized assessment of cardiovascular function, morphology and haemodynamics in PH. Allowing the quantification and characterization of macroscopic cardiovascular blood flow, MR PC imaging offers non-invasive evaluation of haemodynamic alterations associated with PH. Techniques used to study the PH include both the routine two-dimensional (2D) approach measuring predominant velocities through an acquisition plane and the rapidly evolving four-dimensional (4D) PC imaging, which enables the assessment of the complete time-resolved, three-directional blood-flow velocity field in a volume. Numerous parameters such as pulmonary arterial mean velocity, vessel distensibility, flow acceleration time and volume and tricuspid regurgitation peak velocity, as well as the duration and onset of vortical blood flow in the main pulmonary artery, have been explored to either diagnose PH or find non-invasive correlates to right heart catheter parameters. Furthermore, PC imaging-based analysis of pulmonary arterial pulse-wave velocities, wall shear stress and kinetic energy losses grants novel insights into cardiopulmonary remodelling in PH. This review aimed to outline the current applications of 2D and 4D PC imaging in PH and show why this technique has the potential to contribute significantly to early diagnosis and characterization of PH.